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:
- 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.
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:
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.