From: Simon Baxter (Simon.Baxter@xxxxxxxxxxxxxx)
Date: Mon Jul 31 2000 - 20:32:41 GMT-3
I guess the idea is that traffic bridged from the r1/r7 lan is bridged over
the r1/r5 serial link and then selectively (with bridge 1 route ipx, brisge
1 bridge ip etc) routed (or bridged) from the BVI on r5.
I haven't built it, but it sounds straight forward enough??
Simon
-----Original Message-----
From: Kevin Baumgartner [mailto:kbaumgar@cisco.com]
Sent: Tuesday, August 01, 2000 3:54 AM
To: Mark Lewis
Cc: ccielab@groupstudy.com
Subject: Re: IRB (I thought I understood it until...!)
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
connected to r1 & r7 and the serial connection between r1 & r5. So far so
good. However, then you are required to configure IRB on r5. Why? I was
under the (obviously mistaken) impression that with IRB you use it with
multiple interfaces in a bridge-group and it provides routing (ref. Cisco
LAN Switching (CiscoPress)). There's only one interface in the bridge group
on r5. Is this something to do with 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 the 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 the 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.
This is how IRB comes into play.
Kevin
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