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Community Member

eigrp stuck in active

Hi all

Can anyone please explain to me what this is and how it would happen, and what to do to rectify it. I believe it is when a router does not get a response from a query, if so what is the impact on the querying router etc ?

cheers

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Accepted Solutions

Re: eigrp stuck in active

Hi all

Can anyone please explain to me what this is and how it would happen, and what to do to rectify it. I believe it is when a router does not get a response from a query, if so what is the impact on the querying router etc ?

cheers

Hi,

If the successor path is lost & there is no feasible successor path is available, router sends out query messages on all EIGRP enable interfaces & tries to find out an alternative path to the network. It is active state for that route.Now Router is waiting for reply from its neighbors. If reply is missing for 3 min, dat means router didn't get any reply from neighbors, then it becomes stuck in active. In this case, router reset the neighbor relationship with
the router who didn't replied back the query messages sent by the router.

To solve this problem, two method is used -

a) Router summarization
b) EIGRP Stub.

To disbale the stuck in active timer, the following command is used -

Router(config-router)# timers active-time disable.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

6 REPLIES
Cisco Employee

Re: eigrp stuck in active

Hello,

A route is said to be in stuck-in-active state when it has lost its

successor and has set a query to all its neighbors (no feasible successor)

and is yet to get a response. This happens when you have a flat topology and

you have lot of routers on one end and few on the other end and the route in

question belongs to one of those few routers.

Hope this helps.

Regards,

NT

Community Member

Re: eigrp stuck in active

furthermore, you can limit the query either byusing router summarization or using stub router.

Community Member

Re: eigrp stuck in active

Hi,


for an exam, one of the neighbor is down and there is no feasible successor in the topology table,

the roter set a query to all its neighbors.


if the router is having the 5 neighbors it is going to send the multicast message to query it's all the neighbors to know the backup path.

and waiting for the replay from all it is neighbors. once the rotuer recived the replay from all it is neighbors (5) after that once with the updates

it is going to update the routing table.

if any one of the neighbors failed to replay for the query the router will send the unicast to that neighbor up to 16 times and waiting for the replay.

this is also going to take long time depends up on your topology.

think about if that 5 neighbors having each 3 neibhbors the and they to also quering there neighbors to know the feasible successor that will take a long time.

this process is called struck-in-active.


there are four main reasons a route becomes SIA:

The link is unidirectional, so the query can´t possibly be  answered.

The queried router´s resources are unavailable, generally due to  high CPU utilization.

The queried router´s memory is corrupt or otherwise unable to  allow the router to answer the query.

The link between the two routers is of low quality, allowing  just enough packets through to keep the neighbor relationship intact,  but not good enough to allow the replies through.

To sum it up, routes generally become SIA when a neighbor either doesn´t  answer  a query, or either the query or reply took a wrong turn somewhere. I  told you  it wasn´t the easiest thing to troubleshoot!


Stubbed route and router summarizations is the solution for this.


Regards,

Thinakaraj.M

Re: eigrp stuck in active

Hi all

Can anyone please explain to me what this is and how it would happen, and what to do to rectify it. I believe it is when a router does not get a response from a query, if so what is the impact on the querying router etc ?

cheers

Hi,

If the successor path is lost & there is no feasible successor path is available, router sends out query messages on all EIGRP enable interfaces & tries to find out an alternative path to the network. It is active state for that route.Now Router is waiting for reply from its neighbors. If reply is missing for 3 min, dat means router didn't get any reply from neighbors, then it becomes stuck in active. In this case, router reset the neighbor relationship with
the router who didn't replied back the query messages sent by the router.

To solve this problem, two method is used -

a) Router summarization
b) EIGRP Stub.

To disbale the stuck in active timer, the following command is used -

Router(config-router)# timers active-time disable.

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

Community Member

Re: eigrp stuck in active

hi there

thanks for this,

one more question, how does route summarization alleviate this problem ?

cheers

Re: eigrp stuck in active

hi there

thanks for this,

one more question, how does route summarization alleviate this problem ?

cheers

Hi,

Route summarization helps to limit queries, as does configuration of EIGRP stub routers.

* Summarization minimizes the size of routing tables which means less CPU and memory usage and less bandwidth to transmit.
* Summarization reduces the chance of networks becoming stuck-in-active, because it reduces the number of routers the see each query. Therefore the   chances of a query encountering issues is reduced.

NOTE: A router extends the query about a network only if it has an exact match in the routing table.

While EIGRP does not have the stub area options that OSPF does, EIGRP does allow a router to be configured as stub. This is commonly done with a hub-and-spoke configuration where the spoke routers do not have the resources to keep a full routing table. Since the spoke's next hop will always be the hub, all the spoke really needs is a default route. For this reason, the only neighbor an EIGRP stub router can have is the hub router

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

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