L1 ISIS adjacency is up between two routers (Node-1 and Node-2) with MD5 authentication configured. During a maintenance window, an operator was planning to change one of the ISIS hello authentication key from admin to admin123. After removing the hello authentication key from Node-1 (no change on Node-2 side), the ISIS adjacency stayed up. The operator decided to fall back to the original configuration and called Alcatel for support. Which of the following statement best describe the cause of the problem? Select one answer only.

A. The ISIS hello authentication key was not configured properly in the first place, that’s why removing the authentication key does not impact the adjacency

B. The ISIS authentication key is the same as the hello authentication key, therefore removing hello authentication key does not impact the adjacency

C. The system interface is missing from the ISIS configuration, therefore ISIS is not working properly even before the change
D. ISIS hello authentication key is only used for hello packet exchange. It does not affect ISIS adjacency
E. ISIS hello authentication key is not used to bring up ISIS adjacency when traffic-engineering is enabled on the routers