From: Kevin Baumgartner (kbaumgar@xxxxxxxxx)
Date: Mon Jul 31 2000 - 14:54:09 GMT-3
At 04:44 PM 7/31/00 +0000, you wrote:
>Hi people,
>
>This is a question about lab 8, so if you haven't done it yet, avert your eyes
now !
>
>
>
>On lab 8b, you have to configure bridging between the ethernet segment connect
ed to r1 & r7 and the serial connection between r1 & r5. So far so good. Howeve
r, then you are required to configure IRB on r5. Why? I was under the (obviousl
y mistaken) impression that with IRB you use it with multiple interfaces in a b
ridge-group and it provides routing (ref. Cisco LAN Switching (CiscoPress)). Th
ere's only one interface in the bridge group on r5. Is this something to do wit
h encapsulation ??!!
IRB allows routing between and routed network and a bridged network. This can
be IP, IPX, Appletalk and I believe a few other protocols.
The key part about using IRB is that you need to create what is called a "BVI"
interface. This is similar to a physical interface and here you
configure either IP address, IPX, Appletalk for the bridged network. So in lab
8b the IPX network that is defined on r7 has to be define also
on the BVI interface on r5. The great thing now is that you can route between t
he bridged network and the rest of the IPX networks on the
ethernet side of r5.
Just defining bridge-groups on r5 doesn't give you IRB. You need to define t
he BVI interface and apply the network address to it.
The easiest way to thing of why you would use IRB is to see what happens if you
are just using bridge-groups. It's a competely flat network.
Basically one big network for everyone. This is not the really world. There are
going to be a number of subnetted networks already and you
need to somehow put your bridged network as part of this subnetted network. Thi
s is how IRB comes into play.
Kevin
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