ipfw.8 revision 36170
1.Dd July 20, 1996 2.Dt IPFW 8 SMM 3.Os FreeBSD 4.Sh NAME 5.Nm ipfw 6.Nd controlling utility for IP firewall 7.Sh SYNOPSIS 8.Nm 9.Ar file 10.Nm ipfw 11.Oo 12.Fl f 13| 14.Fl q 15.Oc 16flush 17.Nm ipfw 18.Oo 19.Fl q 20.Oc 21zero 22.Op Ar number ... 23.Nm ipfw 24delete 25.Ar number ... 26.Nm ipfw 27.Op Fl aftN 28list 29.Op Ar number ... 30.Nm ipfw 31.Oo 32.Fl ftN 33.Oc 34show 35.Op Ar number ... 36.Nm ipfw 37.Oo 38.Fl q 39.Oc 40add 41.Op Ar number 42.Ar action 43.Op log 44.Ar proto 45from 46.Ar src 47to 48.Ar dst 49.Op via Ar name | ipno 50.Op Ar options 51.Sh DESCRIPTION 52If used as shown in the first synopsis line, the 53.Ar file 54will be read line by line and applied as arguments to the 55.Nm 56command. 57.Pp 58The 59.Nm 60code works by going through the rule-list for each packet, 61until a match is found. 62All rules have two associated counters, a packet count and 63a byte count. 64These counters are updated when a packet matches the rule. 65.Pp 66The rules are ordered by a ``line-number'' from 1 to 65534 that is used 67to order and delete rules. Rules are tried in increasing order, and the 68first rule that matches a packet applies. 69Multiple rules may share the same number and apply in 70the order in which they were added. 71.Pp 72If a rule is added without a number, it is numbered 100 higher 73than the previous rule. If the highest defined rule number is 74greater than 65534, new rules are appended to the last rule. 75.Pp 76The delete operation deletes the first rule with number 77.Ar number , 78if any. 79.Pp 80The list command prints out the current rule set. 81.Pp 82The show command is equivalent to `ipfw -a list'. 83.Pp 84The zero operation zeroes the counters associated with rule number 85.Ar number . 86.Pp 87The flush operation removes all rules. 88.Pp 89Any command beginning with a '#', or being all blank, is ignored. 90.Pp 91One rule is always present: 92.Bd -literal -offset center 9365535 deny all from any to any 94.Ed 95.Pp 96This rule is the default policy, i.e., don't allow anything at all. 97Your job in setting up rules is to modify this policy to match your 98needs. 99.Pp 100However, if the kernel option 101.Dq IPFIREWALL_DEFAULT_TO_ACCEPT 102is active, the rule is instead: 103.Bd -literal -offset center 10465535 allow all from any to any 105.Ed 106.Pp 107This variation lets everything pass through. This option should only be 108activated in particular circumstances, such as if you use the firewall 109system as an on-demand denial-of-service filter that is normally wide open. 110.Pp 111The following options are available: 112.Bl -tag -width flag 113.It Fl a 114While listing, show counter values. See also ``show'' command. 115.It Fl f 116Don't ask for confirmation for commands that can cause problems if misused 117(ie; flush). 118.Ar Note , 119if there is no tty associated with the process, this is implied. 120.It Fl q 121While adding or flushing, be quiet about actions (implies '-f'). This is 122useful for adjusting rules by executing multiple ipfw commands in a script 123(e.g. sh /etc/rc.firewall), or by processing a file of many ipfw rules, 124across a remote login session. If a flush is performed in normal 125(verbose) mode (with the default kernel configuration), it prints a message. 126Because all rules are flushed, the 127message cannot be delivered to the login session, the login session is 128closed and the remainder of the ruleset is not processed. Access to the 129console is required to recover. 130.It Fl t 131While listing, show last match timestamp. 132.It Fl N 133Try to resolve addresses and service names in output. 134.El 135.Pp 136.Ar action : 137.Bl -hang -offset flag -width 1234567890123456 138.It Ar allow 139Allow packets that match rule. 140The search terminates. Aliases are 141.Ar pass , 142.Ar permit , 143and 144.Ar accept . 145.It Ar deny 146Discard packets that match this rule. 147The search terminates. 148.Ar Drop 149is an alias for 150.Ar deny . 151.It Ar reject 152(Deprecated.) Discard packets that match this rule, and try to send an ICMP 153host unreachable notice. 154The search terminates. 155.It Ar unreach code 156Discard packets that match this rule, and try to send an ICMP 157unreachable notice with code 158.Ar code , 159where 160.Ar code 161is a number from zero to 255, or one of these aliases: 162.Ar net , 163.Ar host , 164.Ar protocol , 165.Ar port , 166.Ar needfrag , 167.Ar srcfail , 168.Ar net-unknown , 169.Ar host-unknown , 170.Ar isolated , 171.Ar net-prohib , 172.Ar host-prohib , 173.Ar tosnet , 174.Ar toshost , 175.Ar filter-prohib , 176.Ar host-precedence , 177or 178.Ar precedence-cutoff . 179The search terminates. 180.It Ar reset 181TCP packets only. Discard packets that match this rule, 182and try to send a TCP reset (RST) notice. 183The search terminates. 184.It Ar count 185Update counters for all packets that match rule. 186The search continues with the next rule. 187.It Ar divert port 188Divert packets that match this rule to the 189.Xr divert 4 190socket bound to port 191.Ar port . 192The search terminates. 193.It Ar tee port 194Send a copy of packets matching this rule to the 195.Xr divert 4 196socket bound to port 197.Ar port . 198The search continues with the next rule. 199.It Ar skipto number 200Skip all subsequent rules numbered less than 201.Ar number . 202The search continues with the first rule numbered 203.Ar number 204or higher. 205.El 206.Pp 207If a packet matches more than one 208.Ar divert 209and/or 210.Ar tee 211rule, all but the last are ignored. 212.Pp 213If the kernel was compiled with 214.Dv IPFIREWALL_VERBOSE , 215then when a packet matches a rule with the ``log'' 216keyword a message will be printed on the console. 217If the kernel was compiled with the 218.Dv IPFIREWALL_VERBOSE_LIMIT 219option, then logging will cease after the number of packets 220specified by the option are received for that particular 221chain entry. Logging may then be re-enabled by clearing 222the packet counter for that entry. 223.Pp 224Console logging and the log limit are adjustable dynamically 225through the 226.Xr sysctl 8 227interface. 228.Pp 229.Ar proto : 230.Bl -hang -offset flag -width 1234567890123456 231.It Ar ip 232All packets match. The alias 233.Ar all 234has the same effect. 235.It Ar tcp 236Only TCP packets match. 237.It Ar udp 238Only UDP packets match. 239.It Ar icmp 240Only ICMP packets match. 241.It Ar <number|name> 242Only packets for the specified protocol matches (see 243.Pa /etc/protocols 244for a complete list). 245.El 246.Pp 247.Ar src 248and 249.Ar dst : 250.Bl -hang -offset flag 251.It Ar <address/mask> 252.Op Ar ports 253.El 254.Pp 255The 256.Em <address/mask> 257may be specified as: 258.Bl -hang -offset flag -width 1234567890123456 259.It Ar ipno 260An ipnumber of the form 1.2.3.4. 261Only this exact ip number match the rule. 262.It Ar ipno/bits 263An ipnumber with a mask width of the form 1.2.3.4/24. 264In this case all ip numbers from 1.2.3.0 to 1.2.3.255 will match. 265.It Ar ipno:mask 266An ipnumber with a mask width of the form 1.2.3.4:255.255.240.0. 267In this case all ip numbers from 1.2.0.0 to 1.2.15.255 will match. 268.El 269.Pp 270The sense of the match can be inverted by preceding an address with the 271``not'' modifier, causing all other addresses to be matched instead. This 272does not affect the selection of port numbers. 273.Pp 274With the TCP and UDP protocols, optional 275.Em ports 276may be specified as: 277.Pp 278.Bl -hang -offset flag 279.It Ns {port|port-port} Ns Op ,port Ns Op ,... 280.El 281.Pp 282Service names (from 283.Pa /etc/services ) 284may be used instead of numeric port values. 285A range may only be specified as the first value, 286and the length of the port list is limited to 287.Dv IP_FW_MAX_PORTS 288(as defined in 289.Pa /usr/src/sys/netinet/ip_fw.h ) 290ports. 291.Pp 292Fragmented packets which have a non-zero offset (i.e. not the first 293fragment) will never match a rule which has one or more port 294specifications. See the 295.Ar frag 296option for details on matching fragmented packets. 297.Pp 298Rules can apply to packets when they are incoming, or outgoing, or both. 299The 300.Ar in 301keyword indicates the rule should only match incoming packets. 302The 303.Ar out 304keyword indicates the rule should only match outgoing packets. 305.Pp 306To match packets going through a certain interface, specify 307the interface using 308.Ar via : 309.Bl -hang -offset flag -width 1234567890123456 310.It Ar via ifX 311Packet must be going through interface 312.Ar ifX. 313.It Ar via if* 314Packet must be going through interface 315.Ar ifX , 316where X is any unit number. 317.It Ar via any 318Packet must be going through 319.Em some 320interface. 321.It Ar via ipno 322Packet must be going through the interface having IP address 323.Ar ipno . 324.El 325.Pp 326The 327.Ar via 328keyword causes the interface to always be checked. 329If 330.Ar recv 331or 332.Ar xmit 333is used instead of 334.Ar via , 335then the only receive or transmit interface (respectively) is checked. 336By specifying both, it is possible to match packets based on both receive 337and transmit interface, e.g.: 338.Pp 339.Dl "ipfw add 100 deny ip from any to any out recv ed0 xmit ed1" 340.Pp 341The 342.Ar recv 343interface can be tested on either incoming or outgoing packets, while the 344.Ar xmit 345interface can only be tested on outgoing packets. So 346.Ar out 347is required (and 348.Ar in 349invalid) whenver 350.Ar xmit 351is used. Specifying 352.Ar via 353together with 354.Ar xmit 355or 356.Ar recv 357is invalid. 358.Pp 359A packet may not have a receive or transmit interface: packets originating 360from the local host have no receive interface. while packets destined for 361the local host have no transmit interface. 362.Pp 363Additional 364.Ar options : 365.Bl -hang -offset flag -width 1234567890123456 366.It frag 367Matches if the packet is a fragment and this is not the first fragment 368of the datagram. 369.Ar frag 370may not be used in conjunction with either 371.Ar tcpflags 372or TCP/UDP port specifications. 373.It in 374Matches if this packet was on the way in. 375.It out 376Matches if this packet was on the way out. 377.It ipoptions Ar spec 378Matches if the IP header contains the comma separated list of 379options specified in 380.Ar spec . 381The supported IP options are: 382.Ar ssrr 383(strict source route), 384.Ar lsrr 385(loose source route), 386.Ar rr 387(record packet route), and 388.Ar ts 389(timestamp). 390The absence of a particular option may be denoted 391with a ``!''. 392.It established 393Matches packets that have the RST or ACK bits set. 394TCP packets only. 395.It setup 396Matches packets that have the SYN bit set but no ACK bit. 397TCP packets only. 398.It tcpflags Ar spec 399Matches if the TCP header contains the comma separated list of 400flags specified in 401.Ar spec . 402The supported TCP flags are: 403.Ar fin , 404.Ar syn , 405.Ar rst , 406.Ar psh , 407.Ar ack , 408and 409.Ar urg . 410The absence of a particular flag may be denoted 411with a ``!''. 412A rule which contains a 413.Ar tcpflags 414specification can never match a fragmented packet which has 415a non-zero offset. See the 416.Ar frag 417option for details on matching fragmented packets. 418.It icmptypes Ar types 419Matches if the ICMP type is in the list 420.Ar types . 421The list may be specified as any combination of ranges 422or individual types separated by commas. 423.El 424.Sh CHECKLIST 425Here are some important points to consider when designing your 426rules: 427.Bl -bullet -hang -offset flag 428.It 429Remember that you filter both packets going in and out. 430Most connections need packets going in both directions. 431.It 432Remember to test very carefully. 433It is a good idea to be near the console when doing this. 434.It 435Don't forget the loopback interface. 436.El 437.Sh FINE POINTS 438There is one kind of packet that the firewall will always discard, 439that is an IP fragment with a fragment offset of one. 440This is a valid packet, but it only has one use, to try to circumvent 441firewalls. 442.Pp 443If you are logged in over a network, loading the LKM version of 444.Nm 445is probably not as straightforward as you would think. 446I recommend this command line: 447.Bd -literal -offset center 448modload /lkm/ipfw_mod.o && \e 449ipfw add 32000 allow all from any to any 450.Ed 451.Pp 452Along the same lines, doing an 453.Bd -literal -offset center 454ipfw flush 455.Ed 456.Pp 457in similar surroundings is also a bad idea. 458.Sh PACKET DIVERSION 459A divert socket bound to the specified port will receive all packets diverted 460to that port; see 461.Xr divert 4 . 462If no socket is bound to the destination port, or if the kernel 463wasn't compiled with divert socket support, diverted packets are dropped. 464.Sh EXAMPLES 465This command adds an entry which denies all tcp packets from 466.Em cracker.evil.org 467to the telnet port of 468.Em wolf.tambov.su 469from being forwarded by the host: 470.Pp 471.Dl ipfw add deny tcp from cracker.evil.org to wolf.tambov.su 23 472.Pp 473This one disallows any connection from the entire crackers network to 474my host: 475.Pp 476.Dl ipfw addf deny all from 123.45.67.0/24 to my.host.org 477.Pp 478Here is a good usage of the list command to see accounting records 479and timestamp information: 480.Pp 481.Dl ipfw -at l 482.Pp 483or in short form without timestamps: 484.Pp 485.Dl ipfw -a l 486.Pp 487This rule diverts all incoming packets from 192.168.2.0/24 to divert port 5000: 488.Pp 489.Dl ipfw divert 5000 all from 192.168.2.0/24 to any in 490.Sh SEE ALSO 491.Xr divert 4 , 492.Xr ip 4 , 493.Xr ipfirewall 4 , 494.Xr protocols 5 , 495.Xr services 5 , 496.Xr reboot 8 , 497.Xr sysctl 8 , 498.Xr syslogd 8 499.Sh BUGS 500.Pp 501.Em WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!!WARNING!! 502.Pp 503This program can put your computer in rather unusable state. When 504using it for the first time, work on the console of the computer, and 505do 506.Em NOT 507do anything you don't understand. 508.Pp 509When manipulating/adding chain entries, service and protocol names are 510not accepted. 511.Pp 512Incoming packet fragments diverted by 513.Ar divert 514are reassembled before delivery to the socket, whereas fragments diverted via 515.Ar tee 516are not. 517.Pp 518Port aliases containing dashes cannot be first in a list. 519.Sh AUTHORS 520.An Ugen J. S. Antsilevich , 521.An Poul-Henning Kamp , 522.An Alex Nash , 523.An Archie Cobbs . 524API based upon code written by 525.An Daniel Boulet 526for BSDI. 527.Sh HISTORY 528.Nm 529first appeared in 530.Fx 2.0 . 531