Configuring The Loopback Mode For A Gigabit Ethernet Interface; Configuring The Loopback Mode For An Oc-12 Pos Interface - Cisco 10000 Series Troubleshooting Manual

Using Loopback Tests

Configuring the Loopback Mode for a Gigabit Ethernet Interface

To set loopback mode on a gigabit Ethernet interface, use the loopback command in interface
configuration mode.
loopback [internal | external]
[no] loopback [internal | external]
Where:
•
•
Use the no form of the command to stop the loopback.
In the following example, an internal loopback mode is defined for a gigabit Ethernet interface:
router(config)# interface GigabitEthernet 1/0/0
router(config-if)# loopback internal
If you are performing a hard plug loopback test on a gigabit Ethernet interface, be sure to set the
Tip
loopback type for the interface to external. Otherwise, no packets are transmitted onto the fiber optic
cable.

Configuring the Loopback Mode for an OC-12 POS Interface

To enable loopback testing of data transmitted from the PRE card to the OC-12 POS card and back, use
the loopback command in interface configuration mode:
loopback [line | internal]
[no] loopback [line | internal]
Where:
Both line and internal do the following:
•
•
Use the no form of the command to stop the loopback test.
In the following example, a loopback is set for the OC-12 POS line card in slot 5:
Router(config)# interface pos 5/0/0
Router(config-if)# loopback line
Cisco 10000 Series Router Troubleshooting Guide
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external runs a loopback that requires a loopback connector.
internal runs a loopback at the MAC controller using a serializing/deserializing method (SERDES).
Loop any data received at the OC-12 POS card's network interface back into the network.
Loop any data received at the OC-12 POS card's network interface back into the PRE card.
Chapter 6 Troubleshooting Serial Lines
OL-0439-02