Question NB71 - EIGRP Summarization

[contiva]

Hi,

I'm confused to the correct answer on this one. The correct answer according to H2P is 10.10.10.0/24 and 172.16.0.0/16

surely if RT2 is summarizing then 10.0.0.0/8 is correct as it will summarize at the classful level.

I checked this on packet tracer and GNS - both times RT3 has 10.0.0.0/8 & 172.16.0.0/16 in routing table.

Is H2P answer incorrect?

[b_rasheed]

The auto-summarization in RT1 Router is disabled, this means RT3 and RT2 routing table will have 10.10.10.0/24 and 172.16.0.0/16 but if auto-summarization is enabled on RT1 then RT3 and RT2 routing table will have 10.0.0.0/8 & 172.16.0.0/16


make sure your configurations is correct on RT1 auto-summarization is disabled , RT2, and RT3 auto-summarization is enabled.

Thanks.

[b_rasheed]

contiva,

now I am confused too about this question RT1 is disabled so the answer should be 10.10.10.0/24 and 172.16.10.0/24,  you right about your post.

I think we need the Admin to answer this question and eliminate this confusion.

Thanks.

[dmick]

I just looked this up and think I can clear up the confusion. According to Cisco Academy material:

"An EIGRP router autosummarizes routes ONLY for networks to which it is attached"

So, RT1 (no auto-summary) sends the 10.10.10.0/24 network to RT2. RT2, since it is NOT attached to 10.10.10.0 (or 10.0.0.0 for that matter) passes the classless address to RT3. It does not auto-summarize the 10.10.10.0/24 network because it is not attached to that network.

Hope that clears this up.

[dmick]

Maybe I should simplify my above response:

The 172.16.0.0/16 is auto-summarized by RT2 because RT2 is connected to that network.
The 10.10.10.0/24 is NOT auto-summarized by RT2 because RT2 is NOT connected to that network.

[b_rasheed]

Thank you dmick  for the clarification, now it makes more sense.

[contiva]

Thanks for clearing that up. it was a great help