PFSYNC(4) OpenBSD Programmer's Manual PFSYNC(4)NAMEpfsync - packet filter state table sychronisation interface
SYNOPSIS
pseudo-device pfsyncDESCRIPTION
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).
EXAMPLESpfsync 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 ALSObpf(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.
OpenBSD 4.9 April 29, 2010 OpenBSD 4.9
