The value of the object tmnxIsisIfLevelHelloAuthKey specifies the authentication key string used to verify the authenticity of packets sent by neighboring routers on this IS-IS interface at this level. For authentication to succeed both the authentication key and the authentication type defined by the tmnxIsisIfLevelHelloAuthType variable must match. If tmnxIsisIfLevelHelloAuthType is set to 'password', tmnxIsisIfLevelHelloAuthKey can include any ASCII character. Authentication can be configured globally and applied to all ISIS levels or it can be configured on a per level basis; the most specific value is used. If the value of tmnxIsisIfLevelHelloAuthType is 'useGlobal', then the global values, if any, defined in tmnxIsisIfHelloAuthKey and tmnxIsisIfHelloAuthType are used instead. When read, tmnxIsisIfLevelHelloAuthKey always returns an Octet String of length zero.