Optics and Hardware Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

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Optics and Hardware Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Releases

Configure media side output loopback

Updated: June 16, 2026

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Provides instructions on how to configure media side output loopback in a controlled workflow. Covers prerequisites, execution steps, and result checks needed for successful completion.

In loopback internal or media side output loopback, the loopback signal originating from the NPU is looped back to the same NPU on the media or line side, towards the remote interface. This is indicated by the arrow labeled as 1 in the illustration.

Figure 1. Media Side Output Loopback on the Optical Transceiver
Media Side Output Loopback on the Optical Transceiver

Procedure

  1. Configure media side output loopback.

    Example:

    Router#config
Router(config)#controller optics 0/0/0/9
Router(config-Optics)#secondary-admin-state maintenance
Router(config-Optics)#loopback internal
Loopback is a traffic-affecting operation
Router(config-Optics)#commit
Router(config-Optics)#end

  2. Display the running configuration for media side output loopback.

    Example:

    Router#show run controller optics 0/0/0/9
controller Optics0/0/0/9
 secondary-admin-state maintenance
 loopback internal
!

  3. Verify media side output loopback.

    Example:

    Router#show controller optics 0/0/0/9
Controller State: Up
Transport Admin State: Maintenance
Laser State: On
LED State: Green
FEC State: FEC ENABLED
Optics Status:

Optics Type: QSFPDD 400G FR4
Wavelength: 1301.00 nm
Loopback Host: None
Loopback Media: Internal

Alarm Status:
----------------
Detected Alarms: None
LOS/LOL/Fault Status:
Performance Monitoring: Disable