eigrp feasible successors

Unanswered Question
Feb 16th, 2009

Hi all, after reading my cisco book, it did not mention this, how many feasible successors can you have, can you have multiple, or just one?

I have this problem too.
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mahmoodmkl Mon, 02/16/2009 - 07:57


there can be multiple,they will be in the topology table



Mo'ath Al Rawashdeh Mon, 02/16/2009 - 08:11


By default, the total count of successors and feasible successors for a destination stored in the routing table is limited to four. This limit can be changed in the range from 1 to 6. In more recent versions of Cisco IOS (eg. 12.4), this range is between 1 and 16.


carl_townshend Mon, 02/16/2009 - 08:22

so, if I have 3 links to a destination, when would one of these not be considered as a feasible successor and why?

Mo'ath Al Rawashdeh Mon, 02/16/2009 - 08:30

If the receiving router has a Feasible Distance to a particular network and it receives an update from a neighbour with a lower advertised distance (Reported Distance) to that network, then there is a Feasibility Condition. In this instance, the neighbour becomes a Feasible Successor for that route because it is one hop closer to the destination network.

What you should note here, is that the metric for a neighbour to reach a particular network (i.e. the Reported Distance) must always be less than the metric (Feasible Distance) for the local router to reach that same network. This way routing loops are avoided. This is why routes that have Reported Distances larger than the Feasible Distance are not entered into the Topology table, so that they can never be considered as successors, since the route is likely to loop back through that local router.



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