Link Peer Authentication

PPP implements both the Password Authentication Protocol (PAP) and the Challenge Handshake Authentication Protocol (CHAP). If pppd is invoked with any of the authentication options, it demands that the peer (either calling or called) authenticate itself. The ppp.Auth(4) file contains pairs of either names and secrets for CHAP negotiation, or usernames and passwords for PAP negotiation. If a peer provides a name or username, its secret or password must match that found in the Auth file or the authentication phase fails and the connection is terminated. Each name/secret pair in the Auth file may be followed by address patterns restricting the peer's negotiated IP address. If an address restriction is specified for a particular name and the peer's negotiated IP address does not match the restriction address patterns, pppd terminates the connection.

The rechap interval option instructs pppd to periodically (every interval seconds) challenge the peer to authenticate itself. If the peer fails the new challenge, the link is terminated.