I'm trying to make sure I've got these two straight. Here are my notes, and
I appreciate any feedback on these two bridging techniques:
Concurrent Routing and Bridging (CRB)
Normally, a networking device either bridges or routes protocols across all
of its interfaces. With CRB you can bridge protocols on some interfaces and
route different protocols on other interfaces. You cannot route and bridge
the same protocol on a router.
The major limitation to CRB is that you cannot receive a bridgeable frame
and route it, or inversely, receive a routed packet and bridge the frame.
The two are separate and cannot be forwarded to each other.
Integrated Routing and Bridging (IRB)
IRB allows the router to bridge and route the same protocol on a router. In
order to use IRB you create a Bridged Virtual Interface (BVI). After the
BVI is configured, the router can send routable protocols that were bridged
to the BVI to be routed. For example, an IP packet arrives on a routers
interface as a bridged protocol. The destination is out another interface
that is not configured for bridging. The router then sends the packet to
the appropriate interface to be routed. With IRB you must configure the
protocols that you want the BVI to be able to route.
IRB can be especially useful as a means of connecting bridged and routed
networks during network migrations when the two types of networks must
communicate. It provides a border checkpoint for the two networks to pass
through.
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