How to configure Point to Point Protocol (PPP)

PPP- Point-to-Point Protocol:

PPP is a data link protocol; commonly used to establish a direct connection between two network nods. It can provide connection authentication, transmission encryption privacy and compression.

PPP Features:

Protocol Multiplexing – Multiple NCPs

Optional Authentication – PAP/CHAP

Optional Detection – Provided by LCP

Load Balanching – Multilink PPP

PPP Components:

Link Control Protocol (LCP) : Provides for the establishment, configuration, and maintenance of a PPP link. Protocol-independent options are negotiated by LCP.

Network Control Protocol (NCP): A Separate NCP is used to negotiate the configuration of each network layer protocol (Such as IP) Carried by PPP.

PPP Compression Algorithms:

Stacker: Replaces repetitive data with symbols from a dynamic dictionary (More processor-intensive)

Predictor: Attempts to predict sequential data (more memory-intensive)

Two type of PPP:

Plain text Authentication Protocol (PAP): RFC 1334 Standard. Original, obsolete authentication protocol which relies on the exchange of a plaintext key to authenticate paers. PAP is two-way authentication protocol.

Challenge Handshake Authentication Protocol (CHAP): RFC 1994 standard. Authenticates peers using the MD5 checksum of a pre-shared secret key. CHAP is three-way authentication protocol

Configuration example:

Step 1.

r1#configure terminal

r1(config)#line console 0

r1(config-line)#logging synchronous

Step 2. Create Database

r1#debug ppp negotiation  (To see real time state change)

r1#configure terminal

r1(config)#username r2 password r2  (configure both site. Example on. r2(config)#username r1 password r1  )

r1(config)#username r3 password cisco (This is for CHAP authentication, Both site password mast be same)

In Router r3:

R3(config)#username r1 password cisco

Step 3 :

Configure PAP:

r1(config)#interface serial 0/0

r1(config-if)#encapsulation ppp

r1(config-if)#ppp authentication pap

r1(config-if)#ppp pap sent-username r1 password r1

Configure CHAP:

r1(config)#interface serial 0/0

r1(config-if)#encapsulation ppp

r1(config-if)#ppp authentication chap

Optional, you can configure

r1(config-if)#ppp chap password cisco

r1(config-if)#ppp max-bad-auth 2

r1(config-if)#ppp chap wait

Multilink PPP Configuration:

Configure Multilink Interface:

r1(config)#interface multilink 1

r1(config-if)#ip address ip-address subnet-mask

r1(config-if)#ppp multilink group 1

Configure In Serial Interface:

r1(config)#interface serial 0/0

r1(config-if)#ppp multilink group 1

 

Some troubleshooting Command

r1#show ppp multilink

r1#debug ppp authentication

r1#debug ppp negotiation

r1#debug ppp packet