Diagnosing and Fixing Authentication Problems

pppd debug output shows the message Peer is not authorized to use remote address address.

You are using PAP authentication, and the IP address for the remote peer is not in the /etc/ppp/pap-secrets file.

Add an asterisk (*) after the entry for the peer in the /etc/ppp/pap-secrets file.

pppd debug output shows that LCP comes up but terminates shortly afterward.

The password might be incorrect in the database for the particular security protocol. 

Check the password for the peer in the /etc/ppp/pap-secrets or /etc/ppp/chap-secrets file.