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Cisco CCNP Certification / BSCI Exam Tutorial: Route Summarization Basics |
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As you earn your CCNA and CCNP certification, you're going
to have to get comfortable with manually summarizing routes.
This isn't just another reason to learn binary math (although
it's a good one!), but summarizing routes is a true real-world
skill that can help your network operate more efficiently.
So the question isn't just how to summarize routes, it's why.
When you summarize routes in RIP, IGRP, EIGRP, or OSPF, you're
replacing a series of routes with a summary route and mask.
With RIP, IGRP, and EIGRP, this actually lessens the size
of the routing update packet itself - multiple routes are
replaced with the summary route. For instance, the routes
8.0.0.0/8, 9.0.0.0/8, 10.0.0.0/8, and 11.0.0.0/8 can be summarized
as 8.0.0.0 252.0.0.0. Only the summary address will be found
in the update packet, making it concise yet complete.
Summarizing routes can also make the routing table smaller,
yet still allow for complete IP connectivity when done correctly.
Using the above example, the four more-specific routes will
be replaced by a single summary route. Since the entire routing
table is parsed before the routing process is complete, keeping
the routing table as small as possible does help speed the
routing process as a whole.
To prepare for success on your CCNA and CCNP exam, you've
got to know how to summarize routes as well as the specific
commands for doing so with OSPF, EIGRP, RIP, and IGRP - but
knowing why to summarize routes is just as important as knowing
how! Here are some additional tips on route summarization.
With RIP version 2 and EIGRP, manual route summarization
is configured on the interface that will be advertising the
summary. This is done with the route summarization command
"ip summary-address."
RIP version 2 and EIGRP also both perform autosummarization
on routes that are advertised across classful network boundaries.
This is disabled with the protocol-level command "no
auto-summary".
OSPF offers two different route summarization commands. To
summarize routes from one OSPF area to another, use the "area
range" command; to summarize routes learned via redistribution,
use the "summary-address" command on the ASBR.
With proper planning and an understanding of binary math,
you'll master route summarization quickly with some practice
- and you'll be ready for success on real-world networks as
well as the CCNA and CCNP exams!
About the Author:
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage,
home of free CCNP and CCNA tutorials, The Ultimate CCNA Study
Package, and Ultimate CCNP Study Packages. For a FREE copy
of his latest e-books, “How To Pass The CCNA” and
“How To Pass The CCNP”, just visit the website!
You can also get FREE CCNA and CCNP exam questions every day!
Pass the CCNP exam with The Bryant Advantage!
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