Refer to the exhibit. Both routers are running EIGRP and are connected through by a WAN connection. The connection from R1 to R2 is fine, but the connection from R2 to R1 is broken. The "`show eigrp neighbors`" output from R2 is shown. But when executing "`show ip eigrp neighbors`" on R1 the result is empty. **What can be the source of the problem?** <div><img src="https://skillset.s3.amazonaws.com/img/question/51429/555f620f-0464-40cc-9f78-2d2bac1f0974" /></div>

Refer to the exhibit. Both routers are running EIGRP and are connected through by a WAN connection. The connection from R1 to R2 is fine, but the connection from R2 to R1 is broken.
The "show eigrp neighbors" output from R2 is shown.
But when executing "show ip eigrp neighbors" on R1 the result is empty.
What can be the source of the problem?

The IP addressing is not correct.

There might be a layer 2 issue.

An Access Control List is misconfigured.

There is an AS mismatch under the "router eigrp" of both routers.

The physical link may be broken.

The EIGRP network is not properly configured on R1.

Explanation

R2 can include R1 as EIGRP neighbor as shown in the ouput of "show ip eigrp neighbors", because R1s hello packets can reach R2 normally. Counters such as SRTT (Smooth Round Trip Timer) can help to determine this issue. SRTT is used by EIGRP to measure the time it takes to send a packet and receive an acknowledgement of the packet (in this case is 0, meaning that no acknowledgments have been received). - - - - A potential cause of this problem can be a misconfigured ACL. - - - - - - - Also "previously" suggested as a common cause of this problem is a "layer 2 issue", for example too many CRC errors or a problem with a switch. - - - - - {somebody else had this as an answer, but I believe it is wrong, bad-switch, many CRC-Errors are usually Physical-Layer probs (L1) SEE Scottmac's answer about this @ { https://supportforums.cisco.com/discussion/10582986/what-th-root-cause-crc-errors }