December 2006
Intermediate to advanced
1188 pages
72h 8m
English
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Summarizing Routes in OSPF
Problem
You want to reduce the size of your routing tables without losing any connectivity within your network.
Solution
Using the area x range configuration command on your ABRs allows you summarize routes between OSPF areas:
Router1#configure terminalEnter configuration commands, one per line. End with CNTL/Z. Router1(config)#router ospfRouter1(config-router)#55area100rangeRouter1(config-router)#172.20.0.0 255.255.0.0area0rangeRouter1(config-router)#172.25.0.0 255.255.0.0area2rangeRouter1(config-router)#10.0.0.0 255.0.0.0exitRouter1(config)#endRouter1#
Discussion
The easiest way to see the effect of summarization is to look at
the routing table before and after it is enabled. Here is a sample
routing table before summarization. The ranges that we will be
summarizing are 172.20.0.0/16 and
172.25.0.0/16. We have highlighted
the route with the lowest metric in each of these ranges:
Router2#show ip route ospf 172.16.0.0/24 is subnetted, 1 subnets O IA 172.16.2.0 [110/140] via 10.1.1.2, 00:05:06, Serial0/0 172.20.0.0/16 is variably subnetted, 3 subnets, 3 masks O IA 172.20.10.0/24 [110/1702] via 10.1.1.2, 00:05:06, Serial0/0 O IA 172.20.1.0/30 [110/1692] via 10.1.1.2, 00:05:06, Serial0/0 O IA 172.20.100.1/32 [110/1693] via 10.1.1.2, 00:05:06, Serial0/0 172.25.0.0/16 is variably subnetted, 3 subnets, 2 masks O IA 172.25.25.6/32 [110/141] via 10.1.1.2, 00:05:06, Serial0/0 O IA 172.25.25.1/32 [110/131] via 10.1.1.2, 00:05:06, Serial0/0 O IA 172.25.1.0/24 ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.