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PFSYNC(4)              FreeBSD Kernel Interfaces Manual              PFSYNC(4)

     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

           # 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
     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 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:

                     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.

     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
     interface, using the 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

     Interfaces configuration in /etc/rc.conf:

           network_interfaces="lo0 sis0 sis1 sis2"
           ifconfig_sis0_alias0="inet vhid 1 pass foo"
           ifconfig_sis1_alias0="inet vhid 2 pass bar"

     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 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.

FreeBSD 11.0-PRERELEASE        December 20, 2011       FreeBSD 11.0-PRERELEASE


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