Route summarization helps reduce OSPF traffic and route computation. OSPF, unlike EIGRP, doesn’t support automatic summarization. Also, unlike EIGRP, where you can summarize routes on every router in an EIGRP network, OSFP can summarize routes only on ABRs and ASBRs.
The following command is used for OSPF summarization:
(config-router) area AREA_ID range IP_ADDRESS MASK
To better understand OSPF summarization, consider the following example network:
All three routers are running OSPF and exchanging routers. Before OSPF summarization is configured, the router R1 inside the backbone area has two entries for the networks 220.127.116.11/24 and 18.104.22.168/24 in its routing table.
We could summarize these two subnets on R2, so that R1 receive only one routing update for both subnets. To do that, the following command can be used on R2:
Now, R1 has only one entry in its routing table for R3’s directly connected subnets:
Be careful with summarization. In this case, router R1 thinks that R2 has routes for all subnets in the range 22.214.171.124 – 126.96.36.199. When summarizing, try to be as specific as possible.
Prerequisites for 200-301
200-301 is a single exam, consisting of about 120 questions. It covers a wide range of topics, such as routing and switching, security, wireless networking, and even some programming concepts. As with other Cisco certifications, you can take it at any of the Pearson VUE certification centers.
The recommended training program that can be taken at a Cisco academy is called Implementing and Administering Cisco Solutions (CCNA). The successful completion of a training course will get you a training badge.
Full Version 200-301 Dumps