.\"	$OpenBSD: pfsync.4,v 1.39 2024/01/31 06:50:16 jmc Exp $
.\"
.\" Copyright (c) 2002 Michael Shalayeff
.\" Copyright (c) 2003-2004 Ryan McBride
.\" All rights reserved.
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.Dd $Mdocdate: January 31 2024 $
.Dt PFSYNC 4
.Os
.Sh NAME
.Nm pfsync
.Nd packet filter state table synchronisation interface
.Sh SYNOPSIS
.Cd "pseudo-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 8
on the
.Nm
interface.
If configured with a physical synchronisation interface,
.Nm
will also send state changes out on that interface,
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 .
State changes from packets received by
.Nm
over the network are not rebroadcast.
Updates to states created by a rule marked with the
.Ar no-sync
keyword are ignored by the
.Nm
interface (see
.Xr pf.conf 5
for details).
.Pp
The
.Nm
interface will attempt to collapse multiple state updates into a single
packet where possible.
The maximum number of times a single state can be updated before a
.Nm
packet will be sent out is controlled by the
.Xr ifconfig 8
.Ar maxupd
parameter.
The sending out of a
.Nm
packet will be delayed by a maximum of one second.
.Pp
Where more than one firewall might actively handle packets, e.g. with certain
.Xr ospfd 8 ,
.Xr bgpd 8
or
.Xr carp 4
configurations, it is beneficial to defer transmission of the initial
packet of a connection.
The
.Nm
state insert message is sent immediately; the packet is queued until
either this message is acknowledged by another system, or a timeout has
expired.
This behaviour is enabled with the
.Ar defer
parameter to
.Xr ifconfig 8 .
.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 configures an address on fxp0 and
sets it as the synchronisation interface:
.Bd -literal -offset indent
# ifconfig fxp0 inet 172.19.13.1/28
# ifconfig pfsync0 syncdev fxp0
.Ed
.Pp
By default, state change messages are sent out on the synchronisation
interface using IP multicast packets to the 224.0.0.240 group address.
An alternative destination address for
.Nm
packets can be specified using the
.Ic syncpeer
keyword.
.\" This can be used in combination with
.\" .Xr ipsec 4
.\" to protect the synchronisation traffic.
.\" In such a configuration, the syncdev should be set to the
.\" .Xr enc 4
.\" interface, as this is where the traffic arrives when it is decapsulated,
.\" e.g.:
.\" .Bd -literal -offset indent
.\" # ifconfig pfsync0 syncpeer 10.0.0.2 syncdev enc0
.\" .Ed
.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.
Only run the pfsync protocol on a trusted network \- ideally a network
dedicated to pfsync messages such as a crossover cable between two firewalls.
.\" or specify a peer address and protect the traffic with
.\" .Xr ipsec 4 .
.Pp
.Nm
will increase the
.Xr carp 4
demotion counter for any interface groups associated with the interface
by 32 during initialisation, and by 1 if the
.Nm
link is down or if a bulk update fails.
.Sh EXAMPLES
.Nm
and
.Xr carp 4
can be used together to provide automatic failover of a pair of firewalls
configured in parallel.
One firewall will handle all traffic until it dies, is shut down, or is
manually demoted, at which point the second firewall will take 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
.Pa /etc/hostname.sis0 :
.Dl inet 10.0.0.254 255.255.255.0 NONE
.Pp
.Pa /etc/hostname.sis1 :
.Dl inet 192.168.0.254 255.255.255.0 NONE
.Pp
.Pa /etc/hostname.sis2 :
.Dl inet 192.168.254.254 255.255.255.0 NONE
.Pp
.Pa /etc/hostname.carp0 :
.Bd -literal -offset indent -compact
inet 10.0.0.1 255.255.255.0 10.0.0.255 \e
	vhid 1 carpdev sis0 pass foo
.Ed
.Pp
.Pa /etc/hostname.carp1 :
.Bd -literal -offset indent -compact
inet 192.168.0.1 255.255.255.0 192.168.0.255 \e
	vhid 2 carpdev sis1 pass bar
.Ed
.Pp
.Pa /etc/hostname.pfsync0 :
.Bd -literal -offset indent -compact
syncdev sis2
up
.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
It is preferable that one firewall handle the forwarding of all the traffic,
therefore 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
.Pa /etc/hostname.carp1
would look like this:
.Bd -literal -offset indent
inet 192.168.0.1 255.255.255.0 192.168.0.255 \e
	vhid 2 pass bar advskew 100
.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 bpf 4 ,
.Xr carp 4 ,
.\" .Xr enc 4 ,
.Xr inet 4 ,
.Xr inet6 4 ,
.\" .Xr ipsec 4 ,
.Xr netintro 4 ,
.Xr pf 4 ,
.Xr hostname.if 5 ,
.Xr pf.conf 5 ,
.Xr protocols 5 ,
.Xr ifconfig 8 ,
.Xr ifstated 8 ,
.Xr tcpdump 8
.Sh HISTORY
The
.Nm
device first appeared in
.Ox 3.3 .
.Pp
The
.Nm
protocol and kernel implementation were significantly modified between
.Ox 4.4
and
.Ox 4.5 .
The two protocols are incompatible and will not interoperate.
.Sh BUGS
.Nm
does not currently work with
.Xr ipsec 4 .