From: William Swedberg (swedbergwp@xxxxxxxxx)
Date: Mon Jul 31 2000 - 14:57:36 GMT-3
Let me see if I can explain myself better.
The normal operation of bridging is to drop any packet
that belongs to a protocol that is being routed on a
router. That is why when you want to brige IP without
IRB or CRB you issue the command "no ip routing".
With IRB you are able to bridge a routed protocol on
an interface while routing it on another. Under the
IRB command you tell it what you want to route and
what you don't. In the example of lab8b, you already
have IPX routing turned on R5. If IRB were not turned
on, all IPX traffic coming from R1 would be dropped.
We turn on irb and the bridge interface will execpt
the IPX traffic. Since we want the IPX 700 to
propagate throughout the network, we need to turn this
bridged traffic back into routed. This is done using
the BVI interface. The bridged IPX traffic gets
shuttled to the BVI which in turn ROUTES it to the
other IPX routed interfaces.
CRB allows you to route on some interfaces and brigde
on others. You cannot route a protocol on on
interface and bridge it on another. Bridged
interfaces talk with bridged interfaces and routed -
routed.
Hope this helps...
William Swedberg CCNP CCDP
--- Mark Lewis <markl11@hotmail.com> 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
> ??!!
>
> I've checked the CD-ROM/Caslow/everywhere (I think).
> Any ideas/doc.s to
> reference?
>
> Thanks in advance.
>
> Mark
>
>
>
>
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