To establish EIGRP adjacency on Cisco NX-OS, the global configuration must match the parameters defined at the interface level. Let ' s break down why Option A is the only correct choice:
* The Key Chain Name:
* Looking at the interface command: ip authentication key-chain eigrp NXOS EIGRP
* The first " NXOS " refers to the EIGRP instance name, and " EIGRP " (case-sensitive) is the name of the key chain.
* Option A correctly defines key chain EIGRP. Options B, C, and D use lowercase or entirely different names, which would cause an authentication mismatch.
* The EIGRP Instance Name:
* The interface command ip router eigrp NXOS identifies the EIGRP instance as NXOS.
* Option A and Option B correctly use router eigrp NXOS. Options C and D use " EIGRP " as the instance name, which contradicts the interface-level configuration.
* Authentication Mode:
* The interface specifies MD5: ip authentication mode eigrp NXOS md5.
* While NX-OS often requires the mode to be set on the interface, including it under the router eigrp process (as seen in Option A) ensures the process is configured to handle that authentication type.