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.