EIGRP will not form any neighbor relationships with routers that have
different autonomous system numbers. If the AS numbers are mismatched, no
adjacency is formed. This problem is usually caused by misconfiguration on the
routers.
Figure
shows two
routers running EIGRP.
Debugs and Verification
Figure
shows
the configurations of both routers. Because the two routers have different AS
numbers, using the command show ip eigrp neighbors on both
RTR A and RTB B would show an empty list.
Solution
The
solution is to modify one of the two routers so the AS numbers are the same.
Figure
shows both
routers configured with the same AS number, EIGRP AS 1. At this point, both
routers will be able to establish a neighbor relationship and exchange routing
information.