NAME
pfsync —
packet filter state table
sychronisation interface
SYNOPSIS
pseudo-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(8) 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.
Where more than one firewall might actively handle packets, e.g.
with certain ospfd(8),
bgpd(8) or carp(4) configurations, it is beneficial to defer
transmission of the initial packet of a connection. The
pfsync state insert message is sent immediately; the
packet is queued until either this message is acknowledged by another
system, or a timeout has expired. This behaviour is enabled with the
defer parameter to
ifconfig(8).
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 configures an address on fxp0 and sets it as the synchronisation interface:
# ifconfig fxp0 inet 172.19.13.1/28 # 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).
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):
/etc/hostname.sis0:
inet 10.0.0.254 255.255.255.0 NONE
/etc/hostname.sis1:
inet 192.168.0.254 255.255.255.0 NONE
/etc/hostname.sis2:
inet 192.168.254.254 255.255.255.0 NONE
/etc/hostname.carp0:
inet 10.0.0.1 255.255.255.0 10.0.0.255 vhid 1 pass foo
/etc/hostname.carp1:
inet 192.168.0.1 255.255.255.0 192.168.0.255 vhid 2 pass bar
/etc/hostname.pfsync0:
up 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) interfaces should be set to something higher than the primary's. For example, if firewall B is the backup, its /etc/hostname.carp1 would look like this:
inet 192.168.0.1 255.255.255.0 192.168.0.255 vhid 2 pass bar \ advskew 100
The following must also be added to /etc/sysctl.conf:
net.inet.carp.preempt=1
SEE ALSO
bpf(4), carp(4), enc(4), inet(4), inet6(4), ipsec(4), netintro(4), pf(4), hostname.if(5), pf.conf(5), protocols(5), ifconfig(8), ifstated(8), tcpdump(8)
HISTORY
The pfsync device first appeared in
OpenBSD 3.3.
The pfsync protocol and kernel
implementation were significantly modified between OpenBSD
4.4 and OpenBSD 4.5. The two protocols are
incompatible and will not interoperate.