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IF_BRIDGE(4)           FreeBSD Kernel Interfaces Manual           IF_BRIDGE(4)

NAME
     if_bridge - network bridge device

SYNOPSIS
     device if_bridge

DESCRIPTION
     The if_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.

     Each if_bridge interface is created at runtime using interface cloning.
     This is most easily done with the ifconfig(8) create command or using the
     cloned_interfaces variable in rc.conf(5).

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

     Packet filtering can be used with any firewall package that hooks in via
     the pfil(9) framework.  When filtering is enabled, bridged packets will
     pass through the filter inbound on the originating interface, on the
     bridge interface and outbound on the appropriate interfaces.  Either
     stage can be disabled, this behaviour can be controlled using sysctl(8):

     net.link.bridge.pfil_member      Set to 1 to enable filtering on the
                                      incoming and outgoing member interfaces,
                                      set to 0 to disable it.

     net.link.bridge.pfil_bridge      Set to 1 to enable filtering on the
                                      bridge interface, set to 0 to disable
                                      it.

     net.link.bridge.ipfw             Set to 1 to enable layer2 filtering with
                                      ipfirewall(4), set to 0 to disable it.
                                      This needs to be enabled for dummynet(4)
                                      support.  When ipfw is enabled,
                                      pfil_bridge and pfil_member will be
                                      disabled so that IPFW is not run twice;
                                      these can be re-enabled if desired.

     ARP and REVARP packets are forwarded without being filtered and others
     that are not IP nor IPv6 packets are not forwarded when pfil(9) filtering
     is enabled.  IPFW can filter Ethernet types using mac-type so all packets
     are passed to the filter for processing.

     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 MTU of the first member interface to be added is used as the bridge
     MTU, all additional members are required to have exactly the same value.

EXAMPLES
     The following when placed in the file /etc/rc.conf will cause a bridge
     called ``bridge0'' to be created, and will add the interfaces ``wi0'' and
     ``fxp0'' to the bridge, and then enable packet forwarding.  Such a
     configuration could be used to implement a simple 802.11-to-Ethernet
     bridge (assuming the 802.11 interface is in ad-hoc mode).

           cloned_interfaces="bridge0"
           ifconfig_bridge0="addm wi0 addm fxp0 up"

     Consider a system with two 4-port Ethernet boards.  The following will
     cause a bridge consisting of all 8 ports with Spanning Tree enabled to be
     created:

           ifconfig bridge0 create
           ifconfig bridge0 \
               addm fxp0 stp fxp0 \
               addm fxp1 stp fxp1 \
               addm fxp2 stp fxp2 \
               addm fxp3 stp fxp3 \
               addm fxp4 stp fxp4 \
               addm fxp5 stp fxp5 \
               addm fxp6 stp fxp6 \
               addm fxp7 stp fxp7 \
               up

SEE ALSO
     ifconfig(8), ipfw(4), ipf(4), pf(4)

HISTORY
     The if_bridge driver first appeared in FreeBSD 6.0.

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 if_bridge driver has been heavily modified from the
     original version by
     Jason R. Thorpe <thorpej@wasabisystems.com>.

BUGS
     The if_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.

FreeBSD 11.0-PRERELEASE          June 10, 2005         FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | SEE ALSO | HISTORY | AUTHORS | BUGS

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