Point-to-Point Leased Line Implementation

To setup point-to-point connection between 2 routers:
1. Assign ip address to each interface (must be in same subnet)
2. Issue no shutdown command.
3. Assign clockrate[bps] command to DCE interface.

Data Link Protocols HDLCsupports synchronous transmission, default for Cisco routers. PPPsupports asynchronous transmission, error recovery (not enabled by default). Synchronous = CSU/DSU must operate at same speed on either end of the link. Allows more throughput than asynchronous. Send frames continuously (idle frames when nothing to actually send). :Receiver Ready: another name for the idle frames Asynchronous = no frames sent when idle, requires less expensive hardware. ** Note: ** Routers typically use synchronous connections, modem and end PC use asynchronous

Data Link Protocols




PPP and HDLC Framing
HDLC and PPP Configuration
interface serial 0/0
encapsulation {hdlc | ppp}
compress[predictor | stac | mppc [ignore-pfc]]
show interfaces -> verifies setup
** Note: **
To remove ppp encapsulation, and revert back to hdlc: no encapsulation ppp

PPP Features Link Control Protocol: Features of PPP regardless of the L3 protocol used. : one used per link Control Protocol: L3 specific protocols (for examples, IPCP) :-> one used per L3 protocol :-> Cisco uses additional CP for CDP, called CDPCP

LCP Features

Function	LCP Feature	Description
Error Detection	Link Quality Monitoring (LQM)	Take down a link based on % of errors on a link. Only useful in redundant networks that can afford to take device down.
Looped Link Detection	Magic Number	Using different magic numbers, routers send to each other. If router receives its own number, detect looped link.
Multilink Support	Multilink PPP	Load-balanced between multiple links.
Authentication	PAP/CHAP	Exchange names/password to verify identity.

Looped Link: Bits that the router sends are "looped" back and received by the same router. Router wouldn’t notice, because it is receiving information.
Authentication: Verifying that router x is actually who they claim to be.
PAP and CHAP
Password Authentication Protocol (PAP)

• Sends clear-text passwords

Challenge Handshake Authentication Protocol (CHAP)

• Uses Message Digest 5 (MD5) one-way hashing on passwords
• Passwords themselves never cross the link (random number used)