Cisco HDLC Configuration Tasks

To configure a Cisco HDLC interface:

1. Configure the physical interface on which you want to configure Cisco HDLC.

host1(config)#interface serial 3/1:2/1

2. Select Cisco HDLC as the encapsulation method for the interface.

host1(config-if)#encapsulation hdlc

3. Assign a local IP address to the interface.

host1(config-subif)#ip address 192.32.10.2 255.255.255.0

4. Verify that your configuration changes are correct by checking the state of the interfaces using show commands.

host1#show hdlc interface

    encapsulation hdlc

• Use to specify Cisco HDLC as the encapsulation method for the interface.
• Example

host1(config-if)#encapsulation hdlc

• Use the no version to disable Cisco HDLC on the interface.

    interface serial

• Use to configure a serial interface in the appropriate format (for example, for a CT3 interface, use slot/port:channel/subchannel.subinterface) by selecting a previously configured physical interface on which you want to configure Cisco HDLC.

• slot - system chassis slot
• port - CT3, T3, E3, CT1, or CE1 module I/O port
• channel - T1 (DS1) channel
• subchannel - set of DS0 subchannels. For information on T1 subchannels, see Fractional T1 in ERX Physical Layer Configuration Guide, Chapter 1, Configuring Channelized T3 Interfaces.
• subinterface - user-assigned number that identifies a subinterface
• channel-group - CT1 or CE1 channel group number in the range 1-31

• Example

host1(config)#interface serial 3/1:2/1

• Use the no version to remove the interface or subinterface.

    ip address

• Use to assign an IP address and subnet mask to the interface.
• Example

host1(config-subif)#ip address 192.32.10.2 255.255.255.0

• Use the no version to remove the IP address of the interface.

Optional Tasks

The following tasks are optional.

1. Configure the SLARP keepalive interval.

host1(config-if)#hdlc keepalive 10

2. Enable loopback detection on an interface.

host1(config-if)#hdlc down-when-looped

3. Disable an interface.

host1(config-if)#hdlc shutdown

    hdlc down-when-looped

• Use to enable loopback detection on a Cisco HDLC interface.
• By default, loopback detection is disabled.
• Example

host1(config-if)#hdlc down-when-looped

• Use the no version to disable loopback detection on a Cisco HDLC interface.

    hdlc keepalive

• Use to specify the keepalive timeout value.
• When the keepalive timer expires, the interface increments its own counter; then it compares the value of this counter with the last value received from a peer. If the difference between the values of the two counters is greater than three, the Cisco HDLC interface is declared down. After that, the interface sends a keepalive message containing the value of its counter and the last received value of the peer's counter.
• The system stores the values received in keepalive messages from a peer interface. If the interface is down, the system compares the received value of its own counter with the value from the peer. If the difference between the values of the two counters is less than four, the system declares the interface to be up. Both sides have to configure the same value for the keepalive interval.
• If the keepalive interval is 10 seconds, then a failed link is detected between 30 and 40 seconds after failure.
• The range is 0-6553 seconds. A value of 0 turns keepalive off.
• The default is 10 seconds.
• Example

host1(config-if)#hdlc keepalive 10

• Use the no version to turn off the keepalive feature.

    hdlc shutdown

• Use to terminate a Cisco HDLC session.
• This command administratively disables the interface.
• Example

host1(config-if)#hdlc shutdown

• Use the no version to restart a disabled session.
• The default for each hdlc shutdown command is the no version.

Configuration Example

This example shows how to configure Cisco HDLC over an unchannelized DS3 interface on a cOCx/STMx line module. The example shows the complete configuration procedure, from configuring the SONET interface to assigning an IP address to the Cisco HDLC interface.

1. Create or select a virtual router, vr1.

host1(config)#virtual-router vr1

2. Configure SONET controller, slot 13, port 0.

host1:vr1(config)#controller sonet 13/0

3. Set the SONET clock source to internal.

host1:vr1(config-controll)#clock source internal module

4. Create an OC1 path.

host1:vr1(config-controll)#path 1 oc1 1

5. Create an unchannelized DS3 interface.

host1:vr1(config-controll)#path 1 ds3 1 unchannelized

6. Set the DS3 interface clock source to internal.

host1:vr1(config-controll)#path 1 ds3 1 clock source 
internal module

7. Exit controller configuration mode.

host1:vr1(config-controll)#exit

8. Create or select a serial interface over the DS3 interface.

host1:vr1(config)#interface serial 13/0:1/1

9. Set the encapsulation to Cisco HDLC.

host1:vr1(config-if)#encapsulation hdlc

10. Enable loopback detection on the interface.

host1:vr1(config-if)#hdlc down-when-looped

11. Assign an IP address to the interface.

host1:vr1(config-if)#ip address 160.1.0.1 255.255.255.0