NAME
pfsync —
packet filter state table
sychronisation interface
SYNOPSIS
device pfsync
DESCRIPTION
Thepfsync 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).
pfsync has the following
sysctl(8) tunables:
- net.pfsync.carp_demotion_factor
- Value added to net.inet.carp.demotion while
pfsynctries to perform its bulk update. See carp(4) for more information. Default value is 240.
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.