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Configuring E3 Loopback Capability


You can configure loopback capability between the local E3 interface and the remote channel service unit (CSU), as shown in Figure 1. You can configure the loopback to be local or remote. With local loopback, the E3 interface can transmit packets to the CSU, but receives its own transmission back again and ignores data from the CSU. With remote loopback, packets sent from the CSU are received by the E3 interface, forwarded if there is a valid route, and immediately retransmitted to the CSU.

Figure 1: Remote and Local E3 Loopback
Remote and Local E3 Loopback

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, you 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 configure E3 Loopback capability on an E3 interface:

  1. In the configuration mode go to the [edit interfaces interface-name e3-options] hierarchy level.
  2. Include the loopback statement. Note that the loopback local statement causes the interface to loop within the PIC just before the data reaches the transceiver.
  3. To determine whether a problem is internal or external, loop packets on both the local and the remote router. Include the no-keepalives and encapsulation cisco-hdlc statements at the [edit interfaces interface name] hierarchy level. With this configuration, the link stays up, so you can loop ping packets to a remote router.
  4. Check the error counters in the output of the show interface interface-name extensive to determine whether there is an internal problem or an external problem.
  5. View the configuration by issuing the show command at the [edit interfaces e3-fpc/pic/port ] hierarchy level.
  • You can turn off the loopback capability by removing the loopback statement from the configuration

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