Refer to the exhibit.
EIGRP had converged in AS 1 when the link between router R1 and R2 went down. The console
on router R2 generated the following messages:
*Mar 20 12:12:06: %DUAL-5-NBRCHANGE. IP-EIGRP 1: Neighbor 10.1.4.3 (Serial0) is down:
stuck in active
*Mar 20 12:15:23: %DUAL-3-SIA. Route 10.1.1.0/24 stuck-in-active state in IP-EIGRP 1. Cleaning
up The network administrator issued the show ip eigrp topology active command on R2 to check
the status of the EIGRP network. Which statement best describes the reason for the error
messages?
A.
Incorrect bandwidth configuration on router R3 prevents R2 from establishing neighbor
adjacency.
B.
Incorrect bandwidth configuration on router R5 prevents R2 from establishing neighbor
adjacency.
C.
Router R3 did not reply to the query about network 10.1.1.0/24 sent by router R2 .
D.
Router R5 did not reply to the query about network 10.1.1.0/24 sent by router R2 .
Explanation:
When the link between R1 and R2 is down, R2 loses its successor for the network 10.1.1.0/24. R2
checks its topology table for a feasible successor but it can’t find one. So R2 goes active on the
that route to find a new successor by sending queries out to its neighbors (R3 and R5) requesting
a path to the lost route. Both R3 and R5 also go “active” for the that route. But R5 doesn’t have
any neighbor to ask besides R2 so it will send an “unreachable message” to indicate it has no
alternative path for that route and has no other neighbor to query. R3 also checks its EIRGP
topology table for a feasible successor but it has none, too. Unlike R5, R3 has a neighbor (R4) so
it continues to query this router.
Now suppose there is a problem on the link between R3 and R4 so R4 never receives the query
from R3 and of course, R3 also never receives a reply back from R4. Therefore, R3 can’t reply
back to R2. After about 3 minutes, the “Stuck in active” (SIA) timer on R2 expires and R2 marks
the route 10.1.1.0/24 as “stuck in active” route.
The output line “via 10.1.3.3 (Infinity/Infinity), r, Seiral0, serno 1232 indicates R2 has sent a query
to 10.1.3.3 and is waiting for a reply (the lowercase r).
(Reference:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008010f016.shtml)