Re: Last few days before exam, OSPF --->classful protocol question

From: Kinton Connelly (kinton@xxxxxxxxxxxx)
Date: Wed Sep 13 2000 - 14:40:38 GMT-3

   
I think you almost have it in your #3a (but not b) below. As far as I know,
the best way to do this is to:

1) Have R2 send an "ip default-network" into IGRP pointing to another
classful address that's already in your routing table (if it's not in your
routing table already, a static route will be automatically generated and
this is usually a bad thing in the lab).

2) Do your redistribution between OSPF and IGRP on R2 with the proper
route-maps/distribute-lists.

This should do it for you. R3 won't really see all your redistributed OSPF
routes because of the classful nature of IGRP - but you'll still be able to
reach those networks because of the injected default-network - anything the
router doesn't find in the routing table will be send that way (to R2).

If you search the CCIELAB archives for "ospf;igrp" you'll find a number of
different suggestions for how to do this. Some of those ways are pretty
creative (complicated) but the one I listed above is the one that's worked
for me.

Kinton 

--
Kinton Connelly
CCIE #5867
kinton@oldmedia.com

At 9/13/00, you wrote:
>Just the last few days of cramming here until my lab.
>I have a question about OSPF and Classless routing protocols such as IGRP.
>
>Consider the scenario below.
>
>   ---------------------\        /----------------
>                         \      /
>                          \    /
>10.10.20.128/25           \  /           10.10.30.0/24
>      |                     )(                     |
>      |---------R1----------R2-----------R3--------|
>      |                     )(                     |
>          OSPF AREA 0      /  \    IGRP 100
>                          /    \
>                         /      \
>   ---------------------/        \-----------------
>
>3 routers, R1, R2 and R3.   R2 is performing mutual redistribution between
>IGRP and OSPF.
>We are using different masks, IGRP is a /24 and OSPF a /25.
>My question is this, is there any way of getting routes from OSPF into IGRP?
>As I understand,
>
>1. We must get the mask down to /24 for IGRP to even look at it as it won't
>cope with VLSM.
>2. Normally you could summarize into area 0 with the area range command but
>as we are in area 0 with this route we are out of luck there.
>3. The only way I know of doing this is
>         a. Use the ip default-network and point it to a glassful net
> other than
>your own. (still a default route)
>         b. Create a static route on R2 for 10.10.20.0/24 and redistribute
> that
>static into IGRP. (A static route)
>
>Is there any way other than what I have mentioned above of doing this? I
>would really appreciate any cool walk arounds for this situation. The
>easiest thing to do would be to change the area of this route so we could
>summarize it down to /24, however I am looking for a solution that doesn't
>involve changing the area. I'm not sure there is a solution to this
>situation but there's a lot of smart people on this board so who knows.
>
>

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