The CCNA Basic: OSPF summarization

CCNA 200-301

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2019-12-24

Router summary helps reduce OSPF traffic and routing computing. Unlike EIGRP, OSPF does not support automatic aggregation. In addition, unlike EIGRP, you can summarize routes on each router in an EIGRP network in EIGRP, while OSFP can only summarize routes on ABR and ASBR.

The following command is used for OSPF summarization:

To better understand OSPF summarization, consider the following example network:

All three routers are running OSPF and switching routers. before configuring the OSPF summary, router r1 within the backbone region has two entries for the network 11.0.0/24 and 11.0.1.0/24 in its routing table.

We can summarize the two subnets on R2 so that R1 only receives one route update for both subnets. To do this, you can use the following command on R2:

Now, R1 has only one entry in its routing table for R3’s directly connected subnets:

NOTE

Be careful when summarizing. In this case, router R1 is of the view that R2 has a route for all subnets, ranging from 11.0. 0.0 to 11.0. 0.255. Please try as specific as possible when summarizing.

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