BRIDGE(4)               NetBSD Kernel Interfaces Manual              BRIDGE(4)

     bridge -- network bridge device

     pseudo-device bridge

     The bridge driver creates a logical link between two or more IEEE 802
     networks that use the same (or ``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.

     To use bridge, the administrator must first create the interface and con-
     figure the bridge parameters.  The bridge is created using the
     ifconfig(8) create subcommand.  The learning and forwarding behavior and
     other parameters of a bridge are configured by the brconfig(8) utility.

     A bridge can be used to provide several services, such as a simple
     802.11-to-Ethernet bridge for wireless hosts, and traffic isolation.

     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 interfaces and will
     forward the traffic selectively.

     The bridge driver implements the IEEE 802.1D Spanning Tree protocol
     (STP).  Spanning Tree is used to detect and remove loops in a network

     Transparent filtering for IP and IPv6 packets can be added with the ker-
     nel configuration option options BRIDGE_IPF.

     When filtering is enabled, bridged packets will pass through the filter
     inbound on the originating interface and outbound on the appropriate
     interfaces.  ARP and REVARP packets are forwarded without being filtered
     and others that are not IP nor IPv6 packets are not forwarded when fil-
     tering is enabled.

     Note that packets to and from the bridging host will be seen by the fil-
     ter on the interface with the appropriate address configured as well as
     on the interface on which the packet arrives or departs.

     options(4), brconfig(8), ipf(8)

     The bridge driver first appeared in NetBSD 1.6.

     The bridge driver was originally written by Jason L. Wright
     <> as part of an undergraduate independent study at the
     University of North Carolina at Greensboro.

     This version of the bridge driver has been heavily modified from the
     original version by Jason R. Thorpe <>.

     The bridge driver currently supports only Ethernet and Ethernet-like
     (e.g. 802.11) network devices, with exactly the same interface MTU size
     as the bridge device.

     The bridge driver currently does not support snooping via bpf(4).

NetBSD 4.0                      January 4, 2004                     NetBSD 4.0

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