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BRIDGE(4) NetBSD Kernel Interfaces Manual BRIDGE(4)
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bridge -- network bridge device
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 switch, 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
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.
The bridge driver will enable passing of VLAN tagged packets automati-
cally if the underlying interfaces support it. This is to facilitate XEN
network configurations with xennet(4).
It is not possible to assign an IP address directly to the bridge inter-
face. Instead, assign an IP address to a vether(4) interface which can
be added to the bridge.
l2tp(4), options(4), xennet(4), vether(4), brconfig(8), ipf(8)
The bridge driver first appeared in NetBSD 1.6.
The bridge driver was originally written by Jason L. Wright
<firstname.lastname@example.org> 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 <email@example.com>.
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 10.99 September 27, 2020 NetBSD 10.99