| Engineering Journal 2.4.2: PPP link negotiation PPP ensures interoperability between networking vendors by using several additional protocols, including the following: LCP for negotiating basic line interoperability A family of network control protocols for negotiating individual Layer 3 protocols and their options (such as IP Control Protocol [IPCP] for IP and options such as compression) When the PPP link is negotiated, a link control protocol is negotiated to establish the link, and then additional network control protocols are negotiated. You can use the command show interfaces to check the status of the LCP and the network control protocol and to test the interoperability of the network layers. There are also excellent debug ppp commands for troubleshooting. To configure the serial line to use PPP, use the encapsulation ppp command, as follows: Router(config)# interface serial 0 Router(config-if)# encapsulation ppp