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

Advanced optical behavior

Updated: June 16, 2026

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Introduces advanced optical behavior and outlines the main concept, process, task, principle, and reference areas in this section. Guides technical users to quickly locate the procedures and supporting data they need.

Advanced optical behavior covers ULH optics features, media link-down behavior based on PreFEC degrade, and AppSel provisioning workflows.

Enhanced SOP tolerance mode for ULH optics

This topic explains enhanced SOP tolerance mode for ULH optics and provides the technical context you need before configuration.

An enhanced SOP tolerance mode is an optical module feature that

  • increases resilience to rapid state of polarization (SOP) fluctuations,

  • enables stable ultra long-haul (ULH) coherent signal transmission over challenging fiber environments, and

  • actively compensates for polarization impairments using advanced DSP techniques.

    Feature Name

    Release info

    Description

    Enhanced SOP support for ULH optics

    Release 25.2.1

    Introduced in this release on: Modular Systems (8800 [LC ASIC: Q100 , Q200 , P100]) (select variants only*)

    This feature helps to improve the coherent optics' ability to handle fluctuations in the light's State of Polarization (SOP). It achieves this by enhancing the Digital Signal Processing (DSP) to track and compensate for rapid SOP rotation. The capability ultimately ensures more reliable data transmission, maintains high signal quality, and increases network stability, especially in long-distance and dynamic optical deployments.

    This feature is applicable on:

    • 88-LC0-36FH

    • 88-LC0-36FH-M

    CLI:

    The enh-sop-tol-mode keyword is added to the controller optics command.

Benefits of SOP tolerance mode for ULH optics

Provides reference information for benefits of sop tolerance mode for ulh optics, including key values, supported combinations, and related constraints.

Enhanced SOP tolerance mode provides several benefits.

  • Improved performance: Digitally compensates for dynamic SOP changes to maintain high signal quality and network stability in challenging fiber conditions.

  • Increased robustness: Offers greater resilience to polarization-related impairments, especially crucial for long-haul and subsea optical deployments.

Supported hardware variants

Enhanced SOP tolerance mode is supported on these line cards:

  • 88-LC0-36FH

  • 88-LC0-36FH-M

This section explains functional behavior for the referenced items.

Configure enhanced SOP tolerance mode

Follow this task to configure enhanced SOP tolerance mode.

Use this procedure in the appropriate operating context for your deployment.

Before you begin

Ensure prerequisites for software state, hardware state, and access privileges are met.

Procedure

SUMMARY STEPS

  1. Enable enhanced SOP tolerance mode.
  2. Verify that enhanced SOP tolerance mode is enabled.

DETAILED STEPS

1.

Enable enhanced SOP tolerance mode.

Example:

Router# config
Router(config)# controller optics 0/0/0/14
Router(config-Optics)# enh-sop-tol-mode 1
Router(config-Optics)# commit

The possible values for enhanced SOP tolerance mode are 1 or no enh-sop-tol-mode.

2.

Verify that enhanced SOP tolerance mode is enabled.

Example:

Router# show run 0/0/0/14
!! Building configuration...
!! IOS XR Configuration 25.2.2.09I
!! Last configuration change at Mon Jul 28 18:56:00 2025 by cisco
!
hostname abc
username cisco group root-lr group cisco-support secret 10 $6$g8TGE1mb2o7/BE1.$X1wz3z0fTKp6E0utoKvS6H4CFT0BOmM8PGt6M5MnndzrjnM/gJk.NwgOf5n3SZm2.qaPeRrZar7VQTtNnT16b1
!
line console exec-timeout 0 0
!
interface MgmtEth0/RP0/CPU0/0 ipv4 address dhcp
!
controller Optics0/0/0/14 enh-sop-tol-mode 1
!
interface FourHundredGigE0/0/0/0 description AOC shutdown

Verify that the system reflects the intended configuration state.

What to do next

Continue with related procedures as required by your workflow.

The Media Link-down PreFEC Degrade functionality can be used to protect the media side of the optical transceiver during transmission errors, such as errors due to noise, or data transmission errors.

Table 1. Feature History Table

Feature Name

Release Information

Description

Media Link-down PreFEC Degrade Enablement

Release 26.1.1

Introduced in this release on: Fixed Systems (8400 [ASIC: K100] )(select variants only*)

*This feature is now supported on the Cisco 8404-SYS-D router.

Media Link-down PreFEC Degrade Enablement

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

Media Link-down PreFEC Degrade Enablement

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

Media Link-down PreFEC Degrade Enablement

Release 24.3.1

Introduced in this release on: Fixed Systems (8200 [ASIC: Q200, P100], 8700 [ASIC: P100]); Centralized Systems (8600 [ASIC:Q200]); Modular Systems (8800 [LC ASIC: Q100, Q200, P100])

The Media Link-down PreFEC Degrade functionality can be used to protect the media side of the optical transceiver during transmission errors.

By using this feature, you can proactively switch the traffic to standby path when the BER counter crosses the threshold value. This feature helps to avoid further traffic impact when the optical network reaches more noise or error.

The feature introduces these changes:

CLI:

Modified the controller optics command by adding the media link-down prefec-degrade keyword.

YANG Data Model:

  • New XPaths for Cisco-IOS-XR-controller-optics-oper.yang

  • New XPaths for Cisco-IOS-XR-um-cont-optics-fec-threshold-cfg.yang

(see GitHub, YANG Data Models Navigator)

To use the Media Link-down PreFEC Degrade functionality, you must configure the FEC Alarm Threshold. For information about configuring FEC alarm thresholds, see FEC alarm thresholds.

Prior to this release, the FEC Alarm Threshold functionality enabled you to configure the FEC alarms threshold values to control alarms (raise and clear FEC alarms) on media and host side of the optical transceiver. Using the FEC Alarm Threshold functionality, you can configure the FDD and FED alarm threshold values and set the raise threshold value and clear threshold value values to control alarms.

After you configure FEC Alarm Threshold and enable Media Link-down PreFEC Degrade functionality, you get the alarm notification when the average bit error rate (BER) exceeds the threshold value. This triggers link-down and enables switchover functionality automatically. The traffic is switched to standby path, and remains in the standby path until the alarm is cleared or based on the settings done by the network operator.

Note

In Cisco IOS XR Release 24.3.1, the Link-down PreFEC Degrade feature is supported only on the media side of the optical transceiver.

Follow this task to configure media link-down prefec degrade.

Use this procedure in the appropriate operating context for your deployment.

Before you begin

Ensure prerequisites for software state, hardware state, and access privileges are met.

Procedure

SUMMARY STEPS

  1. Execute the media link-down prefec-degrade command to configure link-down preFEC degrade on the media side of the optics controller.
  2. Execute the show running-config controller optics R/S/I/P command to view the running configuration on the optics controller.
  3. Execute the show controller optics R/S/I/P command to verify link-down preFEC degrade feature on optics controllers.

DETAILED STEPS

1.

Execute the media link-down prefec-degrade command to configure link-down preFEC degrade on the media side of the optics controller.

Example:

Router#config
Router(config)#controller optics 0/2/0/16
Router(config-Optics)#media link-down prefec-degrade
Router(config-Optics)#commit
2.

Execute the show running-config controller optics R/S/I/P command to view the running configuration on the optics controller.

Example:

Router#show running-config controller optics 0/2/0/16
Thu May 13 20:18:55.957 UTC
controller Optics0/2/0/16 media link-down prefec-degrade
!
3.

Execute the show controller optics R/S/I/P command to verify link-down preFEC degrade feature on optics controllers.

Example:

Router#show controller optics 0/2/0/16
Fri May 28 01:04:33.604 UTC
 Controller State: Up
 Transport Admin State: In Service
 Laser State: On
 Media linkdown prefec degrade : Enabled
 LED State: Green
 FEC State: FEC ENABLED
 Optics Status
         Optics Type:  QSFPDD 400G ZRP
         DWDM carrier Info: C BAND, MSA ITU Channel=61, Frequency=193.10THz,
         Wavelength=1552.524nm
         Alarm Status:
         -------------
         Detected Alarms: None
         LOS/LOL/Fault Status:
         Alarm Statistics:
         -------------
         HIGH-RX-PWR = 0            LOW-RX-PWR = 0
         HIGH-TX-PWR = 0            LOW-TX-PWR = 0
         HIGH-LBC = 0               HIGH-DGD = 0
         OOR-CD = 0                 OSNR = 0
         WVL-OOL = 0                MEA  = 0
         IMPROPER-REM = 0
         TX-POWER-PROV-MISMATCH = 0
         Laser Bias Current = 0.0 mA
         Actual TX Power = -40.00 dBm
         RX Power = -40.00 dBm
         RX Signal Power = -40.00 dBm
         Frequency Offset = 0 MHz
         Laser Temperature = 0.00 Celsius
         Laser Age = 0 %
         DAC Rate = 1x1.25
         Performance Monitoring: Enable
         THRESHOLD VALUES
         ----------------
         Parameter                 High Alarm  Low Alarm  High Warning  Low Warning
         ------------------------  ----------  ---------  ------------  -----------
         Rx Power Threshold(dBm)         13.0      -24.0          10.0        -22.0
         Tx Power Threshold(dBm)          0.0      -16.0          -2.0        -14.0
         LBC Threshold(mA)               0.00       0.00          0.00         0.00
         Temp. Threshold(celsius)       80.00      -5.00         75.00         0.00
         Voltage Threshold(volt)         3.46       3.13          3.43         3.16
         LBC High Threshold = 98 %
         Configured Tx Power = -10.00 dBm
         Configured CD High Threshold = -5000 ps/nm
         Configured CD lower Threshold = -5000 ps/nm
         Configured OSNR lower Threshold = 9.00 dB
         Configured DGD Higher Threshold = 80.00 ps
         Baud Rate =  60.1385459900 GBd
         Modulation Type: 16QAM
         Chromatic Dispersion 0 ps/nm
         Configured CD-MIN -26000 ps/nm  CD-MAX 26000 ps/nm
         Second Order Polarization Mode Dispersion = 0.00 ps^2
         Optical Signal to Noise Ratio = 0.00 dB
         Polarization Dependent Loss = 0.00 dB
         Polarization Change Rate = 0.00 rad/s
         Differential Group Delay = 0.00 ps
         Temperature = 21.00 Celsius
         Voltage = 3.42 V
 Transceiver Vendor Details
         Form Factor            : QSFP-DD
         Optics type            : QSFPDD 400G ZRP
         Name                   : CISCO-ACACIA
         OUI Number             : 7c.b2.5c
         Part Number            : DP04QSDD-E30-19E
         Rev Number             : 10
         Serial Number          : ACA244900GN
         PID                    : QDD-400G-ZRP-S
         VID                    : ES03
         Firmware Version       : 161.06
         Date Code(yy/mm/dd)    : 20/12/08
!

Verify that the system reflects the intended configuration state.

What to do next

Continue with related procedures as required by your workflow.

Application select code provisioning

Application select code, also known as AppSel code, is a feature that:

  • allows the host device to choose the operating mode of a QDD module

  • allows you to configure the media code, and

  • specifies how to configure the optical side of a module.

Table 2. Feature History Table

Feature Name

Release Information

Feature Description

Application select code provisioning

 Release 25.2.1 You can now configure application select codes directly on a QDD module by using a CLI. This simplifies provisioning by allowing the selection of advertised application modes such as 400ZR, OpenZR+ and others. The router activates the selected code to ensure compatibility and reduce configuration complexity.

This feature introduces these changes:

CLI:

AppSel code provisioning details

The Common Management Interface Specification (CMIS) specifications set rules for how QDD modules work and how a host device sets them up. CMIS provides a consistent way for host devices, such as routers or switches, to communicate with and control optical modules, regardless of the module manufacturer.

Each QDD module can work in different modes, and these modes are identified by a special code called an AppSel code. This code acts like a unique ID for each mode. Each mode has an application descriptor, which explains how the module handles data. It describes how signals are processed between the connections on the host side and the optical side. The optical side is also known as the media side of the module. The AppSel code also includes a media code, which tells the module how to set up its optical side. The host software uses this media code to control the module’s optical interface. The host software also sets up other components, like the physical layer (PHY), SerDes, and MacPort, to complete the data path.

Modules store a list of the AppSel codes they support in their EEPROM memory. This helps the host system or device know which settings the module can use. Some codes, like 400G-OIF-ZR and 400G-OpenZR+, are standard and follow industry rules. Other codes are custom, made by third-party vendors to give users more options with one module. However, these custom codes can cause problems. For example, Cisco routers may not work well with modules using custom codes if the host system doesn’t recognize them.

This feature allows users to select application modes advertised by the optical module. You can choose all application modes a module supports.

AppSel supports operation modes based on these parameters:

  • Data rate, such as 100GbE or 400GbE

  • Signal type

  • Signal processing between host side and media side

  • Optical configuration, based on the media code, which is part of the AppSel code.

Benefits of AppSel code provisioning

These are the benefits of provisioning AppSel code:

  • Enables you to choose any application mode supported by the optical module for greater flexibility.

  • Enables direct configuration of the NPU, PHY, and optics to match the selected application’s datapath.

  • Removes the need for Cisco IOS XR software to implement new proprietary modes for each vendor, simplifying software requirements.

  • Allows you to directly specify the desired AppSel code, enabling straightforward configuration without requiring Cisco IOS XR software to interpret the mode.

  • Eliminates the extra step of mapping custom vendor codes, reducing delays in supporting new module vendors.

Configuration guidelines for AppSel code provisioning

Configuration guidelines for AppSel code provisioning

  • This feature is not enabled by default. You must configure it to take effect.

  • If you configure a non-default application ID and later remove the configuration, the selected application ID falls back to the default.

  • If you configure a non-default application ID and later overwrite it with an invalid application ID, the selected application ID falls back to default. The system raises an alarm indicating the invalid configuration.

  • The maximum number of applications supported depends upon the module as advertised in the AppSel list.

Restrictions for AppSel code provisioning

These restrictions apply to AppSel code provisioning:

  • The Cisco 8000 series routers do not support In Service Software Upgrade (ISSU) or In Service Software Downgrade (ISSD).

  • Optical Transport Network (OTN) is not supported.

How AppSel code provisioning works

The key components that are involved in the AppSel code provisioning are:

  • Optical side: The optical side or the media side refers to the part of a pluggable module, such as a QDD or other optical transceiver that connects to and communicates with the optical network. It is the interface responsible for converting electrical signals, from the host device, into optical signals for transmission over fiber optic cables, and vice versa for receiving signals.

  • Host side: The host side refers to the part of a pluggable module, such as a QDD or other optical transceiver that interfaces with the host device. A host device is typically a network device like a router, switch, or server. It is responsible for handling and processing electrical signals exchanged between the module and the host device.

  • Optics Driver: The entity that collects all supported application codes from the module. Users can see all supported application codes and select any one of the supported application codes. The optics driver programs the valid application code to the module.

  • Application Codes: The unique codes that represent operational modes of the optical module.

  • Optics Management Agent (MA): The entity that sends the default configuration to the optics driver if no user configuration is provided. It also manages fallback behavior when no application code is selected.

Workflow

These stages describe how AppSel code provisioning process works.

  1. AppSel code identifies the optical module modes when the modules are plugged into a router.

  2. AppSel code points to application descriptor. In this stage, the AppSel code acts as a sequence number for an application descriptor.

  3. The application descriptor defines the configuration. In this stage, the application descriptor describes a functional transmission configuration, including signal processing between host lanes and media lanes.

  4. The AppSel code that contains the media code configure the media side of the optical module.

  5. The router software or the host software applies the media code to configure the optical interface of the optical module.

  6. Based on the module's host side interface, you can configure PHY, NPU SerDes, and MacPort.

  7. The host side and media side configurations complete, establishing the datapath.

Result

The router enables AppSel code provisioning as the datapath is complete between the host side and media side. This ensures that the optical module operates correctly and efficiently in the desired mode, with proper coordination between the host side interface and the media side.

Configure an appsel code on an optical module

Configure the AppSel code to enable the optical module to operate in a specific application mode, such as 400ZR or OpenZR+.

AppSel codes are advertised by the module and must be validated before configuration. This ensures compatibility between the host and the module.

Use this procedure in the appropriate operating context for your deployment.

Before you begin

Ensure the router is running Cisco IOS XR Software Release 25.2.1 or later.

Procedure

SUMMARY STEPS

  1. Identify the AppSel code that needs to be configured on a particular port from the list of available appcodes.
  2. Enter configuration mode on the router.
  3. Identify the controller optics interface and configure breakout to match with the AppSel code that you want to configure.
  4. Configure the AppSel code.
  5. Verify the configuration.

DETAILED STEPS

1.

Identify the AppSel code that needs to be configured on a particular port from the list of available appcodes.

Example:

Router# show controllers optics 0/0/0/0 appsel advertised
Router# show controllers optics 0/0/0/0 appsel detailed
2.

Enter configuration mode on the router.

Example:

Router# conf
3.

Identify the controller optics interface and configure breakout to match with the AppSel code that you want to configure.

Example:

Router(config)# controller optics 0/0/0/0 breakout 4x100
4.

Configure the AppSel code.

Example:

Router(config)# controller optics 0/0/0/0 
appsel simple code 4
   !
!
5.

Verify the configuration.

Example:

Router# #show controllers optics 0/0/0/0 appsel advertised 

Sun Feb  2 20:00:04.884 UTC
-------------------------------------------------------------------------------------------------------------------------------
  App-ID  |  Host-ID                        |  Media-ID                       |  Standard       |  Host     |  Power          |
          |                                 |                                 |                 |  Supported|  Consumption(W) |
          |                                 |                                 |                 |           |                 |
-------------------------------------------------------------------------------------------------------------------------------
  1       |  17    ETH 400GAUI-8 C2M (Annex |  62    OIF 400ZR, DWDM, amplifi |  OIF            |  Yes      |  n/a            |
  2       |  13    ETH 100GAUI-2 C2M (Annex |  62    OIF 400ZR, DWDM, amplifi |  OIF            |  Yes      |  n/a            |
  3       |  17    ETH 400GAUI-8 C2M (Annex |  70    OpenZR+ ZR400-OFEC-16QAM |  OpenZR+        |  Yes      |  n/a            |
  4       |  13    ETH 100GAUI-2 C2M (Annex |  70    OpenZR+ ZR400-OFEC-16QAM |  OpenZR+        |  Yes      |  n/a            |
  5       |  17    ETH 400GAUI-8 C2M (Annex |  199   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  6       |  15    ETH 200GAUI-4 C2M (Annex |  199   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  7       |  13    ETH 100GAUI-2 C2M (Annex |  199   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  8       |  17    ETH 400GAUI-8 C2M (Annex |  196   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  9       |  15    ETH 200GAUI-4 C2M (Annex |  196   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  10      |  13    ETH 100GAUI-2 C2M (Annex |  196   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  11      |  17    ETH 400GAUI-8 C2M (Annex |  200   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  12      |  15    ETH 200GAUI-4 C2M (Annex |  200   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  13      |  13    ETH 100GAUI-2 C2M (Annex |  200   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
  14      |  17    ETH 400GAUI-8 C2M (Annex |  83    OTN-ITU-T FOIC4.8-DO (G. |  OTN-ITU-T      |  Yes      |  n/a            |
  15      |  254   0xC0-0xFE  Vendor Specif |  254   0xC0-0xFE  Vendor Specif |  0xC0-0xFE      |  Yes      |  n/a            |
------------------------------------------------------------------------------------------------------------------------------- 

Router# show controllers optics 0/0/0/0 appsel detailed 

Sun Feb  2 20:00:29.702 UTC
-------------------------------------------------------------------------------------------------------------
  App-ID  |  Host-ID     |  Media-ID    |  Host Lane |  Media Lane|  Host Lane   |  Media Lane  |  Host      |
          |              |              |  Count     |  Count     |  Assign      |  Assign      |  Supported |
          |              |              |            |            |              |              |            |
--------------------------------------------------------------------------------------------------------------
  1       |  17          |  62          |  8         |  1         |  1           |  1           |  Yes       |
  2       |  13          |  62          |  2         |  1         |  85          |  1           |  Yes       |
  3       |  17          |  70          |  8         |  1         |  1           |  1           |  Yes       |
  4       |  13          |  70          |  2         |  1         |  85          |  1           |  Yes       |
  5       |  17          |  199         |  8         |  1         |  1           |  1           |  Yes       |
  6       |  15          |  199         |  4         |  1         |  17          |  1           |  Yes       |
  7       |  13          |  199         |  2         |  1         |  85          |  1           |  Yes       |
  8       |  17          |  196         |  8         |  1         |  1           |  1           |  Yes       |
  9       |  15          |  196         |  4         |  1         |  17          |  1           |  Yes       |
  10      |  13          |  196         |  2         |  1         |  85          |  1           |  Yes       |
  11      |  17          |  200         |  8         |  1         |  1           |  1           |  Yes       |
  12      |  15          |  200         |  4         |  1         |  17          |  1           |  Yes       |
  13      |  13          |  200         |  2         |  1         |  85          |  1           |  Yes       |
  14      |  17          |  83          |  8         |  1         |  1           |  1           |  Yes       |
  15      |  254         |  254         |  8         |  1         |  255         |  1           |  Yes       |
--------------------------------------------------------------------------------------------------------------


Router# show controllers optics 0/0/0/0 appsel active

Sun Feb  2 20:00:47.776 UTC
 Instance           : 1
 App-ID             : 3
 Host-ID            : 17    ETH 400GAUI-8 C2M (Annex
 Media-ID           : 70    OpenZR+ ZR400-OFEC-16QAM
 Host Lane Count    : 8
 Media Lane Count   : 1
 Host Lane Assign   : 0x1
 Media Lane Assign  : 0x1

The optical module operates in the selected application mode, ensuring compatibility and optimal performance.

What to do next

  • Monitor the interface status and confirm the active AppSel code.

  • Ensure alarms are cleared, and the interface is operational.