Log in to the dial-in server as superuser.
Modify the /etc/ppp/options file.
Add the options that are shown in bold for CHAP support.
# cat /etc/ppp/options lock nodefaultroute name CallServe auth |
Create the remaining PPP configuration files to support the trusted callers.
See How to Configure Users of the Dial-in Server and How to Define Communications Over the Serial Line (Dial-in Server).
To configure CHAP authentication credentials for trusted callers, refer to How to Create a CHAP Credentials Database (Dial-in Server).