When establishing a connection using PPP, the initial stage is to negotiate the parameters to be used for the connection. This negotiation has four phases, and you need to be aware of these for configuration and troubleshooting.
- Establish phase Once a connection has been made at the data communication level, the first stage is to negotiate the connection parameters using LCP. This ascertains whether the remote site is also ready to use PPP, as well as the packet sizes and the authentication protocol (PAP, CHAP, MS-CHAP, or none). With this phase complete, LCP switches to the opened state.
- Authenticate phase If required, the passwords are exchanged. When authenticating to PAP, the password is transmitted only once. When using CHAP or MS-CHAP, an encrypted password is sent periodically at configurable intervals. One possibility is that this phase also negotiates a callback via CBCP (Callback Control Protocol).
- Network phase The IPCP protocol is implemented in the device. After the password was transmitted successfully, the network layer IPCP can be established. If the parameters were negotiated successfully, the router module can transmit IP packets on the opened (logical) line.
- Terminate phase In the final phase, the line is closed when the logical connections for all protocols are terminated.
