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

     pfsync -- packet filter state table logging interface

     device pfsync

     The pfsync	interface is a pseudo-device which exposes certain changes to
     the state table used by pf(4).  If	configured with	a physical synchroni-
     sation interface, pfsync will send	state changes out on that interface
     using IP multicast, 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.
     However, state changes from packets received by pfsync over the network
     are not rebroadcast.  States created by a rule marked with	the no-sync
     keyword are omitted from the pfsync interface (see	pf.conf(5) for

     The pfsync	interface will attempt to collapse multiple updates of the
     same state	into one message where possible.  The maximum number of	times
     this can be done before the update	is sent	out is controlled by the
     maxupd parameter to ifconfig (see ifconfig(8) and the example below for
     more details).

     Each packet retrieved on this interface has a header associated with it
     of	length PFSYNC_HDRLEN.  The header indicates the	version	of the proto-
     col, address family, action taken on the following	states,	and the	number
     of	state table entries attached in	this packet.  This structure is
     defined in	<net/if_pfsync.h> as:

	   struct pfsync_header	{
		   u_int8_t version;
		   u_int8_t af;
		   u_int8_t action;
		   u_int8_t count;

     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

     It	is important that the underlying synchronisation interface is up and
     has an IP address assigned.

     By	default, state change messages are sent	out on the synchronisation
     interface using IP	multicast packets.  The	protocol is IP protocol	240,
     PFSYNC, and the multicast group used is  When	a peer address
     is	specified using	the syncpeer keyword, the peer address is used as a
     destination for the pfsync	traffic, and the traffic can then be protected
     using ipsec(4).  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).

     For pfsync	to start its operation automatically at	the system boot	time,
     pfsync_enable and pfsync_syncdev variables	should be used in rc.conf(5).
     It	is not advisable to set	up pfsync with common network interface	con-
     figuration	variables of rc.conf(5)	because	pfsync must start after	its
     syncdev, which cannot be always ensured in	the latter case.

     pfsync and	carp(4)	can be used together to	provide	automatic failover of
     a pair of firewalls configured in parallel.  One firewall handles all
     traffic - if it dies or is	shut down, the second firewall takes over

     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):

     Interfaces	configuration in /etc/rc.conf:

	   network_interfaces="lo0 sis0	sis1 sis2"
	   cloned_interfaces="carp0 carp1"
	   ifconfig_carp0="vhid	1 pass foo"
	   ifconfig_carp1="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
	   pass	on { sis0 sis1 } proto carp

     If	it is preferable that one firewall handle the traffic, 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
     carp1 configuration would look like this:

	   ifconfig_carp1="vhid	2 pass bar advskew 100"

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


     Possibility to view state changes using tcpdump(1)	has not	been ported
     from OpenBSD yet.

     bpf(4), carp(4), ifconfig(8), inet(4), inet6(4), ipsec(4),	netintro(4),
     pf(4), pf.conf(5),	protocols(5), rc.conf(5) ifconfig(8), ifstated(8),

     The pfsync	device first appeared in OpenBSD 3.3.  The pfsync device was
     imported to FreeBSD 5.3.

FreeBSD	8.3			 June 6, 2006			   FreeBSD 8.3


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