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Configuring SONET/SDH Loopback Capability

To configure loopback capability on a SONET/SDH interface, include the loopback statement at the [edit interfaces interface-name sonet-options] hierarchy level:



[edit interfaces so-fpc/pic/port sonet-options]

loopback (local | remote);

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

For more information about configuring BERT, see Interface Diagnostics. For more information about using operational mode commands to test interfaces, see the JUNOS System Basics and Services Command Reference.

To turn off the loopback capability, remove the loopback statement from the configuration:



[edit]
user@host# delete interfaces so-fpc/pic/port sonet-options loopback

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.

You can 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 command:



user@host> show interfaces so-fpc/pic/port extensive

Example: Configuring SONET/SDH Loopback Capability

To determine whether a problem is internal or external, loop packets on both the local and the remote routing platform. To do this, include the no-keepalives and encapsulation cisco-hdlc statements at the [edit interfaces interface-name] hierarchy level, and the loopback local statement at the [edit interfaces interface-name sonet-options] hierarchy level. With this configuration, the link stays up, so you can loop ping packets to a remote routing platform. The loopback local statement causes the interface to loop within the PIC just before the data reaches the transceiver.



[edit interfaces]
so-1/0/0 {
no-keepalives;
encapsulation cisco-hdlc;


sonet-options {
loopback local;
}




unit 0 {


family inet {
address 10.100.100.1/24;
}


}


}

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