.\"	$NetBSD: bridge.4,v 1.3 2002/03/03 19:32:28 tron Exp $
.\"
.\" Copyright 2001 Wasabi Systems, Inc.
.\" All rights reserved.
.\"
.\" Written by Jason R. Thorpe for Wasabi Systems, Inc.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"    must display the following acknowledgement:
.\"	This product includes software developed for the NetBSD Project by
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.Dd August 17, 2001
.Dt BRIDGE 4
.Os
.Sh NAME
.Nm bridge
.Nd network bridge device
.Sh SYNOPSIS
.Cd "pseudo-device bridge"
.Sh DESCRIPTION
The
.Nm
driver creates a logical link between two or more IEEE 802 networks
that use the same (or
.Dq similar enough )
framing format.  For example, it is possible to bridge Ethernet and
802.11 networks together, but it is not possible to bridge Ethernet
and Token Ring together.
.Pp
To use
.Nm bridge ,
the administrator must first create the interface and configure
the bridge parameters.  The bridge is created using the
.Xr ifconfig 8
.Sq create
subcommand.
The learning and forwarding behavior and other parameters of a
bridge are configured by the
.Xr brconfig 8
utility.
.Pp
A bridge can be used to provide several services, such as a simple
802.11-to-Ethernet bridge for wireless hosts, and traffic isolation.
.Pp
A bridge works like a hub, forwarding traffic from one interface
to another.  Multicast and broadcast packets are always forwarded
to all interfaces that are part of the bridge.  For unicast traffic,
the bridge learns which MAC addresses are associated with which segments
will forward the traffic selectively.
.Pp
The
.Nm
driver implements the IEEE 802.1D Spanning Tree protocol (STP).  Spanning
Tree is used to detect and remove loops in a network topology.
.Sh SEE ALSO
.Xr brconfig 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Nx 1.6 .
.Sh AUTHORS
The
.Nm bridge
driver was originally written by
.An Jason L. Wright
.Aq jason@thought.net
as part of an undergraduate independent study at the University of
North Carolina at Greensboro.
.Pp
This version of the
.Nm
driver has been heavily modified from the original version by
.An Jason R. Thorpe
.Aq thorpej@wasabisystems.com .
.Sh BUGS
The
.Nm
driver currently supports only Ethernet and Ethernet-like (e.g. 802.11)
network devices.
.Pp
The
.Nm
driver currently does not support snooping via
.Xr bpf 4
or transparent filtering.