MS-CHAPv2 provides mutual authentication between peers by piggybacking a peer challenge on the Response packet and an authenticator response on the Success packet. MS-CHAPv2 has various features such as: It is enabled by negotiating CHAP Algorithm 0x80 (0x81 for MS-CHAPv2) in LCP option 3, Authentication Protocol. It provides an authenticator-controlled password change mechanism. It provides an authenticator-controlled authentication retry mechanism. It defines failure codes returned in the Failure packet message field. With weak passwords, MS-CHAPv2 is subject to offline dictionary attacks; hence, it can be replaced with EAP-TLS as the authentication mechanism for PPTP.