NAME
bridge —
network bridge device
SYNOPSIS
pseudo-device bridge
DESCRIPTION
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 configure 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
topology.
Transparent filtering for IP and IPv6 packets can be added with the kernel
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 filtering is enabled.
Note that packets to and from the bridging host will be seen by the filter 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
automatically if the underlying interfaces support it. This is to facilitate
XEN network configurations with
xennet(4).
SEE ALSO
etherip(4),
options(4),
xennet(4),
brconfig(8),
ipf(8)
HISTORY
The
bridge driver first appeared in
NetBSD
1.6.
AUTHORS
The
bridge driver was originally written by
Jason L. Wright ⟨jason@thought.net⟩ 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
⟨thorpej@wasabisystems.com⟩.
BUGS
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).