1.\" $NetBSD: bridge.4,v 1.9 2010/01/09 09:44:29 mbalmer Exp $ 2.\" 3.\" Copyright 2001 Wasabi Systems, Inc. 4.\" All rights reserved. 5.\" 6.\" Written by Jason R. Thorpe for Wasabi Systems, Inc. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 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. 23.\" 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 27.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL WASABI SYSTEMS, INC 28.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 29.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 30.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 31.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 32.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 33.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 34.\" POSSIBILITY OF SUCH DAMAGE. 35.\" 36.Dd January 9, 2010 37.Dt BRIDGE 4 38.Os 39.Sh NAME 40.Nm bridge 41.Nd network bridge device 42.Sh SYNOPSIS 43.Cd "pseudo-device bridge" 44.Sh DESCRIPTION 45The 46.Nm 47driver creates a logical link between two or more IEEE 802 networks 48that use the same (or 49.Dq similar enough ) 50framing format. 51For example, it is possible to bridge Ethernet and 802.11 networks together, 52but it is not possible to bridge Ethernet and Token Ring together. 53.Pp 54To use 55.Nm bridge , 56the administrator must first create the interface and configure 57the bridge parameters. 58The bridge is created using the 59.Xr ifconfig 8 60.Cm create 61subcommand. 62The learning and forwarding behavior and other parameters of a 63bridge are configured by the 64.Xr brconfig 8 65utility. 66.Pp 67A bridge can be used to provide several services, such as a simple 68802.11-to-Ethernet bridge for wireless hosts, and traffic isolation. 69.Pp 70A bridge works like a switch, forwarding traffic from one interface 71to another. 72Multicast and broadcast packets are always forwarded to all 73interfaces that are part of the bridge. 74For unicast traffic, the bridge learns which MAC addresses are associated 75with which interfaces and will forward the traffic selectively. 76.Pp 77The 78.Nm 79driver implements the IEEE 802.1D Spanning Tree protocol (STP). 80Spanning Tree is used to detect and remove loops in a network topology. 81.Pp 82Transparent filtering for IP and IPv6 packets can be added with the kernel 83configuration option 84.Cd options BRIDGE_IPF . 85.Pp 86When filtering is enabled, bridged packets will pass through the filter 87inbound on the originating interface and outbound on the appropriate 88interfaces. 89ARP and REVARP packets are forwarded without being filtered and others 90that are not IP nor IPv6 packets are not forwarded when filtering is 91enabled. 92.Pp 93Note that packets to and from the bridging host will be seen by the 94filter on the interface with the appropriate address configured as well 95as on the interface on which the packet arrives or departs. 96.Sh SEE ALSO 97.Xr etherip 4 , 98.Xr options 4 , 99.Xr brconfig 8 , 100.Xr ipf 8 101.Sh HISTORY 102The 103.Nm 104driver first appeared in 105.Nx 1.6 . 106.Sh AUTHORS 107.An -nosplit 108The 109.Nm bridge 110driver was originally written by 111.An Jason L. Wright 112.Aq jason@thought.net 113as part of an undergraduate independent study at the University of 114North Carolina at Greensboro. 115.Pp 116This version of the 117.Nm 118driver has been heavily modified from the original version by 119.An Jason R. Thorpe 120.Aq thorpej@wasabisystems.com . 121.Sh BUGS 122The 123.Nm 124driver currently supports only Ethernet and Ethernet-like (e.g. 802.11) 125network devices, with exactly the same interface MTU size as the bridge device. 126.Pp 127The 128.Nm 129driver currently does not support snooping via 130.Xr bpf 4 . 131