205 lines
6.1 KiB
Groff
205 lines
6.1 KiB
Groff
.\" $NetBSD: bridge.4,v 1.5 2004/01/31 20:14:11 jdc Exp $
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.\"
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.\" Copyright 2001 Wasabi Systems, Inc.
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.\" All rights reserved.
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.\"
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.\" Written by Jason R. Thorpe for Wasabi Systems, Inc.
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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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed for the NetBSD Project by
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.\" Wasabi Systems, Inc.
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.\" 4. The name of Wasabi Systems, Inc. may not be used to endorse
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.\" or promote products derived from this software without specific prior
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.\" written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY WASABI SYSTEMS, INC. ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL WASABI SYSTEMS, INC
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd June 10, 2005
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.Dt IF_BRIDGE 4
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.Os
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.Sh NAME
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.Nm if_bridge
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.Nd network bridge device
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.Sh SYNOPSIS
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.Cd "device if_bridge"
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.Sh DESCRIPTION
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The
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.Nm
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driver creates a logical link between two or more IEEE 802 networks
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that use the same (or
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.Dq "similar enough" )
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framing format.
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For example, it is possible to bridge Ethernet and 802.11 networks together,
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but it is not possible to bridge Ethernet and Token Ring together.
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.Pp
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Each
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.Nm
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interface is created at runtime using interface cloning.
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This is
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most easily done with the
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.Xr ifconfig 8
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.Cm create
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command or using the
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.Va cloned_interfaces
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variable in
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.Xr rc.conf 5 .
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.Pp
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A bridge can be used to provide several services, such as a simple
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802.11-to-Ethernet bridge for wireless hosts, and traffic isolation.
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.Pp
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A bridge works like a hub, forwarding traffic from one interface
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to another.
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Multicast and broadcast packets are always forwarded to all
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interfaces that are part of the bridge.
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For unicast traffic, the bridge learns which MAC addresses are associated
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with which interfaces and will forward the traffic selectively.
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.Pp
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The
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.Nm
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driver implements the IEEE 802.1D Spanning Tree protocol (STP).
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Spanning Tree is used to detect and remove loops in a network topology.
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.Pp
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Packet filtering can be used with any firewall package that hooks in via the
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.Xr pfil 9
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framework.
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When filtering is enabled, bridged packets will pass through the filter
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inbound on the originating interface, on the bridge interface and outbound on
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the appropriate interfaces.
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Either stage can be disabled, this behaviour can be controlled using
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.Xr sysctl 8 :
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.Bl -tag -width ".Va net.link.bridge.pfil_member"
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.It Va net.link.bridge.pfil_member
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Set to
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.Li 1
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to enable filtering on the incoming and outgoing member interfaces, set
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to
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.Li 0
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to disable it.
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.It Va net.link.bridge.pfil_bridge
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Set to
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.Li 1
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to enable filtering on the bridge interface, set
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to
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.Li 0
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to disable it.
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.It Va net.link.bridge.ipfw
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Set to
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.Li 1
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to enable layer2 filtering with
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.Xr ipfirewall 4 ,
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set to
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.Li 0
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to disable it.
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This needs to be enabled for
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.Xr dummynet 4
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support.
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When
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.Va ipfw
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is enabled,
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.Va pfil_bridge
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and
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.Va pfil_member
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will be disabled so that IPFW
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is not run twice; these can be re-enabled if desired.
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.El
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.Pp
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ARP and REVARP packets are forwarded without being filtered and others
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that are not IP nor IPv6 packets are not forwarded when
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.Xr pfil 9
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filtering is enabled.
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IPFW can filter Ethernet types using
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.Cm mac-type
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so all packets are passed to
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the filter for processing.
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.Pp
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Note that packets to and from the bridging host will be seen by the
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filter on the interface with the appropriate address configured as well
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as on the interface on which the packet arrives or departs.
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.Pp
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The MTU of the first member interface to be added is used as the bridge MTU,
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all additional members are required to have exactly the same value.
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.Sh EXAMPLES
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The following when placed in the file
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.Pa /etc/rc.conf
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will cause a bridge called
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.Dq Li bridge0
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to be created, and will add the interfaces
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.Dq Li wi0
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and
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.Dq Li fxp0
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to the bridge, and then enable packet forwarding.
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Such a configuration could be used to implement a simple
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802.11-to-Ethernet bridge (assuming the 802.11 interface is
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in ad-hoc mode).
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.Bd -literal -offset indent
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cloned_interfaces="bridge0"
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ifconfig_bridge0="addm wi0 addm fxp0 up"
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.Ed
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.Pp
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Consider a system with two 4-port Ethernet boards.
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The following will cause a bridge consisting of all 8 ports with Spanning Tree
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enabled to be created:
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.Bd -literal -offset indent
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ifconfig bridge0 create
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ifconfig bridge0 \e
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addm fxp0 stp fxp0 \e
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addm fxp1 stp fxp1 \e
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addm fxp2 stp fxp2 \e
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addm fxp3 stp fxp3 \e
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addm fxp4 stp fxp4 \e
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addm fxp5 stp fxp5 \e
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addm fxp6 stp fxp6 \e
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addm fxp7 stp fxp7 \e
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up
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.Ed
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.Sh SEE ALSO
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.Xr ifconfig 8 ,
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.Xr ipfw 4 ,
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.Xr ipf 4 ,
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.Xr pf 4
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.Sh HISTORY
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The
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.Nm
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driver first appeared in
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.Fx 6.0 .
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.Sh AUTHORS
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The
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.Nm bridge
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driver was originally written by
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.An Jason L. Wright
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.Aq jason@thought.net
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as part of an undergraduate independent study at the University of
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North Carolina at Greensboro.
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.Pp
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This version of the
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.Nm
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driver has been heavily modified from the original version by
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.An Jason R. Thorpe
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.Aq thorpej@wasabisystems.com .
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.Sh BUGS
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The
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.Nm
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driver currently supports only Ethernet and Ethernet-like (e.g., 802.11)
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network devices, with exactly the same interface MTU size as the bridge device.
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