CCIE RS – Written – L2 WAN – Implement and Troubleshoot HDLC

High-Level Data Link Control


  • Bit-oriented code transparent synchronous data link layer protocol
  • Developed by ISO
  • Provides connection-oriented and connectionless service
  • Can be p2p or p2m
  • Framing
    • Synchronous serial communication
    • Asynchronous serial communication
  • Link Configurations
    • Normal Response Mode
    • Asynchronous Response Mode
    • Asyncruonous Balanced Mode


Cisco HDLC control protocol – Serial Line Address Resolution Protocol (SLARP) to maintain serial link keepalives.

HDLC is the default for data encapsulation for serial interfaces

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