From: Peter Van Oene (pvo@xxxxxxxxxxxx)
Date: Fri Apr 27 2001 - 14:45:04 GMT-3
Hey Dave,
Your kinda wrong on a couple fronts :) First off, when packets are sent, they
are sent to specific addresses. One does not send a packet to 192.168.1.16/29,
one sends to 192.168.1.16. Hence, the router will match as many bits as possi
ble and send the packet out the best match interface. How the router matches
bits is the domain of ip classless.
The accurate example would be that if the router in your network had 192.168.2/
24, 192.168.3/24, and a static default route. In classful mode, the packet wo
uld be dropped, in classless, it would match the default and be forwarded.
Pete
*********** REPLY SEPARATOR ***********
On 4/27/2001 at 11:30 AM Swink, Dave wrote:
>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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