Re: Eigrp Query Scope

Hi Everyone,

Here is a short list of the things that limit query scoping. In short,
query is stopped every time the "exact" route is not found in the
topology table. Here is a list of the things that may cause this:

1) Network summarization. The query will be stopped at the "next-hop"
router, as that one will not have an exact match after summarization.
2) Distribute-list filtering. Queries are not affected by distribute
lists, but will effectively get stopped if the "next-hop" router will
not have the network in question after summarization.
3) Stub routers. Well-know scalability feature - stubs do not allow
for transit routing and greatly reduce the amount of queries.
2) Different EIGRP ASes. Generally, queries stop at the AS boundaries.
However, if redistribution is configured between the two ASes, things
may become more complicated.

Look at the following "diagram" with R1 being on the boundary b/w AS1 and AS2:

AS1---R1---AS2

Imagine R1 is doing mutual redistribution between AS1 and AS2 and a
query from AS1 reaches R1. If R1 has no ways to reach the network in
question, it will send a reply and remove the network from the routing
table. This, in turn, will make AS2 process go active (since the
prefix is redistributed) for the SAME network and make R1 initiate
another queury (leaked query) into AS2. The queury will propage AS2
using the regular rules. If somehow the network will be found, R1 will
update the routing table and may re-inject the prefix into AS1.

As for the new query scope in AS2, it may be one hop or more,
depending on the filtering/summarization configuration and/or the
number of mutual redistribution points between AS1 and AS2. In optimal
case, if you are using route summariztion and dont have multiple
redistribution points, the leaked query will travel just one hop deep
into AS2.

HTH

-- 
Petr Lapukhov, petr_at_INE.com
CCIE #16379 (R&S/Security/SP/Voice)
Internetwork Expert, Inc.
http://www.INE.com
Toll Free: 877-224-8987
Outside US: 775-826-4344
2009/8/2 Anantha Subramanian Natarajan <anantha.natarajan_at_gravitant.com>:
> Thanks Joe and your explanation make sense to me .
>
> Regards
> Anantha Subramanian Natarajan
>
> On Sun, Aug 2, 2009 at 4:43 PM, Joe Astorino <jastorino_at_ipexpert.com> wrote:
>
>> I have not heard of that "feature."  It would not really seem to make
>> sense.  Making separate EIGRP AS' is a way to separate the query domains
>> though.
>>
>>
>> On Sun, Aug 2, 2009 at 5:39 PM, Anantha Subramanian Natarajan <
>> anantha.natarajan_at_gravitant.com> wrote:
>>
>>> Hi Joe,
>>>
>>>    Thanks for the effort.I am using a application called "CCIE Command
>>> memorizer".This application has questionaire and answers kind of thing.In
>>> that I read the below phrase and me too googled to find the similiar lines
>>> but couldn't find one.So I thought posting to the group and understand if it
>>> is a common thing to be understood.So sorry didn't have reference to a link.
>>>
>>> Thanks
>>>
>>> Regards
>>> Anantha Subramanian Natarajan
>>>
>>>   On Sun, Aug 2, 2009 at 4:34 PM, Joe Astorino <jastorino_at_ipexpert.com>wrote:
>>>
>>>> Do you have a reference or a link where you saw that phrasing?  I have
>>>> not heard of query scopes extending to neighboring AS in EIGRP.
>>>>
>>>>
>>>> On Sun, Aug 2, 2009 at 5:33 PM, Anantha Subramanian Natarajan <
>>>> anantha.natarajan_at_gravitant.com> wrote:
>>>>
>>>>> Hi Joe,
>>>>>
>>>>>  Thanks for the response .Not specifically looking for a command but
>>>>> trying to understand this phrase "query scope extend to
>>>>> neighboring AS by 1 hop".What this means ?
>>>>>
>>>>> Regards
>>>>> Anantha Subramanian Natarajan
>>>>>
>>>>>   On Sun, Aug 2, 2009 at 4:30 PM, Joe Astorino <jastorino_at_ipexpert.com>wrote:
>>>>>
>>>>>> Hey Anantha,
>>>>>>
>>>>>> I think the main point is probably that the EIGRP query when a route
>>>>>> goes active is going to be limited to the EIGRP AS.  What command are you
>>>>>> looking at specifically?
>>>>>>
>>>>>>   On Sun, Aug 2, 2009 at 4:25 PM, Anantha Subramanian Natarajan <
>>>>>> anantha.natarajan_at_gravitant.com> wrote:
>>>>>>
>>>>>>>  Hi All,
>>>>>>>
>>>>>>>  I was trying to understand various query scope limiting options in
>>>>>>> EIGRP.During that process I was able to understand couple of options
>>>>>>> like
>>>>>>> summarization and stub router.While using "Command Memorizer" tool for
>>>>>>> Lab
>>>>>>> configuration preperation,I found mentioning about using different
>>>>>>> EIGRP AS
>>>>>>> as one of the options.Also it mentions about that the "query scope
>>>>>>> extend to
>>>>>>> neighboring AS by 1 hop".I am trying to understand the menaing of the
>>>>>>> same.Any help on making me understand the same would be really
>>>>>>> appreciated.
>>>>>>>
>>>>>>> Thank you
>>>>>>>
>>>>>>> Regards
>>>>>>> Anantha Subramanian Natarajan
>>>>>>>
>>>>>>>
>>>>>>> Blogs and organic groups at http://www.ccie.net
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________________________________
>>>>>>> Subscription information may be found at:
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>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Regards,
>>>>>>
>>>>>> Joe Astorino - CCIE #24347 R&S
>>>>>> Technical Instructor - IPexpert, Inc.
>>>>>> Cell: +1.586.212.6107
>>>>>> Fax: +1.810.454.0130
>>>>>> Mailto:  jastorino_at_ipexpert.com
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>> Regards,
>>>>
>>>> Joe Astorino - CCIE #24347 R&S
>>>> Technical Instructor - IPexpert, Inc.
>>>> Cell: +1.586.212.6107
>>>> Fax: +1.810.454.0130
>>>> Mailto:  jastorino_at_ipexpert.com
>>>>
>>>
>>>
>>
>>
>> --
>> Regards,
>>
>> Joe Astorino - CCIE #24347 R&S
>> Technical Instructor - IPexpert, Inc.
>> Cell: +1.586.212.6107
>> Fax: +1.810.454.0130
>> Mailto:  jastorino_at_ipexpert.com
>
>
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