Router R1 has been configured with the commands router eigrp 9 and network
172.16.2.0 0.0.0.255, with no other current EIGRP configuration. R1’s (working)
Fa0/0 interface has been configured with IP address 172.16.2.2/26. R1 has found
three EIGRP neighbors reachable via interface Fa0/0, including the router with IP address
172.16.2.20. When the engineer attempts to add the neighbor 172.16.2.20

fa0/0 command in EIGRP configuration mode, which of the following occurs?

A.
Fa0/0 fails.

B.
The command is rejecteD.

C.
The existing three neighbors fail.

D.
The neighborship with 172.16.2.20 fails and then reestablishes.

E.
None of the other answers is correct.

Explanation:
The neighbor 172.16.2.20 fa0/0 command would only be rejected if the IP address
(172.16.2.20) is not inside the range of addresses in the subnet (172.16.2.0/26, range
172.16.2.0–172.16.2.63). This command does not impact interface state. The command
does disable all EIGRP multicasts, and because the three dynamically discovered neighbors
require the EIGRP multicasts, all three neighbors fail. Although 172.16.2.20 is a valid
potential neighbor, both routers must be configured with static neighbor commands, and we
know that 172.16.2.20 was not previously configured with a static neighbor command;
otherwise, it could not have been a neighbor with R1.