16.4. The CHAP secrets file

This requires that you have mutual authentication methods - that is you must allow for both your machine to authenticate the remote server AND the remote server to authenticate your machine.

So, if your machine is fred and the remote is barney, your machine would set name fred remotename barney and the remote machine would set name barney remotename fred in their respective /etc/ppp/options.ttySx files.

The /etc/chap-secrets file for fred would look like

# Secrets for authentication using CHAP
# client        server  secret            acceptable local IP addresses
fred		barney	flintstone
barney		fred	wilma

and for barney

# Secrets for authentication using CHAP
# client        server  secret            acceptable local IP addresses
barney          fred    flintstone
fred		barney	wilma

Note in particular that both machines must have entries for bidirectional authentication. This allows the local machine to authenticate itself to the remote AND the remote machine to authenticate itself to the local machine.