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 244.0.0.240 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.
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: 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:
SEE ALSO¶
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),
tcpdump(1)
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.