We will be using PPP as our serial encapsulation. This will be implemented on each serial interface of any router connected to another router. PPP provides router-to-router connections over both synchronous and asynchronous paths. PPP uses a Link Control Protocol (LCP) for establishing, configuring and testing the connection, and various Network Control Protocols (NCP) for establishing the Layer 3 protocol connection.

We are using PPP as the encapsulation type because it is generally better than HDLC. PPP has better interoperability between vendors, is more secure and can deal with individual Layer 3 protocols more easily. It allows for more control of the data link setup, and can provide error detection.

The router command sequence for PPP is quite simple. Go into the interface configuration for each serial port and then specify PPP as the encapsulation type:

Router(config)# int s0/0
Router(config-if)# encapsulation ppp