invoke-ntp.conf.texi revision 310419
1290001Sglebius@node ntp.conf Notes 2290001Sglebius@section Notes about ntp.conf 3290001Sglebius@pindex ntp.conf 4290001Sglebius@cindex Network Time Protocol (NTP) daemon configuration file format 5290001Sglebius@ignore 6290001Sglebius# 7290001Sglebius# EDIT THIS FILE WITH CAUTION (invoke-ntp.conf.texi) 8290001Sglebius# 9310419Sdelphij# It has been AutoGen-ed November 21, 2016 at 08:01:55 AM by AutoGen 5.18.5 10290001Sglebius# From the definitions ntp.conf.def 11290001Sglebius# and the template file agtexi-file.tpl 12290001Sglebius@end ignore 13290001Sglebius 14290001Sglebius 15290001Sglebius 16290001SglebiusThe 17290001Sglebius@code{ntp.conf} 18290001Sglebiusconfiguration file is read at initial startup by the 19290001Sglebius@code{ntpd(1ntpdmdoc)} 20290001Sglebiusdaemon in order to specify the synchronization sources, 21290001Sglebiusmodes and other related information. 22290001SglebiusUsually, it is installed in the 23290001Sglebius@file{/etc} 24290001Sglebiusdirectory, 25290001Sglebiusbut could be installed elsewhere 26290001Sglebius(see the daemon's 27290001Sglebius@code{-c} 28290001Sglebiuscommand line option). 29290001Sglebius 30290001SglebiusThe file format is similar to other 31290001Sglebius@sc{unix} 32290001Sglebiusconfiguration files. 33290001SglebiusComments begin with a 34290001Sglebius@quoteleft{}#@quoteright{} 35290001Sglebiuscharacter and extend to the end of the line; 36290001Sglebiusblank lines are ignored. 37290001SglebiusConfiguration commands consist of an initial keyword 38290001Sglebiusfollowed by a list of arguments, 39290001Sglebiussome of which may be optional, separated by whitespace. 40290001SglebiusCommands may not be continued over multiple lines. 41290001SglebiusArguments may be host names, 42290001Sglebiushost addresses written in numeric, dotted-quad form, 43290001Sglebiusintegers, floating point numbers (when specifying times in seconds) 44290001Sglebiusand text strings. 45290001Sglebius 46290001SglebiusThe rest of this page describes the configuration and control options. 47290001SglebiusThe 48290001Sglebius"Notes on Configuring NTP and Setting up an NTP Subnet" 49290001Sglebiuspage 50290001Sglebius(available as part of the HTML documentation 51290001Sglebiusprovided in 52290001Sglebius@file{/usr/share/doc/ntp}) 53290001Sglebiuscontains an extended discussion of these options. 54290001SglebiusIn addition to the discussion of general 55290001Sglebius@ref{Configuration Options}, 56290001Sglebiusthere are sections describing the following supported functionality 57290001Sglebiusand the options used to control it: 58290001Sglebius@itemize @bullet 59290001Sglebius@item 60290001Sglebius@ref{Authentication Support} 61290001Sglebius@item 62290001Sglebius@ref{Monitoring Support} 63290001Sglebius@item 64290001Sglebius@ref{Access Control Support} 65290001Sglebius@item 66290001Sglebius@ref{Automatic NTP Configuration Options} 67290001Sglebius@item 68290001Sglebius@ref{Reference Clock Support} 69290001Sglebius@item 70290001Sglebius@ref{Miscellaneous Options} 71290001Sglebius@end itemize 72290001Sglebius 73290001SglebiusFollowing these is a section describing 74290001Sglebius@ref{Miscellaneous Options}. 75290001SglebiusWhile there is a rich set of options available, 76290001Sglebiusthe only required option is one or more 77290001Sglebius@code{pool}, 78290001Sglebius@code{server}, 79290001Sglebius@code{peer}, 80290001Sglebius@code{broadcast} 81290001Sglebiusor 82290001Sglebius@code{manycastclient} 83290001Sglebiuscommands. 84290001Sglebius@node Configuration Support 85290001Sglebius@subsection Configuration Support 86290001SglebiusFollowing is a description of the configuration commands in 87290001SglebiusNTPv4. 88290001SglebiusThese commands have the same basic functions as in NTPv3 and 89290001Sglebiusin some cases new functions and new arguments. 90290001SglebiusThere are two 91290001Sglebiusclasses of commands, configuration commands that configure a 92290001Sglebiuspersistent association with a remote server or peer or reference 93290001Sglebiusclock, and auxiliary commands that specify environmental variables 94290001Sglebiusthat control various related operations. 95290001Sglebius@subsubsection Configuration Commands 96290001SglebiusThe various modes are determined by the command keyword and the 97290001Sglebiustype of the required IP address. 98290001SglebiusAddresses are classed by type as 99290001Sglebius(s) a remote server or peer (IPv4 class A, B and C), (b) the 100290001Sglebiusbroadcast address of a local interface, (m) a multicast address (IPv4 101290001Sglebiusclass D), or (r) a reference clock address (127.127.x.x). 102290001SglebiusNote that 103290001Sglebiusonly those options applicable to each command are listed below. 104290001SglebiusUse 105290001Sglebiusof options not listed may not be caught as an error, but may result 106290001Sglebiusin some weird and even destructive behavior. 107290001Sglebius 108290001SglebiusIf the Basic Socket Interface Extensions for IPv6 (RFC-2553) 109290001Sglebiusis detected, support for the IPv6 address family is generated 110290001Sglebiusin addition to the default support of the IPv4 address family. 111298770SdelphijIn a few cases, including the 112298770Sdelphij@code{reslist} 113298770Sdelphijbillboard generated 114298770Sdelphijby 115298770Sdelphij@code{ntpq(1ntpqmdoc)} 116298770Sdelphijor 117298770Sdelphij@code{ntpdc(1ntpdcmdoc)}, 118298770SdelphijIPv6 addresses are automatically generated. 119290001SglebiusIPv6 addresses can be identified by the presence of colons 120290001Sglebius@quotedblleft{}:@quotedblright{} 121290001Sglebiusin the address field. 122290001SglebiusIPv6 addresses can be used almost everywhere where 123290001SglebiusIPv4 addresses can be used, 124290001Sglebiuswith the exception of reference clock addresses, 125290001Sglebiuswhich are always IPv4. 126290001Sglebius 127290001SglebiusNote that in contexts where a host name is expected, a 128290001Sglebius@code{-4} 129290001Sglebiusqualifier preceding 130290001Sglebiusthe host name forces DNS resolution to the IPv4 namespace, 131290001Sglebiuswhile a 132290001Sglebius@code{-6} 133290001Sglebiusqualifier forces DNS resolution to the IPv6 namespace. 134290001SglebiusSee IPv6 references for the 135290001Sglebiusequivalent classes for that address family. 136290001Sglebius@table @asis 137290001Sglebius@item @code{pool} @kbd{address} @code{[@code{burst}]} @code{[@code{iburst}]} @code{[@code{version} @kbd{version}]} @code{[@code{prefer}]} @code{[@code{minpoll} @kbd{minpoll}]} @code{[@code{maxpoll} @kbd{maxpoll}]} 138298770Sdelphij@item @code{server} @kbd{address} @code{[@code{key} @kbd{key} @kbd{|} @code{autokey}]} @code{[@code{burst}]} @code{[@code{iburst}]} @code{[@code{version} @kbd{version}]} @code{[@code{prefer}]} @code{[@code{minpoll} @kbd{minpoll}]} @code{[@code{maxpoll} @kbd{maxpoll}]} @code{[@code{true}]} 139298770Sdelphij@item @code{peer} @kbd{address} @code{[@code{key} @kbd{key} @kbd{|} @code{autokey}]} @code{[@code{version} @kbd{version}]} @code{[@code{prefer}]} @code{[@code{minpoll} @kbd{minpoll}]} @code{[@code{maxpoll} @kbd{maxpoll}]} @code{[@code{true}]} @code{[@code{xleave}]} 140298770Sdelphij@item @code{broadcast} @kbd{address} @code{[@code{key} @kbd{key} @kbd{|} @code{autokey}]} @code{[@code{version} @kbd{version}]} @code{[@code{prefer}]} @code{[@code{minpoll} @kbd{minpoll}]} @code{[@code{ttl} @kbd{ttl}]} @code{[@code{xleave}]} 141290001Sglebius@item @code{manycastclient} @kbd{address} @code{[@code{key} @kbd{key} @kbd{|} @code{autokey}]} @code{[@code{version} @kbd{version}]} @code{[@code{prefer}]} @code{[@code{minpoll} @kbd{minpoll}]} @code{[@code{maxpoll} @kbd{maxpoll}]} @code{[@code{ttl} @kbd{ttl}]} 142290001Sglebius@end table 143290001Sglebius 144290001SglebiusThese five commands specify the time server name or address to 145290001Sglebiusbe used and the mode in which to operate. 146290001SglebiusThe 147290001Sglebius@kbd{address} 148290001Sglebiuscan be 149290001Sglebiuseither a DNS name or an IP address in dotted-quad notation. 150290001SglebiusAdditional information on association behavior can be found in the 151290001Sglebius"Association Management" 152290001Sglebiuspage 153290001Sglebius(available as part of the HTML documentation 154290001Sglebiusprovided in 155290001Sglebius@file{/usr/share/doc/ntp}). 156290001Sglebius@table @asis 157290001Sglebius@item @code{pool} 158290001SglebiusFor type s addresses, this command mobilizes a persistent 159290001Sglebiusclient mode association with a number of remote servers. 160290001SglebiusIn this mode the local clock can synchronized to the 161290001Sglebiusremote server, but the remote server can never be synchronized to 162290001Sglebiusthe local clock. 163290001Sglebius@item @code{server} 164290001SglebiusFor type s and r addresses, this command mobilizes a persistent 165290001Sglebiusclient mode association with the specified remote server or local 166290001Sglebiusradio clock. 167290001SglebiusIn this mode the local clock can synchronized to the 168290001Sglebiusremote server, but the remote server can never be synchronized to 169290001Sglebiusthe local clock. 170290001SglebiusThis command should 171290001Sglebius@emph{not} 172290001Sglebiusbe used for type 173290001Sglebiusb or m addresses. 174290001Sglebius@item @code{peer} 175290001SglebiusFor type s addresses (only), this command mobilizes a 176290001Sglebiuspersistent symmetric-active mode association with the specified 177290001Sglebiusremote peer. 178290001SglebiusIn this mode the local clock can be synchronized to 179290001Sglebiusthe remote peer or the remote peer can be synchronized to the local 180290001Sglebiusclock. 181290001SglebiusThis is useful in a network of servers where, depending on 182290001Sglebiusvarious failure scenarios, either the local or remote peer may be 183290001Sglebiusthe better source of time. 184290001SglebiusThis command should NOT be used for type 185290001Sglebiusb, m or r addresses. 186290001Sglebius@item @code{broadcast} 187290001SglebiusFor type b and m addresses (only), this 188290001Sglebiuscommand mobilizes a persistent broadcast mode association. 189290001SglebiusMultiple 190290001Sglebiuscommands can be used to specify multiple local broadcast interfaces 191290001Sglebius(subnets) and/or multiple multicast groups. 192290001SglebiusNote that local 193290001Sglebiusbroadcast messages go only to the interface associated with the 194290001Sglebiussubnet specified, but multicast messages go to all interfaces. 195290001SglebiusIn broadcast mode the local server sends periodic broadcast 196290001Sglebiusmessages to a client population at the 197290001Sglebius@kbd{address} 198290001Sglebiusspecified, which is usually the broadcast address on (one of) the 199290001Sglebiuslocal network(s) or a multicast address assigned to NTP. 200290001SglebiusThe IANA 201290001Sglebiushas assigned the multicast group address IPv4 224.0.1.1 and 202290001SglebiusIPv6 ff05::101 (site local) exclusively to 203290001SglebiusNTP, but other nonconflicting addresses can be used to contain the 204290001Sglebiusmessages within administrative boundaries. 205290001SglebiusOrdinarily, this 206290001Sglebiusspecification applies only to the local server operating as a 207290001Sglebiussender; for operation as a broadcast client, see the 208290001Sglebius@code{broadcastclient} 209290001Sglebiusor 210290001Sglebius@code{multicastclient} 211290001Sglebiuscommands 212290001Sglebiusbelow. 213290001Sglebius@item @code{manycastclient} 214290001SglebiusFor type m addresses (only), this command mobilizes a 215290001Sglebiusmanycast client mode association for the multicast address 216290001Sglebiusspecified. 217290001SglebiusIn this case a specific address must be supplied which 218290001Sglebiusmatches the address used on the 219290001Sglebius@code{manycastserver} 220290001Sglebiuscommand for 221290001Sglebiusthe designated manycast servers. 222290001SglebiusThe NTP multicast address 223290001Sglebius224.0.1.1 assigned by the IANA should NOT be used, unless specific 224290001Sglebiusmeans are taken to avoid spraying large areas of the Internet with 225290001Sglebiusthese messages and causing a possibly massive implosion of replies 226290001Sglebiusat the sender. 227290001SglebiusThe 228290001Sglebius@code{manycastserver} 229290001Sglebiuscommand specifies that the local server 230290001Sglebiusis to operate in client mode with the remote servers that are 231290001Sglebiusdiscovered as the result of broadcast/multicast messages. 232290001SglebiusThe 233290001Sglebiusclient broadcasts a request message to the group address associated 234290001Sglebiuswith the specified 235290001Sglebius@kbd{address} 236290001Sglebiusand specifically enabled 237290001Sglebiusservers respond to these messages. 238290001SglebiusThe client selects the servers 239290001Sglebiusproviding the best time and continues as with the 240290001Sglebius@code{server} 241290001Sglebiuscommand. 242290001SglebiusThe remaining servers are discarded as if never 243290001Sglebiusheard. 244290001Sglebius@end table 245290001Sglebius 246290001SglebiusOptions: 247290001Sglebius@table @asis 248290001Sglebius@item @code{autokey} 249290001SglebiusAll packets sent to and received from the server or peer are to 250290001Sglebiusinclude authentication fields encrypted using the autokey scheme 251290001Sglebiusdescribed in 252290001Sglebius@ref{Authentication Options}. 253290001Sglebius@item @code{burst} 254290001Sglebiuswhen the server is reachable, send a burst of eight packets 255290001Sglebiusinstead of the usual one. 256290001SglebiusThe packet spacing is normally 2 s; 257290001Sglebiushowever, the spacing between the first and second packets 258298770Sdelphijcan be changed with the 259298770Sdelphij@code{calldelay} 260298770Sdelphijcommand to allow 261290001Sglebiusadditional time for a modem or ISDN call to complete. 262290001SglebiusThis is designed to improve timekeeping quality 263290001Sglebiuswith the 264290001Sglebius@code{server} 265290001Sglebiuscommand and s addresses. 266290001Sglebius@item @code{iburst} 267290001SglebiusWhen the server is unreachable, send a burst of eight packets 268290001Sglebiusinstead of the usual one. 269290001SglebiusThe packet spacing is normally 2 s; 270290001Sglebiushowever, the spacing between the first two packets can be 271298770Sdelphijchanged with the 272298770Sdelphij@code{calldelay} 273298770Sdelphijcommand to allow 274290001Sglebiusadditional time for a modem or ISDN call to complete. 275290001SglebiusThis is designed to speed the initial synchronization 276290001Sglebiusacquisition with the 277290001Sglebius@code{server} 278290001Sglebiuscommand and s addresses and when 279290001Sglebius@code{ntpd(1ntpdmdoc)} 280290001Sglebiusis started with the 281290001Sglebius@code{-q} 282290001Sglebiusoption. 283290001Sglebius@item @code{key} @kbd{key} 284290001SglebiusAll packets sent to and received from the server or peer are to 285290001Sglebiusinclude authentication fields encrypted using the specified 286290001Sglebius@kbd{key} 287290001Sglebiusidentifier with values from 1 to 65534, inclusive. 288290001SglebiusThe 289290001Sglebiusdefault is to include no encryption field. 290290001Sglebius@item @code{minpoll} @kbd{minpoll} 291290001Sglebius@item @code{maxpoll} @kbd{maxpoll} 292290001SglebiusThese options specify the minimum and maximum poll intervals 293290001Sglebiusfor NTP messages, as a power of 2 in seconds 294290001SglebiusThe maximum poll 295290001Sglebiusinterval defaults to 10 (1,024 s), but can be increased by the 296290001Sglebius@code{maxpoll} 297290001Sglebiusoption to an upper limit of 17 (36.4 h). 298290001SglebiusThe 299290001Sglebiusminimum poll interval defaults to 6 (64 s), but can be decreased by 300290001Sglebiusthe 301290001Sglebius@code{minpoll} 302290001Sglebiusoption to a lower limit of 4 (16 s). 303290001Sglebius@item @code{noselect} 304290001SglebiusMarks the server as unused, except for display purposes. 305290001SglebiusThe server is discarded by the selection algroithm. 306298770Sdelphij@item @code{preempt} 307298770SdelphijSays the association can be preempted. 308298770Sdelphij@item @code{true} 309298770SdelphijMarks the server as a truechimer. 310298770SdelphijUse this option only for testing. 311290001Sglebius@item @code{prefer} 312290001SglebiusMarks the server as preferred. 313290001SglebiusAll other things being equal, 314290001Sglebiusthis host will be chosen for synchronization among a set of 315290001Sglebiuscorrectly operating hosts. 316290001SglebiusSee the 317290001Sglebius"Mitigation Rules and the prefer Keyword" 318290001Sglebiuspage 319290001Sglebius(available as part of the HTML documentation 320290001Sglebiusprovided in 321290001Sglebius@file{/usr/share/doc/ntp}) 322290001Sglebiusfor further information. 323298770Sdelphij@item @code{true} 324298770SdelphijForces the association to always survive the selection and clustering algorithms. 325298770SdelphijThis option should almost certainly 326298770Sdelphij@emph{only} 327298770Sdelphijbe used while testing an association. 328290001Sglebius@item @code{ttl} @kbd{ttl} 329290001SglebiusThis option is used only with broadcast server and manycast 330290001Sglebiusclient modes. 331290001SglebiusIt specifies the time-to-live 332290001Sglebius@kbd{ttl} 333290001Sglebiusto 334290001Sglebiususe on broadcast server and multicast server and the maximum 335290001Sglebius@kbd{ttl} 336290001Sglebiusfor the expanding ring search with manycast 337290001Sglebiusclient packets. 338290001SglebiusSelection of the proper value, which defaults to 339290001Sglebius127, is something of a black art and should be coordinated with the 340290001Sglebiusnetwork administrator. 341290001Sglebius@item @code{version} @kbd{version} 342290001SglebiusSpecifies the version number to be used for outgoing NTP 343290001Sglebiuspackets. 344290001SglebiusVersions 1-4 are the choices, with version 4 the 345290001Sglebiusdefault. 346298770Sdelphij@item @code{xleave} 347298770SdelphijValid in 348298770Sdelphij@code{peer} 349298770Sdelphijand 350298770Sdelphij@code{broadcast} 351298770Sdelphijmodes only, this flag enables interleave mode. 352290001Sglebius@end table 353290001Sglebius@subsubsection Auxiliary Commands 354290001Sglebius@table @asis 355290001Sglebius@item @code{broadcastclient} 356290001SglebiusThis command enables reception of broadcast server messages to 357290001Sglebiusany local interface (type b) address. 358290001SglebiusUpon receiving a message for 359290001Sglebiusthe first time, the broadcast client measures the nominal server 360290001Sglebiuspropagation delay using a brief client/server exchange with the 361290001Sglebiusserver, then enters the broadcast client mode, in which it 362290001Sglebiussynchronizes to succeeding broadcast messages. 363290001SglebiusNote that, in order 364290001Sglebiusto avoid accidental or malicious disruption in this mode, both the 365290001Sglebiusserver and client should operate using symmetric-key or public-key 366290001Sglebiusauthentication as described in 367290001Sglebius@ref{Authentication Options}. 368290001Sglebius@item @code{manycastserver} @kbd{address} @kbd{...} 369290001SglebiusThis command enables reception of manycast client messages to 370290001Sglebiusthe multicast group address(es) (type m) specified. 371290001SglebiusAt least one 372290001Sglebiusaddress is required, but the NTP multicast address 224.0.1.1 373290001Sglebiusassigned by the IANA should NOT be used, unless specific means are 374290001Sglebiustaken to limit the span of the reply and avoid a possibly massive 375290001Sglebiusimplosion at the original sender. 376290001SglebiusNote that, in order to avoid 377290001Sglebiusaccidental or malicious disruption in this mode, both the server 378290001Sglebiusand client should operate using symmetric-key or public-key 379290001Sglebiusauthentication as described in 380290001Sglebius@ref{Authentication Options}. 381290001Sglebius@item @code{multicastclient} @kbd{address} @kbd{...} 382290001SglebiusThis command enables reception of multicast server messages to 383290001Sglebiusthe multicast group address(es) (type m) specified. 384290001SglebiusUpon receiving 385290001Sglebiusa message for the first time, the multicast client measures the 386290001Sglebiusnominal server propagation delay using a brief client/server 387290001Sglebiusexchange with the server, then enters the broadcast client mode, in 388290001Sglebiuswhich it synchronizes to succeeding multicast messages. 389290001SglebiusNote that, 390290001Sglebiusin order to avoid accidental or malicious disruption in this mode, 391290001Sglebiusboth the server and client should operate using symmetric-key or 392290001Sglebiuspublic-key authentication as described in 393290001Sglebius@ref{Authentication Options}. 394290001Sglebius@item @code{mdnstries} @kbd{number} 395290001SglebiusIf we are participating in mDNS, 396290001Sglebiusafter we have synched for the first time 397290001Sglebiuswe attempt to register with the mDNS system. 398290001SglebiusIf that registration attempt fails, 399290001Sglebiuswe try again at one minute intervals for up to 400290001Sglebius@code{mdnstries} 401290001Sglebiustimes. 402290001SglebiusAfter all, 403290001Sglebius@code{ntpd} 404290001Sglebiusmay be starting before mDNS. 405290001SglebiusThe default value for 406290001Sglebius@code{mdnstries} 407290001Sglebiusis 5. 408290001Sglebius@end table 409290001Sglebius@node Authentication Support 410290001Sglebius@subsection Authentication Support 411290001SglebiusAuthentication support allows the NTP client to verify that the 412290001Sglebiusserver is in fact known and trusted and not an intruder intending 413290001Sglebiusaccidentally or on purpose to masquerade as that server. 414290001SglebiusThe NTPv3 415290001Sglebiusspecification RFC-1305 defines a scheme which provides 416290001Sglebiuscryptographic authentication of received NTP packets. 417290001SglebiusOriginally, 418290001Sglebiusthis was done using the Data Encryption Standard (DES) algorithm 419290001Sglebiusoperating in Cipher Block Chaining (CBC) mode, commonly called 420290001SglebiusDES-CBC. 421290001SglebiusSubsequently, this was replaced by the RSA Message Digest 422290001Sglebius5 (MD5) algorithm using a private key, commonly called keyed-MD5. 423290001SglebiusEither algorithm computes a message digest, or one-way hash, which 424290001Sglebiuscan be used to verify the server has the correct private key and 425290001Sglebiuskey identifier. 426290001Sglebius 427290001SglebiusNTPv4 retains the NTPv3 scheme, properly described as symmetric key 428290001Sglebiuscryptography and, in addition, provides a new Autokey scheme 429290001Sglebiusbased on public key cryptography. 430290001SglebiusPublic key cryptography is generally considered more secure 431290001Sglebiusthan symmetric key cryptography, since the security is based 432290001Sglebiuson a private value which is generated by each server and 433290001Sglebiusnever revealed. 434290001SglebiusWith Autokey all key distribution and 435290001Sglebiusmanagement functions involve only public values, which 436290001Sglebiusconsiderably simplifies key distribution and storage. 437290001SglebiusPublic key management is based on X.509 certificates, 438290001Sglebiuswhich can be provided by commercial services or 439290001Sglebiusproduced by utility programs in the OpenSSL software library 440290001Sglebiusor the NTPv4 distribution. 441290001Sglebius 442290001SglebiusWhile the algorithms for symmetric key cryptography are 443290001Sglebiusincluded in the NTPv4 distribution, public key cryptography 444290001Sglebiusrequires the OpenSSL software library to be installed 445290001Sglebiusbefore building the NTP distribution. 446290001SglebiusDirections for doing that 447290001Sglebiusare on the Building and Installing the Distribution page. 448290001Sglebius 449290001SglebiusAuthentication is configured separately for each association 450290001Sglebiususing the 451290001Sglebius@code{key} 452290001Sglebiusor 453290001Sglebius@code{autokey} 454290001Sglebiussubcommand on the 455290001Sglebius@code{peer}, 456290001Sglebius@code{server}, 457290001Sglebius@code{broadcast} 458290001Sglebiusand 459290001Sglebius@code{manycastclient} 460290001Sglebiusconfiguration commands as described in 461290001Sglebius@ref{Configuration Options} 462290001Sglebiuspage. 463290001SglebiusThe authentication 464290001Sglebiusoptions described below specify the locations of the key files, 465290001Sglebiusif other than default, which symmetric keys are trusted 466290001Sglebiusand the interval between various operations, if other than default. 467290001Sglebius 468290001SglebiusAuthentication is always enabled, 469290001Sglebiusalthough ineffective if not configured as 470290001Sglebiusdescribed below. 471290001SglebiusIf a NTP packet arrives 472290001Sglebiusincluding a message authentication 473290001Sglebiuscode (MAC), it is accepted only if it 474290001Sglebiuspasses all cryptographic checks. 475290001SglebiusThe 476290001Sglebiuschecks require correct key ID, key value 477290001Sglebiusand message digest. 478290001SglebiusIf the packet has 479290001Sglebiusbeen modified in any way or replayed 480290001Sglebiusby an intruder, it will fail one or more 481290001Sglebiusof these checks and be discarded. 482290001SglebiusFurthermore, the Autokey scheme requires a 483290001Sglebiuspreliminary protocol exchange to obtain 484290001Sglebiusthe server certificate, verify its 485290001Sglebiuscredentials and initialize the protocol 486290001Sglebius 487290001SglebiusThe 488290001Sglebius@code{auth} 489290001Sglebiusflag controls whether new associations or 490290001Sglebiusremote configuration commands require cryptographic authentication. 491290001SglebiusThis flag can be set or reset by the 492290001Sglebius@code{enable} 493290001Sglebiusand 494290001Sglebius@code{disable} 495290001Sglebiuscommands and also by remote 496290001Sglebiusconfiguration commands sent by a 497290001Sglebius@code{ntpdc(1ntpdcmdoc)} 498298770Sdelphijprogram running on 499290001Sglebiusanother machine. 500290001SglebiusIf this flag is enabled, which is the default 501290001Sglebiuscase, new broadcast client and symmetric passive associations and 502290001Sglebiusremote configuration commands must be cryptographically 503290001Sglebiusauthenticated using either symmetric key or public key cryptography. 504290001SglebiusIf this 505290001Sglebiusflag is disabled, these operations are effective 506290001Sglebiuseven if not cryptographic 507290001Sglebiusauthenticated. 508290001SglebiusIt should be understood 509290001Sglebiusthat operating with the 510290001Sglebius@code{auth} 511290001Sglebiusflag disabled invites a significant vulnerability 512290001Sglebiuswhere a rogue hacker can 513290001Sglebiusmasquerade as a falseticker and seriously 514290001Sglebiusdisrupt system timekeeping. 515290001SglebiusIt is 516290001Sglebiusimportant to note that this flag has no purpose 517290001Sglebiusother than to allow or disallow 518290001Sglebiusa new association in response to new broadcast 519290001Sglebiusand symmetric active messages 520290001Sglebiusand remote configuration commands and, in particular, 521290001Sglebiusthe flag has no effect on 522290001Sglebiusthe authentication process itself. 523290001Sglebius 524290001SglebiusAn attractive alternative where multicast support is available 525290001Sglebiusis manycast mode, in which clients periodically troll 526290001Sglebiusfor servers as described in the 527290001Sglebius@ref{Automatic NTP Configuration Options} 528290001Sglebiuspage. 529290001SglebiusEither symmetric key or public key 530290001Sglebiuscryptographic authentication can be used in this mode. 531290001SglebiusThe principle advantage 532290001Sglebiusof manycast mode is that potential servers need not be 533290001Sglebiusconfigured in advance, 534290001Sglebiussince the client finds them during regular operation, 535290001Sglebiusand the configuration 536290001Sglebiusfiles for all clients can be identical. 537290001Sglebius 538290001SglebiusThe security model and protocol schemes for 539290001Sglebiusboth symmetric key and public key 540290001Sglebiuscryptography are summarized below; 541290001Sglebiusfurther details are in the briefings, papers 542290001Sglebiusand reports at the NTP project page linked from 543290001Sglebius@code{http://www.ntp.org/}. 544290001Sglebius@subsubsection Symmetric-Key Cryptography 545290001SglebiusThe original RFC-1305 specification allows any one of possibly 546290001Sglebius65,534 keys, each distinguished by a 32-bit key identifier, to 547290001Sglebiusauthenticate an association. 548290001SglebiusThe servers and clients involved must 549290001Sglebiusagree on the key and key identifier to 550290001Sglebiusauthenticate NTP packets. 551290001SglebiusKeys and 552290001Sglebiusrelated information are specified in a key 553290001Sglebiusfile, usually called 554290001Sglebius@file{ntp.keys}, 555290001Sglebiuswhich must be distributed and stored using 556290001Sglebiussecure means beyond the scope of the NTP protocol itself. 557290001SglebiusBesides the keys used 558290001Sglebiusfor ordinary NTP associations, 559290001Sglebiusadditional keys can be used as passwords for the 560290001Sglebius@code{ntpq(1ntpqmdoc)} 561290001Sglebiusand 562290001Sglebius@code{ntpdc(1ntpdcmdoc)} 563290001Sglebiusutility programs. 564290001Sglebius 565290001SglebiusWhen 566290001Sglebius@code{ntpd(1ntpdmdoc)} 567290001Sglebiusis first started, it reads the key file specified in the 568290001Sglebius@code{keys} 569290001Sglebiusconfiguration command and installs the keys 570290001Sglebiusin the key cache. 571290001SglebiusHowever, 572290001Sglebiusindividual keys must be activated with the 573290001Sglebius@code{trusted} 574290001Sglebiuscommand before use. 575290001SglebiusThis 576290001Sglebiusallows, for instance, the installation of possibly 577290001Sglebiusseveral batches of keys and 578290001Sglebiusthen activating or deactivating each batch 579290001Sglebiusremotely using 580290001Sglebius@code{ntpdc(1ntpdcmdoc)}. 581290001SglebiusThis also provides a revocation capability that can be used 582290001Sglebiusif a key becomes compromised. 583290001SglebiusThe 584290001Sglebius@code{requestkey} 585290001Sglebiuscommand selects the key used as the password for the 586290001Sglebius@code{ntpdc(1ntpdcmdoc)} 587290001Sglebiusutility, while the 588290001Sglebius@code{controlkey} 589290001Sglebiuscommand selects the key used as the password for the 590290001Sglebius@code{ntpq(1ntpqmdoc)} 591290001Sglebiusutility. 592290001Sglebius@subsubsection Public Key Cryptography 593290001SglebiusNTPv4 supports the original NTPv3 symmetric key scheme 594290001Sglebiusdescribed in RFC-1305 and in addition the Autokey protocol, 595290001Sglebiuswhich is based on public key cryptography. 596290001SglebiusThe Autokey Version 2 protocol described on the Autokey Protocol 597290001Sglebiuspage verifies packet integrity using MD5 message digests 598290001Sglebiusand verifies the source with digital signatures and any of several 599290001Sglebiusdigest/signature schemes. 600290001SglebiusOptional identity schemes described on the Identity Schemes 601290001Sglebiuspage and based on cryptographic challenge/response algorithms 602290001Sglebiusare also available. 603290001SglebiusUsing all of these schemes provides strong security against 604290001Sglebiusreplay with or without modification, spoofing, masquerade 605290001Sglebiusand most forms of clogging attacks. 606290001Sglebius 607290001SglebiusThe Autokey protocol has several modes of operation 608290001Sglebiuscorresponding to the various NTP modes supported. 609290001SglebiusMost modes use a special cookie which can be 610290001Sglebiuscomputed independently by the client and server, 611290001Sglebiusbut encrypted in transmission. 612290001SglebiusAll modes use in addition a variant of the S-KEY scheme, 613290001Sglebiusin which a pseudo-random key list is generated and used 614290001Sglebiusin reverse order. 615290001SglebiusThese schemes are described along with an executive summary, 616290001Sglebiuscurrent status, briefing slides and reading list on the 617290001Sglebius@ref{Autonomous Authentication} 618290001Sglebiuspage. 619290001Sglebius 620290001SglebiusThe specific cryptographic environment used by Autokey servers 621290001Sglebiusand clients is determined by a set of files 622290001Sglebiusand soft links generated by the 623290001Sglebius@code{ntp-keygen(1ntpkeygenmdoc)} 624290001Sglebiusprogram. 625290001SglebiusThis includes a required host key file, 626290001Sglebiusrequired certificate file and optional sign key file, 627290001Sglebiusleapsecond file and identity scheme files. 628290001SglebiusThe 629290001Sglebiusdigest/signature scheme is specified in the X.509 certificate 630290001Sglebiusalong with the matching sign key. 631290001SglebiusThere are several schemes 632290001Sglebiusavailable in the OpenSSL software library, each identified 633290001Sglebiusby a specific string such as 634290001Sglebius@code{md5WithRSAEncryption}, 635290001Sglebiuswhich stands for the MD5 message digest with RSA 636290001Sglebiusencryption scheme. 637290001SglebiusThe current NTP distribution supports 638290001Sglebiusall the schemes in the OpenSSL library, including 639290001Sglebiusthose based on RSA and DSA digital signatures. 640290001Sglebius 641290001SglebiusNTP secure groups can be used to define cryptographic compartments 642290001Sglebiusand security hierarchies. 643290001SglebiusIt is important that every host 644290001Sglebiusin the group be able to construct a certificate trail to one 645290001Sglebiusor more trusted hosts in the same group. 646290001SglebiusEach group 647290001Sglebiushost runs the Autokey protocol to obtain the certificates 648290001Sglebiusfor all hosts along the trail to one or more trusted hosts. 649290001SglebiusThis requires the configuration file in all hosts to be 650290001Sglebiusengineered so that, even under anticipated failure conditions, 651290001Sglebiusthe NTP subnet will form such that every group host can find 652290001Sglebiusa trail to at least one trusted host. 653290001Sglebius@subsubsection Naming and Addressing 654290001SglebiusIt is important to note that Autokey does not use DNS to 655290001Sglebiusresolve addresses, since DNS can't be completely trusted 656290001Sglebiusuntil the name servers have synchronized clocks. 657290001SglebiusThe cryptographic name used by Autokey to bind the host identity 658290001Sglebiuscredentials and cryptographic values must be independent 659290001Sglebiusof interface, network and any other naming convention. 660290001SglebiusThe name appears in the host certificate in either or both 661290001Sglebiusthe subject and issuer fields, so protection against 662290001SglebiusDNS compromise is essential. 663290001Sglebius 664290001SglebiusBy convention, the name of an Autokey host is the name returned 665290001Sglebiusby the Unix 666290001Sglebius@code{gethostname(2)} 667290001Sglebiussystem call or equivalent in other systems. 668290001SglebiusBy the system design 669290001Sglebiusmodel, there are no provisions to allow alternate names or aliases. 670290001SglebiusHowever, this is not to say that DNS aliases, different names 671290001Sglebiusfor each interface, etc., are constrained in any way. 672290001Sglebius 673290001SglebiusIt is also important to note that Autokey verifies authenticity 674290001Sglebiususing the host name, network address and public keys, 675290001Sglebiusall of which are bound together by the protocol specifically 676290001Sglebiusto deflect masquerade attacks. 677290001SglebiusFor this reason Autokey 678298770Sdelphijincludes the source and destination IP addresses in message digest 679290001Sglebiuscomputations and so the same addresses must be available 680290001Sglebiusat both the server and client. 681290001SglebiusFor this reason operation 682290001Sglebiuswith network address translation schemes is not possible. 683290001SglebiusThis reflects the intended robust security model where government 684290001Sglebiusand corporate NTP servers are operated outside firewall perimeters. 685290001Sglebius@subsubsection Operation 686290001SglebiusA specific combination of authentication scheme (none, 687290001Sglebiussymmetric key, public key) and identity scheme is called 688290001Sglebiusa cryptotype, although not all combinations are compatible. 689290001SglebiusThere may be management configurations where the clients, 690290001Sglebiusservers and peers may not all support the same cryptotypes. 691290001SglebiusA secure NTPv4 subnet can be configured in many ways while 692290001Sglebiuskeeping in mind the principles explained above and 693290001Sglebiusin this section. 694290001SglebiusNote however that some cryptotype 695290001Sglebiuscombinations may successfully interoperate with each other, 696290001Sglebiusbut may not represent good security practice. 697290001Sglebius 698290001SglebiusThe cryptotype of an association is determined at the time 699290001Sglebiusof mobilization, either at configuration time or some time 700290001Sglebiuslater when a message of appropriate cryptotype arrives. 701290001SglebiusWhen mobilized by a 702290001Sglebius@code{server} 703290001Sglebiusor 704290001Sglebius@code{peer} 705290001Sglebiusconfiguration command and no 706290001Sglebius@code{key} 707290001Sglebiusor 708290001Sglebius@code{autokey} 709290001Sglebiussubcommands are present, the association is not 710290001Sglebiusauthenticated; if the 711290001Sglebius@code{key} 712290001Sglebiussubcommand is present, the association is authenticated 713290001Sglebiususing the symmetric key ID specified; if the 714290001Sglebius@code{autokey} 715290001Sglebiussubcommand is present, the association is authenticated 716290001Sglebiususing Autokey. 717290001Sglebius 718290001SglebiusWhen multiple identity schemes are supported in the Autokey 719290001Sglebiusprotocol, the first message exchange determines which one is used. 720290001SglebiusThe client request message contains bits corresponding 721290001Sglebiusto which schemes it has available. 722290001SglebiusThe server response message 723290001Sglebiuscontains bits corresponding to which schemes it has available. 724290001SglebiusBoth server and client match the received bits with their own 725290001Sglebiusand select a common scheme. 726290001Sglebius 727290001SglebiusFollowing the principle that time is a public value, 728290001Sglebiusa server responds to any client packet that matches 729290001Sglebiusits cryptotype capabilities. 730290001SglebiusThus, a server receiving 731290001Sglebiusan unauthenticated packet will respond with an unauthenticated 732290001Sglebiuspacket, while the same server receiving a packet of a cryptotype 733290001Sglebiusit supports will respond with packets of that cryptotype. 734290001SglebiusHowever, unconfigured broadcast or manycast client 735290001Sglebiusassociations or symmetric passive associations will not be 736290001Sglebiusmobilized unless the server supports a cryptotype compatible 737290001Sglebiuswith the first packet received. 738290001SglebiusBy default, unauthenticated associations will not be mobilized 739290001Sglebiusunless overridden in a decidedly dangerous way. 740290001Sglebius 741290001SglebiusSome examples may help to reduce confusion. 742290001SglebiusClient Alice has no specific cryptotype selected. 743290001SglebiusServer Bob has both a symmetric key file and minimal Autokey files. 744290001SglebiusAlice's unauthenticated messages arrive at Bob, who replies with 745290001Sglebiusunauthenticated messages. 746290001SglebiusCathy has a copy of Bob's symmetric 747290001Sglebiuskey file and has selected key ID 4 in messages to Bob. 748290001SglebiusBob verifies the message with his key ID 4. 749290001SglebiusIf it's the 750290001Sglebiussame key and the message is verified, Bob sends Cathy a reply 751290001Sglebiusauthenticated with that key. 752290001SglebiusIf verification fails, 753290001SglebiusBob sends Cathy a thing called a crypto-NAK, which tells her 754290001Sglebiussomething broke. 755290001SglebiusShe can see the evidence using the 756290001Sglebius@code{ntpq(1ntpqmdoc)} 757290001Sglebiusprogram. 758290001Sglebius 759290001SglebiusDenise has rolled her own host key and certificate. 760290001SglebiusShe also uses one of the identity schemes as Bob. 761290001SglebiusShe sends the first Autokey message to Bob and they 762290001Sglebiusboth dance the protocol authentication and identity steps. 763290001SglebiusIf all comes out okay, Denise and Bob continue as described above. 764290001Sglebius 765290001SglebiusIt should be clear from the above that Bob can support 766290001Sglebiusall the girls at the same time, as long as he has compatible 767290001Sglebiusauthentication and identity credentials. 768290001SglebiusNow, Bob can act just like the girls in his own choice of servers; 769290001Sglebiushe can run multiple configured associations with multiple different 770290001Sglebiusservers (or the same server, although that might not be useful). 771290001SglebiusBut, wise security policy might preclude some cryptotype 772290001Sglebiuscombinations; for instance, running an identity scheme 773290001Sglebiuswith one server and no authentication with another might not be wise. 774290001Sglebius@subsubsection Key Management 775290001SglebiusThe cryptographic values used by the Autokey protocol are 776290001Sglebiusincorporated as a set of files generated by the 777290001Sglebius@code{ntp-keygen(1ntpkeygenmdoc)} 778290001Sglebiusutility program, including symmetric key, host key and 779290001Sglebiuspublic certificate files, as well as sign key, identity parameters 780290001Sglebiusand leapseconds files. 781290001SglebiusAlternatively, host and sign keys and 782290001Sglebiuscertificate files can be generated by the OpenSSL utilities 783290001Sglebiusand certificates can be imported from public certificate 784290001Sglebiusauthorities. 785290001SglebiusNote that symmetric keys are necessary for the 786290001Sglebius@code{ntpq(1ntpqmdoc)} 787290001Sglebiusand 788290001Sglebius@code{ntpdc(1ntpdcmdoc)} 789290001Sglebiusutility programs. 790290001SglebiusThe remaining files are necessary only for the 791290001SglebiusAutokey protocol. 792290001Sglebius 793290001SglebiusCertificates imported from OpenSSL or public certificate 794290001Sglebiusauthorities have certian limitations. 795290001SglebiusThe certificate should be in ASN.1 syntax, X.509 Version 3 796290001Sglebiusformat and encoded in PEM, which is the same format 797290001Sglebiusused by OpenSSL. 798290001SglebiusThe overall length of the certificate encoded 799290001Sglebiusin ASN.1 must not exceed 1024 bytes. 800290001SglebiusThe subject distinguished 801290001Sglebiusname field (CN) is the fully qualified name of the host 802290001Sglebiuson which it is used; the remaining subject fields are ignored. 803290001SglebiusThe certificate extension fields must not contain either 804290001Sglebiusa subject key identifier or a issuer key identifier field; 805290001Sglebiushowever, an extended key usage field for a trusted host must 806290001Sglebiuscontain the value 807290001Sglebius@code{trustRoot};. 808290001SglebiusOther extension fields are ignored. 809290001Sglebius@subsubsection Authentication Commands 810290001Sglebius@table @asis 811290001Sglebius@item @code{autokey} @code{[@kbd{logsec}]} 812290001SglebiusSpecifies the interval between regenerations of the session key 813290001Sglebiuslist used with the Autokey protocol. 814290001SglebiusNote that the size of the key 815290001Sglebiuslist for each association depends on this interval and the current 816290001Sglebiuspoll interval. 817290001SglebiusThe default value is 12 (4096 s or about 1.1 hours). 818290001SglebiusFor poll intervals above the specified interval, a session key list 819290001Sglebiuswith a single entry will be regenerated for every message 820290001Sglebiussent. 821290001Sglebius@item @code{controlkey} @kbd{key} 822290001SglebiusSpecifies the key identifier to use with the 823290001Sglebius@code{ntpq(1ntpqmdoc)} 824290001Sglebiusutility, which uses the standard 825290001Sglebiusprotocol defined in RFC-1305. 826290001SglebiusThe 827290001Sglebius@kbd{key} 828290001Sglebiusargument is 829290001Sglebiusthe key identifier for a trusted key, where the value can be in the 830290001Sglebiusrange 1 to 65,534, inclusive. 831290001Sglebius@item @code{crypto} @code{[@code{cert} @kbd{file}]} @code{[@code{leap} @kbd{file}]} @code{[@code{randfile} @kbd{file}]} @code{[@code{host} @kbd{file}]} @code{[@code{sign} @kbd{file}]} @code{[@code{gq} @kbd{file}]} @code{[@code{gqpar} @kbd{file}]} @code{[@code{iffpar} @kbd{file}]} @code{[@code{mvpar} @kbd{file}]} @code{[@code{pw} @kbd{password}]} 832290001SglebiusThis command requires the OpenSSL library. 833290001SglebiusIt activates public key 834290001Sglebiuscryptography, selects the message digest and signature 835290001Sglebiusencryption scheme and loads the required private and public 836290001Sglebiusvalues described above. 837290001SglebiusIf one or more files are left unspecified, 838290001Sglebiusthe default names are used as described above. 839290001SglebiusUnless the complete path and name of the file are specified, the 840290001Sglebiuslocation of a file is relative to the keys directory specified 841290001Sglebiusin the 842290001Sglebius@code{keysdir} 843290001Sglebiuscommand or default 844290001Sglebius@file{/usr/local/etc}. 845290001SglebiusFollowing are the subcommands: 846290001Sglebius@table @asis 847290001Sglebius@item @code{cert} @kbd{file} 848290001SglebiusSpecifies the location of the required host public certificate file. 849290001SglebiusThis overrides the link 850290001Sglebius@file{ntpkey_cert_}@kbd{hostname} 851290001Sglebiusin the keys directory. 852290001Sglebius@item @code{gqpar} @kbd{file} 853290001SglebiusSpecifies the location of the optional GQ parameters file. 854290001SglebiusThis 855290001Sglebiusoverrides the link 856290001Sglebius@file{ntpkey_gq_}@kbd{hostname} 857290001Sglebiusin the keys directory. 858290001Sglebius@item @code{host} @kbd{file} 859290001SglebiusSpecifies the location of the required host key file. 860290001SglebiusThis overrides 861290001Sglebiusthe link 862290001Sglebius@file{ntpkey_key_}@kbd{hostname} 863290001Sglebiusin the keys directory. 864290001Sglebius@item @code{iffpar} @kbd{file} 865298770SdelphijSpecifies the location of the optional IFF parameters file. 866298770SdelphijThis overrides the link 867290001Sglebius@file{ntpkey_iff_}@kbd{hostname} 868290001Sglebiusin the keys directory. 869290001Sglebius@item @code{leap} @kbd{file} 870290001SglebiusSpecifies the location of the optional leapsecond file. 871290001SglebiusThis overrides the link 872290001Sglebius@file{ntpkey_leap} 873290001Sglebiusin the keys directory. 874290001Sglebius@item @code{mvpar} @kbd{file} 875290001SglebiusSpecifies the location of the optional MV parameters file. 876298770SdelphijThis overrides the link 877290001Sglebius@file{ntpkey_mv_}@kbd{hostname} 878290001Sglebiusin the keys directory. 879290001Sglebius@item @code{pw} @kbd{password} 880290001SglebiusSpecifies the password to decrypt files containing private keys and 881290001Sglebiusidentity parameters. 882290001SglebiusThis is required only if these files have been 883290001Sglebiusencrypted. 884290001Sglebius@item @code{randfile} @kbd{file} 885290001SglebiusSpecifies the location of the random seed file used by the OpenSSL 886290001Sglebiuslibrary. 887290001SglebiusThe defaults are described in the main text above. 888290001Sglebius@item @code{sign} @kbd{file} 889290001SglebiusSpecifies the location of the optional sign key file. 890290001SglebiusThis overrides 891290001Sglebiusthe link 892290001Sglebius@file{ntpkey_sign_}@kbd{hostname} 893290001Sglebiusin the keys directory. 894290001SglebiusIf this file is 895290001Sglebiusnot found, the host key is also the sign key. 896290001Sglebius@end table 897290001Sglebius@item @code{keys} @kbd{keyfile} 898290001SglebiusSpecifies the complete path and location of the MD5 key file 899290001Sglebiuscontaining the keys and key identifiers used by 900290001Sglebius@code{ntpd(1ntpdmdoc)}, 901290001Sglebius@code{ntpq(1ntpqmdoc)} 902290001Sglebiusand 903290001Sglebius@code{ntpdc(1ntpdcmdoc)} 904290001Sglebiuswhen operating with symmetric key cryptography. 905290001SglebiusThis is the same operation as the 906290001Sglebius@code{-k} 907290001Sglebiuscommand line option. 908290001Sglebius@item @code{keysdir} @kbd{path} 909290001SglebiusThis command specifies the default directory path for 910290001Sglebiuscryptographic keys, parameters and certificates. 911290001SglebiusThe default is 912290001Sglebius@file{/usr/local/etc/}. 913290001Sglebius@item @code{requestkey} @kbd{key} 914290001SglebiusSpecifies the key identifier to use with the 915290001Sglebius@code{ntpdc(1ntpdcmdoc)} 916290001Sglebiusutility program, which uses a 917290001Sglebiusproprietary protocol specific to this implementation of 918290001Sglebius@code{ntpd(1ntpdmdoc)}. 919290001SglebiusThe 920290001Sglebius@kbd{key} 921290001Sglebiusargument is a key identifier 922290001Sglebiusfor the trusted key, where the value can be in the range 1 to 923290001Sglebius65,534, inclusive. 924290001Sglebius@item @code{revoke} @kbd{logsec} 925290001SglebiusSpecifies the interval between re-randomization of certain 926290001Sglebiuscryptographic values used by the Autokey scheme, as a power of 2 in 927290001Sglebiusseconds. 928290001SglebiusThese values need to be updated frequently in order to 929290001Sglebiusdeflect brute-force attacks on the algorithms of the scheme; 930290001Sglebiushowever, updating some values is a relatively expensive operation. 931290001SglebiusThe default interval is 16 (65,536 s or about 18 hours). 932290001SglebiusFor poll 933290001Sglebiusintervals above the specified interval, the values will be updated 934290001Sglebiusfor every message sent. 935290001Sglebius@item @code{trustedkey} @kbd{key} @kbd{...} 936290001SglebiusSpecifies the key identifiers which are trusted for the 937290001Sglebiuspurposes of authenticating peers with symmetric key cryptography, 938290001Sglebiusas well as keys used by the 939290001Sglebius@code{ntpq(1ntpqmdoc)} 940290001Sglebiusand 941290001Sglebius@code{ntpdc(1ntpdcmdoc)} 942290001Sglebiusprograms. 943290001SglebiusThe authentication procedures require that both the local 944290001Sglebiusand remote servers share the same key and key identifier for this 945290001Sglebiuspurpose, although different keys can be used with different 946290001Sglebiusservers. 947290001SglebiusThe 948290001Sglebius@kbd{key} 949290001Sglebiusarguments are 32-bit unsigned 950290001Sglebiusintegers with values from 1 to 65,534. 951290001Sglebius@end table 952290001Sglebius@subsubsection Error Codes 953290001SglebiusThe following error codes are reported via the NTP control 954290001Sglebiusand monitoring protocol trap mechanism. 955290001Sglebius@table @asis 956290001Sglebius@item 101 957290001Sglebius(bad field format or length) 958290001SglebiusThe packet has invalid version, length or format. 959290001Sglebius@item 102 960290001Sglebius(bad timestamp) 961290001SglebiusThe packet timestamp is the same or older than the most recent received. 962290001SglebiusThis could be due to a replay or a server clock time step. 963290001Sglebius@item 103 964290001Sglebius(bad filestamp) 965290001SglebiusThe packet filestamp is the same or older than the most recent received. 966290001SglebiusThis could be due to a replay or a key file generation error. 967290001Sglebius@item 104 968290001Sglebius(bad or missing public key) 969290001SglebiusThe public key is missing, has incorrect format or is an unsupported type. 970290001Sglebius@item 105 971290001Sglebius(unsupported digest type) 972290001SglebiusThe server requires an unsupported digest/signature scheme. 973290001Sglebius@item 106 974290001Sglebius(mismatched digest types) 975290001SglebiusNot used. 976290001Sglebius@item 107 977290001Sglebius(bad signature length) 978290001SglebiusThe signature length does not match the current public key. 979290001Sglebius@item 108 980290001Sglebius(signature not verified) 981290001SglebiusThe message fails the signature check. 982290001SglebiusIt could be bogus or signed by a 983290001Sglebiusdifferent private key. 984290001Sglebius@item 109 985290001Sglebius(certificate not verified) 986290001SglebiusThe certificate is invalid or signed with the wrong key. 987290001Sglebius@item 110 988290001Sglebius(certificate not verified) 989290001SglebiusThe certificate is not yet valid or has expired or the signature could not 990290001Sglebiusbe verified. 991290001Sglebius@item 111 992290001Sglebius(bad or missing cookie) 993290001SglebiusThe cookie is missing, corrupted or bogus. 994290001Sglebius@item 112 995290001Sglebius(bad or missing leapseconds table) 996290001SglebiusThe leapseconds table is missing, corrupted or bogus. 997290001Sglebius@item 113 998290001Sglebius(bad or missing certificate) 999290001SglebiusThe certificate is missing, corrupted or bogus. 1000290001Sglebius@item 114 1001290001Sglebius(bad or missing identity) 1002290001SglebiusThe identity key is missing, corrupt or bogus. 1003290001Sglebius@end table 1004290001Sglebius@node Monitoring Support 1005290001Sglebius@subsection Monitoring Support 1006290001Sglebius@code{ntpd(1ntpdmdoc)} 1007290001Sglebiusincludes a comprehensive monitoring facility suitable 1008290001Sglebiusfor continuous, long term recording of server and client 1009290001Sglebiustimekeeping performance. 1010290001SglebiusSee the 1011290001Sglebius@code{statistics} 1012290001Sglebiuscommand below 1013290001Sglebiusfor a listing and example of each type of statistics currently 1014290001Sglebiussupported. 1015290001SglebiusStatistic files are managed using file generation sets 1016290001Sglebiusand scripts in the 1017290001Sglebius@file{./scripts} 1018298770Sdelphijdirectory of the source code distribution. 1019290001SglebiusUsing 1020290001Sglebiusthese facilities and 1021290001Sglebius@sc{unix} 1022290001Sglebius@code{cron(8)} 1023290001Sglebiusjobs, the data can be 1024290001Sglebiusautomatically summarized and archived for retrospective analysis. 1025290001Sglebius@subsubsection Monitoring Commands 1026290001Sglebius@table @asis 1027290001Sglebius@item @code{statistics} @kbd{name} @kbd{...} 1028290001SglebiusEnables writing of statistics records. 1029290001SglebiusCurrently, eight kinds of 1030290001Sglebius@kbd{name} 1031290001Sglebiusstatistics are supported. 1032290001Sglebius@table @asis 1033290001Sglebius@item @code{clockstats} 1034290001SglebiusEnables recording of clock driver statistics information. 1035290001SglebiusEach update 1036290001Sglebiusreceived from a clock driver appends a line of the following form to 1037290001Sglebiusthe file generation set named 1038290001Sglebius@code{clockstats}: 1039290001Sglebius@verbatim 1040290001Sglebius49213 525.624 127.127.4.1 93 226 00:08:29.606 D 1041290001Sglebius@end verbatim 1042290001Sglebius 1043290001SglebiusThe first two fields show the date (Modified Julian Day) and time 1044290001Sglebius(seconds and fraction past UTC midnight). 1045290001SglebiusThe next field shows the 1046290001Sglebiusclock address in dotted-quad notation. 1047290001SglebiusThe final field shows the last 1048290001Sglebiustimecode received from the clock in decoded ASCII format, where 1049290001Sglebiusmeaningful. 1050290001SglebiusIn some clock drivers a good deal of additional information 1051290001Sglebiuscan be gathered and displayed as well. 1052290001SglebiusSee information specific to each 1053290001Sglebiusclock for further details. 1054290001Sglebius@item @code{cryptostats} 1055290001SglebiusThis option requires the OpenSSL cryptographic software library. 1056290001SglebiusIt 1057290001Sglebiusenables recording of cryptographic public key protocol information. 1058290001SglebiusEach message received by the protocol module appends a line of the 1059290001Sglebiusfollowing form to the file generation set named 1060290001Sglebius@code{cryptostats}: 1061290001Sglebius@verbatim 1062290001Sglebius49213 525.624 127.127.4.1 message 1063290001Sglebius@end verbatim 1064290001Sglebius 1065290001SglebiusThe first two fields show the date (Modified Julian Day) and time 1066290001Sglebius(seconds and fraction past UTC midnight). 1067290001SglebiusThe next field shows the peer 1068290001Sglebiusaddress in dotted-quad notation, The final message field includes the 1069290001Sglebiusmessage type and certain ancillary information. 1070290001SglebiusSee the 1071290001Sglebius@ref{Authentication Options} 1072290001Sglebiussection for further information. 1073290001Sglebius@item @code{loopstats} 1074290001SglebiusEnables recording of loop filter statistics information. 1075290001SglebiusEach 1076290001Sglebiusupdate of the local clock outputs a line of the following form to 1077290001Sglebiusthe file generation set named 1078290001Sglebius@code{loopstats}: 1079290001Sglebius@verbatim 1080290001Sglebius50935 75440.031 0.000006019 13.778190 0.000351733 0.0133806 1081290001Sglebius@end verbatim 1082290001Sglebius 1083290001SglebiusThe first two fields show the date (Modified Julian Day) and 1084290001Sglebiustime (seconds and fraction past UTC midnight). 1085290001SglebiusThe next five fields 1086290001Sglebiusshow time offset (seconds), frequency offset (parts per million - 1087290001SglebiusPPM), RMS jitter (seconds), Allan deviation (PPM) and clock 1088290001Sglebiusdiscipline time constant. 1089290001Sglebius@item @code{peerstats} 1090290001SglebiusEnables recording of peer statistics information. 1091290001SglebiusThis includes 1092290001Sglebiusstatistics records of all peers of a NTP server and of special 1093290001Sglebiussignals, where present and configured. 1094290001SglebiusEach valid update appends a 1095290001Sglebiusline of the following form to the current element of a file 1096290001Sglebiusgeneration set named 1097290001Sglebius@code{peerstats}: 1098290001Sglebius@verbatim 1099290001Sglebius48773 10847.650 127.127.4.1 9714 -0.001605376 0.000000000 0.001424877 0.000958674 1100290001Sglebius@end verbatim 1101290001Sglebius 1102290001SglebiusThe first two fields show the date (Modified Julian Day) and 1103290001Sglebiustime (seconds and fraction past UTC midnight). 1104290001SglebiusThe next two fields 1105290001Sglebiusshow the peer address in dotted-quad notation and status, 1106290001Sglebiusrespectively. 1107290001SglebiusThe status field is encoded in hex in the format 1108290001Sglebiusdescribed in Appendix A of the NTP specification RFC 1305. 1109290001SglebiusThe final four fields show the offset, 1110290001Sglebiusdelay, dispersion and RMS jitter, all in seconds. 1111290001Sglebius@item @code{rawstats} 1112290001SglebiusEnables recording of raw-timestamp statistics information. 1113290001SglebiusThis 1114290001Sglebiusincludes statistics records of all peers of a NTP server and of 1115290001Sglebiusspecial signals, where present and configured. 1116290001SglebiusEach NTP message 1117290001Sglebiusreceived from a peer or clock driver appends a line of the 1118290001Sglebiusfollowing form to the file generation set named 1119290001Sglebius@code{rawstats}: 1120290001Sglebius@verbatim 1121290001Sglebius50928 2132.543 128.4.1.1 128.4.1.20 3102453281.584327000 3102453281.58622800031 02453332.540806000 3102453332.541458000 1122290001Sglebius@end verbatim 1123290001Sglebius 1124290001SglebiusThe first two fields show the date (Modified Julian Day) and 1125290001Sglebiustime (seconds and fraction past UTC midnight). 1126290001SglebiusThe next two fields 1127290001Sglebiusshow the remote peer or clock address followed by the local address 1128290001Sglebiusin dotted-quad notation. 1129290001SglebiusThe final four fields show the originate, 1130290001Sglebiusreceive, transmit and final NTP timestamps in order. 1131290001SglebiusThe timestamp 1132290001Sglebiusvalues are as received and before processing by the various data 1133290001Sglebiussmoothing and mitigation algorithms. 1134290001Sglebius@item @code{sysstats} 1135290001SglebiusEnables recording of ntpd statistics counters on a periodic basis. 1136290001SglebiusEach 1137290001Sglebiushour a line of the following form is appended to the file generation 1138290001Sglebiusset named 1139290001Sglebius@code{sysstats}: 1140290001Sglebius@verbatim 1141290001Sglebius50928 2132.543 36000 81965 0 9546 56 71793 512 540 10 147 1142290001Sglebius@end verbatim 1143290001Sglebius 1144290001SglebiusThe first two fields show the date (Modified Julian Day) and time 1145290001Sglebius(seconds and fraction past UTC midnight). 1146290001SglebiusThe remaining ten fields show 1147290001Sglebiusthe statistics counter values accumulated since the last generated 1148290001Sglebiusline. 1149290001Sglebius@table @asis 1150290001Sglebius@item Time since restart @code{36000} 1151290001SglebiusTime in hours since the system was last rebooted. 1152290001Sglebius@item Packets received @code{81965} 1153290001SglebiusTotal number of packets received. 1154290001Sglebius@item Packets processed @code{0} 1155290001SglebiusNumber of packets received in response to previous packets sent 1156290001Sglebius@item Current version @code{9546} 1157290001SglebiusNumber of packets matching the current NTP version. 1158290001Sglebius@item Previous version @code{56} 1159290001SglebiusNumber of packets matching the previous NTP version. 1160290001Sglebius@item Bad version @code{71793} 1161290001SglebiusNumber of packets matching neither NTP version. 1162290001Sglebius@item Access denied @code{512} 1163290001SglebiusNumber of packets denied access for any reason. 1164290001Sglebius@item Bad length or format @code{540} 1165290001SglebiusNumber of packets with invalid length, format or port number. 1166290001Sglebius@item Bad authentication @code{10} 1167290001SglebiusNumber of packets not verified as authentic. 1168290001Sglebius@item Rate exceeded @code{147} 1169290001SglebiusNumber of packets discarded due to rate limitation. 1170290001Sglebius@end table 1171290001Sglebius@item @code{statsdir} @kbd{directory_path} 1172290001SglebiusIndicates the full path of a directory where statistics files 1173290001Sglebiusshould be created (see below). 1174290001SglebiusThis keyword allows 1175290001Sglebiusthe (otherwise constant) 1176290001Sglebius@code{filegen} 1177290001Sglebiusfilename prefix to be modified for file generation sets, which 1178290001Sglebiusis useful for handling statistics logs. 1179290001Sglebius@item @code{filegen} @kbd{name} @code{[@code{file} @kbd{filename}]} @code{[@code{type} @kbd{typename}]} @code{[@code{link} | @code{nolink}]} @code{[@code{enable} | @code{disable}]} 1180290001SglebiusConfigures setting of generation file set name. 1181290001SglebiusGeneration 1182290001Sglebiusfile sets provide a means for handling files that are 1183290001Sglebiuscontinuously growing during the lifetime of a server. 1184290001SglebiusServer statistics are a typical example for such files. 1185290001SglebiusGeneration file sets provide access to a set of files used 1186290001Sglebiusto store the actual data. 1187290001SglebiusAt any time at most one element 1188290001Sglebiusof the set is being written to. 1189290001SglebiusThe type given specifies 1190290001Sglebiuswhen and how data will be directed to a new element of the set. 1191290001SglebiusThis way, information stored in elements of a file set 1192290001Sglebiusthat are currently unused are available for administrational 1193290001Sglebiusoperations without the risk of disturbing the operation of ntpd. 1194290001Sglebius(Most important: they can be removed to free space for new data 1195290001Sglebiusproduced.) 1196290001Sglebius 1197290001SglebiusNote that this command can be sent from the 1198290001Sglebius@code{ntpdc(1ntpdcmdoc)} 1199290001Sglebiusprogram running at a remote location. 1200290001Sglebius@table @asis 1201290001Sglebius@item @code{name} 1202290001SglebiusThis is the type of the statistics records, as shown in the 1203290001Sglebius@code{statistics} 1204290001Sglebiuscommand. 1205290001Sglebius@item @code{file} @kbd{filename} 1206290001SglebiusThis is the file name for the statistics records. 1207290001SglebiusFilenames of set 1208290001Sglebiusmembers are built from three concatenated elements 1209290001Sglebius@code{prefix}, 1210290001Sglebius@code{filename} 1211290001Sglebiusand 1212290001Sglebius@code{suffix}: 1213290001Sglebius@table @asis 1214290001Sglebius@item @code{prefix} 1215290001SglebiusThis is a constant filename path. 1216290001SglebiusIt is not subject to 1217290001Sglebiusmodifications via the 1218290001Sglebius@kbd{filegen} 1219290001Sglebiusoption. 1220290001SglebiusIt is defined by the 1221290001Sglebiusserver, usually specified as a compile-time constant. 1222290001SglebiusIt may, 1223290001Sglebiushowever, be configurable for individual file generation sets 1224290001Sglebiusvia other commands. 1225290001SglebiusFor example, the prefix used with 1226290001Sglebius@kbd{loopstats} 1227290001Sglebiusand 1228290001Sglebius@kbd{peerstats} 1229290001Sglebiusgeneration can be configured using the 1230290001Sglebius@kbd{statsdir} 1231290001Sglebiusoption explained above. 1232290001Sglebius@item @code{filename} 1233290001SglebiusThis string is directly concatenated to the prefix mentioned 1234290001Sglebiusabove (no intervening 1235290001Sglebius@quoteleft{}/@quoteright{}). 1236290001SglebiusThis can be modified using 1237290001Sglebiusthe file argument to the 1238290001Sglebius@kbd{filegen} 1239290001Sglebiusstatement. 1240290001SglebiusNo 1241290001Sglebius@file{..} 1242290001Sglebiuselements are 1243290001Sglebiusallowed in this component to prevent filenames referring to 1244290001Sglebiusparts outside the filesystem hierarchy denoted by 1245290001Sglebius@kbd{prefix}. 1246290001Sglebius@item @code{suffix} 1247290001SglebiusThis part is reflects individual elements of a file set. 1248290001SglebiusIt is 1249290001Sglebiusgenerated according to the type of a file set. 1250290001Sglebius@end table 1251290001Sglebius@item @code{type} @kbd{typename} 1252290001SglebiusA file generation set is characterized by its type. 1253290001SglebiusThe following 1254290001Sglebiustypes are supported: 1255290001Sglebius@table @asis 1256290001Sglebius@item @code{none} 1257290001SglebiusThe file set is actually a single plain file. 1258290001Sglebius@item @code{pid} 1259290001SglebiusOne element of file set is used per incarnation of a ntpd 1260290001Sglebiusserver. 1261290001SglebiusThis type does not perform any changes to file set 1262290001Sglebiusmembers during runtime, however it provides an easy way of 1263290001Sglebiusseparating files belonging to different 1264290001Sglebius@code{ntpd(1ntpdmdoc)} 1265290001Sglebiusserver incarnations. 1266290001SglebiusThe set member filename is built by appending a 1267290001Sglebius@quoteleft{}.@quoteright{} 1268290001Sglebiusto concatenated 1269290001Sglebius@kbd{prefix} 1270290001Sglebiusand 1271290001Sglebius@kbd{filename} 1272290001Sglebiusstrings, and 1273290001Sglebiusappending the decimal representation of the process ID of the 1274290001Sglebius@code{ntpd(1ntpdmdoc)} 1275290001Sglebiusserver process. 1276290001Sglebius@item @code{day} 1277290001SglebiusOne file generation set element is created per day. 1278290001SglebiusA day is 1279290001Sglebiusdefined as the period between 00:00 and 24:00 UTC. 1280290001SglebiusThe file set 1281290001Sglebiusmember suffix consists of a 1282290001Sglebius@quoteleft{}.@quoteright{} 1283290001Sglebiusand a day specification in 1284290001Sglebiusthe form 1285290001Sglebius@code{YYYYMMdd}. 1286290001Sglebius@code{YYYY} 1287290001Sglebiusis a 4-digit year number (e.g., 1992). 1288290001Sglebius@code{MM} 1289290001Sglebiusis a two digit month number. 1290290001Sglebius@code{dd} 1291290001Sglebiusis a two digit day number. 1292290001SglebiusThus, all information written at 10 December 1992 would end up 1293290001Sglebiusin a file named 1294290001Sglebius@kbd{prefix} 1295290001Sglebius@kbd{filename}.19921210. 1296290001Sglebius@item @code{week} 1297290001SglebiusAny file set member contains data related to a certain week of 1298290001Sglebiusa year. 1299290001SglebiusThe term week is defined by computing day-of-year 1300290001Sglebiusmodulo 7. 1301290001SglebiusElements of such a file generation set are 1302290001Sglebiusdistinguished by appending the following suffix to the file set 1303290001Sglebiusfilename base: A dot, a 4-digit year number, the letter 1304290001Sglebius@code{W}, 1305290001Sglebiusand a 2-digit week number. 1306290001SglebiusFor example, information from January, 1307290001Sglebius10th 1992 would end up in a file with suffix 1308290001Sglebius.No . Ns Ar 1992W1 . 1309290001Sglebius@item @code{month} 1310290001SglebiusOne generation file set element is generated per month. 1311290001SglebiusThe 1312290001Sglebiusfile name suffix consists of a dot, a 4-digit year number, and 1313290001Sglebiusa 2-digit month. 1314290001Sglebius@item @code{year} 1315290001SglebiusOne generation file element is generated per year. 1316290001SglebiusThe filename 1317290001Sglebiussuffix consists of a dot and a 4 digit year number. 1318290001Sglebius@item @code{age} 1319290001SglebiusThis type of file generation sets changes to a new element of 1320290001Sglebiusthe file set every 24 hours of server operation. 1321290001SglebiusThe filename 1322290001Sglebiussuffix consists of a dot, the letter 1323290001Sglebius@code{a}, 1324290001Sglebiusand an 8-digit number. 1325290001SglebiusThis number is taken to be the number of seconds the server is 1326290001Sglebiusrunning at the start of the corresponding 24-hour period. 1327290001SglebiusInformation is only written to a file generation by specifying 1328290001Sglebius@code{enable}; 1329290001Sglebiusoutput is prevented by specifying 1330290001Sglebius@code{disable}. 1331290001Sglebius@end table 1332290001Sglebius@item @code{link} | @code{nolink} 1333290001SglebiusIt is convenient to be able to access the current element of a file 1334290001Sglebiusgeneration set by a fixed name. 1335290001SglebiusThis feature is enabled by 1336290001Sglebiusspecifying 1337290001Sglebius@code{link} 1338290001Sglebiusand disabled using 1339290001Sglebius@code{nolink}. 1340290001SglebiusIf link is specified, a 1341290001Sglebiushard link from the current file set element to a file without 1342290001Sglebiussuffix is created. 1343290001SglebiusWhen there is already a file with this name and 1344290001Sglebiusthe number of links of this file is one, it is renamed appending a 1345290001Sglebiusdot, the letter 1346290001Sglebius@code{C}, 1347298770Sdelphijand the pid of the 1348298770Sdelphij@code{ntpd(1ntpdmdoc)} 1349298770Sdelphijserver process. 1350290001SglebiusWhen the 1351290001Sglebiusnumber of links is greater than one, the file is unlinked. 1352290001SglebiusThis 1353290001Sglebiusallows the current file to be accessed by a constant name. 1354290001Sglebius@item @code{enable} @code{|} @code{disable} 1355290001SglebiusEnables or disables the recording function. 1356290001Sglebius@end table 1357290001Sglebius@end table 1358290001Sglebius@end table 1359290001Sglebius@node Access Control Support 1360290001Sglebius@subsection Access Control Support 1361290001SglebiusThe 1362290001Sglebius@code{ntpd(1ntpdmdoc)} 1363290001Sglebiusdaemon implements a general purpose address/mask based restriction 1364290001Sglebiuslist. 1365290001SglebiusThe list contains address/match entries sorted first 1366290001Sglebiusby increasing address values and and then by increasing mask values. 1367290001SglebiusA match occurs when the bitwise AND of the mask and the packet 1368290001Sglebiussource address is equal to the bitwise AND of the mask and 1369290001Sglebiusaddress in the list. 1370290001SglebiusThe list is searched in order with the 1371290001Sglebiuslast match found defining the restriction flags associated 1372290001Sglebiuswith the entry. 1373290001SglebiusAdditional information and examples can be found in the 1374290001Sglebius"Notes on Configuring NTP and Setting up a NTP Subnet" 1375290001Sglebiuspage 1376290001Sglebius(available as part of the HTML documentation 1377290001Sglebiusprovided in 1378290001Sglebius@file{/usr/share/doc/ntp}). 1379290001Sglebius 1380290001SglebiusThe restriction facility was implemented in conformance 1381290001Sglebiuswith the access policies for the original NSFnet backbone 1382290001Sglebiustime servers. 1383290001SglebiusLater the facility was expanded to deflect 1384290001Sglebiuscryptographic and clogging attacks. 1385290001SglebiusWhile this facility may 1386290001Sglebiusbe useful for keeping unwanted or broken or malicious clients 1387290001Sglebiusfrom congesting innocent servers, it should not be considered 1388290001Sglebiusan alternative to the NTP authentication facilities. 1389290001SglebiusSource address based restrictions are easily circumvented 1390290001Sglebiusby a determined cracker. 1391290001Sglebius 1392290001SglebiusClients can be denied service because they are explicitly 1393298770Sdelphijincluded in the restrict list created by the 1394298770Sdelphij@code{restrict} 1395298770Sdelphijcommand 1396290001Sglebiusor implicitly as the result of cryptographic or rate limit 1397290001Sglebiusviolations. 1398290001SglebiusCryptographic violations include certificate 1399290001Sglebiusor identity verification failure; rate limit violations generally 1400290001Sglebiusresult from defective NTP implementations that send packets 1401290001Sglebiusat abusive rates. 1402290001SglebiusSome violations cause denied service 1403290001Sglebiusonly for the offending packet, others cause denied service 1404290001Sglebiusfor a timed period and others cause the denied service for 1405298770Sdelphijan indefinite period. 1406290001SglebiusWhen a client or network is denied access 1407298770Sdelphijfor an indefinite period, the only way at present to remove 1408290001Sglebiusthe restrictions is by restarting the server. 1409290001Sglebius@subsubsection The Kiss-of-Death Packet 1410290001SglebiusOrdinarily, packets denied service are simply dropped with no 1411290001Sglebiusfurther action except incrementing statistics counters. 1412290001SglebiusSometimes a 1413290001Sglebiusmore proactive response is needed, such as a server message that 1414290001Sglebiusexplicitly requests the client to stop sending and leave a message 1415290001Sglebiusfor the system operator. 1416290001SglebiusA special packet format has been created 1417290001Sglebiusfor this purpose called the "kiss-of-death" (KoD) packet. 1418290001SglebiusKoD packets have the leap bits set unsynchronized and stratum set 1419290001Sglebiusto zero and the reference identifier field set to a four-byte 1420290001SglebiusASCII code. 1421290001SglebiusIf the 1422290001Sglebius@code{noserve} 1423290001Sglebiusor 1424290001Sglebius@code{notrust} 1425290001Sglebiusflag of the matching restrict list entry is set, 1426290001Sglebiusthe code is "DENY"; if the 1427290001Sglebius@code{limited} 1428290001Sglebiusflag is set and the rate limit 1429290001Sglebiusis exceeded, the code is "RATE". 1430290001SglebiusFinally, if a cryptographic violation occurs, the code is "CRYP". 1431290001Sglebius 1432290001SglebiusA client receiving a KoD performs a set of sanity checks to 1433290001Sglebiusminimize security exposure, then updates the stratum and 1434290001Sglebiusreference identifier peer variables, sets the access 1435290001Sglebiusdenied (TEST4) bit in the peer flash variable and sends 1436290001Sglebiusa message to the log. 1437290001SglebiusAs long as the TEST4 bit is set, 1438290001Sglebiusthe client will send no further packets to the server. 1439290001SglebiusThe only way at present to recover from this condition is 1440290001Sglebiusto restart the protocol at both the client and server. 1441290001SglebiusThis 1442290001Sglebiushappens automatically at the client when the association times out. 1443290001SglebiusIt will happen at the server only if the server operator cooperates. 1444290001Sglebius@subsubsection Access Control Commands 1445290001Sglebius@table @asis 1446290001Sglebius@item @code{discard} @code{[@code{average} @kbd{avg}]} @code{[@code{minimum} @kbd{min}]} @code{[@code{monitor} @kbd{prob}]} 1447290001SglebiusSet the parameters of the 1448290001Sglebius@code{limited} 1449290001Sglebiusfacility which protects the server from 1450290001Sglebiusclient abuse. 1451290001SglebiusThe 1452290001Sglebius@code{average} 1453290001Sglebiussubcommand specifies the minimum average packet 1454290001Sglebiusspacing, while the 1455290001Sglebius@code{minimum} 1456290001Sglebiussubcommand specifies the minimum packet spacing. 1457290001SglebiusPackets that violate these minima are discarded 1458290001Sglebiusand a kiss-o'-death packet returned if enabled. 1459290001SglebiusThe default 1460290001Sglebiusminimum average and minimum are 5 and 2, respectively. 1461298770SdelphijThe 1462298770Sdelphij@code{monitor} 1463298770Sdelphijsubcommand specifies the probability of discard 1464290001Sglebiusfor packets that overflow the rate-control window. 1465290001Sglebius@item @code{restrict} @code{address} @code{[@code{mask} @kbd{mask}]} @code{[@kbd{flag} @kbd{...}]} 1466290001SglebiusThe 1467290001Sglebius@kbd{address} 1468290001Sglebiusargument expressed in 1469290001Sglebiusdotted-quad form is the address of a host or network. 1470290001SglebiusAlternatively, the 1471290001Sglebius@kbd{address} 1472290001Sglebiusargument can be a valid host DNS name. 1473290001SglebiusThe 1474290001Sglebius@kbd{mask} 1475290001Sglebiusargument expressed in dotted-quad form defaults to 1476290001Sglebius@code{255.255.255.255}, 1477290001Sglebiusmeaning that the 1478290001Sglebius@kbd{address} 1479290001Sglebiusis treated as the address of an individual host. 1480290001SglebiusA default entry (address 1481290001Sglebius@code{0.0.0.0}, 1482290001Sglebiusmask 1483290001Sglebius@code{0.0.0.0}) 1484290001Sglebiusis always included and is always the first entry in the list. 1485290001SglebiusNote that text string 1486290001Sglebius@code{default}, 1487290001Sglebiuswith no mask option, may 1488290001Sglebiusbe used to indicate the default entry. 1489290001SglebiusIn the current implementation, 1490290001Sglebius@code{flag} 1491290001Sglebiusalways 1492290001Sglebiusrestricts access, i.e., an entry with no flags indicates that free 1493290001Sglebiusaccess to the server is to be given. 1494290001SglebiusThe flags are not orthogonal, 1495290001Sglebiusin that more restrictive flags will often make less restrictive 1496290001Sglebiusones redundant. 1497290001SglebiusThe flags can generally be classed into two 1498290001Sglebiuscategories, those which restrict time service and those which 1499290001Sglebiusrestrict informational queries and attempts to do run-time 1500290001Sglebiusreconfiguration of the server. 1501290001SglebiusOne or more of the following flags 1502290001Sglebiusmay be specified: 1503290001Sglebius@table @asis 1504290001Sglebius@item @code{ignore} 1505290001SglebiusDeny packets of all kinds, including 1506290001Sglebius@code{ntpq(1ntpqmdoc)} 1507290001Sglebiusand 1508290001Sglebius@code{ntpdc(1ntpdcmdoc)} 1509290001Sglebiusqueries. 1510290001Sglebius@item @code{kod} 1511290001SglebiusIf this flag is set when an access violation occurs, a kiss-o'-death 1512290001Sglebius(KoD) packet is sent. 1513290001SglebiusKoD packets are rate limited to no more than one 1514290001Sglebiusper second. 1515290001SglebiusIf another KoD packet occurs within one second after the 1516290001Sglebiuslast one, the packet is dropped. 1517290001Sglebius@item @code{limited} 1518290001SglebiusDeny service if the packet spacing violates the lower limits specified 1519298770Sdelphijin the 1520298770Sdelphij@code{discard} 1521298770Sdelphijcommand. 1522290001SglebiusA history of clients is kept using the 1523290001Sglebiusmonitoring capability of 1524290001Sglebius@code{ntpd(1ntpdmdoc)}. 1525290001SglebiusThus, monitoring is always active as 1526290001Sglebiuslong as there is a restriction entry with the 1527290001Sglebius@code{limited} 1528290001Sglebiusflag. 1529290001Sglebius@item @code{lowpriotrap} 1530290001SglebiusDeclare traps set by matching hosts to be low priority. 1531290001SglebiusThe 1532290001Sglebiusnumber of traps a server can maintain is limited (the current limit 1533290001Sglebiusis 3). 1534290001SglebiusTraps are usually assigned on a first come, first served 1535290001Sglebiusbasis, with later trap requestors being denied service. 1536290001SglebiusThis flag 1537290001Sglebiusmodifies the assignment algorithm by allowing low priority traps to 1538290001Sglebiusbe overridden by later requests for normal priority traps. 1539290001Sglebius@item @code{nomodify} 1540290001SglebiusDeny 1541290001Sglebius@code{ntpq(1ntpqmdoc)} 1542290001Sglebiusand 1543290001Sglebius@code{ntpdc(1ntpdcmdoc)} 1544290001Sglebiusqueries which attempt to modify the state of the 1545290001Sglebiusserver (i.e., run time reconfiguration). 1546290001SglebiusQueries which return 1547290001Sglebiusinformation are permitted. 1548290001Sglebius@item @code{noquery} 1549290001SglebiusDeny 1550290001Sglebius@code{ntpq(1ntpqmdoc)} 1551290001Sglebiusand 1552290001Sglebius@code{ntpdc(1ntpdcmdoc)} 1553290001Sglebiusqueries. 1554290001SglebiusTime service is not affected. 1555290001Sglebius@item @code{nopeer} 1556290001SglebiusDeny packets which would result in mobilizing a new association. 1557290001SglebiusThis 1558290001Sglebiusincludes broadcast and symmetric active packets when a configured 1559290001Sglebiusassociation does not exist. 1560290001SglebiusIt also includes 1561290001Sglebius@code{pool} 1562290001Sglebiusassociations, so if you want to use servers from a 1563290001Sglebius@code{pool} 1564290001Sglebiusdirective and also want to use 1565290001Sglebius@code{nopeer} 1566290001Sglebiusby default, you'll want a 1567290001Sglebius@code{restrict source ...} @code{line} @code{as} @code{well} @code{that} @code{does} 1568290001Sglebius@item not 1569290001Sglebiusinclude the 1570290001Sglebius@code{nopeer} 1571290001Sglebiusdirective. 1572290001Sglebius@item @code{noserve} 1573290001SglebiusDeny all packets except 1574290001Sglebius@code{ntpq(1ntpqmdoc)} 1575290001Sglebiusand 1576290001Sglebius@code{ntpdc(1ntpdcmdoc)} 1577290001Sglebiusqueries. 1578290001Sglebius@item @code{notrap} 1579290001SglebiusDecline to provide mode 6 control message trap service to matching 1580290001Sglebiushosts. 1581298770SdelphijThe trap service is a subsystem of the 1582298770Sdelphij@code{ntpq(1ntpqmdoc)} 1583298770Sdelphijcontrol message 1584290001Sglebiusprotocol which is intended for use by remote event logging programs. 1585290001Sglebius@item @code{notrust} 1586290001SglebiusDeny service unless the packet is cryptographically authenticated. 1587290001Sglebius@item @code{ntpport} 1588290001SglebiusThis is actually a match algorithm modifier, rather than a 1589290001Sglebiusrestriction flag. 1590290001SglebiusIts presence causes the restriction entry to be 1591290001Sglebiusmatched only if the source port in the packet is the standard NTP 1592290001SglebiusUDP port (123). 1593290001SglebiusBoth 1594290001Sglebius@code{ntpport} 1595290001Sglebiusand 1596290001Sglebius@code{non-ntpport} 1597290001Sglebiusmay 1598290001Sglebiusbe specified. 1599290001SglebiusThe 1600290001Sglebius@code{ntpport} 1601290001Sglebiusis considered more specific and 1602290001Sglebiusis sorted later in the list. 1603290001Sglebius@item @code{version} 1604290001SglebiusDeny packets that do not match the current NTP version. 1605290001Sglebius@end table 1606290001Sglebius 1607290001SglebiusDefault restriction list entries with the flags ignore, interface, 1608290001Sglebiusntpport, for each of the local host's interface addresses are 1609290001Sglebiusinserted into the table at startup to prevent the server 1610290001Sglebiusfrom attempting to synchronize to its own time. 1611290001SglebiusA default entry is also always present, though if it is 1612290001Sglebiusotherwise unconfigured; no flags are associated 1613290001Sglebiuswith the default entry (i.e., everything besides your own 1614290001SglebiusNTP server is unrestricted). 1615290001Sglebius@end table 1616290001Sglebius@node Automatic NTP Configuration Options 1617290001Sglebius@subsection Automatic NTP Configuration Options 1618290001Sglebius@subsubsection Manycasting 1619290001SglebiusManycasting is a automatic discovery and configuration paradigm 1620290001Sglebiusnew to NTPv4. 1621290001SglebiusIt is intended as a means for a multicast client 1622290001Sglebiusto troll the nearby network neighborhood to find cooperating 1623290001Sglebiusmanycast servers, validate them using cryptographic means 1624290001Sglebiusand evaluate their time values with respect to other servers 1625290001Sglebiusthat might be lurking in the vicinity. 1626290001SglebiusThe intended result is that each manycast client mobilizes 1627290001Sglebiusclient associations with some number of the "best" 1628290001Sglebiusof the nearby manycast servers, yet automatically reconfigures 1629290001Sglebiusto sustain this number of servers should one or another fail. 1630290001Sglebius 1631290001SglebiusNote that the manycasting paradigm does not coincide 1632290001Sglebiuswith the anycast paradigm described in RFC-1546, 1633290001Sglebiuswhich is designed to find a single server from a clique 1634290001Sglebiusof servers providing the same service. 1635290001SglebiusThe manycast paradigm is designed to find a plurality 1636290001Sglebiusof redundant servers satisfying defined optimality criteria. 1637290001Sglebius 1638290001SglebiusManycasting can be used with either symmetric key 1639290001Sglebiusor public key cryptography. 1640290001SglebiusThe public key infrastructure (PKI) 1641290001Sglebiusoffers the best protection against compromised keys 1642290001Sglebiusand is generally considered stronger, at least with relatively 1643290001Sglebiuslarge key sizes. 1644290001SglebiusIt is implemented using the Autokey protocol and 1645290001Sglebiusthe OpenSSL cryptographic library available from 1646290001Sglebius@code{http://www.openssl.org/}. 1647290001SglebiusThe library can also be used with other NTPv4 modes 1648290001Sglebiusas well and is highly recommended, especially for broadcast modes. 1649290001Sglebius 1650290001SglebiusA persistent manycast client association is configured 1651298770Sdelphijusing the 1652298770Sdelphij@code{manycastclient} 1653298770Sdelphijcommand, which is similar to the 1654298770Sdelphij@code{server} 1655298770Sdelphijcommand but with a multicast (IPv4 class 1656290001Sglebius@code{D} 1657290001Sglebiusor IPv6 prefix 1658290001Sglebius@code{FF}) 1659290001Sglebiusgroup address. 1660290001SglebiusThe IANA has designated IPv4 address 224.1.1.1 1661290001Sglebiusand IPv6 address FF05::101 (site local) for NTP. 1662290001SglebiusWhen more servers are needed, it broadcasts manycast 1663290001Sglebiusclient messages to this address at the minimum feasible rate 1664290001Sglebiusand minimum feasible time-to-live (TTL) hops, depending 1665290001Sglebiuson how many servers have already been found. 1666290001SglebiusThere can be as many manycast client associations 1667290001Sglebiusas different group address, each one serving as a template 1668290001Sglebiusfor a future ephemeral unicast client/server association. 1669290001Sglebius 1670290001SglebiusManycast servers configured with the 1671290001Sglebius@code{manycastserver} 1672290001Sglebiuscommand listen on the specified group address for manycast 1673290001Sglebiusclient messages. 1674290001SglebiusNote the distinction between manycast client, 1675290001Sglebiuswhich actively broadcasts messages, and manycast server, 1676290001Sglebiuswhich passively responds to them. 1677290001SglebiusIf a manycast server is 1678290001Sglebiusin scope of the current TTL and is itself synchronized 1679290001Sglebiusto a valid source and operating at a stratum level equal 1680290001Sglebiusto or lower than the manycast client, it replies to the 1681290001Sglebiusmanycast client message with an ordinary unicast server message. 1682290001Sglebius 1683290001SglebiusThe manycast client receiving this message mobilizes 1684290001Sglebiusan ephemeral client/server association according to the 1685290001Sglebiusmatching manycast client template, but only if cryptographically 1686290001Sglebiusauthenticated and the server stratum is less than or equal 1687290001Sglebiusto the client stratum. 1688290001SglebiusAuthentication is explicitly required 1689290001Sglebiusand either symmetric key or public key (Autokey) can be used. 1690290001SglebiusThen, the client polls the server at its unicast address 1691290001Sglebiusin burst mode in order to reliably set the host clock 1692290001Sglebiusand validate the source. 1693290001SglebiusThis normally results 1694290001Sglebiusin a volley of eight client/server at 2-s intervals 1695290001Sglebiusduring which both the synchronization and cryptographic 1696290001Sglebiusprotocols run concurrently. 1697290001SglebiusFollowing the volley, 1698290001Sglebiusthe client runs the NTP intersection and clustering 1699290001Sglebiusalgorithms, which act to discard all but the "best" 1700290001Sglebiusassociations according to stratum and synchronization 1701290001Sglebiusdistance. 1702290001SglebiusThe surviving associations then continue 1703290001Sglebiusin ordinary client/server mode. 1704290001Sglebius 1705290001SglebiusThe manycast client polling strategy is designed to reduce 1706290001Sglebiusas much as possible the volume of manycast client messages 1707290001Sglebiusand the effects of implosion due to near-simultaneous 1708290001Sglebiusarrival of manycast server messages. 1709290001SglebiusThe strategy is determined by the 1710290001Sglebius@code{manycastclient}, 1711290001Sglebius@code{tos} 1712290001Sglebiusand 1713290001Sglebius@code{ttl} 1714290001Sglebiusconfiguration commands. 1715290001SglebiusThe manycast poll interval is 1716290001Sglebiusnormally eight times the system poll interval, 1717290001Sglebiuswhich starts out at the 1718290001Sglebius@code{minpoll} 1719290001Sglebiusvalue specified in the 1720290001Sglebius@code{manycastclient}, 1721290001Sglebiuscommand and, under normal circumstances, increments to the 1722290001Sglebius@code{maxpolll} 1723290001Sglebiusvalue specified in this command. 1724290001SglebiusInitially, the TTL is 1725298770Sdelphijset at the minimum hops specified by the 1726298770Sdelphij@code{ttl} 1727298770Sdelphijcommand. 1728290001SglebiusAt each retransmission the TTL is increased until reaching 1729290001Sglebiusthe maximum hops specified by this command or a sufficient 1730290001Sglebiusnumber client associations have been found. 1731290001SglebiusFurther retransmissions use the same TTL. 1732290001Sglebius 1733290001SglebiusThe quality and reliability of the suite of associations 1734290001Sglebiusdiscovered by the manycast client is determined by the NTP 1735290001Sglebiusmitigation algorithms and the 1736290001Sglebius@code{minclock} 1737290001Sglebiusand 1738290001Sglebius@code{minsane} 1739290001Sglebiusvalues specified in the 1740290001Sglebius@code{tos} 1741290001Sglebiusconfiguration command. 1742290001SglebiusAt least 1743290001Sglebius@code{minsane} 1744290001Sglebiuscandidate servers must be available and the mitigation 1745290001Sglebiusalgorithms produce at least 1746290001Sglebius@code{minclock} 1747290001Sglebiussurvivors in order to synchronize the clock. 1748290001SglebiusByzantine agreement principles require at least four 1749290001Sglebiuscandidates in order to correctly discard a single falseticker. 1750290001SglebiusFor legacy purposes, 1751290001Sglebius@code{minsane} 1752290001Sglebiusdefaults to 1 and 1753290001Sglebius@code{minclock} 1754290001Sglebiusdefaults to 3. 1755290001SglebiusFor manycast service 1756290001Sglebius@code{minsane} 1757290001Sglebiusshould be explicitly set to 4, assuming at least that 1758290001Sglebiusnumber of servers are available. 1759290001Sglebius 1760290001SglebiusIf at least 1761290001Sglebius@code{minclock} 1762290001Sglebiusservers are found, the manycast poll interval is immediately 1763290001Sglebiusset to eight times 1764290001Sglebius@code{maxpoll}. 1765290001SglebiusIf less than 1766290001Sglebius@code{minclock} 1767290001Sglebiusservers are found when the TTL has reached the maximum hops, 1768290001Sglebiusthe manycast poll interval is doubled. 1769290001SglebiusFor each transmission 1770290001Sglebiusafter that, the poll interval is doubled again until 1771290001Sglebiusreaching the maximum of eight times 1772290001Sglebius@code{maxpoll}. 1773290001SglebiusFurther transmissions use the same poll interval and 1774290001SglebiusTTL values. 1775290001SglebiusNote that while all this is going on, 1776290001Sglebiuseach client/server association found is operating normally 1777290001Sglebiusit the system poll interval. 1778290001Sglebius 1779290001SglebiusAdministratively scoped multicast boundaries are normally 1780290001Sglebiusspecified by the network router configuration and, 1781290001Sglebiusin the case of IPv6, the link/site scope prefix. 1782290001SglebiusBy default, the increment for TTL hops is 32 starting 1783290001Sglebiusfrom 31; however, the 1784290001Sglebius@code{ttl} 1785290001Sglebiusconfiguration command can be 1786290001Sglebiusused to modify the values to match the scope rules. 1787290001Sglebius 1788290001SglebiusIt is often useful to narrow the range of acceptable 1789290001Sglebiusservers which can be found by manycast client associations. 1790290001SglebiusBecause manycast servers respond only when the client 1791290001Sglebiusstratum is equal to or greater than the server stratum, 1792290001Sglebiusprimary (stratum 1) servers fill find only primary servers 1793290001Sglebiusin TTL range, which is probably the most common objective. 1794290001SglebiusHowever, unless configured otherwise, all manycast clients 1795290001Sglebiusin TTL range will eventually find all primary servers 1796290001Sglebiusin TTL range, which is probably not the most common 1797290001Sglebiusobjective in large networks. 1798290001SglebiusThe 1799290001Sglebius@code{tos} 1800290001Sglebiuscommand can be used to modify this behavior. 1801290001SglebiusServers with stratum below 1802290001Sglebius@code{floor} 1803290001Sglebiusor above 1804290001Sglebius@code{ceiling} 1805290001Sglebiusspecified in the 1806290001Sglebius@code{tos} 1807290001Sglebiuscommand are strongly discouraged during the selection 1808290001Sglebiusprocess; however, these servers may be temporally 1809290001Sglebiusaccepted if the number of servers within TTL range is 1810290001Sglebiusless than 1811290001Sglebius@code{minclock}. 1812290001Sglebius 1813290001SglebiusThe above actions occur for each manycast client message, 1814290001Sglebiuswhich repeats at the designated poll interval. 1815290001SglebiusHowever, once the ephemeral client association is mobilized, 1816290001Sglebiussubsequent manycast server replies are discarded, 1817290001Sglebiussince that would result in a duplicate association. 1818290001SglebiusIf during a poll interval the number of client associations 1819290001Sglebiusfalls below 1820290001Sglebius@code{minclock}, 1821290001Sglebiusall manycast client prototype associations are reset 1822290001Sglebiusto the initial poll interval and TTL hops and operation 1823290001Sglebiusresumes from the beginning. 1824290001SglebiusIt is important to avoid 1825290001Sglebiusfrequent manycast client messages, since each one requires 1826290001Sglebiusall manycast servers in TTL range to respond. 1827290001SglebiusThe result could well be an implosion, either minor or major, 1828290001Sglebiusdepending on the number of servers in range. 1829290001SglebiusThe recommended value for 1830290001Sglebius@code{maxpoll} 1831290001Sglebiusis 12 (4,096 s). 1832290001Sglebius 1833290001SglebiusIt is possible and frequently useful to configure a host 1834290001Sglebiusas both manycast client and manycast server. 1835290001SglebiusA number of hosts configured this way and sharing a common 1836290001Sglebiusgroup address will automatically organize themselves 1837290001Sglebiusin an optimum configuration based on stratum and 1838290001Sglebiussynchronization distance. 1839290001SglebiusFor example, consider an NTP 1840290001Sglebiussubnet of two primary servers and a hundred or more 1841290001Sglebiusdependent clients. 1842290001SglebiusWith two exceptions, all servers 1843290001Sglebiusand clients have identical configuration files including both 1844290001Sglebius@code{multicastclient} 1845290001Sglebiusand 1846290001Sglebius@code{multicastserver} 1847290001Sglebiuscommands using, for instance, multicast group address 1848290001Sglebius239.1.1.1. 1849290001SglebiusThe only exception is that each primary server 1850290001Sglebiusconfiguration file must include commands for the primary 1851290001Sglebiusreference source such as a GPS receiver. 1852290001Sglebius 1853290001SglebiusThe remaining configuration files for all secondary 1854290001Sglebiusservers and clients have the same contents, except for the 1855290001Sglebius@code{tos} 1856290001Sglebiuscommand, which is specific for each stratum level. 1857290001SglebiusFor stratum 1 and stratum 2 servers, that command is 1858290001Sglebiusnot necessary. 1859290001SglebiusFor stratum 3 and above servers the 1860290001Sglebius@code{floor} 1861290001Sglebiusvalue is set to the intended stratum number. 1862290001SglebiusThus, all stratum 3 configuration files are identical, 1863290001Sglebiusall stratum 4 files are identical and so forth. 1864290001Sglebius 1865290001SglebiusOnce operations have stabilized in this scenario, 1866290001Sglebiusthe primary servers will find the primary reference source 1867290001Sglebiusand each other, since they both operate at the same 1868290001Sglebiusstratum (1), but not with any secondary server or client, 1869290001Sglebiussince these operate at a higher stratum. 1870290001SglebiusThe secondary 1871290001Sglebiusservers will find the servers at the same stratum level. 1872290001SglebiusIf one of the primary servers loses its GPS receiver, 1873290001Sglebiusit will continue to operate as a client and other clients 1874290001Sglebiuswill time out the corresponding association and 1875290001Sglebiusre-associate accordingly. 1876290001Sglebius 1877290001SglebiusSome administrators prefer to avoid running 1878290001Sglebius@code{ntpd(1ntpdmdoc)} 1879290001Sglebiuscontinuously and run either 1880290001Sglebius@code{sntp(1sntpmdoc)} 1881290001Sglebiusor 1882290001Sglebius@code{ntpd(1ntpdmdoc)} 1883290001Sglebius@code{-q} 1884290001Sglebiusas a cron job. 1885290001SglebiusIn either case the servers must be 1886290001Sglebiusconfigured in advance and the program fails if none are 1887290001Sglebiusavailable when the cron job runs. 1888290001SglebiusA really slick 1889290001Sglebiusapplication of manycast is with 1890290001Sglebius@code{ntpd(1ntpdmdoc)} 1891290001Sglebius@code{-q}. 1892290001SglebiusThe program wakes up, scans the local landscape looking 1893290001Sglebiusfor the usual suspects, selects the best from among 1894290001Sglebiusthe rascals, sets the clock and then departs. 1895290001SglebiusServers do not have to be configured in advance and 1896290001Sglebiusall clients throughout the network can have the same 1897290001Sglebiusconfiguration file. 1898290001Sglebius@subsubsection Manycast Interactions with Autokey 1899290001SglebiusEach time a manycast client sends a client mode packet 1900290001Sglebiusto a multicast group address, all manycast servers 1901290001Sglebiusin scope generate a reply including the host name 1902290001Sglebiusand status word. 1903290001SglebiusThe manycast clients then run 1904290001Sglebiusthe Autokey protocol, which collects and verifies 1905290001Sglebiusall certificates involved. 1906290001SglebiusFollowing the burst interval 1907290001Sglebiusall but three survivors are cast off, 1908290001Sglebiusbut the certificates remain in the local cache. 1909290001SglebiusIt often happens that several complete signing trails 1910290001Sglebiusfrom the client to the primary servers are collected in this way. 1911290001Sglebius 1912290001SglebiusAbout once an hour or less often if the poll interval 1913290001Sglebiusexceeds this, the client regenerates the Autokey key list. 1914290001SglebiusThis is in general transparent in client/server mode. 1915290001SglebiusHowever, about once per day the server private value 1916290001Sglebiusused to generate cookies is refreshed along with all 1917290001Sglebiusmanycast client associations. 1918290001SglebiusIn this case all 1919290001Sglebiuscryptographic values including certificates is refreshed. 1920290001SglebiusIf a new certificate has been generated since 1921290001Sglebiusthe last refresh epoch, it will automatically revoke 1922290001Sglebiusall prior certificates that happen to be in the 1923290001Sglebiuscertificate cache. 1924290001SglebiusAt the same time, the manycast 1925290001Sglebiusscheme starts all over from the beginning and 1926290001Sglebiusthe expanding ring shrinks to the minimum and increments 1927290001Sglebiusfrom there while collecting all servers in scope. 1928310419Sdelphij@subsubsection Broadcast Options 1929310419Sdelphij@table @asis 1930310419Sdelphij@item @code{tos} @code{[@code{bcpollbstep} @kbd{gate}]} 1931310419SdelphijThis command provides a way to delay, 1932310419Sdelphijby the specified number of broadcast poll intervals, 1933310419Sdelphijbelieving backward time steps from a broadcast server. 1934310419SdelphijBroadcast time networks are expected to be trusted. 1935310419SdelphijIn the event a broadcast server's time is stepped backwards, 1936310419Sdelphijthere is clear benefit to having the clients notice this change 1937310419Sdelphijas soon as possible. 1938310419SdelphijAttacks such as replay attacks can happen, however, 1939310419Sdelphijand even though there are a number of protections built in to 1940310419Sdelphijbroadcast mode, attempts to perform a replay attack are possible. 1941310419SdelphijThis value defaults to 0, but can be changed 1942310419Sdelphijto any number of poll intervals between 0 and 4. 1943290001Sglebius@subsubsection Manycast Options 1944290001Sglebius@table @asis 1945290001Sglebius@item @code{tos} @code{[@code{ceiling} @kbd{ceiling} | @code{cohort} @code{@{} @code{0} | @code{1} @code{@}} | @code{floor} @kbd{floor} | @code{minclock} @kbd{minclock} | @code{minsane} @kbd{minsane}]} 1946290001SglebiusThis command affects the clock selection and clustering 1947290001Sglebiusalgorithms. 1948290001SglebiusIt can be used to select the quality and 1949290001Sglebiusquantity of peers used to synchronize the system clock 1950290001Sglebiusand is most useful in manycast mode. 1951290001SglebiusThe variables operate 1952290001Sglebiusas follows: 1953290001Sglebius@table @asis 1954290001Sglebius@item @code{ceiling} @kbd{ceiling} 1955290001SglebiusPeers with strata above 1956290001Sglebius@code{ceiling} 1957290001Sglebiuswill be discarded if there are at least 1958290001Sglebius@code{minclock} 1959290001Sglebiuspeers remaining. 1960290001SglebiusThis value defaults to 15, but can be changed 1961290001Sglebiusto any number from 1 to 15. 1962290001Sglebius@item @code{cohort} @code{@{0 | 1@}} 1963290001SglebiusThis is a binary flag which enables (0) or disables (1) 1964290001Sglebiusmanycast server replies to manycast clients with the same 1965290001Sglebiusstratum level. 1966290001SglebiusThis is useful to reduce implosions where 1967290001Sglebiuslarge numbers of clients with the same stratum level 1968290001Sglebiusare present. 1969290001SglebiusThe default is to enable these replies. 1970290001Sglebius@item @code{floor} @kbd{floor} 1971290001SglebiusPeers with strata below 1972290001Sglebius@code{floor} 1973290001Sglebiuswill be discarded if there are at least 1974290001Sglebius@code{minclock} 1975290001Sglebiuspeers remaining. 1976290001SglebiusThis value defaults to 1, but can be changed 1977290001Sglebiusto any number from 1 to 15. 1978290001Sglebius@item @code{minclock} @kbd{minclock} 1979290001SglebiusThe clustering algorithm repeatedly casts out outlier 1980290001Sglebiusassociations until no more than 1981290001Sglebius@code{minclock} 1982290001Sglebiusassociations remain. 1983290001SglebiusThis value defaults to 3, 1984290001Sglebiusbut can be changed to any number from 1 to the number of 1985290001Sglebiusconfigured sources. 1986290001Sglebius@item @code{minsane} @kbd{minsane} 1987290001SglebiusThis is the minimum number of candidates available 1988290001Sglebiusto the clock selection algorithm in order to produce 1989290001Sglebiusone or more truechimers for the clustering algorithm. 1990290001SglebiusIf fewer than this number are available, the clock is 1991290001Sglebiusundisciplined and allowed to run free. 1992290001SglebiusThe default is 1 1993290001Sglebiusfor legacy purposes. 1994290001SglebiusHowever, according to principles of 1995290001SglebiusByzantine agreement, 1996290001Sglebius@code{minsane} 1997290001Sglebiusshould be at least 4 in order to detect and discard 1998290001Sglebiusa single falseticker. 1999290001Sglebius@end table 2000290001Sglebius@item @code{ttl} @kbd{hop} @kbd{...} 2001290001SglebiusThis command specifies a list of TTL values in increasing 2002290001Sglebiusorder, up to 8 values can be specified. 2003290001SglebiusIn manycast mode these values are used in turn 2004290001Sglebiusin an expanding-ring search. 2005290001SglebiusThe default is eight 2006290001Sglebiusmultiples of 32 starting at 31. 2007290001Sglebius@end table 2008290001Sglebius@node Reference Clock Support 2009290001Sglebius@subsection Reference Clock Support 2010290001SglebiusThe NTP Version 4 daemon supports some three dozen different radio, 2011290001Sglebiussatellite and modem reference clocks plus a special pseudo-clock 2012290001Sglebiusused for backup or when no other clock source is available. 2013290001SglebiusDetailed descriptions of individual device drivers and options can 2014290001Sglebiusbe found in the 2015290001Sglebius"Reference Clock Drivers" 2016290001Sglebiuspage 2017290001Sglebius(available as part of the HTML documentation 2018290001Sglebiusprovided in 2019290001Sglebius@file{/usr/share/doc/ntp}). 2020290001SglebiusAdditional information can be found in the pages linked 2021290001Sglebiusthere, including the 2022290001Sglebius"Debugging Hints for Reference Clock Drivers" 2023290001Sglebiusand 2024290001Sglebius"How To Write a Reference Clock Driver" 2025290001Sglebiuspages 2026290001Sglebius(available as part of the HTML documentation 2027290001Sglebiusprovided in 2028290001Sglebius@file{/usr/share/doc/ntp}). 2029290001SglebiusIn addition, support for a PPS 2030290001Sglebiussignal is available as described in the 2031290001Sglebius"Pulse-per-second (PPS) Signal Interfacing" 2032290001Sglebiuspage 2033290001Sglebius(available as part of the HTML documentation 2034290001Sglebiusprovided in 2035290001Sglebius@file{/usr/share/doc/ntp}). 2036290001SglebiusMany 2037290001Sglebiusdrivers support special line discipline/streams modules which can 2038290001Sglebiussignificantly improve the accuracy using the driver. 2039290001SglebiusThese are 2040290001Sglebiusdescribed in the 2041290001Sglebius"Line Disciplines and Streams Drivers" 2042290001Sglebiuspage 2043290001Sglebius(available as part of the HTML documentation 2044290001Sglebiusprovided in 2045290001Sglebius@file{/usr/share/doc/ntp}). 2046290001Sglebius 2047290001SglebiusA reference clock will generally (though not always) be a radio 2048290001Sglebiustimecode receiver which is synchronized to a source of standard 2049290001Sglebiustime such as the services offered by the NRC in Canada and NIST and 2050290001SglebiusUSNO in the US. 2051290001SglebiusThe interface between the computer and the timecode 2052290001Sglebiusreceiver is device dependent, but is usually a serial port. 2053290001SglebiusA 2054290001Sglebiusdevice driver specific to each reference clock must be selected and 2055290001Sglebiuscompiled in the distribution; however, most common radio, satellite 2056290001Sglebiusand modem clocks are included by default. 2057290001SglebiusNote that an attempt to 2058290001Sglebiusconfigure a reference clock when the driver has not been compiled 2059290001Sglebiusor the hardware port has not been appropriately configured results 2060290001Sglebiusin a scalding remark to the system log file, but is otherwise non 2061290001Sglebiushazardous. 2062290001Sglebius 2063290001SglebiusFor the purposes of configuration, 2064290001Sglebius@code{ntpd(1ntpdmdoc)} 2065290001Sglebiustreats 2066290001Sglebiusreference clocks in a manner analogous to normal NTP peers as much 2067290001Sglebiusas possible. 2068290001SglebiusReference clocks are identified by a syntactically 2069290001Sglebiuscorrect but invalid IP address, in order to distinguish them from 2070290001Sglebiusnormal NTP peers. 2071290001SglebiusReference clock addresses are of the form 2072290001Sglebius@code{127.127.}@kbd{t}.@kbd{u}, 2073290001Sglebiuswhere 2074290001Sglebius@kbd{t} 2075290001Sglebiusis an integer 2076290001Sglebiusdenoting the clock type and 2077290001Sglebius@kbd{u} 2078290001Sglebiusindicates the unit 2079290001Sglebiusnumber in the range 0-3. 2080290001SglebiusWhile it may seem overkill, it is in fact 2081290001Sglebiussometimes useful to configure multiple reference clocks of the same 2082290001Sglebiustype, in which case the unit numbers must be unique. 2083290001Sglebius 2084290001SglebiusThe 2085290001Sglebius@code{server} 2086290001Sglebiuscommand is used to configure a reference 2087290001Sglebiusclock, where the 2088290001Sglebius@kbd{address} 2089290001Sglebiusargument in that command 2090290001Sglebiusis the clock address. 2091290001SglebiusThe 2092290001Sglebius@code{key}, 2093290001Sglebius@code{version} 2094290001Sglebiusand 2095290001Sglebius@code{ttl} 2096290001Sglebiusoptions are not used for reference clock support. 2097290001SglebiusThe 2098290001Sglebius@code{mode} 2099290001Sglebiusoption is added for reference clock support, as 2100290001Sglebiusdescribed below. 2101290001SglebiusThe 2102290001Sglebius@code{prefer} 2103290001Sglebiusoption can be useful to 2104290001Sglebiuspersuade the server to cherish a reference clock with somewhat more 2105290001Sglebiusenthusiasm than other reference clocks or peers. 2106290001SglebiusFurther 2107290001Sglebiusinformation on this option can be found in the 2108290001Sglebius"Mitigation Rules and the prefer Keyword" 2109290001Sglebius(available as part of the HTML documentation 2110290001Sglebiusprovided in 2111290001Sglebius@file{/usr/share/doc/ntp}) 2112290001Sglebiuspage. 2113290001SglebiusThe 2114290001Sglebius@code{minpoll} 2115290001Sglebiusand 2116290001Sglebius@code{maxpoll} 2117290001Sglebiusoptions have 2118290001Sglebiusmeaning only for selected clock drivers. 2119290001SglebiusSee the individual clock 2120290001Sglebiusdriver document pages for additional information. 2121290001Sglebius 2122290001SglebiusThe 2123290001Sglebius@code{fudge} 2124290001Sglebiuscommand is used to provide additional 2125290001Sglebiusinformation for individual clock drivers and normally follows 2126290001Sglebiusimmediately after the 2127290001Sglebius@code{server} 2128290001Sglebiuscommand. 2129290001SglebiusThe 2130290001Sglebius@kbd{address} 2131290001Sglebiusargument specifies the clock address. 2132290001SglebiusThe 2133290001Sglebius@code{refid} 2134290001Sglebiusand 2135290001Sglebius@code{stratum} 2136290001Sglebiusoptions can be used to 2137290001Sglebiusoverride the defaults for the device. 2138290001SglebiusThere are two optional 2139290001Sglebiusdevice-dependent time offsets and four flags that can be included 2140290001Sglebiusin the 2141290001Sglebius@code{fudge} 2142290001Sglebiuscommand as well. 2143290001Sglebius 2144290001SglebiusThe stratum number of a reference clock is by default zero. 2145290001SglebiusSince the 2146290001Sglebius@code{ntpd(1ntpdmdoc)} 2147290001Sglebiusdaemon adds one to the stratum of each 2148290001Sglebiuspeer, a primary server ordinarily displays an external stratum of 2149290001Sglebiusone. 2150290001SglebiusIn order to provide engineered backups, it is often useful to 2151290001Sglebiusspecify the reference clock stratum as greater than zero. 2152290001SglebiusThe 2153290001Sglebius@code{stratum} 2154290001Sglebiusoption is used for this purpose. 2155290001SglebiusAlso, in cases 2156290001Sglebiusinvolving both a reference clock and a pulse-per-second (PPS) 2157290001Sglebiusdiscipline signal, it is useful to specify the reference clock 2158290001Sglebiusidentifier as other than the default, depending on the driver. 2159290001SglebiusThe 2160290001Sglebius@code{refid} 2161290001Sglebiusoption is used for this purpose. 2162290001SglebiusExcept where noted, 2163290001Sglebiusthese options apply to all clock drivers. 2164290001Sglebius@subsubsection Reference Clock Commands 2165290001Sglebius@table @asis 2166290001Sglebius@item @code{server} @code{127.127.}@kbd{t}.@kbd{u} @code{[@code{prefer}]} @code{[@code{mode} @kbd{int}]} @code{[@code{minpoll} @kbd{int}]} @code{[@code{maxpoll} @kbd{int}]} 2167290001SglebiusThis command can be used to configure reference clocks in 2168290001Sglebiusspecial ways. 2169290001SglebiusThe options are interpreted as follows: 2170290001Sglebius@table @asis 2171290001Sglebius@item @code{prefer} 2172290001SglebiusMarks the reference clock as preferred. 2173290001SglebiusAll other things being 2174290001Sglebiusequal, this host will be chosen for synchronization among a set of 2175290001Sglebiuscorrectly operating hosts. 2176290001SglebiusSee the 2177290001Sglebius"Mitigation Rules and the prefer Keyword" 2178290001Sglebiuspage 2179290001Sglebius(available as part of the HTML documentation 2180290001Sglebiusprovided in 2181290001Sglebius@file{/usr/share/doc/ntp}) 2182290001Sglebiusfor further information. 2183290001Sglebius@item @code{mode} @kbd{int} 2184290001SglebiusSpecifies a mode number which is interpreted in a 2185290001Sglebiusdevice-specific fashion. 2186290001SglebiusFor instance, it selects a dialing 2187290001Sglebiusprotocol in the ACTS driver and a device subtype in the 2188290001Sglebiusparse 2189290001Sglebiusdrivers. 2190290001Sglebius@item @code{minpoll} @kbd{int} 2191290001Sglebius@item @code{maxpoll} @kbd{int} 2192290001SglebiusThese options specify the minimum and maximum polling interval 2193290001Sglebiusfor reference clock messages, as a power of 2 in seconds 2194290001SglebiusFor 2195290001Sglebiusmost directly connected reference clocks, both 2196290001Sglebius@code{minpoll} 2197290001Sglebiusand 2198290001Sglebius@code{maxpoll} 2199290001Sglebiusdefault to 6 (64 s). 2200290001SglebiusFor modem reference clocks, 2201290001Sglebius@code{minpoll} 2202290001Sglebiusdefaults to 10 (17.1 m) and 2203290001Sglebius@code{maxpoll} 2204290001Sglebiusdefaults to 14 (4.5 h). 2205290001SglebiusThe allowable range is 4 (16 s) to 17 (36.4 h) inclusive. 2206290001Sglebius@end table 2207290001Sglebius@item @code{fudge} @code{127.127.}@kbd{t}.@kbd{u} @code{[@code{time1} @kbd{sec}]} @code{[@code{time2} @kbd{sec}]} @code{[@code{stratum} @kbd{int}]} @code{[@code{refid} @kbd{string}]} @code{[@code{mode} @kbd{int}]} @code{[@code{flag1} @code{0} @code{|} @code{1}]} @code{[@code{flag2} @code{0} @code{|} @code{1}]} @code{[@code{flag3} @code{0} @code{|} @code{1}]} @code{[@code{flag4} @code{0} @code{|} @code{1}]} 2208290001SglebiusThis command can be used to configure reference clocks in 2209290001Sglebiusspecial ways. 2210290001SglebiusIt must immediately follow the 2211290001Sglebius@code{server} 2212290001Sglebiuscommand which configures the driver. 2213290001SglebiusNote that the same capability 2214290001Sglebiusis possible at run time using the 2215290001Sglebius@code{ntpdc(1ntpdcmdoc)} 2216290001Sglebiusprogram. 2217290001SglebiusThe options are interpreted as 2218290001Sglebiusfollows: 2219290001Sglebius@table @asis 2220290001Sglebius@item @code{time1} @kbd{sec} 2221290001SglebiusSpecifies a constant to be added to the time offset produced by 2222290001Sglebiusthe driver, a fixed-point decimal number in seconds. 2223290001SglebiusThis is used 2224290001Sglebiusas a calibration constant to adjust the nominal time offset of a 2225290001Sglebiusparticular clock to agree with an external standard, such as a 2226290001Sglebiusprecision PPS signal. 2227290001SglebiusIt also provides a way to correct a 2228290001Sglebiussystematic error or bias due to serial port or operating system 2229290001Sglebiuslatencies, different cable lengths or receiver internal delay. 2230290001SglebiusThe 2231290001Sglebiusspecified offset is in addition to the propagation delay provided 2232290001Sglebiusby other means, such as internal DIPswitches. 2233290001SglebiusWhere a calibration 2234290001Sglebiusfor an individual system and driver is available, an approximate 2235290001Sglebiuscorrection is noted in the driver documentation pages. 2236290001SglebiusNote: in order to facilitate calibration when more than one 2237290001Sglebiusradio clock or PPS signal is supported, a special calibration 2238290001Sglebiusfeature is available. 2239290001SglebiusIt takes the form of an argument to the 2240290001Sglebius@code{enable} 2241290001Sglebiuscommand described in 2242290001Sglebius@ref{Miscellaneous Options} 2243290001Sglebiuspage and operates as described in the 2244290001Sglebius"Reference Clock Drivers" 2245290001Sglebiuspage 2246290001Sglebius(available as part of the HTML documentation 2247290001Sglebiusprovided in 2248290001Sglebius@file{/usr/share/doc/ntp}). 2249290001Sglebius@item @code{time2} @kbd{secs} 2250290001SglebiusSpecifies a fixed-point decimal number in seconds, which is 2251290001Sglebiusinterpreted in a driver-dependent way. 2252290001SglebiusSee the descriptions of 2253290001Sglebiusspecific drivers in the 2254290001Sglebius"Reference Clock Drivers" 2255290001Sglebiuspage 2256290001Sglebius(available as part of the HTML documentation 2257290001Sglebiusprovided in 2258290001Sglebius@file{/usr/share/doc/ntp}). 2259290001Sglebius@item @code{stratum} @kbd{int} 2260290001SglebiusSpecifies the stratum number assigned to the driver, an integer 2261290001Sglebiusbetween 0 and 15. 2262290001SglebiusThis number overrides the default stratum number 2263290001Sglebiusordinarily assigned by the driver itself, usually zero. 2264290001Sglebius@item @code{refid} @kbd{string} 2265290001SglebiusSpecifies an ASCII string of from one to four characters which 2266290001Sglebiusdefines the reference identifier used by the driver. 2267290001SglebiusThis string 2268290001Sglebiusoverrides the default identifier ordinarily assigned by the driver 2269290001Sglebiusitself. 2270290001Sglebius@item @code{mode} @kbd{int} 2271290001SglebiusSpecifies a mode number which is interpreted in a 2272290001Sglebiusdevice-specific fashion. 2273290001SglebiusFor instance, it selects a dialing 2274290001Sglebiusprotocol in the ACTS driver and a device subtype in the 2275290001Sglebiusparse 2276290001Sglebiusdrivers. 2277290001Sglebius@item @code{flag1} @code{0} @code{|} @code{1} 2278290001Sglebius@item @code{flag2} @code{0} @code{|} @code{1} 2279290001Sglebius@item @code{flag3} @code{0} @code{|} @code{1} 2280290001Sglebius@item @code{flag4} @code{0} @code{|} @code{1} 2281290001SglebiusThese four flags are used for customizing the clock driver. 2282290001SglebiusThe 2283290001Sglebiusinterpretation of these values, and whether they are used at all, 2284290001Sglebiusis a function of the particular clock driver. 2285290001SglebiusHowever, by 2286290001Sglebiusconvention 2287290001Sglebius@code{flag4} 2288290001Sglebiusis used to enable recording monitoring 2289290001Sglebiusdata to the 2290290001Sglebius@code{clockstats} 2291290001Sglebiusfile configured with the 2292290001Sglebius@code{filegen} 2293290001Sglebiuscommand. 2294290001SglebiusFurther information on the 2295290001Sglebius@code{filegen} 2296290001Sglebiuscommand can be found in 2297290001Sglebius@ref{Monitoring Options}. 2298290001Sglebius@end table 2299290001Sglebius@end table 2300290001Sglebius@node Miscellaneous Options 2301290001Sglebius@subsection Miscellaneous Options 2302290001Sglebius@table @asis 2303290001Sglebius@item @code{broadcastdelay} @kbd{seconds} 2304290001SglebiusThe broadcast and multicast modes require a special calibration 2305290001Sglebiusto determine the network delay between the local and remote 2306290001Sglebiusservers. 2307290001SglebiusOrdinarily, this is done automatically by the initial 2308290001Sglebiusprotocol exchanges between the client and server. 2309290001SglebiusIn some cases, 2310290001Sglebiusthe calibration procedure may fail due to network or server access 2311290001Sglebiuscontrols, for example. 2312290001SglebiusThis command specifies the default delay to 2313290001Sglebiusbe used under these circumstances. 2314290001SglebiusTypically (for Ethernet), a 2315290001Sglebiusnumber between 0.003 and 0.007 seconds is appropriate. 2316290001SglebiusThe default 2317290001Sglebiuswhen this command is not used is 0.004 seconds. 2318290001Sglebius@item @code{calldelay} @kbd{delay} 2319290001SglebiusThis option controls the delay in seconds between the first and second 2320290001Sglebiuspackets sent in burst or iburst mode to allow additional time for a modem 2321290001Sglebiusor ISDN call to complete. 2322290001Sglebius@item @code{driftfile} @kbd{driftfile} 2323290001SglebiusThis command specifies the complete path and name of the file used to 2324290001Sglebiusrecord the frequency of the local clock oscillator. 2325290001SglebiusThis is the same 2326290001Sglebiusoperation as the 2327290001Sglebius@code{-f} 2328290001Sglebiuscommand line option. 2329290001SglebiusIf the file exists, it is read at 2330290001Sglebiusstartup in order to set the initial frequency and then updated once per 2331290001Sglebiushour with the current frequency computed by the daemon. 2332290001SglebiusIf the file name is 2333290001Sglebiusspecified, but the file itself does not exist, the starts with an initial 2334290001Sglebiusfrequency of zero and creates the file when writing it for the first time. 2335290001SglebiusIf this command is not given, the daemon will always start with an initial 2336290001Sglebiusfrequency of zero. 2337290001Sglebius 2338290001SglebiusThe file format consists of a single line containing a single 2339290001Sglebiusfloating point number, which records the frequency offset measured 2340290001Sglebiusin parts-per-million (PPM). 2341290001SglebiusThe file is updated by first writing 2342290001Sglebiusthe current drift value into a temporary file and then renaming 2343290001Sglebiusthis file to replace the old version. 2344290001SglebiusThis implies that 2345290001Sglebius@code{ntpd(1ntpdmdoc)} 2346290001Sglebiusmust have write permission for the directory the 2347290001Sglebiusdrift file is located in, and that file system links, symbolic or 2348290001Sglebiusotherwise, should be avoided. 2349290001Sglebius@item @code{dscp} @kbd{value} 2350290001SglebiusThis option specifies the Differentiated Services Control Point (DSCP) value, 2351298770Sdelphija 6-bit code. 2352298770SdelphijThe default value is 46, signifying Expedited Forwarding. 2353301301Sdelphij@item @code{enable} @code{[@code{auth} | @code{bclient} | @code{calibrate} | @code{kernel} | @code{mode7} | @code{monitor} | @code{ntp} | @code{stats} | @code{peer_clear_digest_early} | @code{unpeer_crypto_early} | @code{unpeer_crypto_nak_early} | @code{unpeer_digest_early}]} 2354301301Sdelphij@item @code{disable} @code{[@code{auth} | @code{bclient} | @code{calibrate} | @code{kernel} | @code{mode7} | @code{monitor} | @code{ntp} | @code{stats} | @code{peer_clear_digest_early} | @code{unpeer_crypto_early} | @code{unpeer_crypto_nak_early} | @code{unpeer_digest_early}]} 2355290001SglebiusProvides a way to enable or disable various server options. 2356290001SglebiusFlags not mentioned are unaffected. 2357290001SglebiusNote that all of these flags 2358290001Sglebiuscan be controlled remotely using the 2359290001Sglebius@code{ntpdc(1ntpdcmdoc)} 2360290001Sglebiusutility program. 2361290001Sglebius@table @asis 2362290001Sglebius@item @code{auth} 2363290001SglebiusEnables the server to synchronize with unconfigured peers only if the 2364290001Sglebiuspeer has been correctly authenticated using either public key or 2365290001Sglebiusprivate key cryptography. 2366290001SglebiusThe default for this flag is 2367290001Sglebius@code{enable}. 2368290001Sglebius@item @code{bclient} 2369290001SglebiusEnables the server to listen for a message from a broadcast or 2370290001Sglebiusmulticast server, as in the 2371290001Sglebius@code{multicastclient} 2372290001Sglebiuscommand with default 2373290001Sglebiusaddress. 2374290001SglebiusThe default for this flag is 2375290001Sglebius@code{disable}. 2376290001Sglebius@item @code{calibrate} 2377290001SglebiusEnables the calibrate feature for reference clocks. 2378290001SglebiusThe default for 2379290001Sglebiusthis flag is 2380290001Sglebius@code{disable}. 2381290001Sglebius@item @code{kernel} 2382290001SglebiusEnables the kernel time discipline, if available. 2383290001SglebiusThe default for this 2384290001Sglebiusflag is 2385290001Sglebius@code{enable} 2386290001Sglebiusif support is available, otherwise 2387290001Sglebius@code{disable}. 2388290001Sglebius@item @code{mode7} 2389290001SglebiusEnables processing of NTP mode 7 implementation-specific requests 2390290001Sglebiuswhich are used by the deprecated 2391290001Sglebius@code{ntpdc(1ntpdcmdoc)} 2392290001Sglebiusprogram. 2393290001SglebiusThe default for this flag is disable. 2394290001SglebiusThis flag is excluded from runtime configuration using 2395290001Sglebius@code{ntpq(1ntpqmdoc)}. 2396290001SglebiusThe 2397290001Sglebius@code{ntpq(1ntpqmdoc)} 2398290001Sglebiusprogram provides the same capabilities as 2399290001Sglebius@code{ntpdc(1ntpdcmdoc)} 2400290001Sglebiususing standard mode 6 requests. 2401290001Sglebius@item @code{monitor} 2402290001SglebiusEnables the monitoring facility. 2403290001SglebiusSee the 2404290001Sglebius@code{ntpdc(1ntpdcmdoc)} 2405290001Sglebiusprogram 2406290001Sglebiusand the 2407290001Sglebius@code{monlist} 2408290001Sglebiuscommand or further information. 2409290001SglebiusThe 2410290001Sglebiusdefault for this flag is 2411290001Sglebius@code{enable}. 2412290001Sglebius@item @code{ntp} 2413290001SglebiusEnables time and frequency discipline. 2414290001SglebiusIn effect, this switch opens and 2415290001Sglebiuscloses the feedback loop, which is useful for testing. 2416290001SglebiusThe default for 2417290001Sglebiusthis flag is 2418290001Sglebius@code{enable}. 2419301301Sdelphij@item @code{peer_clear_digest_early} 2420301301SdelphijBy default, if 2421301301Sdelphij@code{ntpd(1ntpdmdoc)} 2422301301Sdelphijis using autokey and it 2423301301Sdelphijreceives a crypto-NAK packet that 2424301301Sdelphijpasses the duplicate packet and origin timestamp checks 2425301301Sdelphijthe peer variables are immediately cleared. 2426301301SdelphijWhile this is generally a feature 2427301301Sdelphijas it allows for quick recovery if a server key has changed, 2428301301Sdelphija properly forged and appropriately delivered crypto-NAK packet 2429301301Sdelphijcan be used in a DoS attack. 2430301301SdelphijIf you have active noticable problems with this type of DoS attack 2431301301Sdelphijthen you should consider 2432301301Sdelphijdisabling this option. 2433301301SdelphijYou can check your 2434301301Sdelphij@code{peerstats} 2435301301Sdelphijfile for evidence of any of these attacks. 2436301301SdelphijThe 2437301301Sdelphijdefault for this flag is 2438301301Sdelphij@code{enable}. 2439290001Sglebius@item @code{stats} 2440290001SglebiusEnables the statistics facility. 2441290001SglebiusSee the 2442290001Sglebius@ref{Monitoring Options} 2443290001Sglebiussection for further information. 2444290001SglebiusThe default for this flag is 2445290001Sglebius@code{disable}. 2446294905Sdelphij@item @code{unpeer_crypto_early} 2447294905SdelphijBy default, if 2448294905Sdelphij@code{ntpd(1ntpdmdoc)} 2449294905Sdelphijreceives an autokey packet that fails TEST9, 2450294905Sdelphija crypto failure, 2451294905Sdelphijthe association is immediately cleared. 2452294905SdelphijThis is almost certainly a feature, 2453294905Sdelphijbut if, in spite of the current recommendation of not using autokey, 2454294905Sdelphijyou are 2455294905Sdelphij.B still 2456294905Sdelphijusing autokey 2457294905Sdelphij.B and 2458294905Sdelphijyou are seeing this sort of DoS attack 2459294905Sdelphijdisabling this flag will delay 2460294905Sdelphijtearing down the association until the reachability counter 2461294905Sdelphijbecomes zero. 2462294905SdelphijYou can check your 2463294905Sdelphij@code{peerstats} 2464294905Sdelphijfile for evidence of any of these attacks. 2465294905SdelphijThe 2466294905Sdelphijdefault for this flag is 2467294905Sdelphij@code{enable}. 2468294905Sdelphij@item @code{unpeer_crypto_nak_early} 2469294905SdelphijBy default, if 2470294905Sdelphij@code{ntpd(1ntpdmdoc)} 2471294905Sdelphijreceives a crypto-NAK packet that 2472294905Sdelphijpasses the duplicate packet and origin timestamp checks 2473294905Sdelphijthe association is immediately cleared. 2474294905SdelphijWhile this is generally a feature 2475294905Sdelphijas it allows for quick recovery if a server key has changed, 2476294905Sdelphija properly forged and appropriately delivered crypto-NAK packet 2477294905Sdelphijcan be used in a DoS attack. 2478294905SdelphijIf you have active noticable problems with this type of DoS attack 2479294905Sdelphijthen you should consider 2480294905Sdelphijdisabling this option. 2481294905SdelphijYou can check your 2482294905Sdelphij@code{peerstats} 2483294905Sdelphijfile for evidence of any of these attacks. 2484294905SdelphijThe 2485294905Sdelphijdefault for this flag is 2486294905Sdelphij@code{enable}. 2487294905Sdelphij@item @code{unpeer_digest_early} 2488294905SdelphijBy default, if 2489294905Sdelphij@code{ntpd(1ntpdmdoc)} 2490294905Sdelphijreceives what should be an authenticated packet 2491294905Sdelphijthat passes other packet sanity checks but 2492294905Sdelphijcontains an invalid digest 2493294905Sdelphijthe association is immediately cleared. 2494294905SdelphijWhile this is generally a feature 2495294905Sdelphijas it allows for quick recovery, 2496294905Sdelphijif this type of packet is carefully forged and sent 2497294905Sdelphijduring an appropriate window it can be used for a DoS attack. 2498294905SdelphijIf you have active noticable problems with this type of DoS attack 2499294905Sdelphijthen you should consider 2500294905Sdelphijdisabling this option. 2501294905SdelphijYou can check your 2502294905Sdelphij@code{peerstats} 2503294905Sdelphijfile for evidence of any of these attacks. 2504294905SdelphijThe 2505294905Sdelphijdefault for this flag is 2506294905Sdelphij@code{enable}. 2507290001Sglebius@end table 2508290001Sglebius@item @code{includefile} @kbd{includefile} 2509290001SglebiusThis command allows additional configuration commands 2510290001Sglebiusto be included from a separate file. 2511290001SglebiusInclude files may 2512290001Sglebiusbe nested to a depth of five; upon reaching the end of any 2513290001Sglebiusinclude file, command processing resumes in the previous 2514290001Sglebiusconfiguration file. 2515290001SglebiusThis option is useful for sites that run 2516290001Sglebius@code{ntpd(1ntpdmdoc)} 2517290001Sglebiuson multiple hosts, with (mostly) common options (e.g., a 2518290001Sglebiusrestriction list). 2519290001Sglebius@item @code{leapsmearinterval} @kbd{seconds} 2520290001SglebiusThis EXPERIMENTAL option is only available if 2521290001Sglebius@code{ntpd(1ntpdmdoc)} 2522290001Sglebiuswas built with the 2523290001Sglebius@code{--enable-leap-smear} 2524290001Sglebiusoption to the 2525290001Sglebius@code{configure} 2526290001Sglebiusscript. 2527290001SglebiusIt specifies the interval over which a leap second correction will be applied. 2528290001SglebiusRecommended values for this option are between 2529290001Sglebius7200 (2 hours) and 86400 (24 hours). 2530290001Sglebius.Sy DO NOT USE THIS OPTION ON PUBLIC-ACCESS SERVERS! 2531290001SglebiusSee http://bugs.ntp.org/2855 for more information. 2532290001Sglebius@item @code{logconfig} @kbd{configkeyword} 2533290001SglebiusThis command controls the amount and type of output written to 2534290001Sglebiusthe system 2535290001Sglebius@code{syslog(3)} 2536290001Sglebiusfacility or the alternate 2537290001Sglebius@code{logfile} 2538290001Sglebiuslog file. 2539290001SglebiusBy default, all output is turned on. 2540290001SglebiusAll 2541290001Sglebius@kbd{configkeyword} 2542290001Sglebiuskeywords can be prefixed with 2543290001Sglebius@quoteleft{}=@quoteright{}, 2544290001Sglebius@quoteleft{}+@quoteright{} 2545290001Sglebiusand 2546290001Sglebius@quoteleft{}-@quoteright{}, 2547290001Sglebiuswhere 2548290001Sglebius@quoteleft{}=@quoteright{} 2549290001Sglebiussets the 2550290001Sglebius@code{syslog(3)} 2551290001Sglebiuspriority mask, 2552290001Sglebius@quoteleft{}+@quoteright{} 2553290001Sglebiusadds and 2554290001Sglebius@quoteleft{}-@quoteright{} 2555290001Sglebiusremoves 2556290001Sglebiusmessages. 2557290001Sglebius@code{syslog(3)} 2558290001Sglebiusmessages can be controlled in four 2559290001Sglebiusclasses 2560290001Sglebius(@code{clock}, @code{peer}, @code{sys} and @code{sync}). 2561290001SglebiusWithin these classes four types of messages can be 2562290001Sglebiuscontrolled: informational messages 2563290001Sglebius(@code{info}), 2564290001Sglebiusevent messages 2565290001Sglebius(@code{events}), 2566290001Sglebiusstatistics messages 2567290001Sglebius(@code{statistics}) 2568290001Sglebiusand 2569290001Sglebiusstatus messages 2570290001Sglebius(@code{status}). 2571290001Sglebius 2572290001SglebiusConfiguration keywords are formed by concatenating the message class with 2573290001Sglebiusthe event class. 2574290001SglebiusThe 2575290001Sglebius@code{all} 2576290001Sglebiusprefix can be used instead of a message class. 2577290001SglebiusA 2578290001Sglebiusmessage class may also be followed by the 2579290001Sglebius@code{all} 2580290001Sglebiuskeyword to enable/disable all 2581298770Sdelphijmessages of the respective message class. 2582298770SdelphijThus, a minimal log configuration 2583290001Sglebiuscould look like this: 2584290001Sglebius@verbatim 2585290001Sglebiuslogconfig =syncstatus +sysevents 2586290001Sglebius@end verbatim 2587290001Sglebius 2588290001SglebiusThis would just list the synchronizations state of 2589290001Sglebius@code{ntpd(1ntpdmdoc)} 2590290001Sglebiusand the major system events. 2591290001SglebiusFor a simple reference server, the 2592290001Sglebiusfollowing minimum message configuration could be useful: 2593290001Sglebius@verbatim 2594290001Sglebiuslogconfig =syncall +clockall 2595290001Sglebius@end verbatim 2596290001Sglebius 2597290001SglebiusThis configuration will list all clock information and 2598290001Sglebiussynchronization information. 2599290001SglebiusAll other events and messages about 2600290001Sglebiuspeers, system events and so on is suppressed. 2601290001Sglebius@item @code{logfile} @kbd{logfile} 2602290001SglebiusThis command specifies the location of an alternate log file to 2603290001Sglebiusbe used instead of the default system 2604290001Sglebius@code{syslog(3)} 2605290001Sglebiusfacility. 2606298770SdelphijThis is the same operation as the 2607298770Sdelphij@code{-l} 2608298770Sdelphijcommand line option. 2609290001Sglebius@item @code{setvar} @kbd{variable} @code{[@code{default}]} 2610290001SglebiusThis command adds an additional system variable. 2611290001SglebiusThese 2612290001Sglebiusvariables can be used to distribute additional information such as 2613290001Sglebiusthe access policy. 2614290001SglebiusIf the variable of the form 2615290001Sglebius@code{name}@code{=}@kbd{value} 2616290001Sglebiusis followed by the 2617290001Sglebius@code{default} 2618290001Sglebiuskeyword, the 2619290001Sglebiusvariable will be listed as part of the default system variables 2620290001Sglebius(@code{rv} command)). 2621290001SglebiusThese additional variables serve 2622290001Sglebiusinformational purposes only. 2623290001SglebiusThey are not related to the protocol 2624290001Sglebiusother that they can be listed. 2625290001SglebiusThe known protocol variables will 2626290001Sglebiusalways override any variables defined via the 2627290001Sglebius@code{setvar} 2628290001Sglebiusmechanism. 2629290001SglebiusThere are three special variables that contain the names 2630290001Sglebiusof all variable of the same group. 2631290001SglebiusThe 2632290001Sglebius@code{sys_var_list} 2633290001Sglebiusholds 2634290001Sglebiusthe names of all system variables. 2635290001SglebiusThe 2636290001Sglebius@code{peer_var_list} 2637290001Sglebiusholds 2638290001Sglebiusthe names of all peer variables and the 2639290001Sglebius@code{clock_var_list} 2640290001Sglebiusholds the names of the reference clock variables. 2641290001Sglebius@item @code{tinker} @code{[@code{allan} @kbd{allan} | @code{dispersion} @kbd{dispersion} | @code{freq} @kbd{freq} | @code{huffpuff} @kbd{huffpuff} | @code{panic} @kbd{panic} | @code{step} @kbd{step} | @code{stepback} @kbd{stepback} | @code{stepfwd} @kbd{stepfwd} | @code{stepout} @kbd{stepout}]} 2642290001SglebiusThis command can be used to alter several system variables in 2643290001Sglebiusvery exceptional circumstances. 2644290001SglebiusIt should occur in the 2645290001Sglebiusconfiguration file before any other configuration options. 2646290001SglebiusThe 2647290001Sglebiusdefault values of these variables have been carefully optimized for 2648290001Sglebiusa wide range of network speeds and reliability expectations. 2649290001SglebiusIn 2650290001Sglebiusgeneral, they interact in intricate ways that are hard to predict 2651290001Sglebiusand some combinations can result in some very nasty behavior. 2652290001SglebiusVery 2653290001Sglebiusrarely is it necessary to change the default values; but, some 2654290001Sglebiusfolks cannot resist twisting the knobs anyway and this command is 2655290001Sglebiusfor them. 2656290001SglebiusEmphasis added: twisters are on their own and can expect 2657290001Sglebiusno help from the support group. 2658290001Sglebius 2659290001SglebiusThe variables operate as follows: 2660290001Sglebius@table @asis 2661290001Sglebius@item @code{allan} @kbd{allan} 2662290001SglebiusThe argument becomes the new value for the minimum Allan 2663290001Sglebiusintercept, which is a parameter of the PLL/FLL clock discipline 2664290001Sglebiusalgorithm. 2665290001SglebiusThe value in log2 seconds defaults to 7 (1024 s), which is also the lower 2666290001Sglebiuslimit. 2667290001Sglebius@item @code{dispersion} @kbd{dispersion} 2668290001SglebiusThe argument becomes the new value for the dispersion increase rate, 2669290001Sglebiusnormally .000015 s/s. 2670290001Sglebius@item @code{freq} @kbd{freq} 2671290001SglebiusThe argument becomes the initial value of the frequency offset in 2672290001Sglebiusparts-per-million. 2673290001SglebiusThis overrides the value in the frequency file, if 2674290001Sglebiuspresent, and avoids the initial training state if it is not. 2675290001Sglebius@item @code{huffpuff} @kbd{huffpuff} 2676290001SglebiusThe argument becomes the new value for the experimental 2677290001Sglebiushuff-n'-puff filter span, which determines the most recent interval 2678290001Sglebiusthe algorithm will search for a minimum delay. 2679290001SglebiusThe lower limit is 2680290001Sglebius900 s (15 m), but a more reasonable value is 7200 (2 hours). 2681290001SglebiusThere 2682290001Sglebiusis no default, since the filter is not enabled unless this command 2683290001Sglebiusis given. 2684290001Sglebius@item @code{panic} @kbd{panic} 2685290001SglebiusThe argument is the panic threshold, normally 1000 s. 2686290001SglebiusIf set to zero, 2687290001Sglebiusthe panic sanity check is disabled and a clock offset of any value will 2688290001Sglebiusbe accepted. 2689290001Sglebius@item @code{step} @kbd{step} 2690290001SglebiusThe argument is the step threshold, which by default is 0.128 s. 2691290001SglebiusIt can 2692290001Sglebiusbe set to any positive number in seconds. 2693290001SglebiusIf set to zero, step 2694290001Sglebiusadjustments will never occur. 2695290001SglebiusNote: The kernel time discipline is 2696290001Sglebiusdisabled if the step threshold is set to zero or greater than the 2697290001Sglebiusdefault. 2698290001Sglebius@item @code{stepback} @kbd{stepback} 2699290001SglebiusThe argument is the step threshold for the backward direction, 2700290001Sglebiuswhich by default is 0.128 s. 2701290001SglebiusIt can 2702290001Sglebiusbe set to any positive number in seconds. 2703290001SglebiusIf both the forward and backward step thresholds are set to zero, step 2704290001Sglebiusadjustments will never occur. 2705290001SglebiusNote: The kernel time discipline is 2706290001Sglebiusdisabled if 2707290001Sglebiuseach direction of step threshold are either 2708290001Sglebiusset to zero or greater than .5 second. 2709290001Sglebius@item @code{stepfwd} @kbd{stepfwd} 2710290001SglebiusAs for stepback, but for the forward direction. 2711290001Sglebius@item @code{stepout} @kbd{stepout} 2712290001SglebiusThe argument is the stepout timeout, which by default is 900 s. 2713290001SglebiusIt can 2714290001Sglebiusbe set to any positive number in seconds. 2715290001SglebiusIf set to zero, the stepout 2716290001Sglebiuspulses will not be suppressed. 2717290001Sglebius@end table 2718290001Sglebius@item @code{rlimit} @code{[@code{memlock} @kbd{Nmegabytes} | @code{stacksize} @kbd{N4kPages} @code{filenum} @kbd{Nfiledescriptors}]} 2719290001Sglebius@table @asis 2720290001Sglebius@item @code{memlock} @kbd{Nmegabytes} 2721290001SglebiusSpecify the number of megabytes of memory that should be 2722290001Sglebiusallocated and locked. 2723290001SglebiusProbably only available under Linux, this option may be useful 2724290001Sglebiuswhen dropping root (the 2725290001Sglebius@code{-i} 2726290001Sglebiusoption). 2727290001SglebiusThe default is 32 megabytes on non-Linux machines, and -1 under Linux. 2728290001Sglebius-1 means "do not lock the process into memory". 2729290001Sglebius0 means "lock whatever memory the process wants into memory". 2730290001Sglebius@item @code{stacksize} @kbd{N4kPages} 2731290001SglebiusSpecifies the maximum size of the process stack on systems with the 2732290001Sglebius@code{mlockall()} 2733290001Sglebiusfunction. 2734290001SglebiusDefaults to 50 4k pages (200 4k pages in OpenBSD). 2735290001Sglebius@item @code{filenum} @kbd{Nfiledescriptors} 2736298770SdelphijSpecifies the maximum number of file descriptors ntpd may have open at once. 2737298770SdelphijDefaults to the system default. 2738290001Sglebius@end table 2739290001Sglebius@item @code{trap} @kbd{host_address} @code{[@code{port} @kbd{port_number}]} @code{[@code{interface} @kbd{interface_address}]} 2740290001SglebiusThis command configures a trap receiver at the given host 2741290001Sglebiusaddress and port number for sending messages with the specified 2742290001Sglebiuslocal interface address. 2743290001SglebiusIf the port number is unspecified, a value 2744290001Sglebiusof 18447 is used. 2745290001SglebiusIf the interface address is not specified, the 2746290001Sglebiusmessage is sent with a source address of the local interface the 2747290001Sglebiusmessage is sent through. 2748290001SglebiusNote that on a multihomed host the 2749290001Sglebiusinterface used may vary from time to time with routing changes. 2750290001Sglebius 2751290001SglebiusThe trap receiver will generally log event messages and other 2752290001Sglebiusinformation from the server in a log file. 2753290001SglebiusWhile such monitor 2754290001Sglebiusprograms may also request their own trap dynamically, configuring a 2755290001Sglebiustrap receiver will ensure that no messages are lost when the server 2756290001Sglebiusis started. 2757290001Sglebius@item @code{hop} @kbd{...} 2758290001SglebiusThis command specifies a list of TTL values in increasing order, up to 8 2759290001Sglebiusvalues can be specified. 2760290001SglebiusIn manycast mode these values are used in turn in 2761290001Sglebiusan expanding-ring search. 2762290001SglebiusThe default is eight multiples of 32 starting at 2763290001Sglebius31. 2764290001Sglebius@end table 2765290001Sglebius 2766290001SglebiusThis section was generated by @strong{AutoGen}, 2767290001Sglebiususing the @code{agtexi-cmd} template and the option descriptions for the @code{ntp.conf} program. 2768290001SglebiusThis software is released under the NTP license, <http://ntp.org/license>. 2769290001Sglebius 2770290001Sglebius@menu 2771290001Sglebius* ntp.conf Files:: Files 2772290001Sglebius* ntp.conf See Also:: See Also 2773290001Sglebius* ntp.conf Bugs:: Bugs 2774290001Sglebius* ntp.conf Notes:: Notes 2775290001Sglebius@end menu 2776290001Sglebius 2777290001Sglebius@node ntp.conf Files 2778290001Sglebius@subsection ntp.conf Files 2779290001Sglebius@table @asis 2780290001Sglebius@item @file{/etc/ntp.conf} 2781290001Sglebiusthe default name of the configuration file 2782290001Sglebius@item @file{ntp.keys} 2783290001Sglebiusprivate MD5 keys 2784290001Sglebius@item @file{ntpkey} 2785290001SglebiusRSA private key 2786290001Sglebius@item @file{ntpkey_}@kbd{host} 2787290001SglebiusRSA public key 2788290001Sglebius@item @file{ntp_dh} 2789290001SglebiusDiffie-Hellman agreement parameters 2790290001Sglebius@end table 2791290001Sglebius@node ntp.conf See Also 2792290001Sglebius@subsection ntp.conf See Also 2793290001Sglebius@code{ntpd(1ntpdmdoc)}, 2794290001Sglebius@code{ntpdc(1ntpdcmdoc)}, 2795290001Sglebius@code{ntpq(1ntpqmdoc)} 2796290001Sglebius 2797290001SglebiusIn addition to the manual pages provided, 2798290001Sglebiuscomprehensive documentation is available on the world wide web 2799290001Sglebiusat 2800290001Sglebius@code{http://www.ntp.org/}. 2801290001SglebiusA snapshot of this documentation is available in HTML format in 2802290001Sglebius@file{/usr/share/doc/ntp}. 2803290001Sglebius@* 2804290001Sglebius 2805290001Sglebius@* 2806290001SglebiusDavid L. Mills, @emph{Network Time Protocol (Version 4)}, RFC5905 2807290001Sglebius@node ntp.conf Bugs 2808290001Sglebius@subsection ntp.conf Bugs 2809290001SglebiusThe syntax checking is not picky; some combinations of 2810290001Sglebiusridiculous and even hilarious options and modes may not be 2811290001Sglebiusdetected. 2812290001Sglebius 2813290001SglebiusThe 2814290001Sglebius@file{ntpkey_}@kbd{host} 2815290001Sglebiusfiles are really digital 2816290001Sglebiuscertificates. 2817290001SglebiusThese should be obtained via secure directory 2818290001Sglebiusservices when they become universally available. 2819290001Sglebius@node ntp.conf Notes 2820290001Sglebius@subsection ntp.conf Notes 2821290001SglebiusThis document was derived from FreeBSD. 2822