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.

net.pfsync.pfsync_buckets
The number of pfsync buckets. This affects the performance and memory tradeoff. Defaults to
twice the number of CPUs. Change only if benchmarks show this helps on your workload.

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