Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 8 Troubleshooting the Cisco Catalyst 6509
Troubleshooting Serial Lines
Configuring a T3 Controller to Respond to Remote Loopback Commands
The equipment customer loopback command allows a port to respond to loopback commands from
remote T3 equipment. The equipment network loopback causes a controller to ignore remote T3
loopback commands.
Syntax:
equipment [customer | network] loopback
Example:
To enable the controller’s ability to respond to remote loopback requests, type:
Router(config)# controller T3 1/0/0
Router(config-controller)#equipment customer loopback
To prevent a controller from responding to remote loopback commands, type:
Router(config)# controller T3 1/0/0
Router(config-controller)#equipment network loopback
Note Remote loopbacks are available only when you use c-bit parity framing.
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:
• external runs a loopback that requires a loopback connector.
• internal runs a loopback at the MAC controller using a serializing/deserializing method (SERDES).
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
Tip If you are performing a hard plug loopback test on a gigabit Ethernet interface, be sure to set the
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 Cisco 10000 ESR 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]