1. The configuration on the interface shows that the authentication mode configured on the interface is CHAP. However, the authentication mode configured on the server is unknown.
2. Run the debugging pppoe-client command to enable debugging. The debugging information shows that the authentication fails. The server uses PAP authentication mode. The authentication fails because the authentication modes on the client and server are different.
3. Run the ppp pap local-user client password cipher client123 command on Dialer1 to set the authentication mode to PAP. The fault is then rectified.
PPPoE authentication will fail if inconsistent PPP authentication modes are used on the PPPoE server and client. It is recommended that you configure both CHAP and PAP authentication modes on the AR router. The AR router will dynamically determine the authentication mode based on packets exchanged with the PPPoE server.