particular network layer protocol used or it can be independent of that. Two different protocols are used for that purpose :

Link Control Protocol

This protocol is used to agree upon the encapsulation format option, packet size, misconfiguration errors, etc. It can also negotiate authentication parameters.

Network Control Protocol

This protocol is used to manage the specific needs of the network layer protocol being used. For example, assignment and management of IP addresses may be difficult for a circuit-switched point-to-point link. Network Control Protocol can be used to manage that.

In the Link Establishment Phase, only Link Control Protocol packets are used to agree upon the configuration parameters. In the network-layer protocol phase, network control protocol packets handle configuration dependent on the network layer protocol.

Authentication Phase

If a peer needs to be authenticated, a PPP link must be handled before Network Control Protocol packets are exchanged. PPP uses the Authentication Phase for that purpose.

There are two types of authentication protocols that can be used :

• Password Authentication Protocol
• Challenge Handshake Authentication Protocol

Password Authentication Protocol

In a Password Authentication Protocol or PAP, a peer is repeatedly requested for an ID/password pair until authentication is accepted. On receiving invalid authentication parameters after multiple times, the link is terminated.

In PAP, passwords are transmitted in an unencrypted format over the PPP link, making this protocol not secure.

Challenge Handshake Authentication Protocol

A Challenge Handshake Authentication Protocol, or CHAP, relies on periodic peer validation instead of authentication only at the beginning of the link establishment.

It uses a challenge-response mechanism for authentication. The authenticator sends a challenge to the peer. The peer receives the challenge and calculates the response using a complex algorithm and the challenge. The response is then sent back to the authenticator. The authenticator receives the response and verifies it using the same algorithm and the input challenge.

In terms of security, CHAP is much more secure than PAP

Network Layer Protocol Phase

Each network layer protocol, such as IP, IPX, or AppleTalk, must be separately configured by the Network Control Protocol in a PPP link. The Network Layer Protocol Phase takes care of that.

Link Termination Phase

This phase terminates the PPP link. Upon closing the link, PPP informs the network-layer protocol to take proper action.

Point-to-Point Protocol and Tunnels

A tunnel can be created between two virtual network interfaces. PPP can assign IP addresses to these virtual network interfaces, which are used to transfer data between the two networks on both sides of the tunnel.

Many protocols, like SSH, SSL, L2TP, PPTP, etc, can be used to tunnel data over IP networks. PPTP or Point-to-Point Tunneling Protocol, is a form of PPP between hosts using Microsoft Point-to-Point Encryption or MPPE for encryption and Microsoft Point-to-Point Compression or MPPC for compression.

This article provides some basic information on how the Point-to-Point Protocol works. I hope it helps. Readers who want to know more about how different cryptographic algorithms work and how they are used in various secure network protocols may want to refer to the book Cryptography And Public Key Infrastructure.

Security Fundamentals Practice Tests

The Security Fundamentals Practice Tests test one’s fundamental knowledge of cyber security. The practice tests are good for those who are preparing for various certification exams like the CCNA, CCNP, or CompTIA. They are also good for students and IT/security professionals who want to improve their understanding of cybersecurity.