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
