CRB - route OR bridge on a per-protocol basis
IRB - route and bridge in whatever combination you wish
these technologies are (I would imagine) rarely used these days, anyone use
much real bridging out there still (aside from SR/TLB maybe)? I would think
that most bridging is done with switches these days, and the IRB is done
with ISL-attached routers or L3 cards (RSP/MSM/MSFC)
Andy
----- Original Message -----
From: "Dennis Laganiere"
To:
Sent: Sunday, April 29, 2001 8:17 PM
Subject: IRB and CRB [7:2476]
> 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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