How to configure HDLC?

Configuring High-Level Data Link Control (HDLC) on a serial interface primarily involves using the encapsulation hdlc command within the interface configuration.

HDLC Configuration Steps

The basic steps to configure HDLC are outlined below:

1. Enter Global Configuration Mode: Access the global configuration mode on your networking device. This is usually done with a command like configure terminal.

2. Enter Interface Configuration Mode: Select the specific serial interface you want to configure. For example:

   interface Serial0/0/0

3. Set Encapsulation to HDLC: Use the encapsulation hdlc command. According to the reference, serial interfaces default to HDLC, so this step is often unnecessary unless you are reverting from another encapsulation type like PPP.

   encapsulation hdlc

Configuration Example

Here's a concise example demonstrating the configuration:

configure terminal
interface Serial0/0/0
encapsulation hdlc
end

Default HDLC Encapsulation

• HDLC is often the default encapsulation method on serial interfaces. Therefore, explicit configuration may not always be required unless you are switching from a different encapsulation protocol.

Reverting to HDLC

• If you previously configured a different encapsulation type (e.g., PPP) and wish to return to HDLC, the encapsulation hdlc command is necessary.

In summary, configuring HDLC involves navigating to the interface configuration and setting the encapsulation to HDLC. However, it's worth remembering that HDLC is often the default.