HDLC is a data link protocol used on synchronous serial data links. Because the standardized HDLC cannot support multiple protocols on a single link (lack of a mechanism to indicate which protocol is carried), Cisco developped a proprietary version of HDLC, called cHDLC, with a proprietary field acting as a protocol field. This field makes it possible for a single serial link to accommodate multiple network-layer protocols.
Cisco’s HDLC is a point-to-point protocol that can only be used on serial links or leased lines between two Cisco devices. PPP has to be used when communicating with non-Cisco devices. HDLC is the default encapsulation on serial links in a Cisco router. However, to change the encapsulation back to HDLC from PPP, use the following command from interface configuration mode:
With a back-to-back serial connection, the ISR router connected to the DCE end of the serial cable provides the clock signal for the serial link. This clock is received by the DTE device. The clock rate command in the interface configuration mode enables the router at the DCE end of the cable to provide the clock signal for the serial link. The default clock rate is 64000.
This lab will test your ability to configure HDLC back to back connection on a serial link between two Cisco ISR routers in Packet Tracer 7.1 . Practicing this labs will help you to get ready for your CCNA certification exam.
1. Use the connected laptops to find the DCE and DTE routers. You can connect to the routers using CLI.
2. Configure the routers with the following parameters :
- Clock : 250000
- HDLC link between the routers
- DCE router IP : 192.168.10.5/30
- DTE router IP : 192.168.10.6/30
3. Check IP connectivity between the two routers using the ping command.