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.

Content 5.6 Troubleshooting EIGRP 5.6.4 Stuck in active – methodology for troubleshooting The methods for troubleshooting an EIGRP stuck in active problem with the show ip eigrp topology active command is useful only when the problem is happening. When the stuck in active event is over and the network stabilizes, it is extremely difficult, if not impossible, to backtrack the problem and find out the cause. Figure shows the flowchart for troubleshooting the EIGRP stuck in active problem. Consider the network shown for an example of troubleshooting the EIGRP stuck in active problem. Router A has a FastEthernet interface with network 20.2.1.0/24 that just went away. Router A does not have a feasible successor to go to as a backup route. Router A has no choice but to put the 20.2.1.0/24 route into active state and query its neighbor, Router B. Notice the output of show ip eigrp topology active in Router A. The 20.2.1.0/24 route has gone away for 1 minute and 12 seconds, and the neighbor that has not responded is listed as 10.1.1.2 from Serial 0/0, which is Router B. The next step is to Telnet to Router B to see the active route status in Router B. Figure shows the active route status in Router B by performing the command show ip eigrp topology active. The command show ip eigrp topology active on Router B shows that the route 20.2.1.0/24 is also in active status in Router B and that it has gone active for 1 minute and 23 seconds. Most importantly, Router B cannot reply to Router A about 20.2.1.0/24 because Router B is still waiting for the neighbor with IP address of 10.1.3.2 (Router D) from Serial 1/2 to reply to the query. The next step is to go to Router D to see the status of the active route 20.2.1.0/24 to see why Router D has not replied to the query. Figure shows the output of show ip eigrp topology active on Router D. Router D also put the router 20.2.1.0/24 in active state, and it has been in active state for 1 minute and 43 seconds. Router D can not answer the query from Router B because Router D is waiting for the router with the IP address of 10.1.5.2 from Serial 1/2 (Router E) to respond to the query. The next step is to go to Router E to see the status of the active route 20.2.1.0/24 and to find out why Router E is not replying to the query. Figure shows the status of the active route on Router E. The output for show ip eigrp topology active did not show anything for Router E. This indicates that, as far as Router E is concerned, there are no routes in active state. The next step is to Telnet back to Router D to double-check whether the router is still in the active state for route 20.2.1.0/24. Telnetting back to Router D shows that Router D is still in active state for route 20.2.1.0/24, but Router E does not have any routes in active state. To summarize the event so far:

Router A went active for route 20.2.1.0/.24 and is waiting for Router B to reply to its query.
Router B cannot reply because it is waiting for the query response from Router D.
Router D cannot reply because it is waiting for Router E to reply to the query.
Finally, the show ip eigrp topology active command in Router E shows that Router E does not think that any routes are active, while going back to Router D shows that the route 20.2.1.0/24 is still in active state.

From this sequence of events, you can see that there is clearly a discrepancy between Router D and Router E. More investigation is needed between these two routers. A look at Router D and Router E CPU utilization and memory usage does not show a problem. The CPU utilization and available memory are normal for both routers. Look at the Router D neighbor list to see if there is a problem with the neighbors. Figure shows the Router D EIGRP neighbor list. Notice that there is a problem in Router D with EIGRP sending a reliable packet to the neighbor with IP address of 10.1.5.2 (Router E). The Q count is 1, and performing the show ip eigrp neighbors command a few times in succession shows that the Q count is not decrementing. The RTO counter is at its maximum value of 5000ns. This indicates that Router D is trying to send a reliable packet to Router E, but Router E never acknowledges the reliable packet back to Router D. Because Router E does not appear to have a high CPU or memory problem, the link should be tested for reliability between Router D and Router E. Figure shows the output of a ping from Router D to Router E. The ping test shows the success rate of 0 percent. This test shows that a link problem exists between Router D and Router E. The link is capable of passing a multicast packet to establish an EIGRP neighbor relationship, but it is having problems transmitting a unicast packet. This link problem is the root cause of the EIGRP stuck in active problem in this example. The way to troubleshoot the EIGRP stuck in active problem is to chase the query, hop by hop, and find out the status of the active route at each hop.