PPP is a Wide Area Network (WAN) protocol that provides OSI layer 2 (data-link layer) services for router-to-router and host-to-network connections (over synchronous and asynchronous circuits) using a serial interface. It is commonly used by PCs to connect to an Internet Service Provider (ISP) via a dial-up phone line (asynchronous host-to network) or as a WAN encapsulation method between LANs (synchronous router-to-router). PPP is an international, standardized and widely used protocol developed by the Internet Engineering Task Force (IETF). PPP is considered a part of the TCP/IP protocol suite and supports a number of LAN protocols such as IP and IPX and various methods of security authentication such as PAP and CHAP. PPP can be used on various physical media, including twisted pair, fiber or satellite transmission. It uses a variation of High-Speed Data Link Control (HDLC) for packet encapsulation.
Synchronous Serial Ports:
Nearly all Wide Area Network (WAN) links used with Internetwoks are "serial" meaning they transmit bits one after another in a series along a wire or fiber cable. Routers have Synchronous serial ports for WAN connections. They are not the same as the Asynchronous serial connection ports found on PCs and are capable of much higher data rates. Most routers have at least one Synchronous serial port for WAN connection and two Asynchronous serial ports; a Console port for local connection and an AUX port for remote configuration of the router.
Configuration of PPP connections
Step 1 Enter interface configuration mode for the desired interface.
Router(config)# interface serial x.x
Step 2 Configure the interface for PPP encapsulation:
Router(config-if)# encapsulation ppp
Step 3 Configure the interface for PPP Authentication (CHAP)
Router(config-if)# ppp authentication chap
Router(config-if)# ppp chap hostname
Router(config-if)# ppp chap password