An authentication mechanism renders a communications network impervious to unauthorized requests for interaction termination or cessation. In a release authentication mode of operation, the authentication mechanism protects against an unauthorized connection release message directed to a mobile node ( 30 ) of the network, e.g., a mobile station such as a user equipment unit, thereby thwarting an attempt to request an unauthorized connection release procedure concerning a connection involving the mobile node. In a detach authentication mode of operation, the authentication mechanism protects against an unauthorized detach message deceptively transmitted on behalf of a mobile node, thereby thwarting an attempt to request an unauthorized detach procedure for the mobile node. In its modes of operation, the authentication mechanism involves a first node (N i ) of the communications network at which authentication key is provided. The first node of the network uses the authentication key to derive an authentication indicia related to the authentication key. The first node (N i ) provides the authentication indicia to a second node (N r ) of the network. Subsequently, when an interaction termination operation is to occur (e.g., connection release or detach), the first node includes the authentication key in an interaction termination message transmitted over an air interface between the first node and the second node. As a condition for performing an interaction termination operation, the second node (N r ) confirms that the authentication key (which was included in the interaction termination message) is, in fact, related to the authentication indicia.