| PFSYNC(4) | Device Drivers Manual | PFSYNC(4) |
pfsync — packet
filter state table sychronisation interface
device pfsync
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.
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).
pfsync has the following
sysctl(8) tunables:
pfsync tries to perform its bulk update. See
carp(4) for more information. Default value is 240.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
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)
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.
| August 18, 2017 | Debian |