1 .\" $OpenBSD: pfsync.4,v 1.14 2004/03/21 19:47:59 miod Exp $
2 .\" $DragonFly: src/share/man/man4/pfsync.4,v 1.4 2006/05/26 19:39:39 swildner Exp $
4 .\" Copyright (c) 2002 Michael Shalayeff
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32 .Nd packet filter states table logging interface
38 interface is a pseudo-device which exposes certain changes to the state
41 State changes can be viewed by invoking
46 If configured with a physical synchronisation interface,
48 will also send state changes out on that interface using IP multicast,
49 and insert state changes received on that interface from other systems
52 By default, all local changes to the state table are exposed via
54 However, state changes from packets received by
56 over the network are not rebroadcast.
57 States created by a rule marked with the
59 keyword are omitted from the
67 interface will attempt to collapse multiple updates of the same
68 state into one message where possible.
69 The maximum number of times this can be done before the update is sent out
75 and the example below for more details)
77 Each packet retrieved on this interface has a header associated
80 The header indicates the version of the protocol, address family,
81 action taken on the following states and the number of state
82 table entries attached in this packet.
83 This structure, defined in
84 .In net/pf/if_pfsync.h
86 .Bd -literal -offset indent
87 struct pfsync_header {
94 .Sh NETWORK SYNCHRONISATION
95 States can be synchronised between two or more firewalls using this
96 interface, by specifying a synchronisation interface using
98 For example, the following command sets fxp0 as the synchronisation
100 .Bd -literal -offset indent
101 # ifconfig pfsync0 syncif fxp0
104 State change messages are sent out on the synchronisation
105 interface using IP multicast packets.
106 The protocol is IP protocol 240, PFSYNC, and the multicast group
109 It is important that the synchronisation interface be on a trusted
110 network as there is no authentication on the protocol and it would
111 be trivial to spoof packets which create states, bypassing the pf ruleset.
112 Ideally, this is a network dedicated to pfsync messages,
113 i.e. a crossover cable between two firewalls.
115 There is a one-to-one correspondence between packets seen by
119 interface, and packets sent out on the synchronisation interface, i.e.\&
120 a packet with 4 state deletion messages on
122 means that the same 4 deletions were sent out on the synchronisation
124 However, the actual packet contents may differ as the messages
125 sent over the network are "compressed" where possible, containing
126 only the necessary information.
128 .Bd -literal -offset indent
129 # ifconfig pfsync0 up syncif fxp0 maxupd 64
130 # tcpdump -s1500 -evtni pfsync0
145 device first appeared in
147 and was imported into
149 by Devon H. O'Dell and Simon Schubert.