1 .\" $NetBSD: bridge.4,v 1.5 2004/01/31 20:14:11 jdc Exp $
3 .\" Copyright 2001 Wasabi Systems, Inc.
4 .\" All rights reserved.
6 .\" Written by Jason R. Thorpe for Wasabi Systems, Inc.
8 .\" Redistribution and use in source and binary forms, with or without
9 .\" modification, are permitted provided that the following conditions
11 .\" 1. Redistributions of source code must retain the above copyright
12 .\" notice, this list of conditions and the following disclaimer.
13 .\" 2. Redistributions in binary form must reproduce the above copyright
14 .\" notice, this list of conditions and the following disclaimer in the
15 .\" documentation and/or other materials provided with the distribution.
16 .\" 3. All advertising materials mentioning features or use of this software
17 .\" must display the following acknowledgement:
18 .\" This product includes software developed for the NetBSD Project by
19 .\" Wasabi Systems, Inc.
20 .\" 4. The name of Wasabi Systems, Inc. may not be used to endorse
21 .\" or promote products derived from this software without specific prior
22 .\" written permission.
24 .\" THIS SOFTWARE IS PROVIDED BY WASABI SYSTEMS, INC. ``AS IS'' AND
25 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
26 .\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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43 .Nd network bridge device
45 To compile this driver into the kernel,
46 place the following line in your
47 kernel configuration file:
48 .Bd -ragged -offset indent
49 .Cd "device if_bridge"
52 Alternatively, to load the driver as a
53 module at boot time, place the following lines in
55 .Bd -literal -offset indent
62 driver creates a logical link between two or more IEEE 802 networks
64 .Dq "similar enough" )
66 For example, it is possible to bridge Ethernet and 802.11 networks together,
67 but it is not possible to bridge Ethernet and Token Ring together.
71 interface is created at runtime using interface cloning.
73 most easily done with the
83 interface randomly chooses a link (MAC) address in the range reserved for
84 locally administered addresses when it is created.
85 The address can be changed by assigning the desired link address using
88 A bridge can be used to provide several services, such as a simple
89 802.11-to-Ethernet bridge for wireless hosts, and traffic isolation.
91 A bridge works like a hub, forwarding traffic from one interface
93 Multicast and broadcast packets are always forwarded to all
94 interfaces that are part of the bridge.
95 For unicast traffic, the bridge learns which MAC addresses are associated
96 with which interfaces and will forward the traffic selectively.
98 All the bridged member interfaces need to be up in order to pass network traffic.
99 These can be enabled using
102 .Va ifconfig_ Ns Ao Ar interface Ac Ns Li ="up"
106 The MTU of the first member interface to be added is used as the bridge MTU.
107 All additional members are required to have exactly the same value.
109 The TXCSUM capability is disabled for any interface added to the bridge, and it
110 is restored when the interface is removed again.
114 where the packets are discarded after
116 processing, and are not processed or forwarded further.
117 This can be used to multiplex the input of two or more interfaces into a single
120 This is useful for reconstructing the traffic for network taps
121 that transmit the RX/TX signals out through two separate interfaces.
125 driver implements the Rapid Spanning Tree Protocol (RSTP or 802.1w) with
126 backwards compatibility with the legacy Spanning Tree Protocol (STP).
127 Spanning Tree is used to detect and remove loops in a network topology.
129 RSTP provides faster spanning tree convergence than legacy STP, the protocol
130 will exchange information with neighbouring switches to quickly transition to
131 forwarding without creating loops.
133 The code will default to RSTP mode but will downgrade any port connected to a
134 legacy STP network so is fully backward compatible.
135 A bridge can be forced to operate in STP mode without rapid state transitions
141 The bridge can log STP port changes to
144 .Va net.link.bridge.log_stp
149 Packet filtering can be used with any firewall package that hooks in via the
152 When filtering is enabled, bridged packets will pass through the filter
153 inbound on the originating interface, on the bridge interface and outbound on
154 the appropriate interfaces.
155 Either stage can be disabled.
156 The filtering behaviour can be controlled using
158 .Bl -tag -width ".Va net.link.bridge.pfil_onlyip"
159 .It Va net.link.bridge.pfil_onlyip
160 Controls the handling of non-IP packets which are not passed to
164 to only allow IP packets to pass (subject to firewall rules), set to
166 to unconditionally pass all non-IP Ethernet frames.
167 .It Va net.link.bridge.pfil_member
170 to enable filtering on the incoming and outgoing member interfaces, set
174 .It Va net.link.bridge.pfil_bridge
177 to enable filtering on the bridge interface, set
181 .It Va net.link.bridge.ipfw
184 to enable layer2 filtering with
189 This needs to be enabled for
198 will be disabled so that IPFW
199 is not run twice; these can be re-enabled if desired.
200 .It Va net.link.bridge.ipfw_arp
203 to enable layer2 ARP filtering with
213 ARP and REVARP packets are forwarded without being filtered and others
214 that are not IP nor IPv6 packets are not forwarded when
217 IPFW can filter Ethernet types using
219 so all packets are passed to
220 the filter for processing.
222 Note that packets to and from the bridging host will be seen by the
223 filter on the interface with the appropriate address configured as well
224 as on the interface on which the packet arrives or departs.
226 The following when placed in the file
228 will cause a bridge called
230 to be created, and will add the interfaces
234 to the bridge, and then enable packet forwarding.
235 Such a configuration could be used to implement a simple
236 802.11-to-Ethernet bridge (assuming the 802.11 interface is
238 .Bd -literal -offset indent
239 cloned_interfaces="bridge0"
240 ifconfig_bridge0="addm ath0 addm fxp0 up"
243 For the bridge to forward packets all member interfaces and the bridge need
245 The above example would also require:
246 .Bd -literal -offset indent
247 ifconfig_ath0="up ssid my_ap mode 11g mediaopt hostap"
251 Consider a system with two 4-port Ethernet boards.
252 The following will cause a bridge consisting of all 8 ports with Rapid Spanning
253 Tree enabled to be created:
254 .Bd -literal -offset indent
255 ifconfig bridge0 create
257 addm fxp0 stp fxp0 \e
258 addm fxp1 stp fxp1 \e
259 addm fxp2 stp fxp2 \e
260 addm fxp3 stp fxp3 \e
261 addm fxp4 stp fxp4 \e
262 addm fxp5 stp fxp5 \e
263 addm fxp6 stp fxp6 \e
264 addm fxp7 stp fxp7 \e
268 The bridge can be used as a regular host interface at the same time as bridging
269 between its member ports.
270 In this example, the bridge connects em0 and em1, and will receive its IP
271 address through DHCP:
272 .Bd -literal -offset indent
273 cloned_interfaces="bridge0"
274 ifconfig_bridge0="addm em0 addm em1 DHCP"
279 The bridge can tunnel Ethernet across an IP internet using the EtherIP
281 This can be combined with
283 to provide an encrypted connection.
286 interface and set the local and remote IP addresses for the
287 tunnel, these are reversed on the remote bridge.
288 .Bd -literal -offset indent
290 ifconfig gif0 tunnel 1.2.3.4 5.6.7.8 up
291 ifconfig bridge0 create
292 ifconfig bridge0 addm fxp0 addm gif0 up
303 driver first appeared in
309 driver was originally written by
311 .Aq jason@thought.net
312 as part of an undergraduate independent study at the University of
313 North Carolina at Greensboro.
317 driver has been heavily modified from the original version by
319 .Aq thorpej@wasabisystems.com .
321 Rapid Spanning Tree Protocol (RSTP) support was added by
323 .Aq thompsa@FreeBSD.org .
327 driver currently supports only Ethernet and Ethernet-like (e.g., 802.11)
328 network devices, with exactly the same interface MTU size as the bridge device.
330 Only wireless interfaces in hostap mode can be bridged due to the 802.11
331 framing format, bridging a wireless client is not supported yet.