Route Summarization - manual method or AS subnet mask?

[d-tischendorf]

Hi All,

  I have a question on the best (if any) approach to reduce my routing table. My network is configured such that each building on multiple campuses uses a 10.0.0.0/16 network. i.e. Bldg 5 uses 10.5.0.0/16, Bldg 6 uses 10.6.0.0/16, etc. Given this layout, I see two options.

1. Configure manual route summarization on my links to the core

int ser1/0

  ip summary-address eigrp 1 10.5.0.0 255.255.0.0

int ser1/1

  ip summary-address eigrp 1 10.5.0.0 255.255.0.0

router eigrp 1

  network 10.0.0.0

2. Configure the applicable /16 network under my eigrp AS#.

router eigrp 1

  network 10.5.0.0 0.0.255.255

Would one of these methods be "better" than the other for any reason?

Thanks!

[Richard Burts · Accepted solution]

Yes.

Method 1 is best because it is the only one that produces the results that you want.

In method 2 specifying the network and mask under router EIGRP does not change what is advertised. It only limits the range of addresses on interfaces that the router will include into EIGRP.

HTH

Rick

[d-tischendorf]

Rick, that's perfect. It took a few minutes for the lightbulb to go on after reading your explanation a few times, but that's exactly what I was looking for. Thanks!

[Richard Burts]

I am glad that my response did help you to figure out what is going on in those two alternatives. Many people do not understand correctly that using the mask on the EIGRP network statement does not have anything to do with what EIGRP advertises.

Thank you for using the rating system to mark this question as answered. It makes the forum more useful when people can read a question and can know that a solution was found. Your marking has contributed to that process.

HTH

Rick

[fb_webuser]

Auto route summarization is one of the features of EIGRP, provided there are two or more network statements under EIGRP. so you need to advertise all the subnets in lieu of just advertising 10.0.0.0

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Posted by WebUser Neeraj Jagga from Cisco Support Community App

[fb_webuser]

Hi, we featured our question on our pages. Check out some more responses here: http://www.facebook.com/CiscoSupportCommunity/posts/391273870894989

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Posted by WebUser Cisco NetPro from Cisco Support Community App