Enabling PPP on an Interface
To set PPP as the encapsulation method used by a serial interface, use the encapsulation ppp interface configuration command.
The following example enables PPP encapsulation on interface serial 0/0/0:
R3# configure terminal
R3(config)# interface serial 0/0/0
R3(config-if)# encapsulation ppp
The encapsulation ppp interface command has no arguments. Remember that if PPP is not configured on a Cisco router, the default encapsulation for serial interfaces is HDLC.
The figure shows that routers R1 and R2 have been configured with both an IPv4 and an IPv6 address on the serial interfaces. PPP is a Layer 2 encapsulation that supports various Layer 3 protocols including IPv4 and IPv6.