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| 5.6 |  | Troubleshooting EIGRP |
| 5.6.3 |  | Stuck in active – determining the problem |

When troubleshooting an EIGRP stuck in active problem, two questions need to be answered:

1. Why is the route active?
2. Why is the route stuck?

Determining why the route is active is not necessarily a difficult task. Sometimes, the route that constantly is going active could be due to a flapping link. Or, if the route is a host route (/32 route), it is possible that it is from a dial-in connection that gets disconnected. A more important and difficult task is determining why an active route becomes stuck. Usually, an active route gets stuck for one of the following reasons:

- Bad or congested link
- Low router resources, such as low memory or high CPU processing on the router
- Long query range
- Excessive redundancy

By default, the stuck in active timer is only 180 seconds. If the EIGRP neighbor does not hear a reply for the query in 180 seconds, neighbors are reset. This adds difficulty in troubleshooting EIGRP routes stuck in active because when an active route is stuck, there is only 180 seconds to track down the active route query path and find the cause.

Debugs and Verification
The tool that helps troubleshoot the EIGRP stuck in active error is the show ip eigrp topology active command. Figure shows sample output from this command. This command shows what routes are currently active, how long the routes have been active, and which neighbors have and have not replied to the query. From the output, it can be determined which neighbors have not replied to the query. Track the query path and find the status of the query by hopping to the neighbors that have not replied.

As the output indicates, the route for 20.2.1.0 is in active state and has been active for 1 minute and 43 seconds. Query-origin is Successor Origin, which means that the successor to this route sends the query to this router. At this point, it has received replies from 10.1.3.1 and 10.2.4.1. The reply is infinity, which means that these two routers also do not know about 20.2.1.0. The most important output of the show ip eigrp topology active command is the Remaining replies section. This router shows that the neighbor 10.1.5.2 from interface Serial 1/2 has not replied to the query.

To proceed further with troubleshooting, the next step is to Telnet to the 10.1.5.2 router to see the status of its EIGRP active routes, using the same show ip eigrp topology active command. Sometimes, the router does not list the neighbors that have not replied to the queries under the Remaining replies section.

Figure shows another example of the show ip eigrp topology active command output. The only difference between the two outputs is the list of neighbors that have not replied to the router. However, this does not mean that all of the neighbors have replied to the queries. The neighbor 1.1.1.2 has a lowercase r next to the address of 1.1.1.2. This also means that the neighbor has not replied to the queries.

In other words, the router has two ways of representing neighbors that have not replied to the queries. One way, is to have them listed under the Remaining replies: section. The other is to have an r next to the neighbor interface IP address. When using the show ip eigrp topology active command, the router can use any combination of these methods to represent neighbors that have not yet replied to the queries.

The neighbors that have not replied to the queries are 1.1.1.2 and 10.1.5.2. Only one of the non-replying neighbors 10.1.5.2 is listed under the Remaining replies: section. The other neighbor, 1.1.1.2, that has not replied is listed with the other replying neighbor. To summarize, when issuing the show ip eigrp topology active command, the most important part to look for is the neighbors that have not replied to the query. To look for such a neighbor, look for neighbors that have the r next to their interface IP address.