This link talks about how enabling IP Classless changes routing behaviour.
IP classless will forward packets that it does not have an exact match for
in the routing table to the best supernet. There is a good example of this
presented by following the link.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios11/cbook/cip.htm
#xtocid105176
In classless routing protocols this is necessary because classfull routing
protocols may give a summary route of 172.16.0.0/16 to represent networks
172.16.1.0/24 and 172.16.2.0 If IP classless was not enabled on the
router recieving this summary address the packets with a destination address
of say 172.16.1.1/24 would be dropped. IP classless will enable these
packets to be forwarded to the supernet or summary address 172.16.0.0.
-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx]On Behalf Of
Ednilson Rosa
Sent: Saturday, March 03, 2001 9:53 AM
To: associate@xxxxxxxxxxxxxx
Subject: Re: Ip Classless [1:2315]
That´s right! But what I wanted to know is about the use of "IP CLASSLESS"
command in IOS. What I already know is that it is not related with using a
Classless or Classfull routing protocol. I´ve read somethings about it but
it is not quite clear to me yet...
Ednilson Rosa
Analista de Suporte Técnico
CPM S/A - Filial Salvador - BA
----- Original Message -----
From:
To:
Sent: Saturday, March 03, 2001 1:47 AM
Subject: Re: Ip Classless [1:2315]
I've just been learning about classless/classful routing and here's what
we've come up with.
Classless routing just routes via ip address without the mask. Classful
routing routes with ip addresses and subnet masks.
Classless routing is OSPF, EIGRP. RIPv2, IS-IS, and BGP-4. They require the
same subnet on ALL routes propagated through them. They also allow
auto-summarization due to being on the same subnet.
Classful routing is IGRP, and RIPv1, which allows routing across multiple
class networks (A,B,C) or multiple subnets. This is possible due to the
inclusion of subnet masks in the routing tables.
I think I've left out something, but offhand on a Friday night I just don't
remember.
on 3/2/01 10:26 PM, Ednilson Rosa at egr.cisco@xxxxxxxxxx wrote:
> Hi ALL,
>
> Can some clarify when one should use IP CLASSLESS comand (and when =
> should not use it)???
>
> Thanks,
>
> Ednilson Rosa
> Analista de Suporte T=E9cnico
> CPM S/A - Filial Salvador - BA
>
>
>
>
> Message Posted at:
> http://www.groupstudy.com/form/read.php?f=1&i=2315&t=2315
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