what could be the problem?

Refer to the exhibit.

From R1, a network administrator is able to ping the serial interface of R2 but, unable to ping any of
the subnets attached to RouterB. Based on the partial outputs in the exhibit, what could be the
problem?

A.
EIGRP does not support VLSM.

B.
The EIGRP network statements are incorrectly configured.

C.
The IP addressing on the serial interface of RouterA is incorrect.

D.
The routing protocol has summarized on the classful boundary.

E.
EIGRP has been configured with an invalid autonomous system number.

Explanation:

CCNA – EIGRP Common Question Reference:
http://www.orbitco-ccna-pastquestions.com/CCNA—EIGRP-Common-Question.php

If you look carefully at the R2 ip route, you will discover that the R2 does not learn any network from
R1; this is because the routing protocol used here (EIGRP) performs auto summary when advertising
routes to peers across a network. So in this case the address 172.17.0.0/26 is a summarized address.
If the router was configured with no auto summary command, R2 LAN addresses would have been
advertised and reached.