Manual Summarization at ABRs

The more difficult task with OSPF route summarization occurs when planning the design of IP address blocks and OSPF areas. When the IP addressing plan and OSPF design have been completed, if the subnet numbers inside an area happen to be from the same general range, and none of the subnets in that range exist in other OSPF areas, a reasonable summary route can be created at the ABRs connected to that area. Without first having such a reasonable block of addresses, route summarization might not be a useful option.

After a range of subnets has been chosen for summarization, the parameters in the area range command must be planned. This command defines the parameters for the summary route, most notably the origin area ...

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