pfsync (4)

Leading comments

	$OpenBSD: pfsync.4,v 1.28 2009/02/17 10:05:18 dlg Exp $

 Copyright (c) 2002 Michael Shalayeff
 Copyright (c) 2003-2004 Ryan McBride
 All rights reserved.

 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:
 1. Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
 2. Redistributions in binary form must reproduce the above c...

(The comments found at the beginning of the groff file "man4/pfsync.4freebsd".)

NAME

pfsync - packet filter state table sychronisation interface

SYNOPSIS

device pfsync

DESCRIPTION

The ifconfig 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 ifconfig interface. If configured with a physical synchronisation interface, ifconfig 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 . State changes from packets received by ifconfig over the network are not rebroadcast. Updates to states created by a rule marked with the no-sync keyword are ignored by the ifconfig interface (see pf.conf5 for details).

The ifconfig 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 ifconfig 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 ifconfig 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 244.0.0.240 group address. An alternative destination address for ifconfig 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).

ifconfig has the following sysctl(8) tunables:

net.pfsync.carp_demotion_factor

Value added to net.inet.carp.demotion while ifconfig tries to perform its bulk update. See carp(4) for more information. Default value is 240.

EXAMPLES

ifconfig 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 ifconfig 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 ifconfig 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: 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

SEE ALSO

bpf(4), carp(4), enc(4), inet(4), inet6(4), ipsec(4), netintro(4), pf(4), pf.conf5, protocols(5), rc.conf5, ifconfig(8), tcpdump(1)

HISTORY

The ifconfig device first appeared in Ox 3.3 . It was first imported to Fx 5.3 .

The ifconfig protocol and kernel implementation were significantly modified in Fx 9.0 . The newer protocol is not compatible with older one and will not interoperate with it.