task 4.6 : AD of 5

why does the SG adds the AD of 5, when summarizing the 200.0.0.0 addresses on R6 ?

1. it should automatically be 5 by default for eigrp summary ?

2. moreover, the show ip route in the SG indicates an AD of 90 on R2 : shouldn't it be 5 ?

Comments

  • 1)
    ip summary-address eigrp as-number ip-address mask [admin-distance]
    admin-distance - (Optional) Administrative distance. A value from 0 to 255

    The ip summary-address eigrp command is used to configure interface-level address summarization. EIGRP summary routes are given an administrative distance value of 5 by default.

    "show ip route" command output shows that this route is directly connected and there is no AD information:
    D 200.0.0.0/22 is a summary, 00:00:30, Null0

    But you can see AD of summary address:
    Rack1R6#show ip route 200.0.0.0
    Routing entry for 200.0.0.0/22
    Known via "eigrp 100", distance 5, metric 128256, type internal

    2)
    The AD is not advertised with the route.
    The summarizing router uses the configured AD to determine whether the null route for the summary should be put into its routing table. Another routers see the summary as standard EIGRP route.
    So, on Rack1R6 you see this route with AD of 5, and on Rack1R2 you see this route with AD of 90.
  • Thank you.

    Cristal clear for question 2.

    To come back to my first question : if we had not added "5" at the end of the summarization command, it would not have made any difference ?

    If we had typed "10" or even "180", R6 would still have added this summary route into its routing table, since R6 does not have a better AD for this exact summary ?
  • If you had not added any admin-distance at the end of the summarization command, it would be 5 by default. And in the running config you'll see 5.
    You are right. If you had typed 1-254, R6 would still have added this summary route into routing table, since R6 does not have a better AD for this exact summary.
    But if you had typed 255, R6 would not added this summary, because if the administrative distance is 255, the router does not believe the source of that route and does not install the route in the routing table.
  • I have a different question. The task only specifies "first octet of 200". Does it mean 200.0.0.0 255.0.0.0? How do you decide the mask should be /22 as in the solution guide? Although the requirement said it should not overlap IP addr space, does it mean any mask from /16 to /24 will meet the requirement?

    Help from anyone please? :)
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