This read-create enumerated value selects the authentication scheme, none or plaintext, used to protect Level 1 and point-to-point hello packets sent on this circuit. Enabling plaintext authentication guards against misconfigured or rogue devices accidentally or maliciously forming a Level 1 adjacency, though it only provides a basic deterrent since the password travels unencrypted. A security-conscious administrator would set csIsisCircL1AuthType to plaintext(2) on an access-layer circuit shared with less-trusted equipment and configure a matching password in csIsisCircL1Password.