Basic question on EIGRP Query Scoping, Summarization

Answered Question
Sep 7th, 2009
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Hi, I have a question regarding EIGRP Query Scoping:


Please see attached diagram for detail and question.


My rationale:the exercise mentioned that EIGRP is configured as default configuration. That means that EIGRP summarizes routes by default. Therefore, don't we have a case of EIGRP Scoping - Network summarization in this case? If so, I thought that since the router is summarizing routes, queries should stop one hop away from the point of summarization. So my answer to this question would be that EIGRP queries should not go beyound RouterB. I am wrong though.





Correct Answer by Peter Paluch about 7 years 9 months ago

Hello Marlon,


I can only confirm what Rick has written: the document you have posted does not contain addressing information in the exhibit. What I see is only a topology of four routers but absolutely no addressing information is present in the exhibit.


I can give you only a general answer here: You are correct that if summarization is taking place then the query will be stopped one hop after the point of summarization. However, assuming that the automatic summarization is activated, if the entire network is addressed using only subnets of the major network 10.0.0.0/8, no summarization will actually take place and therefore, the scope of the query will not be limited.


While the term "Query Scoping" sounds very advanced and technical, it is actually nothing exceptional. Its logic stems from the fundamental fact that if a router asks about a network that is not present in the neighbor's EIGRP topology and routing table, the neighbor will immediately respond with a reply indicating an unreachable network.


I believe you have already seen this document but I suggest having a look at this URL - it contains a table of query/reply processing which is, in my opinion, quite illustrative:


http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#queryrange


Best regards,

Peter


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Richard Burts Mon, 09/07/2009 - 14:26
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Marlon


I do not know where this question came from and I wonder if you have provided us with all the information provided from the original source. The question mentions a specific subnet, but the information that you provide about the topology gives no information about subnets - and therefore no information about whether EIGRP auto summarization is a factor or not.


HTH


Rick


news2010a Mon, 09/07/2009 - 15:01
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You can rest assured the question is complete. The aforementioned subnet is listed on the attachment. Thanks.

Richard Burts Mon, 09/07/2009 - 17:12
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Marlon


Unless there is a serious error in my software rendering your attachment, the only reference to 10.10.0.0 is in the formulation of the question, and not in the figure or anywhere else.


HTH


Rick

news2010a Tue, 09/08/2009 - 09:25
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Hi folks, thanks for your usual attempt to help. Much appreciated.


The exercise contained no further information on IP addresses on routers. It is all I got and I found that strange too.

Correct Answer
Peter Paluch Mon, 09/07/2009 - 22:33
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Hello Marlon,


I can only confirm what Rick has written: the document you have posted does not contain addressing information in the exhibit. What I see is only a topology of four routers but absolutely no addressing information is present in the exhibit.


I can give you only a general answer here: You are correct that if summarization is taking place then the query will be stopped one hop after the point of summarization. However, assuming that the automatic summarization is activated, if the entire network is addressed using only subnets of the major network 10.0.0.0/8, no summarization will actually take place and therefore, the scope of the query will not be limited.


While the term "Query Scoping" sounds very advanced and technical, it is actually nothing exceptional. Its logic stems from the fundamental fact that if a router asks about a network that is not present in the neighbor's EIGRP topology and routing table, the neighbor will immediately respond with a reply indicating an unreachable network.


I believe you have already seen this document but I suggest having a look at this URL - it contains a table of query/reply processing which is, in my opinion, quite illustrative:


http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#queryrange


Best regards,

Peter


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