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Configuring SONET/SDH Loopback Capability to Identify a Problem as Internal or External

 

Configuring SONET/SDH Loopback Capability

To configure loopback capability on a SONET/SDH interface:

  1. In configuration mode, go to the [edit interfaces interface-name sonet-options] hierarchy level.
  2. Configure the loopback option as local loopback, remote loopback, or payload.Note

    To exchange BERT patterns between a local router and a remote router, include the loopback remote statement in the interface configuration at the remote end of the link. From the local router, issue the test interface command.

For more information about configuring BERT, see Configuring Interface Diagnostics Tools to Test the Physical Layer Connections. For more information about using operational mode commands to test interfaces, see the CLI Explorer.

To turn off the loopback capability:

  1. In configuration mode, go to the [edit] hierarchy level.
  2. Remove the loopback option to turn off the loopback capability.

For channel 0 on channelized interfaces only, you can include the loopback statement at the [edit interfaces interface-name interface-type-options] hierarchy level. The loopback setting configured for channel 0 applies to all channels on the channelized interface. The loopback statement is ignored if you include it at this hierarchy level in the configuration of other channels. To configure loopbacks on individual channels, you must include the channel-type-options loopback statement in the configuration for each channel. This allows each channel to be put in loopback mode independently.

For example, for DS3 channels on a channelized OC12 interface, the sonet-options loopback statement is supported only for channel 0; it is ignored if included in the configuration for channels 1 through 11. The SONET/SDH loopback configured for channel 0 applies to all 12 channels equally. To configure loopbacks on the individual DS3 channels, you must include the t3-options loopback statement in the configuration for each channel. This allows each DS3 channel can be put in loopback mode independently.

Displaying SONET/SDH Loopback Capability Configuration

Purpose

To display the loopback capability configuration in SONET/SDH.

Action

To display loopback capability, for example on the so-1/0/0 interface, perform the following steps:

  1. In configuration mode, go to the [edit interfaces interface-name] hierarchy level, where the interface-name is so-1/0/0.
  2. Display the loopback capability by issuing the show operational mode command.
  3. The following output is displayed.

    With this configuration, the link stays up, so you can loop ping packets to a remote router. The loopback local statement causes the interface to loop within the PIC just before the data reaches the transceiver.

Determining Whether the Problem Is Internal or External with Loopback Capability

Problem

Description: Problem is internal or external.

Solution

To determine whether a problem is internal or external, you have to loop packets on both the local and the remote router using the loopback capability.

To loop packets on both the local and the remote router, perform the following steps:

  1. In configuration mode, go to the [edit interfaces interface-name] hierarchy level.
  2. Configure the no-keepalives and encapsulation cisco-hdlc options.
  3. In configuration mode, go to the [edit interfaces interface-name sonet-options] hierarchy level.
  4. Configure the loopback local option. This option causes the interface to loop within the PIC just before the data reaches the transceiver.

You can also determine whether there is an internal problem or an external problem by checking the error counters in the output of the show interface interface-name extensive operational mode command.