This read-create enumerated value selects whether Level 2 hello packets on this circuit are sent unauthenticated or with plaintext authentication. It works the same way as the Level 1 authentication type but protects backbone-level adjacencies instead, which is important because a rogue Level 2 adjacency could inject false reachability into the entire backbone. An operator securing a core interconnect between autonomous IS-IS domains would set csIsisCircL2AuthType to plaintext(2) and configure csIsisCircL2Password to match on both ends.