.\"	$OpenBSD: pfsync.4,v 1.28 2009/02/17 10:05:18 dlg Exp $
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.\" Copyright (c) 2002 Michael Shalayeff
.\" Copyright (c) 2003-2004 Ryan McBride
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.Dd November 08, 2023
.Dt PFSYNC 4
.Os
.Sh NAME
.Nm pfsync
.Nd packet filter state table sychronisation 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,
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
.Ar maxupd
parameter to ifconfig
(see
.Xr ifconfig 8
and the example below for more details).
The sending out of a
.Nm
packet will be delayed by a maximum of one second.
.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 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.
Either 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
Support for
.Nm
transport over IPv6 was introduced in
.Fx 14.0 .
To set up
.Nm
using multicast with IPv6 link-local addresses, the
.Ic syncpeer
must be set to the
.Nm
multicast address and the
.Ic syncdev
to the interface where
.Nm
traffic is expected.
.Bd -literal -offset indent
# ifconfig pfsync0 syncpeer ff12::f0 syncdev vtnet0
.Ed
.Pp
When new features are introduced to
.Xr pf 4
the format of messages used by
.Nm
might change.
.Nm
will by default use the latest format.
If synchronization with a peer running an older version of FreeBSD is needed the
.Ar version
parameter can be used.
E.g.:
.Bd -literal -offset indent
# ifconfig pfsync0 version 1301
.Ed
.Pp
Currently the following versions are supported:
.Bl -tag -width indent
.It Cm 1301
FreeBSD releases 13.2 and older.
Compatibility with FreeBSD 13.1 has been verified.
.It Cm 1400
FreeBSD release 14.0.
.El
.Pp
.Nm
has the following
.Xr sysctl 8
tunables:
.Bl -tag -width ".Va net.pfsync"
.It Va net.pfsync.carp_demotion_factor
Value added to
.Va net.inet.carp.demotion
while
.Nm
tries to perform its bulk update.
See
.Xr carp 4
for more information.
Default value is 240.
.It Va net.pfsync.pfsync_buckets
The number of
.Nm
buckets.
This affects the performance and memory tradeoff.
Defaults to twice the number of CPUs.
Change only if benchmarks show this helps on your workload.
.El
.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
Interfaces configuration in
.Pa /etc/rc.conf :
.Bd -literal -offset indent
network_interfaces="lo0 sis0 sis1 sis2"
ifconfig_sis0="10.0.0.254/24"
ifconfig_sis0_alias0="inet 10.0.0.1/24 vhid 1 pass foo"
ifconfig_sis1="192.168.0.254/24"
ifconfig_sis1_alias0="inet 192.168.0.1/24 vhid 2 pass bar"
ifconfig_sis2="192.168.254.254/24"
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
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
vhids 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_sis1_alias0="inet 192.168.0.1/24 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 tcpdump 1 ,
.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 pf.conf 5 ,
.Xr protocols 5 ,
.Xr rc.conf 5 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Nm
device first appeared in
.Ox 3.3 .
It was first imported to
.Fx 5.3 .
.Pp
The
.Nm
protocol and kernel implementation were significantly modified in
.Fx 9.0 .
The newer protocol is not compatible with older one and will not interoperate
with it.