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Examine the exhibit.
Router R2 has been configured with the following OSPF router command:
area 1 range 130.31.96.0 255.255.224.0
Which addresses listed will be summarized by R2 into area 0? (Choose all that apply.)
- 130.31.128.0/23
- 130.31.112.0/20
- 130.31.130.0/24
- 130.31.160.0/22
- 130.31.104.0/21
Explanation:
The command area 1 range130.31.96.0 255.255.224.0 is used to summarize the IP network addresses from 130.31.96.0/24 to 130.31.127.0/24 in area 1. Addresses 130.31.112.0/20 and 130.31.104.0/21 are both in that range of network addresses.
To determine if an address is a part of a summary, put the summary address and summary mask in binary format. Do the same with the address and the summary mask you are examining, as shown below:
130.31.96.0 10000010.00001111.01100000.00000000
130.31.112.0 10000010.00001111.01110000.00000000
255.255.224.0 11111111.11111111.11100000.00000000
If the address you are testing and the summary address agree to the point where the mask stops, then the test address is part of the summary. In this case, they agree through the 27th bit, so this address is a part of the summary. The same is true for the 130.31.104.0 address.
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 is:
area area id range ip-address mask
The area id parameter is the number of the area whose networks are being summarized. For example, in the network shown in the exhibit, to summarize the networks within area 1 to 130.31.96.0/19 you would configure router R2 with the command area 1 range 130.31.96.0 255.255.224.0. This would not affect the routing tables of the routers within area 1, but instead make the routing tables of areas 0 and 2 smaller. These other routers would only have the summary route listed instead of the individual networks. Router 3 would only see the summary route 130.31.96.0/19.
Objective:
Layer 3 Technologies
Sub-Objective:
Configure and verify manual and autosummarization with any routing protocol
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