4000 Router Series Layer 2 - WAN Configuration Guide

Configuring HDLC

This feature is supported only on routers installed with SAE, E1, E1-F, T1, T1-F, POS, CPOS, CT3, or CE3

interface modules. For more information about interface modules, see HP MSR Router Series Interface

Module Guide.

High-level Data Link Control (HDLC) is a bit-oriented link layer protocol. Its most prominent feature is that

it can transmit any type of bit stream transparently.

• HDLC supports point-to-point link only and does not support point-to-multipoint link.

• HDLC supports neither IP address negotiation nor authentication. It uses keepalive packets to check

link status.

• HDLC works only on synchronous interfaces or synchronous/asynchronous interfaces in

synchronous mode. This protocol is supported by serial interfaces that operate in synchronous mode

and POS interfaces.

Enabling HDLC encapsulation on an interface

Ste

Command

Remarks

1. Enter system view.

system-view N/A

2. Enter synchronous-mode serial

interface view or POS

interface view.

interface interface-type

interface-number

N/A

3. Enable HDLC encapsulation

on the interface.

link-protocol hdlc

PPP is encapsulated by default.

Configuring the link status polling interval

HDLC can regularly check link status. If an interface uses HDLC as the link layer protocol, the link layer

sends keepalive packets to the peer at an interval specified by the timer-hold command. A keepalive

packet carries the local sending sequence number and the previous sending sequence number of the

peer. After an interface receives a keepalive packet that carries its previous sending sequence number,

it increments the previous sending sequence number by 1 in the keepalive packet to be sent next time.

Otherwise, it uses the previous sending sequence number. If an interface fails to receive keepalive

packets carrying its previous sending sequence number within five polling intervals, it considers the link

faulty and reports a link layer down event.

When you configure the polling interval, follows these restrictions and guidelines:

• Setting the link status polling interval to 0 disables link status check.

• HP recommends that you set the same interval for the two ends of a link.

• If the network has a long delay or is experiencing congestion, you can increase the polling interval

to prevent the link from being closed.

To configure the link status polling interval: