QuestionQ394

Layer 3 Technologies

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Refer to the exhibit. The network administrator configured the Chicago router for mutual redistribution of the LA and NewYork routes with OSPF routes, with the OSPF routes summarized into one EIGRP route using the longest summary mask:

router eigrp 100  
 redistribute ospf 1 metric 10 10 10 10 10  
router ospf 1  
 redistribute eigrp 100 subnets  
!  
interface E 0/0  
 ip summary-address eigrp 100 172.16.0.0 255.255.0.0  

After this configuration, the New York router receives all the specific LA routes but not the summary route. Which configuration set resolves the issue on the Chicago router?

  • A router eigrp 100 summary-address 172.16.8.0 255.255.252.0
  • B interface E 0/1 ip summary-address eigrp 100 172.16.8.0 255.255.252.0
  • C router eigrp 100 summary-address 172.16.0.0 255.255.0.0
  • D interface E 0/1 ip summary-address eigrp 100 172.16.0.0 255.255.0.0
Explanation

The contiguous LA networks 172.16.8.0/24 through 172.16.11.0/24 aggregate to 172.16.8.0/22 (255.255.252.0), the longest valid single summary. EIGRP manual summarization is applied on the interface that advertises the routes; Chicago advertises toward NewYork through E0/1, so the summary must be configured there. Cisco documents ip summary-address eigrp as an interface-configuration command for EIGRP address summarization.

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