.\"	$OpenBSD: pfsync.4,v 1.12 2003/12/24 19:49:00 mcbride Exp $
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.\" 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 1
.Sh DESCRIPTION
The
.Nm
interface is a pseudo-device which exposes certain changes to the state
table used by
.Xr pf 4 .
State changes can be viewed by invoking
.Xr tcpdump 8
on the
.Nm
interface.
If configured with a physical synchronisation interface,
.Nm
will also send state changes out on that interface using IP multicast,
and insert state changes recieved on that interface from other systems
into the state table.
.Pp
By default, all local changes to the state table are exposed via
.Nm .
However, state changes from packets recieved by
.Nm
over the network are not rebroadcast.
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).
.Pp
The
.Nm
interface will 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)
.Pp
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:
.Bd -literal -offset indent
struct pfsync_header {
	u_int8_t version;
	u_int8_t af;
	u_int8_t action;
	u_int8_t count;
};
.Ed
.Sh NETWORK SYNCHRONISATION
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.
.Bd -literal -offset indent
# ifconfig pfsync0 syncif fxp0
.Ed
.Pp
State change messages are sent out on the synchronisation
interface using IP multicast packets.
The protocol is IP protocol 240, PFSYNC, and the multicast group
used is 224.0.0.240.
.Pp
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,
i.e. a crossover cable between two firewalls.
.Pp
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.
.Sh EXAMPLES
.Bd -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 .