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PFSYNC(4)                BSD Kernel Interfaces Manual                PFSYNC(4)

     pfsync -- packet filter state table synchronisation interface

     pseudo-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(8) on the pfsync interface.  If configured with a physical syn-
     chronisation 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 con-
     trolled 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

     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
           # ifconfig pfsync0 syncdev fxp0

     By default, state change messages are sent out on the synchronisation
     interface using IP multicast packets to the 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 configura-
     tion, 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 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 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 subnet; sis1 is the internal
     interface, on the subnet; and sis2 is the pfsync inter-
     face, using the subnet.  A crossover cable connects the
     two firewalls via their sis2 interfaces.  On all three interfaces, fire-
     wall A uses the .254 address, while firewall B uses .253.  The interfaces
     are configured as follows (firewall A unless otherwise indicated):


           inet NONE


           inet NONE


           inet NONE


           inet vhid 1 pass foo


           inet vhid 2 pass bar


           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 traf-
     fic, 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 vhid 2 pass bar \
                   advskew 100

     The following must also be added to /etc/sysctl.conf:


     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),

     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.

BSD                            February 1, 2015                            BSD