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263 lines
7.5 KiB
Groff
263 lines
7.5 KiB
Groff
.\" $OpenBSD: pfsync.4,v 1.24 2006/10/23 07:05:49 jmc Exp $
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.\"
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.\" Copyright (c) 2002 Michael Shalayeff
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.\" Copyright (c) 2003-2004 Ryan McBride
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF MIND,
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.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 6, 2006
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.Dt PFSYNC 4
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.Os
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.Sh NAME
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.Nm pfsync
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.Nd packet filter state table logging interface
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.Sh SYNOPSIS
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.Cd "device pfsync"
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.Sh DESCRIPTION
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The
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.Nm
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interface is a pseudo-device which exposes certain changes to the state
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table used by
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.Xr pf 4 .
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.\" XXX: not yet!
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.\" State changes can be viewed by invoking
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.\" .Xr tcpdump 1
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.\" on the
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.\" .Nm
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.\" interface.
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If configured with a physical synchronisation interface,
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.Nm
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will send state changes out on that interface using IP multicast,
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and insert state changes received on that interface from other systems
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into the state table.
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.Pp
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By default, all local changes to the state table are exposed via
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.Nm .
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However, state changes from packets received by
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.Nm
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over the network are not rebroadcast.
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States created by a rule marked with the
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.Ar no-sync
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keyword are omitted from the
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.Nm
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interface (see
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.Xr pf.conf 5
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for details).
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.Pp
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The
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.Nm
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interface will attempt to collapse multiple updates of the same
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state into one message where possible.
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The maximum number of times this can be done before the update is sent out
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is controlled by the
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.Ar maxupd
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parameter to ifconfig
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(see
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.Xr ifconfig 8
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and the example below for more details).
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.Pp
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Each packet retrieved on this interface has a header associated
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with it of length
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.Dv PFSYNC_HDRLEN .
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The header indicates the version of the protocol, address family,
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action taken on the following states, and the number of state
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table entries attached in this packet.
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This structure is defined in
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.Aq Pa net/if_pfsync.h
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as:
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.Bd -literal -offset indent
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struct pfsync_header {
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u_int8_t version;
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u_int8_t af;
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u_int8_t action;
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u_int8_t count;
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};
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.Ed
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.Sh NETWORK SYNCHRONISATION
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States can be synchronised between two or more firewalls using this
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interface, by specifying a synchronisation interface using
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.Xr ifconfig 8 .
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For example, the following command sets fxp0 as the synchronisation
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interface:
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.Bd -literal -offset indent
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# ifconfig pfsync0 syncdev fxp0
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.Ed
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.Pp
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It is important that the underlying synchronisation interface is up
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and has an IP address assigned.
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.Pp
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By default, state change messages are sent out on the synchronisation
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interface using IP multicast packets.
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The protocol is IP protocol 240, PFSYNC, and the multicast group
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used is 224.0.0.240.
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When a peer address is specified using the
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.Ic syncpeer
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keyword, the peer address is used as a destination for the pfsync traffic,
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and the traffic can then be protected using
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.Xr ipsec 4 .
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In such a configuration, the syncdev should be set to the
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.Xr enc 4
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interface, as this is where the traffic arrives when it is decapsulated,
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e.g.:
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.Bd -literal -offset indent
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# ifconfig pfsync0 syncpeer 10.0.0.2 syncdev enc0
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.Ed
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.Pp
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It is important that the pfsync traffic be well secured
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as there is no authentication on the protocol and it would
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be trivial to spoof packets which create states, bypassing the pf ruleset.
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Either run the pfsync protocol on a trusted network \- ideally a network
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dedicated to pfsync messages such as a crossover cable between two firewalls,
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or specify a peer address and protect the traffic with
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.Xr ipsec 4 .
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.Pp
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For
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.Nm
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to start its operation automatically at the system boot time,
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.Va pfsync_enable
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and
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.Va pfsync_syncdev
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variables should be used in
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.Xr rc.conf 5 .
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It is not advisable to set up
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.Nm
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with common network interface configuration variables of
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.Xr rc.conf 5
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because
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.Nm
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must start after its
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.Cm syncdev ,
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which cannot be always ensured in the latter case.
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.\" XXX: not yet!
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.\" .Pp
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.\" There is a one-to-one correspondence between packets seen by
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.\" .Xr bpf 4
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.\" on the
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.\" .Nm
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.\" interface, and packets sent out on the synchronisation interface, i.e.\&
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.\" a packet with 4 state deletion messages on
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.\" .Nm
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.\" means that the same 4 deletions were sent out on the synchronisation
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.\" interface.
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.\" However, the actual packet contents may differ as the messages
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.\" sent over the network are "compressed" where possible, containing
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.\" only the necessary information.
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.Sh EXAMPLES
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.Nm
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and
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.Xr carp 4
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can be used together to provide automatic failover of a pair of firewalls
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configured in parallel.
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One firewall handles all traffic \- if it dies or
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is shut down, the second firewall takes over automatically.
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.Pp
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Both firewalls in this example have three
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.Xr sis 4
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interfaces.
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sis0 is the external interface, on the 10.0.0.0/24 subnet; sis1 is the
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internal interface, on the 192.168.0.0/24 subnet; and sis2 is the
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.Nm
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interface, using the 192.168.254.0/24 subnet.
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A crossover cable connects the two firewalls via their sis2 interfaces.
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On all three interfaces, firewall A uses the .254 address, while firewall B
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uses .253.
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The interfaces are configured as follows (firewall A unless otherwise
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indicated):
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.Pp
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Interfaces configuration in
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.Pa /etc/rc.conf :
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.Bd -literal -offset indent
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network_interfaces="lo0 sis0 sis1 sis2"
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cloned_interfaces="carp0 carp1"
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ifconfig_sis0="10.0.0.254/24"
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ifconfig_sis1="192.168.0.254/24"
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ifconfig_sis2="192.168.254.254/24"
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ifconfig_carp0="vhid 1 pass foo 10.0.0.1/24"
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ifconfig_carp1="vhid 2 pass bar 192.168.0.1/24"
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pfsync_enable="YES"
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pfsync_syncdev="sis2"
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.Ed
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.Pp
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.Xr pf 4
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must also be configured to allow
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.Nm
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and
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.Xr carp 4
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traffic through.
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The following should be added to the top of
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.Pa /etc/pf.conf :
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.Bd -literal -offset indent
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pass quick on { sis2 } proto pfsync
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pass on { sis0 sis1 } proto carp
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.Ed
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.Pp
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If it is preferable that one firewall handle the traffic,
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the
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.Ar advskew
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on the backup firewall's
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.Xr carp 4
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interfaces should be set to something higher than
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the primary's.
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For example, if firewall B is the backup, its
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carp1 configuration would look like this:
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.Bd -literal -offset indent
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ifconfig_carp1="vhid 2 pass bar advskew 100 192.168.0.1/24"
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.Ed
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.Pp
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The following must also be added to
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.Pa /etc/sysctl.conf :
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.Bd -literal -offset indent
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net.inet.carp.preempt=1
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.Ed
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.Sh BUGS
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Possibility to view state changes using
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.Xr tcpdump 1
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has not been ported from
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.Ox
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yet.
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.Sh SEE ALSO
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.Xr bpf 4 ,
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.Xr carp 4 ,
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.Xr ifconfig 8 ,
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.Xr inet 4 ,
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.Xr inet6 4 ,
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.Xr ipsec 4 ,
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.Xr netintro 4 ,
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.Xr pf 4 ,
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.Xr pf.conf 5 ,
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.Xr protocols 5 ,
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.Xr rc.conf 5
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.Xr ifconfig 8 ,
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.Xr ifstated 8 ,
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.Xr tcpdump 8
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.Sh HISTORY
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The
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.Nm
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device first appeared in
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.Ox 3.3 .
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The
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.Nm
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device was imported to
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.Fx 5.3 .
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