If you are experiencing an error message similar to "Machine not authorized to use this PPP address" when attempting to connect to the Internet using a Point-to-Point Protocol (PPP) connection on a Linux machine, it could be due to a problem with the PPP configuration, the network configuration, or the authentication credentials.
Here are some possible solutions to this issue:
Check the PPP configuration to make sure that the authentication parameters are correctly specified. The auth parameter in the PPP configuration file specifies the authentication method that will be used to authenticate the connection. Make sure that the correct authentication method is specified and that the necessary credentials are provided.
Check the network configuration to make sure that the correct IP address and netmask are being assigned to the PPP interface. The local_ip and remote_ip parameters in the PPP configuration file specify the IP addresses that will be assigned to the local and remote ends of the PPP connection, respectively. Make sure that these parameters are correctly configured.
Check the authentication credentials to make sure that they are correct and that they are being passed to the PPP daemon correctly. The PPP daemon uses the pap-secrets and chap-secrets files to store the PAP and CHAP authentication credentials, respectively. Make sure that these files are correctly configured and that the credentials are valid.
Check the firewall configuration to make sure that the PPP port is not being blocked. If the machine is behind a firewall, make sure that the firewall is configured to allow incoming connections on the PPP port.
If none of these solutions resolves the issue, you may need to consult the PPP documentation and online resources for further troubleshooting guidance. It's important to note that troubleshooting issues with PPP can be complex and may require a good understanding of the PPP configuration and the underlying system.