PFSYNC(4)

NAME
pfsync - packet filter state table sychronisation interface

SYNOPSIS
device pfsync

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.

pfsync has the following sysctl(8) tunables:

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.

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.