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02.16.07
Cisco CCNP / BSCI Exam: Using OSPF's
 By
Chris Bryant
BSCI exam success, not to mention earning your CCNP, can come down to your OSPF route summarization skills.
There are a few different commands and situations you need to be ready for, and one of these situations is the proper use of the "summary-address" command.
The summary-address command should be used on an ASBR in order to summarize routes that are being injected into the OSPF domain via redistribution. In the following example, four routes are being redisitributed into OSPF on R1, making R1 an ASBR.
To summarize networks learned by redistribution, use the OSPF command summary-address. You can probably do this summarization in your head, but do so before continuing with the lab.
The external routes have been successfully summarized. Note that the summary route is still marked as an E2 route.
Theres an interesting route installed into R1s OSPF table as well.
When you configure summary routes in OSPF, a route to null0 will be installed into the OSPF routing table. This helps to prevent routing loops. Any packets destined for the routes that have been summarized will have a longer match in the routing table....
... and packets that do not match one of the summarized routes but do match the summary route will be dropped.
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (www.thebryantadvantage.com), home of FREE CCNA and CCNP tutorials and daily exam questions, as well as The Ultimate CCNA and CCNP Study Packages.
For a FREE copy of his latest e-books, "How To Pass The CCNA" or "How To Pass The CCNP", and for free daily exam question, visit the website and download your copies!
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