From: Swink, Dave (DSwink@xxxxxxxxxxxxx)
Date: Fri Apr 27 2001 - 13:30:11 GMT-3
I am going to give this explanation a try and get it all wrong.
OSPF, as a classless routing protocol, will handle routes to different size
subnets within a major network. For example the routing table could have
routes to 192.168.1.16/29 and 192.168.1.32/28.
The additional functionality that "ip classless" provides is that if a
packet is being routed to 192.168.1.16/29 but the routing table only has a
route to a larger subnet that 192.168.1.16/29 would be a part of, such as
192.168.1.0/25, the packet would be routed to 192.168.1.0/25 rather than
just being dropped because the specific subnet of 192.168.1.16/29 is not in
the routing table.
I apologize if this is all wrong and I confuse things worse than before!
Dave Swink
-----Original Message-----
From: David Goldsmith [mailto:dgoldsmi@cisco.com]
Sent: Friday, April 27, 2001 10:57 AM
To: Peter Van Oene
Cc: ccielab@groupstudy.com
Subject: Re: ip classless
Peter,
I don't believe that's true, I have tried this in the lab with OSPF and it
does change the behavior of the router. If I get time I will verify with
ISIS. Ip classless is to
have the router function classless or classful mode.
Thanks,
Dave G.
Peter Van Oene wrote:
> However, it has been verified that configuring IS-IS or OSPF on a router
will automatically place the router in classless mode regardless of the ip
classless nob's setting
>
> *********** REPLY SEPARATOR ***********
>
> On 4/27/2001 at 2:57 PM Atif Awan wrote:
>
> >This command changes the router's lookup algorithm. No doubt OSPF is a
> >classless protocol but it only provides the router with the routes, it
> >does
> >not in any way affect the way a router determines how to forward packets
(
> >that is using the classful or the classless algorithm ).
> >
> >>From: "radha rani" <radhaccie@hotmail.com>
> >>Reply-To: "radha rani" <radhaccie@hotmail.com>
> >>To: ccielab@groupstudy.com
> >>Subject: ip classless
> >>Date: Fri, 27 Apr 2001 10:00:06 -0400
> >>
> >>I have a question re: ip classless. My understanding is that if there
is
> >>no
> >>specific route for a subnet in the routing table, this command allows
the
> >>router to forward packets to unknown destinations using the default
route.
> >>This being the case when the destination is a subnet of a network which
is
> >>known to the router.
> >>
> >>My question is : since OSPF is a classless protocol, why do I need this
> >>command to have the router forward packets using the default route. I
see
> >>this all the time where the router will not utilize the default route
> >until
> >>this command is added.
> >>
> >>I can unserstand needing it with IGRP/RIP but why with OSPF?
> >>
> >>Can someone expalin. Thanks so much.
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