Modular QoS Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Release

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Modular QoS Configuration Guide for Cisco 8000 Series Routers, Cisco IOS XR Release

Global pause frames for High Bandwidth Memory congestion

Updated: June 9, 2026

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Explains global pause frames for HBM congestion, including congestion response behavior, configuration recommendations, and procedures for protecting traffic during HBM resource pressure.

A global pause frame (X-Off) for High Bandwidth Memory (HBM) congestion is a pause-protection functionality that

prevents packet drops on Priority Flow Control (PFC)–enabled queues when HBM bandwidth is saturated
ensures simultaneous pausing of all active lossless queues to maintain traffic integrity, and
preserves bandwidth guarantees during extreme congestion without impacting uncongested queues.

When HBM congestion occurs (see High Bandwidth Memory congestion detection), global pause frames (X-Off) are triggered for all PFC-enabled queues, regardless of whether those queues caused the congestion.

Idle queues that are not receiving traffic do not transmit X-Off signals.

This selective behavior ensures that congestion protection does not activate prematurely or unnecessarily, avoiding performance degradation in unaffected queues.

This functionality operates only when PFC is configured in buffer-extended mode and HBM congestion detection is enabled.

Table 1. Feature History Table
Feature Name	Release Information	Feature Description
Global Pause Frames for High Bandwidth Memory Congestion	Release 7.5.4	We ensure no packet drops on PFC-enabled queues due to High Bandwidth Memory (HBM) congestion. Such prevention of drops is possible because we have enabled the triggering of global pause frames (X-Off) whenever there's HBM congestion. This functionality is disabled by default. You have the following options to enable it: CLI: hw-module profile npu memory buffer-extended bandwidth-congestion-protect enable YANG Data Model: Cisco-IOS-XR-um-8000-hw-module-profile-cfg (see GitHub, YANG Data Models Navigator) This feature introduces the show hw-module bandwidth-congestion-protect command to view the status of the global X-Off configuration.

Recommendations for configuring global pause frames for High Bandwidth Memory congestion

Follow these recommendations when enabling and configuring global pause frames (X-Off) for High Bandwidth Memory (HBM) congestion to ensure consistent lossless behavior and stable Priority Flow Control (PFC) operation.

Distance Limitation: This functionality is not supported when devices operating in buffer-extended mode are more than 0.5 km apart.
Headroom Limit: Configuring the command hw-module profile npu memory buffer-extended bandwidth-congestion-protect enable on line cards with headroom values greater than 6,144,000 bytes can cause a commit failure or prevent the feature from activating.
Reload Requirement: You must reload the line card after enabling the command hw-module profile npu memory buffer-extended bandwidth-congestion-protect enable for the configuration to take effect.
Supported Hardware: This functionality is supported only on 88-LC0-36FH and 88-LC0-36FH-M line cards.

Configure global pause frames for High Bandwidth Memory congestion

Use this procedure to enable and verify global pause frames (X-off) for High Bandwidth Memory (HBM) congestion on line cards configured with the buffer-extended mode.

This task ensures lossless behavior by pausing all Priority Flow Control enabled queues when HBM utilization crosses the congestion threshold.

This feature applies to buffer-extended mode. It prevents packet drops during extreme congestion by triggering a global X-off condition. You must reload the line card for the configuration to take effect.

Procedure

Enable global pause (X-off) protection for HBM congestion.

Example:

Router#config
Router(config)#hw-module profile npu buffer-extended location 0/1/CPU0 bandwidth-congestion-protect enable
Router(config)#commit

Verify global X-off configuration status.

Example:

Router#show hw-module bandwidth-congestion-protect location 0/1/CPU0
Location   Configured     Applied          Action         
-----------------------------------------------------------
0/1/CPU0     Yes             No               Reload

The table lists possible outputs for different command and commit actions.

Table 2. Command Output Scenarios
If you configured...	Configured field displays...	Applied field displays..	Then Action field displays...
Configure the hw-module profile npu memory buffer-extended command	Yes	No	Reload
Use the no form of the hw-module profile npu memory buffer-extended command after configuring it, but before reloading the line card	No	No	N/A
Configure the hw-module profile npu memory buffer-extended command for a supported variant and reload the line card	Yes	Yes, Active Note Yes indicates that the configuration is programmed to the hardware, Active indicates that the global X-off functionality is active on the hardware.	N/A
Use the no form of the hw-module profile npu memory buffer-extended command when it is active and commit without reloading the line card	No Note At this stage, the output displays the user action and not the hardware status.	No Note At this stage, the output displays the user action and not the hardware status.	Reload
Reload the line card after committing the no form of the hw-module profile npu memory buffer-extended command	No Note At this stage, the output displays the hardware status.	No Note At this stage, the output displays the hardware status.	N/A

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