.\"
.\" $FreeBSD$
.\"
.Dd September 28, 1998
.Dt BRIDGE 4
.Os
.Sh NAME
.Nm bridge
.Nd bridging support
.Sh SYNOPSIS
.Cd "options BRIDGE"
.Sh DESCRIPTION
.Fx
supports bridging on Ethernet-type interfaces.
.Pp
Runtime operation of the
.Nm
is controlled by several
.Xr sysctl 8
variables.
The
.Va net.link.ether.bridge
variable can be set to
.Li 1
to enable bridging, or set to
.Li 0
to disable it.
.Pp
The
.Va net.link.ether.bridge_ipfw
variable can be set to
.Li 1
to enable
.Xr ipfw 8
filtering on bridged packets.
Note that
.Xr ipfw 8
rules only apply
to IP packets.
Non-IP packets are subject to the default
.Xr ipfw 8
rule
(number 65535)
which must be an
.Cm allow
rule if ARP and other non-IP packets need to flow through the
.Nm .
.Pp
The
.Nm
configuration is controlled by the
.Va net.link.ether.bridge_cfg
variable.
It consists of a comma-separated list of
.Ar interface : Ns Ar cluster
pairs, where all interfaces with the same
.Ar cluster
number will
be bridged together.
.Pp
Another
variable reinitializes the
.Nm ;
this is required if bridged
configurations include loadable interfaces.
After loading new interface drivers, setting the
.Va net.link.ether.bridge_refresh
variable to
.Li 1
will cause the
.Nm
to reinitialize itself.
.Sh EXAMPLES
The following command will cause the
.Li ep0
and
.Li fxp0
interfaces to be bridged together, and the
.Li fxp1
and
.Li de0
interfaces to be bridged together:
.Pp
.Dl "sysctl -w net.link.ether.bridge_cfg ep0:0,fxp0:0,fxp1:1,de0:1"
.Sh BUGS
Care must be taken not to construct loops in the
.Nm
topology.
The kernel supports only a primitive form of loop detection, by disabling
some interfaces when a loop is detected.
No support for a daemon running the
spanning tree algorithm is currently provided.
.Pp
With bridging active, interfaces are in promiscuous mode,
thus causing some load on the system to receive and filter
out undesired traffic.
.Pp
Extended functionality to enable bridging selectively on clusters
of interfaces is still in the works.
.Pp
Interfaces that cannot be put into promiscuous mode or that don't
support sending packets with arbitrary Ethernet source addresses
are not compatible with bridging.
.Sh SEE ALSO
.Xr ip 4 ,
.Xr ng_bridge 4 ,
.Xr ipfw 8 ,
.Xr sysctl 8
.Sh HISTORY
.Nm
bridging was introduced in
.Fx 2.2.8
by
.An Luigi Rizzo Aq luigi@iet.unipi.it .