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Basic question on EIGRP topology table

Answered Question
Oct 6th, 2006
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Imagine I have the EIGRP topology as shown below. I read some EIGRP whitepaper but the info is not clear to me.


In order to find out which routes below will be installed on the routing table, as long as entries are in "P-Passive" state AND routes contains Feasible Successors they will be transferred to the routing table. Is that correct ? If I want to find out which routes will get transferred from EIGRP topology to the routing table, when looking at the EIGRP topology table do I have to consider the Reported Distance information or consider the number of Feasible Successors listed at all ?


>sh ip eigrp topology


Codes:P-Passive, A-Active,U-Update,Q-Query,R-Reply

r-Reply status


P 10.1.5.0/24, 1 successors, FD is 7693056

via 10.1.18.1 (7693056/5514496), serial 0/0/0

via 10.1.17.1 (11026532/5514496), Serial 0/1/0

via 10.1.20.1 (12035653/5514496), serial 0/0/1

Correct Answer by mmorris11 about 10 years 10 months ago

Feasable successors only exist in the topology table and only get transferred to the routing table if the current successor fails. This is done immediately without querying neighbors and as such is one of the unique strengths of EIGRP in the way of convergence. Further, as you probably know, routes with a reported distance higher than the FD of the successor do not go into the topology table but can be viewed with the command: sh ip eigrp topology all-links


HTH pls rate!

Correct Answer by royalblues about 10 years 10 months ago

Hi


The feasible successors are not installed in the routing table. They are listed on the topology table as backup routes for the destination.

If the route to the destination via the successor is no longer valid, eigrp immediately changes the feasible successor as the successor and does not do any computation.


based on this in the above scenario

the fisrt entry would make it to the routing table and the remaining two routes will be used as FS as they satisfy the FC


HTH

Narayan

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Correct Answer
royalblues Fri, 10/06/2006 - 08:02
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  • Green, 3000 points or more

Hi


The feasible successors are not installed in the routing table. They are listed on the topology table as backup routes for the destination.

If the route to the destination via the successor is no longer valid, eigrp immediately changes the feasible successor as the successor and does not do any computation.


based on this in the above scenario

the fisrt entry would make it to the routing table and the remaining two routes will be used as FS as they satisfy the FC


HTH

Narayan

Correct Answer
mmorris11 Fri, 10/06/2006 - 08:06
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  • Silver, 250 points or more

Feasable successors only exist in the topology table and only get transferred to the routing table if the current successor fails. This is done immediately without querying neighbors and as such is one of the unique strengths of EIGRP in the way of convergence. Further, as you probably know, routes with a reported distance higher than the FD of the successor do not go into the topology table but can be viewed with the command: sh ip eigrp topology all-links


HTH pls rate!

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