1.\" $NetBSD: bridge.4,v 1.3 2002/03/03 19:32:28 tron 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 August 17, 2001 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. For example, it is possible to bridge Ethernet and 51802.11 networks together, but it is not possible to bridge Ethernet 52and Token Ring together. 53.Pp 54To use 55.Nm bridge , 56the administrator must first create the interface and configure 57the bridge parameters. The bridge is created using the 58.Xr ifconfig 8 59.Sq create 60subcommand. 61The learning and forwarding behavior and other parameters of a 62bridge are configured by the 63.Xr brconfig 8 64utility. 65.Pp 66A bridge can be used to provide several services, such as a simple 67802.11-to-Ethernet bridge for wireless hosts, and traffic isolation. 68.Pp 69A bridge works like a hub, forwarding traffic from one interface 70to another. Multicast and broadcast packets are always forwarded 71to all interfaces that are part of the bridge. For unicast traffic, 72the bridge learns which MAC addresses are associated with which segments 73will forward the traffic selectively. 74.Pp 75The 76.Nm 77driver implements the IEEE 802.1D Spanning Tree protocol (STP). Spanning 78Tree is used to detect and remove loops in a network topology. 79.Sh SEE ALSO 80.Xr brconfig 8 81.Sh HISTORY 82The 83.Nm 84driver first appeared in 85.Nx 1.6 . 86.Sh AUTHORS 87The 88.Nm bridge 89driver was originally written by 90.An Jason L. Wright 91.Aq jason@thought.net 92as part of an undergraduate independent study at the University of 93North Carolina at Greensboro. 94.Pp 95This version of the 96.Nm 97driver has been heavily modified from the original version by 98.An Jason R. Thorpe 99.Aq thorpej@wasabisystems.com . 100.Sh BUGS 101The 102.Nm 103driver currently supports only Ethernet and Ethernet-like (e.g. 802.11) 104network devices. 105.Pp 106The 107.Nm 108driver currently does not support snooping via 109.Xr bpf 4 110or transparent filtering. 111