PFSYNC(4) FreeBSD Kernel Interfaces Manual PFSYNC(4)
NAME
pfsync - packet filter state table synchronisation interface
SYNOPSIS
device pfsync
In loader.conf(5):
net.pfsync.pfsync_buckets
In sysctl.conf(5):
net.pfsync.carp_demotion_factor
DESCRIPTION
The pfsync interface is a pseudo-device which exposes certain changes to
the state table used by pf(4). State changes can be viewed by invoking
tcpdump(1) on the pfsync interface. If configured with a physical
synchronisation interface, pfsync will also send state changes out on
that interface, and insert state changes received on that interface from
other systems into the state table.
By default, all local changes to the state table are exposed via pfsync.
State changes from packets received by pfsync over the network are not
rebroadcast. Updates to states created by a rule marked with the no-sync
keyword are ignored by the pfsync interface (see pf.conf(5) for details).
The pfsync 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 pfsync packet will be sent out is
controlled by the maxupd parameter to ifconfig (see ifconfig(8) and the
example below for more details). The sending out of a pfsync packet will
be delayed by a maximum of one second.
NETWORK SYNCHRONISATION
States can be synchronised between two or more firewalls using this
interface, by specifying a synchronisation interface using ifconfig(8).
For example, the following command sets fxp0 as the synchronisation
interface:
# ifconfig pfsync0 syncdev fxp0
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 pfsync packets can be specified
using the syncpeer keyword. This can be used in combination with
ipsec(4) to protect the synchronisation traffic. In such a
configuration, the syncdev should be set to the enc(4) interface, as this
is where the traffic arrives when it is decapsulated, e.g.:
# ifconfig pfsync0 syncpeer 10.0.0.2 syncdev enc0
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 ipsec(4).
Support for pfsync transport over IPv6 was introduced in FreeBSD 14.0.
To set up pfsync using multicast with IPv6 link-local addresses, the
syncpeer must be set to the pfsync multicast address and the syncdev to
the interface where pfsync traffic is expected.
# ifconfig pfsync0 syncpeer ff12::f0 syncdev vtnet0
When new features are introduced to pf(4) the format of messages used by
pfsync might change. pfsync will by default use the latest format. If
synchronization with a peer running an older version of FreeBSD is needed
the version parameter can be used. E.g.:
# ifconfig pfsync0 version 1301
Currently the following versions are supported:
1301 FreeBSD releases 13.2 and older. Compatibility with FreeBSD 13.1
has been verified.
1400 FreeBSD release 14.0.
1500 FreeBSD release 15.0.
SYSCTL VARIABLES
The following variables can be entered at the loader(8) prompt, set in
loader.conf(5), or changed at runtime with sysctl(8):
net.pfsync.carp_demotion_factor
Value added to net.inet.carp.demotion while pfsync tries to
perform its bulk update. See carp(4) for more information.
Default value is 240.
LOADER TUNABLES
The following tunable may be set in loader.conf(5) or at the loader(8)
prompt:
net.pfsync.pfsync_buckets
The number of pfsync 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.
EXAMPLES
pfsync and 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.
Both firewalls in this example have three 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 pfsync
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):
Interfaces configuration in /etc/rc.conf:
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"
pf(4) must also be configured to allow pfsync and carp(4) traffic
through. The following should be added to the top of /etc/pf.conf:
pass quick on { sis2 } proto pfsync keep state (no-sync)
pass on { sis0 sis1 } proto carp keep state (no-sync)
It is preferable that one firewall handle the forwarding of all the
traffic, therefore the advskew on the backup firewall's 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:
ifconfig_sis1_alias0="inet 192.168.0.1/24 vhid 2 pass bar advskew 100"
The following must also be added to /etc/sysctl.conf:
net.inet.carp.preempt=1
SEE ALSO
tcpdump(1), bpf(4), carp(4), enc(4), inet(4), inet6(4), ipsec(4),
netintro(4), pf(4), pf.conf(5), protocols(5), rc.conf(5), ifconfig(8)
HISTORY
The pfsync device first appeared in OpenBSD 3.3. It was first imported
to FreeBSD 5.3.
The pfsync protocol and kernel implementation were significantly modified
in FreeBSD 9.0. The newer protocol is not compatible with older one and
will not interoperate with it.
FreeBSD 15.1-STABLE-HBSD November 8, 2023 PFSYNC(4)