CISCO 8000 Series Routers Configure Priority Flow Control User Guide

: June 15, 2024
: Cisco

Table of Contents

8000 Series Routers Configure Priority Flow Control
Product Information
Specifications
Product Usage Instructions
1. Overview
2. Configuration
Q: What line cards support Priority Flow Control?
Q: What modes are supported for Priority Flow Control?
Q: How do I configure Priority Flow Control in buffer-internal
Q: What is the purpose of configuring performance capacity or

8000 Series Routers Configure Priority Flow Control

Product Information

Specifications

Feature Name: Priority Flow Control
Supported Line Cards: Cisco 8808 and Cisco 8812 Modular Chassis
Line Cards
Supported Modes: Buffer-internal and Buffer-extended
Release Information: Release 7.5.3

Product Usage Instructions

1. Overview

Priority Flow Control is a feature that prevents frame loss due
to congestion by using pause frames on a per class-of-service (CoS)
basis. It is similar to 802.x Flow Control or link-level flow
control (LFC).

2. Configuration

To configure Priority Flow Control, follow these steps:

Access the command line interface of the product.
Enter the “hw-module profile priority-flow-control”
command.
Specify the desired mode (buffer-internal or
buffer-extended).
Configure the PFC threshold values, if applicable.
Save the configuration.

2.1 Buffer-Internal Mode Configuration

In buffer-internal mode, the PFC threshold configurations are
deprecated in the pause command. Use the “hw-module profile
priority-flow-control” command to configure PFC threshold
values.

Restrictions and Guidelines for Buffer-Internal Mode

Configuration:

Insert restrictions and guidelines here…

2.2 Buffer-Extended Mode Configuration

In buffer-extended mode, in addition to configuring the PFC
threshold values, you are required to configure the performance
capacity or headroom values to achieve lossless behavior and
efficient use of bandwidth and resources.

Configuration Steps for Buffer-Extended Mode:

Access the command line interface of the product.
Enter the “hw-module profile priority-flow-control”
command.
Specify the desired mode as buffer-extended.
Configure the PFC threshold values.
Configure the performance capacity or headroom values.
Save the configuration.

FAQ

Q: What line cards support Priority Flow Control?

A: Priority Flow Control is supported on Cisco 8808 and Cisco
8812 Modular Chassis Line Cards.

Q: What modes are supported for Priority Flow Control?

A: Priority Flow Control is supported in both buffer-internal
and buffer-extended modes.

Q: How do I configure Priority Flow Control in buffer-internal

mode?

A: To configure Priority Flow Control in buffer-internal mode,
use the “hw-module profile priority-flow-control” command. Refer to
the user manual for detailed configuration steps.

Q: What is the purpose of configuring performance capacity or

headroom values in buffer-extended mode?

A: Configuring performance capacity or headroom values in
buffer-extended mode ensures better provisioning and workload
balance, resulting in lossless behavior, efficient use of
bandwidth, and resources.

Configure Priority Flow Control

· Priority Flow Control Overview, on page 1 · Configurable ECN Threshold and Maximum Marking Probability Values, on page 10 · Priority Flow Control Watchdog Overview, on page 15

Priority Flow Control Overview

Table 1: Feature History Table
Feature Name
Priority Flow Control on Cisco 8808 and Cisco 8812 Modular Chassis Line Cards

Release Information Release 7.5.3

Shortlink Priority Flow Control Release 7.3.3

Feature Description
Priority Flow Control is now supported on the following line card in the buffer-internal mode:
· 88-LC0-34H14FH
The feature is supported in the buffer-internal and buffer-extended modes on:
· 88-LC0-36FH
Apart from the buffer-external mode, support for this feature now extends to the buffer-internal mode on the following line cards:
· 88-LC0-36FH-M
· 8800-LC-48H
This feature and the hw-module profile priority-flow-control command are supported on 88-LC0-36FH line card.

Configure Priority Flow Control 1

Priority Flow Control Overview

Configure Priority Flow Control

Feature Name

Release Information

Priority Flow Control Support on Cisco 8800 36×400 GbE QSFP56-DD Line Cards (88-LC0-36FH-M)

Release 7.3.15

Priority Flow Control

Release 7.3.1

Feature Description
This feature and the hw-module profile priority-flow-control command are supported on 88-LC0-36FH-M and 8800-LC-48H line cards.
All previous functionalities and benefits of this feature are available on these line cards. However, the buffer-internal mode is not supported.
In addition, to use the buffer-extended mode on these line cards, you are required to configure the performance capacity or headroom values. This configuration requirement ensures that you can better provision and balance workloads to achieve lossless behavior, which in turn ensures efficient use of bandwidth and resources.
This feature and the hw-module profile priority-flow-control command are not supported.

Priority-based Flow Control (IEEE 802.1Qbb), which is also referred to as Class-based Flow Control (CBFC) or Per Priority Pause (PPP), is a mechanism that prevents frame loss that is due to congestion. PFC is similar to 802.x Flow Control (pause frames) or link-level flow control (LFC). However, PFC functions on a per class-of-service (CoS) basis.
During congestion, PFC sends a pause frame to indicate the CoS value to pause. A PFC pause frame contains a 2-octet timer value for each CoS that indicates the length of time to pause the traffic. The unit of time for the timer is specified in pause quanta. A quanta is the time required for transmitting 512 bits at the speed of the port. The range is from 0 through 65535 quanta.
PFC asks the peer to stop sending frames of a particular CoS value by sending a pause frame to a well-known multicast address. This pause frame is a one-hop frame and isn’t forwarded when received by the peer. When the congestion mitigates, the router stops sending the PFC frames to the upstream node.
You can configure PFC for each line card using the hw-module profile priority- flow-control command in one of two modes:
· buffer-internal
· buffer-extended

Configure Priority Flow Control 2

Configure Priority Flow Control

buffer-internal mode

Note PFC threshold configurations are deprecated in pause command. Use the hw- module profile priority-flow-control command to configure PFC threshold configurations.
Related Topics · Configure Priority Flow Control, on page 5
· Priority Flow Control Watchdog Overview, on page 15
buffer-internal mode
Use this mode if PFC-enabled devices aren’t more than 1 km apart. You can set values for pause-threshold, headroom (both related to PFC), and ECN for the traffic class using the hw-module profile priority-flow-control command in this mode. The buffer-internal configuration applies to all ports that the line card hosts, which mean that you can configure a set of these values per line card. The existing queue limit and ECN configuration in the queueing policy attached to the interface has no impact in this mode. The effective queue limit for this mode = pause-threshold + headroom (in bytes)
Restrictions and Guidelines
The following restrictions and guidelines apply while configuring the PFC threshold values using the buffer-internal mode.
· The PFC feature isn’t supported on fixed chassis systems. · Ensure that there’s no breakout configured on a chassis that has the PFC configured. Configuring PFC
and breakout on the same chassis may lead to unexpected behavior, including traffic loss. · The feature isn’t supported on bundle and non-bundle sub- interface queues. · The feature is supported on 40GbE, 100 GbE, and 400 GbE interfaces. · The feature isn’t supported in the 4xVOQ queueing mode. · The feature isn’t supported when sharing of VOQ counters is configured.
buffer-extended mode
Use this mode for PFC-enabled devices with long-haul connections. You can set the value for pause-threshold using the hw-module profile priority-flow- control command in this mode. You must, however, configure the queuing policy attached to the interface to set the ECN and queueing limits. The buffer- extended configuration applies to all ports that the line card hosts, which mean that you can configure a set of these values per line card.

Configure Priority Flow Control 3

Important Considerations

Configure Priority Flow Control

Configuration Guidelines · Important points while configuring the buffer- extended mode on 88-LC0-36FH-M line cards: · Apart from pause-threshold, you must also configure values for headroom. · The headroom value range is from 4 through 75000. · Specify pause-threshold and headroom values in units of kilobytes (KB) or megabytes (MB).
· Important points while configuring the buffer-extended mode on 8800-LC-48H line cards: · Configure values only for pause-threshold. Don’t configure headroom values. · Configure pause-threshold in units of milliseconds (ms) or microseconds. · Don’t use units of kilobytes (KB) or megabytes (MB) units, even though the CLI displays them as options. Only use units of milliseconds (ms) or microseconds.

(Also see Configure Priority Flow Control, on page 5)

Important Considerations
· If you configure PFC values in the buffer-internal mode, then the ECN value for the line card is derived from the buffer-internal configuration. If you configure PFC values in the buffer-extended mode, then the ECN value is derived from the policy map. (For details on the ECN feature, see Explicit Congestion Notification.)
· The buffer-internal and buffer-extended modes can’t coexist on the same line card.
· If you add or remove traffic-class actions on a line card, you must reload the line card.
· When using the buffer-internal mode, you can change values of the following parameters without having to reload the line card. However, if you add a new traffic class and configure these values for the first time on that traffic class, you must reload the line card for the values to come into effect.
· pause-threshold
· headroom
· ECN

· If you add or remove ECN configuration using the hw-module profile priority- flow-control command, you must reload the line card for the ECN changes to take effect.
· The PFC threshold value ranges for the buffer-internal mode are as follows.

Threshold

Configured (bytes)

pause (min)

307200

pause (max)

422400

headroom (min)

345600

headroom (max)

537600

Configure Priority Flow Control 4

Configure Priority Flow Control

Hardware Support for Priority Flow Control

Threshold ecn (min) ecn (max)

Configured (bytes) 153600 403200

· For a traffic-class, the ECN value must always be lesser than the configured pause-threshold value.
· The combined configured values for pause-threshold and headroom must not exceed 844800 bytes. Else, the configuration is rejected.
· The pause-threshold value range for buffer-extended mode is from 2 milliseconds (ms) through 25 ms and from 2000 microseconds through 25000 microseconds.

Hardware Support for Priority Flow Control
The table lists the PIDs that support PFC per release and the PFC mode in which the support is available.
Table 2: PFC Hardware Support Matrix

Release Release 7.3.15

PID · 88-LC0-36FH-M · 88-LC0-36FH

PFC Mode buffer-extended

Release 7.0.11

8800-LC-48H

buffer-internal

Configure Priority Flow Control
You can configure PFC to enable the no-drop behavior for the CoS as defined by the active network QoS policy.

Note The system enables shortlink PFC by default when you enable PFC.
Configuration Example You must accomplish the following to complete the PFC configuration: 1. Enable PFC at the interface level. 2. Configure ingress classification policy. 3. Attach the PFC policy to the interface. 4. Configure PFC threshold values using either the buffer-internal or buffer-extended mode.
Router# configure Router(config)# priority-flow-control mode on /Configure ingress classification policy/

Configure Priority Flow Control 5

Configure Priority Flow Control

Router(config)# class-map match-any prec7 Router(config-cmap)# match precedence Router(config)# class-map match-any tc7 /Ingress policy attach/ Router(config-if)# service-policy input QOS_marking /Egress policy attach/ Router(config-if)# service-policy output qos_queuing Router(config-pmap-c)# exit Router(config-pmap)# exit Router(config)#show controllers npu priority- flow-control location
Running Configuration
Interface Level interface HundredGigE0/0/0/0
priority-flow-control mode on
Ingress: class-map match-any prec7
match precedence 7
end-class-map
!
class-map match-any prec6
match precedence 6
end-class-map
!
class-map match-any prec5
match precedence 5
end-class-map
!
class-map match-any prec4
match precedence 4
end-class-map
!
class-map match-any prec3 match precedence 3 end-class-map ! class-map match- any prec2 match precedence 2 end-class-map ! class-map match-any prec1 match precedence 1 end-class-map ! ! policy-map QOS_MARKING

Configure Priority Flow Control 6

Configure Priority Flow Control
class prec7 set traffic-class 7 set qos-group 7
! class prec6
set traffic-class 6 set qos-group 6 ! class prec5 set traffic-class 5 set qos- group 5 ! class prec4 set traffic-class 4 set qos-group 4 ! class prec3 set traffic-class 3 set qos-group 3 ! class prec2 set traffic-class 2 set qos- group 2 ! class prec1 set traffic-class 1 set qos-group 1 ! class class- default set traffic-class 0 set qos-group 0 !
Egress: class-map match-any tc7
match traffic-class 7 end-class-map ! class-map match-any tc6 match traffic- class 6 end-class-map ! class-map match-any tc5 match traffic-class 5 end- class-map
!
class-map match-any tc4
match traffic-class 4
end-class-map
!
class-map match-any tc3
match traffic-class 3
end-class-map
!

Configure Priority Flow Control
Configure Priority Flow Control 7

Configure Priority Flow Control

class-map match-any tc2 match traffic-class 2 end-class-map ! class-map match- any tc1 match traffic-class 1 end-class-map ! policy-map QOS_QUEUING class tc7
priority level 1 shape average percent 10 ! class tc6 bandwidth remaining ratio 1 queue-limit 100 ms ! class tc5 bandwidth remaining ratio 20 queue- limit 100 ms ! class tc4 bandwidth remaining ratio 20 random-detect ecn random-detect 6144 bytes 100 mbytes ! class tc3 bandwidth remaining ratio 20 random-detect ecn random-detect 6144 bytes 100 mbytes ! class tc2 bandwidth remaining ratio 5 queue-limit 100 ms ! class tc1 bandwidth remaining ratio 5 queue-limit 100 ms ! class class-default bandwidth remaining ratio 20 queue- limit 100 ms ! [buffer-extended] hw-module profile priority-flow-control location 0/0/CPU0 buffer-extended traffic-class 3 pause-threshold 10 ms buffer-extended traffic-class 4 pause-threshold 10 ms
!
[buffer-internal] hw-module profile priority-flow-control location 0/1/CPU0 buffer-internal traffic-class 3 pause-threshold 403200 bytes headroom 441600 bytes ecn
224640 bytes buffer-internal traffic-class 4 pause-threshold 403200 bytes headroom 441600 bytes ecn
224640 bytes
Verification
Router#sh controllers hundredGigE0/0/0/22 priority-flow-control Priority flow control information for interface HundredGigE0/0/0/22:

Configure Priority Flow Control 8

Configure Priority Flow Control

Priority Flow Control:

Total Rx PFC Frames : 0

Total Tx PFC Frames : 313866

Rx Data Frames Dropped: 0

CoS Status Rx Frames

— —— ———-

0 on

0

1 on

0

2 on

0

3 on

0

4 on

0

5 on

0

6 on

0

7 on

0

/[buffer-internal]/ Router#show controllers hundredGigE 0/9/0/24 priority- flow-control

Priority flow control information for interface HundredGigE0/9/0/24:

Priority Flow Control:

Total Rx PFC Frames : 0

Total Tx PFC Frames : 313866

Rx Data Frames Dropped: 0

CoS Status Rx Frames

— —— ———-

0 on

0

1 on

0

2 on

0

3 on

0

4 on

0

5 on

0

6 on

0

7 on

0

…

/[buffer-internal, tc3 & tc4 configured. TC4 doesn’t have ECN]/

Router#show controllers npu priority-flow-control location

Location Id:

0/1/CPU0

PFC:

Enabled

PFC-Mode:

buffer-internal

TC Pause

Headroom

ECN

——————————————————-

3 86800 bytes

120000 bytes 76800 bytes

4 86800 bytes

120000 bytes Not-configured

/[buffer-extended PFC, tc3 & tc4 configured]/

Router#show controllers npu priority-flow-control location

Location Id:

0/1/CPU0

PFC:

Enabled

PFC-Mode:

buffer-extended

TC Pause

———–

3 5000 us

4 10000 us

/[No PFC]/

Router#show controllers npu priority-flow-control location

Location Id:

0/1/CPU0

PFC:

Disabled

Configure Priority Flow Control 9

Configurable ECN Threshold and Maximum Marking Probability Values

Configure Priority Flow Control

Related Topics · Priority Flow Control Overview, on page 1
Related Commands hw-module profile priority-flow-control location

Configurable ECN Threshold and Maximum Marking Probability Values

Table 3: Feature History Table

Feature Name

Release Information

Configurable ECN Threshold and Release 7.5.4 Maximum Marking Probability Values

Feature Description
While configuring PFC in the buffer-internal mode, you can now optimize congestion notification from the end router to the transmitting router, thus preventing the aggressive throttle of the source traffic. This optimization is possible because we’ve provided the flexibility to configure the minimum and maximum values for the ECN threshold and the maximum value for marking probability. With these values configured, the probability percentage marking is applied linearly, starting at the ECN minimum threshold till the ECN Max threshold.
Earlier releases fixed the maximum ECN marking probability at 100% at the maximum ECN threshold.
This functionality adds the following options to the hw-module profile priority-flow-control command:
· max-threshold
· probability-percentage

ECN Threshold and Maximum Marking Probability Values
So far, the maximum ECN marking probability was not configurable and was fixed at 100%. You couldn’t configure the ECN maximum threshold value either. Such an arrangement of preset marking probabilities and

Configure Priority Flow Control 10

Configure Priority Flow Control

Benefits of Configurable ECN Threshold and Maximum Marking Probability Values

fixed maximum threshold values meant traffic rates began to drop as a function of the queue length. Because of the linear increase in the ECN marking probability–and the consequent congestion signaling from the end host to the transmitting host–traffic rates could begin slowing down even if your link had the necessary bandwidth.
With this feature, you can configure the minimum and maximum ECN threshold values and, depending on your link capability and traffic requirements, configure a marking probability such that the number of packets being marked between the minimum and maximum thresholds is reduced.
The figure depicts the feature implementation visually, where:
· Pmax denotes the configurable maximum marking probability.
· The ECN mark probability is 1 from the maximum threshold to the tail drop threshold.
· Mark probability increases linearly from 0 at the minimum threshold to Pmax at the maximum threshold.
Figure 1: ECN Mark Probability vs. Queue Length (VOQ Fill Levels)

You configure the max-threshold and probability-percentage options for this feature in the hw-module profile priority-flow-control command. We have provided you the flexibility to choose one of these configuration options:
· Default max-threshold and probability-percentage values. · Configurable max- threshold and probability-percentage values. · PFC in the buffer-internal mode without the new options, as you did before Release 7.5.4.
See Configure ECN Threshold and Maximum Marking Probability Values, on page 13 for details.
Benefits of Configurable ECN Threshold and Maximum Marking Probability Values
A lower mark probability allows the end host to better identify the aggressor flow in the queue and only throttle it without impacting other well-behaved flows. This in turn leads to optimized and efficient deployment and usage of bandwidth.
Configure Priority Flow Control 11

ECN Threshold and Maximum Marking Probability Values: FAQs

Configure Priority Flow Control

ECN Threshold and Maximum Marking Probability Values: FAQs
· What if I set the ECN marking probability percentage to 100%? ECN Marking is linear once queue length exceeds the ECN minimum value. The tail drop comes into play when the average queue size reaches the marking probability percentage of 100%.
· How does traffic behave beyond my configured value of maximum ECN marking probability? Let us say you’ve set the maximum ECN marking probability to 5%. Any more increase in the average queue length beyond 5% shifts the marking probability to 100%, and Tail Drop and the FIFO Queue comes into effect.
Guidelines and Limitations
· This functionality is available only when you configure PFC in the buffer- internal mode. · If you configure PFC values in the buffer-internal mode, the ECN value for the line card is derived from
the buffer-internal configuration, unlike in the buffer-extended mode where the ECN value is derived from the policy map. · Line Cards that support this functionality:
· 88-LC0-36FH · 88-LC0-36FH-M
· The following interface types support this functionality: · Physical interfaces · Bundle interfaces · Subinterfaces · Bundle subinterfaces
· This functionality is supported for all interface speeds. · If you have a policy map with one or multiple classes with maximum ECN marking probability enabled,
you can: · Apply the map to any of the supported interface types. · Remove the map from any of the supported interface types. · Modify the map while you’re attaching it to multiple interfaces.
· The probability percentage option is supported only with random-detect ecn configured in the same class. Else, the policy is rejected when applied on an interface. (Not sure this is applicable. Please confirm.)
· Ensure that the probability percentage configuration is the same for all traffic classes because this is a device-level configuration.

Configure Priority Flow Control 12

Configure Priority Flow Control

Configure ECN Threshold and Maximum Marking Probability Values

Table 4: Useful Tips

If you…

…you must…

Want to switch from the default configuration mode 1. Use the no form of the hw-module profile

to the custom configuration mode

priority-flow-control command to remove the

OR

existing configuration.

Want to switch from the custom configuration mode 2. Configure the new mode and settings using the

to the default configuration

hw-module profile priority-flow-control

command.

3. Reload the line card

Configured PFC in buffer-internal mode without configuring the max-threshold and probability-percentage parameters, but now want to configure them

1. Configure the max-threshold and probability-percentage parameters using the hw-module profile priority-flow-control command.
2. Reload the line card.

Want to change the buffer-internal parameters in the Configure the buffer- internal parameters using the

custom mode

hw-module profile priority-flow-control command.

You needn’t reload the line card.

Want to continue configuring PFC in buffer-internal Configure the buffer- internal parameters using the

mode the way you did in releases prior toRelease hw-module profile priority- flow-control command,

7.5.4.

but ensure that you only configure values for

pause-threshold, headroom, and ecn. If you don’t

configure values for max-threshold, the router takes

the ecn value as the ECN maximum threshold value.

See Option 3 under Configure ECN Threshold and Maximum Marking Probability Values, on page 13 for details.

Configure ECN Threshold and Maximum Marking Probability Values
To configure the ECN maximum threshold and maximum probability values: 1. Enable PFC at the interface level.
Router(config)#int fourHundredGigE 0/6/0/1 Router(config-if)#priority-flow- control mode on
2. [Option 1: Default configuration mode] Configure PFC in buffer-internal mode with pre-defined buffer values enabled along with default max-threshold and probability-percentage values.
Router(config)#hw-module profile priority-flow-control location 0/6/0/1 Router (config-pfc-loc)#buffer-extended traffic-class 3 Router(config-pfc-loc )#buffer-extended traffic-class 4 Router(config-pfc-loc)#commit

Configure Priority Flow Control 13

Configure ECN Threshold and Maximum Marking Probability Values

Configure Priority Flow Control

[Option 2: Custom configuration mode] Configure PFC in buffer-internal mode with custom values for all parameters including max-threshold and probability- percentage.
Router(config)#hw-module profile priority-flow-control location 0/6/0/1 Router (config-pfc-loc)#buffer-internal traffic-class 3 pause-threshold 1574400 bytes headroom 1651200 bytes ecn 629760 bytes max-threshold 1416960 bytes probability-percentage 50 Router(config-pfc-loc)#buffer-internal traffic-class 4 pause-threshold 1574400 bytes headroom 1651200 bytes ecn 629760 bytes max- threshold 1416960 bytes probability-percentage 50 Router(config-pfc- loc)#commit
[Option 3: Without max-threshold and probability-percentage parameters] Based on your requirements, you can also configure PFC in buffer-internal mode without these parameters.
Router(config)#hw-module profile priority-flow-control location 0/6/0/1 Router (config-pfc-loc)#buffer-internal traffic-class 3 pause-threshold 1574400 bytes headroom 1651200 bytes ecn 629760 bytes Router(config-pfc-loc)#buffer-internal traffic-class 4 pause-threshold 1574400 bytes headroom 1651200 bytes ecn 629760 bytes Router(config-pfc-loc)#commit

Note See Useful Tips at ECN Threshold and Maximum Marking Probability Values: FAQs, on page 12 to know more about the nuances of switching between configuration modes.
Running Configuration
[Option 1: Default configuration mode] /Interface Level/ priority-flow- control mode on ! /Line card/ hw-module profile priority-flow-control location 0/6/0/1
buffer-extended traffic-class 3 buffer-extended traffic-class 4 !
[Option 2: Custom configuration mode] /Interface Level/ priority-flow- control mode on ! /Line card/
hw-module profile priority-flow-control location 0/6/0/1 buffer-internal traffic-class 3 pause-threshold 1574400 bytes headroom 1651200 bytes ecn
629760 bytes max-threshold 1416960 bytes probability-percentage 50 buffer- internal traffic-class 4 pause-threshold 1574400 bytes headroom 1651200 bytes ecn
629760 bytes max-threshold 1416960 bytes probability-percentage 50 !
[Option 3: Without max-threshold and probability-percentage parameters] /Interface Level/ priority-flow-control mode on ! /Line card/
buffer-internal traffic-class 3 pause-threshold 1574400 bytes headroom 1651200 bytes ecn 629760 bytes

Configure Priority Flow Control 14

Configure Priority Flow Control

Priority Flow Control Watchdog Overview

buffer-internal traffic-class 4 pause-threshold 1574400 bytes headroom 1651200 bytes ecn 629760 bytes !
Verification
[Option 1: Default configuration mode] Router#show controllers npu priority- flow-control location all

Location:

0/6/CPU0

PFC:

Enabled

PFC Mode:

buffer-internal

TC Pause-threshold Headroom

ECN

ECN-MAX

Prob-per

——————————————————————————

3 1574400 bytes

1651200 bytes 629760 bytes 1416960 bytes 5

4 1574400 bytes

1651200 bytes 629760 bytes 1416960 bytes 5

[Option 2: Custom configuration mode]

Router#show controllers npu priority-flow-control location all

Location:

0/6/CPU0

PFC:

Enabled

PFC Mode:

buffer-internal

TC Pause-threshold Headroom

ECN

ECN-MAX

Prob-per

——————————————————————————

3 1574400 bytes

1651200 bytes 629760 bytes 1416960 bytes 50

4 1574400 bytes

1651200 bytes 629760 bytes 1416960 bytes 50

[Option 3: Without max-threshold and probability-percentage parameters]

Router#show controllers npu priority-flow-control location all

Location:

0/6/CPU0

PFC:

Enabled

PFC Mode:

buffer-internal

TC Pause-threshold Headroom

ECN

ECN-MAX

Prob-per

——————————————————————————

3 1574400 bytes

1651200 bytes 629760 bytes not-configured not-configured

4 1574400 bytes

1651200 bytes 629760 bytes not-configured not-configured

Priority Flow Control Watchdog Overview
PFC Watchdog is a mechanism to identify any PFC storms (queue-stuck condition) in the network. It also prevents the PFC from propagating on the network and running in a loop. You can configure a PFC watchdog interval to detect whether packets in a no-drop queue are drained within a specified time period. When the time period is exceeded, all outgoing packets are dropped on interfaces that match the PFC queue that is not being drained.
This requires monitoring PFC receiving on each port and detecting ports seeing an unusual number of sustained pause frames. Once detected, the watchdog module can enforce several actions on such ports, which include generating a syslog message for network management systems, shutting down the queue, and autorestoring the queue (after the PFC storm stops).
Here’s how the PFC Watchdog works:
1. The Watchdog module monitors the PFC-enabled queues to determine the reception of an unusual amount of PFC pause frames in a given interval (Watchdog interval.)
2. Your hardware notifies the Watchdog module when too many PFC frames are received and traffic on the corresponding queues is halted for a time interval.

Configure Priority Flow Control 15

Configure a Priority Flow Control Watchdog Interval

Configure Priority Flow Control

3. On receiving such notifications, the Watchdog module starts the shutdown timer and moves the queue state to wait-to-shutdown state.
4. At regular intervals during the shutdown interval, the queue is checked for PFC frames and if the traffic in the queue is stuck. If the traffic isn’t stuck because the queue didn’t receive any PFC frames, the queue moves back to the monitored state.
5. If the traffic is stuck for a longer time and the shutdown-timer expires, the queue switches to a drop state and the PFC Watchdog begins to drop all packets.
6. At regular intervals, the Watchdog checks the queue for PFC frames and whether the traffic in the queue is still stuck. If traffic is stuck in the queue as PFC packets keep arriving, the queue remains in the drop or shutdown state.
7. When the traffic’s no longer stuck, the autorestore timer starts. At regular intervals, the module checks if the queue is stuck because of PFC frames.
8. If the queue receives PFC frames during the last autorestore interval, the auto-restore timer is reset upon expiry.
9. If the queue receives no PFC frames during the last autorestore interval, the Watchdog module restores the queue, and traffic resumes.
Related Topics · Priority Flow Control Overview, on page 1
Configure a Priority Flow Control Watchdog Interval
You can configure PFC Watchdog parameters (Watchdog interval, shutdown multiplier, auto-restore multiplier) at the global or interface levels. Note that:
· When global Watchdog mode is disabled or off, Watchdog is disabled on all interfaces. This condition is regardless of the interface level Watchdog mode settings.
· When global Watchdog mode is enabled or on, the interface level Watchdog mode configuration settings override the global Watchdog mode values.
· When you configure interface level Watchdog attributes such as interval, shutdown multiplier, and auto-restore multiplier, they override the global Watchdog attributes.
Note Configuring the PFC mode and its policies is a prerequisite for PFC Watchdog.
Configuration Example You can configure the Watchdog at the global or at the interface level.

Configure Priority Flow Control 16

Configure Priority Flow Control

Configure a Priority Flow Control Watchdog Interval

Note Watchdog is enabled by default, with system default values of:
Watchdog interval = 100 ms
Shutdown multiplier = 1
Auto-restart multiplier = 10
P/0/RP0/CPU0:ios#show controllers hundredGigE 0/2/0/0 priority-flow-control
Priority flow control information for interface HundredGigE0/2/0/0:
Priority flow control watchdog configuration: (D) : Default value U : Unconfigured ——————————————————————————-Configuration Item Global Interface Effective ——————————————————————————-PFC watchdog state : U U Enabled(D) Poll interval : U U 100(D) Shutdown multiplier : U U 1(D) Auto-restore multiplier : U U 10(D) RP/0/RP0/CPU0:ios#config RP/0/RP0/CPU0:ios(config)#priority-flow- control watchdog mode off RP/0/RP0/CPU0:ios(config)#commit
RP/0/RP0/CPU0:ios(config)#do show controllers hundredGigE 0/2/0/0 priority- flo$
Priority flow control information for interface HundredGigE0/2/0/0:
Priority flow control watchdog configuration: (D) : Default value U : Unconfigured ——————————————————————————-Configuration Item Global Interface Effective ——————————————————————————-PFC watchdog state : Disabled U Disabled Poll interval : U U 100(D) Shutdown multiplier : U U 1(D) Auto-restore multiplier : U U 10(D)
RP/0/RP0/CPU0:ios(config)#interface hundredGigE 0/2/0/0 priority-flow-control $ RP/0/RP0/CPU0:ios(config)#commit
RP/0/RP0/CPU0:ios(config)#do show controllers hundredGigE 0/2/0/0 priority- flo$
Priority flow control information for interface HundredGigE0/2/0/0:
Priority flow control watchdog configuration: (D) : Default value U : Unconfigured ——————————————————————————-Configuration Item Global Interface Effective ——————————————————————————-PFC watchdog state : Disabled Enabled Disabled Poll interval : U U 100(D) Shutdown multiplier : U U 1(D) Auto- restore multiplier : U U 10(D)
Configure Priority Flow Control 17

Configure a Priority Flow Control Watchdog Interval

Configure Priority Flow Control

RP/0/RP0/CPU0:ios(config)#interface hundredGigE 0/2/0/1 priority-flow-control $ RP/0/RP0/CPU0:ios(config)#commit
RP/0/RP0/CPU0:ios(config)#do show controllers hundredGigE 0/2/0/1 priority- flo$
Priority flow control information for interface HundredGigE0/2/0/1:
Priority flow control watchdog configuration: (D) : Default value U: Unconfigured ——————————————————————————-Configuration Item Global Interface Effective ——————————————————————————-PFC watchdog state : Enabled Disabled Disabled Poll interval : U U 100(D) Shutdown multiplier : U U 1(D) Auto- restore multiplier : U U 10(D)
Verification
To verify that the PFC Watchdog is enabled globally, run the sh run priority- flow-control watchdog mode command.
Router#sh run priority-flow-control watchdog mode priority-flow-control watchdog mode on
To verify your PFC Watchdog global configuration, run the priority-flow- control watchdog command.
Router#sh run priority-flow-control watchdog
priority-flow-control watchdog interval 100 priority-flow-control watchdog auto-restore-multiplier 2 priority-flow-control watchdog mode on priority- flow-control watchdog shutdown-multiplier 2
Related Topics
· Priority Flow Control Watchdog Overview, on page 15

Configure Priority Flow Control 18