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