PPP Concepts

PPP Concepts

PPP CONCEPTS

One of the most common types of WAN connection is the point-to-point connection. Point-to-point connections are used to connect LANs to service provider WANs, and to connect LAN segments within an Enterprise network. A LAN-to-WAN point-to-point connection is also referred to as a serial connection or leased-line connection, because the lines are leased from a carrier (usually a telephone company) and are dedicated for use by the company leasing the lines.PPP encapsulates data frames for transmission over Layer 2 physical links.

PPP contains three main components:

1. HDLC protocol for encapsulating datagrams over point-to-point links.
2. Extensible Link Control Protocol (LCP) to establish, configure, and test the data link connection.
3. Family of Network Control Protocols (NCPs) for establishing and configuring different network layer protocols.

The LCP provides automatic configuration of the interfaces at each end, including:

• Handling varying limits on packet size
• Detecting common misconfiguration errors
• Terminating the link
• Determining when a link is functioning properly or when it is failing

After the LCP has configured and authenticated the basic link, the appropriate NCP is invoked to complete the specific configuration of the network layer protocol being used. Each network protocol has a corresponding NCP. Each NCP has a corresponding RFC. There are NCPs for IP, IPX, AppleTalk, and many others. NCPs use the same packet format as the LCPs. When the NCP has successfully configured the network layer protocol, the network protocol is in the open state on the established LCP link.

AUTHENTICATION:

Peer routers exchange authentication messages. Two authentication choices are Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP). Authentication is explained in the next section.