Copyright (c) 2002 Michael Shalayeff
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.Dd November 29, 2002 .Dt PFSYNC 4 .Os .Sh NAME .Nm pfsync .Nd packet filter states table logging interface .Sh SYNOPSIS .Sy pseudo-device Nm pfsync .Sh DESCRIPTION The .Nm interface is the interface to the packet filter, .Xr pf 4 , exposing all the changes to the state table. This allows for both debugging of rulesets and monitoring for changes in the table by invoking .Xr tcpdump 8 on the .Nm interface. States created by a rule marked with the .Ar no-sync keyword are omitted from the .Nm interface (see .Xr pf.conf 5 for details).
p States can be synchronised between two or more firewalls using this interface, by specifying a synchronisation interface using .Xr ifconfig 8 . For example, the following command sets fxp0 as the synchronisation interface. d -literal -offset indent # ifconfig pfsync0 syncif fxp0 .Ed
p State change messages are sent out on the synchronisation interface using IP multicast packets. The protocol is IP protocol 136, PFSYNC, and the multicast group used is 224.0.0.136.
p It is important that the synchronisation interface be on a trusted network as there is no authentication on the protocol and it would be trivial to spoof packets which create states, bypassing the pf ruleset. Ideally, this is a network dedicated to pfsync messages, ie. a crossover cable between two firewalls.
p There is a one-to-one correspondence between packets seen by .Xr bpf 4 on the .Nm interface, and packets sent out on the synchronisation interface, i.e. a packet with 4 state deletion messages on .Nm means that the same 4 deletions were sent out on the synchronisation interface. However, the actual packet contents may differ as the messages sent over the network are "compressed" where possible, containing only the necessary information.
p The .Nm interface will also attempt to collapse multiple updates of the same state into one message where possible. The maximum number of times this can be done before the update is sent out is controlled by the .Ar maxupd to ifconfig. (see .Xr ifconfig 8 and the example below for more details)
p Each packet retrieved on this interface has a header associated with it of length .Dv PFSYNC_HDRLEN . The header indicates the version of the protocol, address family, action taken on the following states and the number of state table entries attached in this packet. This structure, defined in .Aq Pa net/if_pfsync.h looks like: d -literal -offset indent struct pfsync_header { u_int8_t version; u_int8_t af; u_int8_t action; u_int8_t count; }; .Ed .Sh EXAMPLES d -literal -offset indent # ifconfig pfsync0 up syncif fxp0 maxupd 64 # tcpdump -s1500 -evtni pfsync0 .Ed .Sh SEE ALSO .Xr bpf 4 , .Xr inet 4 , .Xr inet6 4 , .Xr netintro 4 , .Xr pf 4 , .Xr pf.conf 5 , .Xr protocols 5 , .Xr ifconfig 8 , .Xr tcpdump 8 .Sh HISTORY The .Nm device first appeared in .Ox 3.3 .