12-14-2013 09:41 PM - edited 03-07-2019 05:05 PM
What does EIGRP Stuck inactive state mean?
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12-15-2013 12:23 AM
Hi,
The EIGRP Stuck In Active, or SIA in short, means that the router is involved in a diffusing computation for a new path to some network, and this computation seems to be stalled because some expected replies have not arrived in a reasonable time.
In EIGRP, the diffusing computation is a process of asking the neighboring routers to assist in locating a replacement path to a network for which the usable path has been lost. In a diffusing computation, a router sends Query packets to its neighbors, informing them about its current distance from the destination, and asking them for their own distance. If the neighbor is not affected by the Query, it just sends a Reply packet right away with its own current distance to the destination. If the Query has affected the neighbor in such a way that it also lost the path to the destination (which could have happened if that router was using us as its next hop), it will send a Query on its own to its own neighbors. After sending a Query to its neighbors, a router must wait for Reply packets from all routers to arrive, and only then it can make the selection and start sending Replies itself. If, in this chain of events, any router has trouble getting all Reply packets its needs, the diffusing computation can not be completed, and the new path to the destination can not be established. This situation is called Stuck in Active, and is, to be honest, EIGRP's Achilles heel.
In well behaved networks, SIA states should not happen. They occur with, say, overloaded links, overutilized CPUs on routers, bugs in IOS, etc., but normally, they should not appear. By default, a SIA state is declared if the diffusing computation could not be completed in 3 minutes (180 seconds).
Feel welcome to ask further!
Best regards,
Peter
12-15-2013 12:23 AM
Hi,
The EIGRP Stuck In Active, or SIA in short, means that the router is involved in a diffusing computation for a new path to some network, and this computation seems to be stalled because some expected replies have not arrived in a reasonable time.
In EIGRP, the diffusing computation is a process of asking the neighboring routers to assist in locating a replacement path to a network for which the usable path has been lost. In a diffusing computation, a router sends Query packets to its neighbors, informing them about its current distance from the destination, and asking them for their own distance. If the neighbor is not affected by the Query, it just sends a Reply packet right away with its own current distance to the destination. If the Query has affected the neighbor in such a way that it also lost the path to the destination (which could have happened if that router was using us as its next hop), it will send a Query on its own to its own neighbors. After sending a Query to its neighbors, a router must wait for Reply packets from all routers to arrive, and only then it can make the selection and start sending Replies itself. If, in this chain of events, any router has trouble getting all Reply packets its needs, the diffusing computation can not be completed, and the new path to the destination can not be established. This situation is called Stuck in Active, and is, to be honest, EIGRP's Achilles heel.
In well behaved networks, SIA states should not happen. They occur with, say, overloaded links, overutilized CPUs on routers, bugs in IOS, etc., but normally, they should not appear. By default, a SIA state is declared if the diffusing computation could not be completed in 3 minutes (180 seconds).
Feel welcome to ask further!
Best regards,
Peter
09-09-2015 05:32 PM
Hello Peter,
I know its a fairly old post but I just feel that asking a question here would be more relevant than another post. I just want to understand here that how crucial is the part where you say " If the neighbor is not affected by the Query, it just sends a Reply packet right away with its own current distance to the destination."
So lets say we have a scenario where a link goes down along a path which is neither a Successor or Feasible Successor. So in essence, no one is effected from the point of view of a particular destination. So how would the routers along this path respond ??
Cheers
G
09-12-2015 11:39 AM
Hello,
So lets say we have a scenario where a link goes down along a path which is neither a Successor or Feasible Successor. So in essence, no one is effected from the point of view of a particular destination. So how would the routers along this path respond ??
Consider the following exhibit.
Let's focus on R2, and assume that the R2/R3 link goes down. From R2's viewpoint:
In your question, you went slightly wrong in asking about a situation that by definition can not occur: If a failure on a path does not affect a particular network, routers won't be querying for that network in the first place.
Does this make any sense?
Best regards,
Peter
03-12-2016 08:37 AM
Makes a lot of sense...got caught up in too any words..lol.. Thanks a lot for the clarification.
Cheers
G
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