R0106-HP MSR Router Series Layer 2 - WAN Configuration Guide(V7)

Configuring HDLC

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

interface modules.

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 keepalives 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. An HDLC-enabled interface sends keepalives to the peer at an

interval specified by the timer-hold command. A keepalive carries the local sending sequence number

and the previous sending sequence number of the peer.

After an interface receives a keepalive carrying its previous sending sequence number, it increments the

previous sending sequence number by 1 in the next keepalive. Otherwise, it uses the previous sending

sequence number. If an interface fails to receive keepalives carrying its previous sending sequence

number within five polling intervals, it performs the following tasks:

• Considers the link faulty.

• 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: