Last Updated on August 1, 2021 by Admin 1
You have configured OSPF on your network and enabled route summarization on an area border router (ABR) with the following command:Router(config-router)# area 3 range 18.104.22.168 255.255.248.0
What does the 3 specify in this command?
- The ID of the OSPF backbone
- The number of networks summarized in the area
- The ID of the area about which routes will be summarized
- The ID of the area to which the summary route information will be sent
The 3 in the area range command specifies the area that contains the routes that are to be summarized. In OSPF, you can only configure summarization on the border routers. The summaries need to be of routes within a single area. You summarize the routes of an area so that routers in another area do not see the individual networks, just the summary. The correct command syntax is shown below:
area number range ip-address mask
The number parameter is the number of the area whose networks are being summarized. For example, in the network shown in the graphic below, to summarize the networks within area 2 to 10.1.0.0/16, you would configure router A with the command area 2 range 10.1.0.0 255.255.0.0. This would not affect the routing tables of the routers within area 2, but instead make the routing tables of areas 0 and 1 smaller. These other routers would only have the summary route listed instead of the individual networks. Router C would only see the summary route 10.1.0.0/16.
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