.\"	$OpenBSD: pfsync.4,v 1.27 2008/06/03 19:51:02 jmc Exp $
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.\" Copyright (c) 2002 Michael Shalayeff
.\" Copyright (c) 2003-2004 Ryan McBride
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.Dd April 21, 2018
.Dt PFSYNC 4
.Os
.Sh NAME
.Nm pfsync
.Nd packet filter state table logging interface
.Sh SYNOPSIS
.Cd "device pfsync"
.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 1
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 received 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 received 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
parameter 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 is defined in
.Aq Pa net/pf/if_pfsync.h
as:
.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 syncdev fxp0
.Ed
.Pp
By default, 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.
An alternative destination address for
.Nm
packets can be specified using the
.Ic syncpeer
keyword.
.Pp
It is important that the pfsync traffic be well secured
as there is no authentication on the protocol and it would
be trivial to spoof packets which create states, bypassing the pf ruleset.
Either run the pfsync protocol on a trusted network \- ideally a network
dedicated to pfsync messages such as 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 USING PFSYNC WITH CARP
.Nm
and
.Xr carp 4
can be used together to provide automatic failover of a pair of firewalls
configured in parallel.
One firewall handles all traffic \- if it dies or
is shut down, the second firewall takes over automatically.
.Pp
Both firewalls in this example have three
.Xr sis 4
interfaces.
sis0 is the external interface, on the 10.0.0.0/24 subnet; sis1 is the
internal interface, on the 192.168.0.0/24 subnet; and sis2 is the
.Nm
interface, using the 192.168.254.0/24 subnet.
A crossover cable connects the two firewalls via their sis2 interfaces.
On all three interfaces, firewall A uses the .254 address, while firewall B
uses .253.
The interfaces are configured as follows (firewall A unless otherwise
indicated):
.Pp
Interfaces configuration in
.Pa /etc/rc.conf :
.Bd -literal -offset indent
network_interfaces="lo0 sis0 sis1 sis2"
cloned_interfaces="carp0 carp1"
ifconfig_sis0="10.0.0.254/24"
ifconfig_sis1="192.168.0.254/24"
ifconfig_sis2="192.168.254.254/24"
ifconfig_carp0="vhid 1 pass foo 10.0.0.1/24"
ifconfig_carp1="vhid 2 pass bar 192.168.0.1/24"
pfsync_enable="YES"
pfsync_syncdev="sis2"
.Ed
.Pp
.Xr pf 4
must also be configured to allow
.Nm
and
.Xr carp 4
traffic through.
The following should be added to the top of
.Pa /etc/pf.conf :
.Bd -literal -offset indent
pass quick on { sis2 } proto pfsync keep state (no-sync)
pass on { sis0 sis1 } proto carp keep state (no-sync)
.Ed
.Pp
If it is preferable that one firewall handle the traffic,
the
.Ar advskew
on the backup firewall's
.Xr carp 4
interfaces should be set to something higher than
the primary's.
For example, if firewall B is the backup, its
carp1 configuration would look like this:
.Bd -literal -offset indent
ifconfig_carp1="vhid 2 pass bar advskew 100 192.168.0.1/24"
.Ed
.Pp
The following must also be added to
.Pa /etc/sysctl.conf :
.Bd -literal -offset indent
net.inet.carp.preempt=1
.Ed
.Sh SEE ALSO
.Xr tcpdump 1 ,
.Xr bpf 4 ,
.Xr carp 4 ,
.Xr inet 4 ,
.Xr inet6 4 ,
.Xr netintro 4 ,
.Xr pf 4 ,
.Xr pf.conf 5 ,
.Xr protocols 5 ,
.Xr ifconfig 8
.\".Xr ifstated 8 ,
.Sh HISTORY
The
.Nm
device first appeared in
.Ox 3.3
and was imported into
.Dx 1.1
by Devon H. O'Dell and Simon Schubert.