1.\" Copyright 2001 Wasabi Systems, Inc. 2.\" All rights reserved. 3.\" 4.\" Written by Jason R. Thorpe for Wasabi Systems, Inc. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed for the NetBSD Project by 17.\" Wasabi Systems, Inc. 18.\" 4. The name of Wasabi Systems, Inc. may not be used to endorse 19.\" or promote products derived from this software without specific prior 20.\" written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY WASABI SYSTEMS, INC. ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 24.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 25.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL WASABI SYSTEMS, INC 26.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 27.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 28.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 29.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 30.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 31.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 32.\" POSSIBILITY OF SUCH DAMAGE. 33.\" 34.\" $NetBSD: bridge.4,v 1.7 2005/06/23 12:47:38 peter Exp $ 35.\" $DragonFly: src/share/man/man4/bridge.4,v 1.6 2005/12/21 16:37:15 corecode Exp $ 36.\" 37.Dd January 4, 2004 38.Dt BRIDGE 4 39.Os 40.Sh NAME 41.Nm bridge 42.Nd network bridge device 43.Sh SYNOPSIS 44.Cd "pseudo-device bridge" 45.Sh DESCRIPTION 46The 47.Nm 48driver creates a logical link between two or more IEEE 802 networks 49that use the same (or 50.Dq similar enough ) 51framing format. 52For example, it is possible to bridge Ethernet and 802.11 networks together, 53but it is not possible to bridge Ethernet and Token Ring together. 54.Pp 55To use 56.Nm bridge , 57the administrator must first create the interface and configure 58the bridge parameters. 59The bridge is created using the 60.Xr ifconfig 8 61.Cm create 62subcommand. 63The learning and forwarding behavior and other parameters of a 64bridge are configured by the 65.Xr brconfig 8 66utility. 67.Pp 68A bridge can be used to provide several services, such as a simple 69802.11-to-Ethernet bridge for wireless hosts, and traffic isolation. 70.Pp 71A bridge works like a hub, forwarding traffic from one interface 72to another. 73Multicast and broadcast packets are always forwarded to all 74interfaces that are part of the bridge. 75For unicast traffic, the bridge learns which MAC addresses are associated 76with which interfaces and will forward the traffic selectively. 77.Pp 78The 79.Nm 80driver implements the IEEE 802.1D Spanning Tree protocol (STP). 81Spanning Tree is used to detect and remove loops in a network topology. 82.Pp 83Packet filtering can be used with any firewall package that hooks in via the 84.Xr pfil 9 85framework. 86When filtering is enabled, bridged packets will pass through the filter 87inbound on the originating interface, on the bridge interface and outbound on 88the appropriate interfaces. 89Either stage can be disabled, this behaviour can be controlled using 90.Xr sysctl 8 : 91Set 92.Va net.link.bridge.pfil_member 93to 94.Li 1 95to enable filtering on the incoming and outgoing member interfaces 96and set 97.Va net.link.bridge.pfil_bridge 98to 99.Li 1 100to enable filtering on the bridge interface. 101.Pp 102ARP and REVARP packets are forwarded without being filtered and others 103that are not IP nor IPv6 packets are not forwarded when filtering is 104enabled. 105.Pp 106Note that packets to and from the bridging host will be seen by the 107filter on the interface with the appropriate address configured as well 108as on the interface on which the packet arrives or departs. 109.Pp 110The MTU of the first member interface to be added is used as the bridge MTU, 111all additional members are required to have exactly the same value. 112.Sh SEE ALSO 113.Xr brconfig 8 , 114.Xr pf 4 115.Sh HISTORY 116The 117.Nm 118driver first appeared in 119.Ox 2.5 120and found its way into 121.Dx 1.3.7 . 122.Sh AUTHORS 123.An -nosplit 124The 125.Nm bridge 126driver was originally written by 127.An Jason L. Wright 128.Aq jason@thought.net 129as part of an undergraduate independent study at the University of 130North Carolina at Greensboro. 131.Pp 132This version of the 133.Nm 134driver has been heavily modified from the original version by 135.An Jason R. Thorpe 136.Aq thorpej@wasabisystems.com . 137.Sh BUGS 138The 139.Nm 140driver currently supports only Ethernet and Ethernet-like (e.g. 802.11) 141network devices, with exactly the same interface MTU size as the bridge device. 142