PPP

Serial Port - CSU/DSU A digital modem can a router's serial port to a service provider

Connector types:

• V.35 connector: supports speed of 2.048 Mbps using a rectangular connector 
• DB-60 connector: a 60-pin (also know as a cisco 5-in-1 connector) that is supported on serveral cisco router models)
• Smart Serial connector: a high-desnity connector that allows a WAN interface card (WIC) to have two serial connections instead of just one.
• EIA/TIA-232 connector: a 25-pin D-connector that supports of 64 kbps for short distance 

What protocol is running at layer 2?

HDLC (High level Data Link Control) the default layer 2 protocol used by cisco routers on serial interfaces

Note: cisco uses their own proprietary version of HDLC

DCE connector:  Data Communication Equipment DCE ( the end of a serial cable that provides clocking)

DTE connector: Data Terminal Equipment (the end of a serial cable that receive the clocking)

PPP (Point-to-Point) protocol 

a layer 2 encapsulation commonly used on leased lines, which supports authentications, compression, error detection and correction, and logical multi-link interface 

LCP (link control protocol)

a protocol used by PPP to setup, maintain, and teardown a connection

NCP (network control protocol) the protocols used to negotiate the configuration of protocols being transmitted over PPP link

Setup Serial connection with PPP 

1. Change encapsulations to PPP
2. Setup PAP authentication (username & password )
3. setup chap authentication 
4. traffic compress stac
5. reliable-link
6. Multi-link 

R1(config-if)#encapsulation ppp

R2(config-if)#encapsulation ppp

One Way authentication ( server - client authentication)

R1(config)#username papuser password pappassword

R1(config-if)#ppp authentication pap

R2(config-if)#ppp pap sent-username papuser password pappassword

setup ppp authentication chap 

R1(config)#username R2 password chappassword

R1(config-if)#ppp authentication chap

R1(config-if)#compress stac

R1(config-if)#ppp reliable-link

R2(config)#interface multilink 1

R1(config-if)#ppp multilink

R1(config-if)#ip address 10.1.1.1 255.255.255.252

on interface level 

ser0/0 and ser 0/1

R1(config-if)#no ip address

R1(config-if)#ppp multilink group 1

R2(config)#username R1 password chappassword

R2(config-if)#ppp authentication chap

R2(config-if)#compress stac

R2(config-if)#ppp reliable-link

R2(config)#interface multilink 1

ser0/0 and ser 0/1

R2(config-if)#no ip address

R2(config-if)#ppp multilink group 1