Ubuntu Manpage: pfsync — packet filter state table sychronisation interface

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NAME

     pfsync — packet filter state table sychronisation interface

SYNOPSIS

     device pfsync

DESCRIPTION

     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.

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 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 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).

pfsync has the following sysctl(8) tunables:

net.pfsync.carp_demotion_factor
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.

EXAMPLES

     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 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):

     Interfaces configuration in /etc/rc.conf:

           network_interfaces="lo0 sis0 sis1 sis2"
           ifconfig_sis0="10.0.0.254/24"
           ifconfig_sis0_alias0="inet 10.0.0.1/24 vhid 1 pass foo"
           ifconfig_sis1="192.168.0.254/24"
           ifconfig_sis1_alias0="inet 192.168.0.1/24 vhid 2 pass bar"
           ifconfig_sis2="192.168.254.254/24"
           pfsync_enable="YES"
           pfsync_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) 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 192.168.0.1/24 vhid 2 pass bar advskew 100"

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

           net.inet.carp.preempt=1

HISTORY