Enabling Local or Network Loopback

You can enable loopback tests on the router at the following layers in the interface stack:

• SONET/SDH section layer
• T1/E1 over SONET/SDH VT layer
• T3 layer
• T1/E1 over T3 layer

See Interface Stack for a description of the layers.

To enable local or network loopback:

1. Select a controller.
2. Configure local or network loopback at the desired layers in the interface.

loopback

• Use to configure the type of loopback at the SONET/SDH section layer.
• Specify one of the following options:
  • local—Loops the data back toward the router; on supported line modules, also sends an alarm indication signal (AIS) out toward the network.
  • network—Loops the data toward the network before the data reaches the frame.
• Example

  host1(config)#controller sonet 4/0

  host1(config-controller)#loopback network

• Use the no version to disable loopback.
• See loopback.

path ds1|e1 loopback

• Use to configure a loopback at the T1/E1 over SONET/SDH VT layer.
• Specify one of the following options:
  • local—Loops the router output data back toward the router at the T1/E1 framer; on supported line modules, also sends an alarm indication signal (AIS) out toward the network.
  • network { line | payload }
    • Specify the line keyword to loop the data back toward the network before the T1/E1 framer and automatically set a local loopback at the HDLC controllers.
    • Specify the payload keyword to loop the payload data back toward the network at the T1/E1 framer and automatically set a local loopback at the HDLC controllers.
• Example

  host1(config-controll)#path 12 ds1 1/3/4 loopback network line

• Use the no version to clear the local loopback configuration.
• See path ds1|e1 loopback.

path ds3 loopback

• Use to configure a loopback at the T3 layer.
• Specify one of the following options:
  • local—Loops the data back toward the router; on supported line modules, also sends an alarm indication signal (AIS) out toward the network.
  • network { line | payload }
    • Specify the line keyword to loop the data toward the network before the data reaches the framer.
    • Specify the payload keyword to loop the data toward the network after the framer has processed the data.
• Example

  host1(config-controll)#controller sonet 5/0

  host1(config-controll)#path 12 ds3 1 loopback local

• Use the no version to turn off the loopback.
• See path ds3 loopback.

path ds3 t1 loopback

• Use to configure a loopback at the T1 over T3 layer.
• Specify one of the following options:
  • local—Loops the router output data back toward the router at the T1 framer; on supported line modules, also sends an alarm indication signal (AIS) out toward the network.
  • network { line | payload }
    • Specify the line keyword to loop the data back toward the network before the T1 framer and automatically set a local loopback at the HDLC controllers.
    • Specify the payload keyword to loop the payload data back toward the network at the T1 framer and automatically set a local loopback at the HDLC controllers.
• Example

  host1(config-controll)#path 12 ds3 2 t1 14 loopback network line

• Use the no version to clear the local loopback configuration.
• See path ds3 t1 loopback.

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