Optics and Hardware Configuration Guide for Cisco 8000 Series Routers

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Loopback on optical transceivers

Updated: June 16, 2026

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Introduces loopback on optical transceivers and explains the core idea and technical context. Highlights the main characteristics and usage guidance needed before configuration.

You can now enable loopback functionality on the optical transceivers.

  • Loopback Internal or Media Side Output Loopback

  • Loopback Line or Media Side Input Loopback

  • Host Loopback Internal or Host Side Input Loopback

  • Host Loopback Line or Host Side Output Loopback

Table 1. Feature History Table

Feature Name

Release Information

Description

Loopback on Optical Transceivers

Release 25.4.1

Introduced in this release on: Fixed Systems (8010 [ASIC: A100])(select variants only*)

*This feature is supported on:

  • 8011-32Y8L2H2FH

  • 8011-12G12X4Y-A/D

Loopback on Optical Transceivers

Release 25.1.1

Introduced in this release on: Fixed Systems (8700 [ASIC: K100], 8010 [ASIC: A100])(select variants only*)

*This feature is supported on:

  • 8712-MOD-M

  • 8011-4G24Y4H-I

Loopback on Optical Transceivers

Release 24.4.1

Introduced in this release on: Fixed Systems (8200 [ASIC: P100], 8700 [ASIC: P100])(select variants only*); Modular Systems (8800 [LC ASIC: P100])(select variants only*)

*This feature is now supported on:

  • 8212-48FH-M

  • 8711-32FH-M

  • 88-LC1-12TH24FH-E

  • 88-LC1-36EH

  • 88-LC1-52Y8H-EM

Loopback on Optical Transceivers

Release 7.11.1

You can now easily detect link failures between the optical transceiver and an external device such as a router by creating a loopback within the transceiver itself. Enabling loopback detects the fault in the physical or network connections, such as, traffic loss or a faulty optical transceiver.

The loopback configuration allows incoming traffic within the transceiver to be redirected back to its source. By analyzing the loopback signals received at the source, it becomes possible to detect physical connectivity failures or network issues, such as packet loss or a malfunctioning transceiver.

The feature introduces these changes:

CLI:

Modified the controller optics command by adding the keywords:

  • host loopback internal

  • host loopback line

  • loopback internal

  • loopback line

The information loopback keyword is added to the show controller optics command.

YANG Data Model:

New XPaths for Cisco-IOS-XR-controller-optics-cfg.yang

(see GitHub, YANG Data Models Navigator)

The optical transceiver is divided into two sides, the host side, which is positioned towards the router, and the media side, which is positioned towards the wire or cable media. It is possible to enable loopback on both the host side and media side of the optical transceiver.

Note

Loopback can be performed only when the controller state is active (UP) and in the maintenance mode.

There are four types of loopback:

Note

Configuring the internal loopback brings up the host interface and configuring the line loopback brings up the remote interface.