ospf: reverse summary-address usage (answers)

From: Daniel C. Young (danyoung99@xxxxxxxxxxxx)
Date: Sun Aug 05 2001 - 21:47:04 GMT-3


   
I have answered my own questions.

For reverse summary-address to work, all that you need is to mutually
redistribute. You do not need to disable split-horizon, and you do not need
to redistribute connected. Just make sure that the routes you want to
summarize get mutually redistributed. It works with both rip and igrp, but
only for shorter-mask networks.

For longer-mask networks, there still maybe a workaround. If the longer-mask
networks are over frame-relay, then you can change the ospf network type to
p2m, which will treat the network as a collection of p2p links.

Daniel

-----Original Message-----
From: Daniel C. Young [mailto:danyoung99@mediaone.net]
Sent: Sunday, August 05, 2001 4:51 PM
To: 'Padhu (LFG)'; 'ccielab@groupstudy.com'
Subject: ospf: reverse summary-address usage

Group,

Backgound: Some of you have advocated the use of reverse summary-address to
solve the VLSM/FLSM issue. That is, instead of using summary-address to
summarize external routes going into OSPF, you can use it to summarize ospf
routes into external routing domains.

Testbed: Fatkid labs 502 and 501.

501 has a /28 ospf subnet that a rip domain needs to see. I configured the
summary-address statement to convert it to a /24 mask on r3, who is the ASBR
for the rip domain. Works great!

502 has a /22 ospf subnet that an igrp domain needs to see. Summary-address
did not anywhere, except on a separate ospf process on r2, who is the ASBR
for the other ospf process. This created another problem where the longest
matching rule preffered the "summary" route to the null0. Nonetheless, the
summary-address itself worked.

Conclusion: Normal summary-address can summarize for longer-mask networks.
Reverse summary-address can summarize for shorter-mask networks in rip.
Reverse summary-address does not work for longer-mask networks in igrp.

Question: Does reverse summary-address work for shorter-mask network igrp as
well? Can you perform a reverse summary-address for longer-mask networks in
rip?

Regards,
Daniel
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