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 input loopback

Updated: June 16, 2026

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

In loopback line or media side input loopback, the signals received at the media side are looped back to the media side, indicating that the received data on the media is transmitted back to the media, that is, towards the remote interface. This is indicated by the arrow labeled as 1 in the illustration.

Figure 1. Media Side Input Loopback on the Optical Transceiver

Procedure

  1. Configure media side input loopback.

    Example:

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

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

    Example:

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

  3. Verify media side input 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: Line

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