What is PPP?
A point-to-point connection is the most common type of WAN connection. PPP connections are used to connect LANs to service provider WANs and to connect LAN segments within an organization 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.
Primary Purpose in Network Communication:
Establishing Direct Network Connections: PPP’s primary purpose is to establish a direct network connection between two nodes, such as a computer and an Internet Service Provider (ISP) over a phone line or other physical media.
Internet Access: It is widely used to provide internet access, particularly in dial-up and DSL connections. Users authenticate themselves using PPP to access ISP services.
Transporting Multiprotocol Traffic: PPP’s ability to encapsulate multiple network layer protocols makes it versatile for transporting various types of network traffic, essential for multi-protocol environments.
Flexibility and Compatibility: Its ability to operate over various types of physical media and support multiple protocols makes it a flexible choice for diverse networking environments.
Security: Through its authentication features, PPP provides a level of security by ensuring that only authorized users can establish a connection, which is crucial for preventing unauthorized access.
Error Handling: PPP’s error detection features ensure data integrity during transmission, which is vital for maintaining reliable and stable network communications.
Note: The default serial encapsulation method when you connect two Cisco routers is HDLC. This means Cisco HDLC can only work with other Cisco devices. However, when you need to connect to a non-Cisco router, you should use PPP encapsulation.
The basic purpose of PPP at this point is to transport layer-3 packets across a Data Link layer point-to-point link. This is one of many advantages to using PPP, it is not proprietary.
PPP can be used over twisted pair, fiber-optic lines, and satellite transmission. PPP provides transport over ATM, Frame Relay, ISDN, and optical links. For security, PPP allows you to authenticate or secure connections using either Password Authentication Protocol (PAP) or the more effective Challenge Handshake Authentication Protocol (CHAP).
Key features of PPP include:
Encapsulation of Multiple Network Layer Protocols: PPP is designed to encapsulate packets for various network protocols (such as IP, IPX) and route them to their destinations, allowing for multiprotocol support.
HDLC: A method for encapsulating datagrams over serial links.
Authentication: PPP supports authentication methods such as PAP (Password Authentication Protocol) and CHAP (Challenge Handshake Authentication Protocol), enhancing security by requiring credentials before establishing the connection.
Link Control Protocol: The LCP is used to establish, configure, and test the data link connection. It’s flexible in handling different sizes of packets, detecting a looped-back link, configuration errors, and terminating the link.
Error Detection: It has mechanisms for detecting common errors like dropped or mis ordered packets, ensuring reliable data transmission.
Asynchronous and Synchronous Links: PPP can operate over both asynchronous (like serial RS-232 connections) and synchronous (like ISDN) communication links.
Network Control Protocol: NCP is used for establishing and configuring different Network layer protocols. PPP enables the simultaneous use of multiple Network layer protocols. Some of the more familiar NPCs are:
i. Internet Protocol Control Protocol
ii. AppleTalk Control Protocol
iii. Novell IPX Control Protocol
iv. Cisco Systems Control Protocol
v. SNA Control Protocol
vi. Compression Control Protocol.
Summary of Establishing a Point-to-Point WAN Connection with PPP
■ PPP is a common Layer 2 protocol for the WAN. Two components of PPP exist: LCP negotiates the connection and NCP encapsulates traffic.
■ You can configure PPP to use PAP or CHAP. PAP sends everything in plain text. CHAP uses an MD5 hash.
■ Common PPP verification commands include a show interface to verify PPP encapsulation and debug ppp negotiation to verify the LCP handshake.
PPP Configuration Options
