⚡

PPP

  • Point to Point
  • Multipoint (Frame Relay, X.25, ATM)
HDLC is vendor specific. Default on serial interfaces.
int s0
	encapsulation ppp

Link Control Protocol

Flag (01111110)
Address (11111111)
Control (00000011)
Protocol (C021)
LCP DATA
CRC
  • Link Establishment and configuration negotiation
  • Link Quality Determination
  • Allow network-layer protocol establishment
  • Link termination
 
MRU - maximum receive unit
Compression can be done with Hardware card or Software
 
Software Compression
int s0
	compress [stac|predictor|mppc]
  • mppc - Microsoft end point (ios > 11.1)
 
LQR - Link Quality Report
  • packets and bytes received
  • compares to what has been sent, error %
 
Magic Numbers
  • Detects loops in the line
  • Modem in loopback

Authentication

Optional
Password Auth Protocol (PAP)
  • name and password sent in clear text
  • Matched to Local or AAA database
Challenge handshake auth protocol (CHAP)
  • same shared secret on both devices
  • R1 sends a challenge
  • R2 encrypts with shared secret
  • R1 encrypts with shared secret and checks for match