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NetBSD 6.1.5 - man page for pfsync (netbsd section 4)

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

     pfsync -- packet filter state table logging 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 synchronisation interface, pfsync will also send state changes
     out on that interface using IP multicast, and insert state changes received on that inter-
     face 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 cre-
     ated by a rule marked with the no-sync keyword are omitted from the pfsync interface (see
     pf.conf(5) for details).

     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 protocol, 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 interface:

	   # ifconfig pfsync0 syncdev fxp0

     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.

     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) (it is not supported at the moment on NetBSD
     due to the lack of any encapsulation pseudo-device).

     There is a one-to-one correspondence between packets seen by bpf(4) on the pfsync interface,
     and packets sent out on the synchronisation interface, i.e. a packet with 4 state deletion
     messages on pfsync means that the same 4 deletions were sent out on the synchronisation
     interface.  However, the actual packet contents may differ as the messages sent over the
     network are "compressed" where possible, containing only the necessary information.

     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 automatically.

     Both firewalls in this example have three sis(4) interfaces.  sis0 is the external inter-
     face, on the subnet; sis1 is the internal interface, on the sub-
     net; 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 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
	   pass on { sis0 sis1 } proto carp

     If it is preferable that one firewall handle the traffic, the advskew on the backup fire-
     wall's carp(4) interfaces should be set to something higher than the primary's.  For exam-
     ple, if firewall B is the backup, its /etc/ifconfig.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), inet(4), inet6(4), ipsec(4), netintro(4), pf(4), ifconfig.if(5),
     pf.conf(5), protocols(5), ifconfig(8), tcpdump(8)

     The pfsync device first appeared in OpenBSD 3.3.

     pfsync is not available when using pf(4) as a kernel module.

BSD					  April 12, 2010				      BSD

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