The integrated service (IntServ) model is a multiple-service model that can accommodate diverse QoS requirements. This service model provides the most granularly differentiated QoS by identifying and guaranteeing definite QoS for each data flow.

In the IntServ model, an application must request service from the network before it sends data. IntServ signals the service request with the RSVP. All nodes receiving the request reserve resources as requested and maintain state information for the application flow.

The IntServ model demands high storage and processing capabilities because it requires all nodes along the transmission path to maintain resource state information for each flow. This model is suitable for small-sized or edge networks. However, it is not suitable for large-sized networks, for example, the core layer of the Internet, where billions of flows are present.

DiffServ model

The differentiated service (DiffServ) model is a multiple-service model that can meet diverse QoS requirements. It is easy to implement and extend. DiffServ does not signal the network to reserve resources before sending data, as IntServ does.

QoS techniques in a network

The QoS techniques include the following features:

· Traffic classification.

· Traffic policing.

The following section briefly introduces these QoS techniques.

All QoS techniques in this document are based on the DiffServ model.

Figure 1 Position of the QoS techniques in a network

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As shown in Figure 1, traffic classification and traffic policing mainly implement the following functions:

· Traffic classification—Uses match criteria to assign packets with the same characteristics to a traffic class. Based on traffic classes, you can provide differentiated services.

· Traffic policing—Polices flows and imposes penalties to prevent aggressive use of network resources. You can apply traffic policing to both incoming and outgoing traffic of a port.

QoS processing flow in a device

Figure 2 briefly describes how the QoS module processes traffic.

1. Traffic classifier identifies and classifies traffic for subsequent QoS actions.

2. The QoS module takes various QoS actions on classified traffic as configured, depending on the traffic processing phase and network status. For example, you can configure traffic policing for incoming traffic.

Figure 2 QoS processing flow

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QoS configuration approaches

You can configure QoS by using the MQC approach or non-MQC approach.

In the modular QoS configuration (MQC) approach, you configure QoS service parameters by using QoS policies. A QoS policy defines QoS actions to take on different classes of traffic and can be applied to an object (such as an interface) to control traffic.

In the non-MQC approach, you configure QoS service parameters without using a QoS policy. For example, you can use the rate limit feature to set a rate limit on an interface without using a QoS policy.

Some features support both approaches, but some support only one.

Configuring a QoS policy

About QoS policies

A QoS policy has the following components:

· Traffic class—Defines criteria to match packets.

· Traffic behavior—Defines QoS actions to take on matching packets.

By associating a traffic class with a traffic behavior, a QoS policy can perform the QoS actions on matching packets.

A QoS policy can have multiple class-behavior associations.

QoS policy tasks at a glance

To configure a QoS policy, perform the following tasks:

1. Defining a traffic class

2. Defining a traffic behavior

3. Defining a QoS policy

4. (Optional.) Configuring policy nesting

5. Applying the QoS policy

¡ Applying the QoS policy to an interface

¡ Applying the QoS policy globally

¡ Applying the QoS policy to a control plane

¡ Applying the QoS policy in control-plane management view

6. (Optional.) Setting the QoS policy-based traffic rate statistics collection period for an interface

Defining a traffic class

1. Enter system view.

system-view

2. Create a traffic class and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

3. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information, see the if-match command in ACL and QoS Command Reference.

Defining a traffic behavior

1. Enter system view.

system-view

2. Create a traffic behavior and enter traffic behavior view.

traffic behavior behavior-name

3. Configure an action in the traffic behavior.

By default, no action is configured for a traffic behavior.

For more information about configuring an action, see the subsequent chapters for traffic policing, traffic filtering, priority marking, and so on.

Defining a QoS policy

1. Enter system view.

system-view

2. Create a QoS policy and enter QoS policy view.

qos policy policy-name

3. Associate a traffic class with a traffic behavior to create a class-behavior association in the QoS policy.

classifier classifier-name behavior behavior-name [ insert-before before-classifier-name ]

By default, a traffic class is not associated with a traffic behavior.

Repeat this step to create more class-behavior associations.

Configuring policy nesting

About this task

A QoS policy configuration can contain a parent policy and a child policy.

Policy nesting allows you to create a child policy in the view of a traffic behavior of the parent policy.

You can nest a QoS policy in a traffic behavior to reclassify the traffic class associated with the behavior. Then the system performs the actions defined in the QoS policy on the reclassified traffic. The QoS policy nested in the traffic behavior is called the child policy. The QoS policy that nests the behavior is called the parent policy.

Prerequisites

Before configuring policy nesting, define a child policy (see "Defining a QoS policy").

Procedure

1. Enter system view.

system-view

2. Define a traffic class for the parent policy.

a. Create a traffic class for the parent policy and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

b. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information about configuring match criteria, see ACL and QoS Command Reference.

c. Return to system view.

quit

3. Nest the child QoS policy in the traffic behavior of the parent policy.

a. Create a traffic behavior for the parent policy and enter traffic behavior view.

traffic behavior behavior-name

b. Nest the child QoS policy.

traffic-policy policy-name

By default, policy nesting is not configured.

c. Return to system view.

quit

4. Create the parent policy and enter parent policy view.

qos policy policy-name

5. Associate the class with the behavior in the parent policy.

classifier classifier-name behavior behavior-name

By default, a class is not associated with a behavior.

Applying the QoS policy

Application destinations

You can apply a QoS policy to the following destinations:

· Interface—The QoS policy takes effect on the traffic sent or received on the interface.

· Control plane—The QoS policy takes effect on the traffic received on the control plane.

· Management interface control plane—The QoS policy takes effect on the traffic sent from the management interface to the control plane.

Restrictions and guidelines for applying a QoS policy

You can modify traffic classes, traffic behaviors, and class-behavior associations in a QoS policy even after it is applied (except that it is applied to a user profile). If a traffic class uses an ACL for traffic classification, you can delete or modify the ACL.

Applying the QoS policy to an interface

Restrictions and guidelines

A QoS policy can be applied to multiple interfaces. However, only one QoS policy can be applied to one direction (inbound or outbound) of an interface.

The QoS policy applied to the outgoing traffic on an interface does not regulate local packets. Local packets refer to critical protocol packets sent by the local system for operation maintenance. The most common local packets include link maintenance, RIP, and SSH packets.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Apply the QoS policy to the interface.

qos apply policy policy-name { inbound | outbound }

By default, no QoS policy is applied to an interface.

Applying the QoS policy globally

About this task

You can apply a QoS policy globally to the inbound or outbound direction of all ports.

Hardware and feature compatibility

Hardware	Feature compatibility
F5010, F5020, F5020-GM, F5030, F5030-6GW, F5040, F5060, F5080, F5000-AI-20, F5000-AI-40, F5000-V30, F5000-C, F5000-S, F5000-M, F5000-A	No
F1000-AI-20, F1000-AI-30, F1000-AI-50, F1000-AI-60, F1000-AI-70, F1000-AI-80, F1000-AI-90	No
F1003-L, F1005-L, F1010-L	No
F1005, F1010	No
F1020, F1020-GM, F1030, F1030-GM, F1050, F1060, F1070, F1070-GM, F1070-GM-L, F1080, F1090, F1000-V70	No
F1000-AK1110, F1000-AK1120, F1000-AK1130, F1000-AK1140	No
F1000-AK1212, F1000-AK1222, F1000-AK1232, F1000-AK1312, F1000-AK1322, F1000-AK1332	No
F1000-AK1414, F1000-AK1424, F1000-AK1434, F1000-AK1514, F1000-AK1524, F1000-AK1534, F1000-AK1614	No
F1000-AK108, F1000-AK109, F1000-AK110, F1000-AK115, F1000-AK120, F1000-AK125, F1000-AK710	No
F1000-AK130, F1000-AK135, F1000-AK140, F1000-AK145, F1000-AK150, F1000-AK155, F1000-AK160, F1000-AK165, F1000-AK170, F1000-AK175, F1000-AK180, F1000-AK185, F1000-GM-AK370, F1000-GM-AK380, F1000-AK711	No
LSU3FWCEA0, LSUM1FWCEAB0, LSX1FWCEA1	No
LSXM1FWDF1, LSUM1FWDEC0, IM-NGFWX-IV, LSQM1FWDSC0, LSWM1FWD0, LSPM6FWD, LSQM2FWDSC0	No
vFW1000, vFW2000	Yes

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Restrictions and guidelines

When you apply a QoS policy globally, the QoS policy is applied on all IRF member devices. If the hardware resources of an IRF member device are insufficient, applying a QoS policy globally might fail on the IRF member device. The system does not automatically roll back the QoS policy configuration already applied to other IRF member devices. To ensure consistency, you must use the undo qos apply policy global command to manually remove the QoS policy configuration applied to them.

Procedure

1. Enter system view.

system-view

2. Apply the QoS policy globally.

qos apply policy policy-name global { inbound | outbound }

By default, no QoS policy is applied globally.

Applying the QoS policy to a control plane

About this task

A device provides the user plane and the control plane.

· User plane—The units at the user plane are responsible for receiving, transmitting, and switching (forwarding) packets, such as various dedicated forwarding chips. They deliver super processing speeds and throughput.

· Control plane—The units at the control plane are processing units running most routing and switching protocols. They are responsible for protocol packet resolution and calculation, such as CPUs. Compared with user plane units, the control plane units allow for great packet processing flexibility but have lower throughput.

When the user plane receives packets that it cannot recognize or process, it transmits them to the control plane. If the transmission rate exceeds the processing capability of the control plane, the control plane will be busy handling undesired packets. As a result, the control plane will fail to handle legitimate packets correctly or timely. As a result, protocol performance is affected.

To address this problem, apply a QoS policy to the control plane to take QoS actions, such as traffic filtering or traffic policing, on inbound traffic. This ensures that the control plane can correctly receive, transmit, and process packets.

A predefined control plane QoS policy uses the protocol type or protocol group type to identify the type of packets sent to the control plane. You can use protocol types or protocol group types in if-match commands in traffic class view for traffic classification. Then you can reconfigure traffic behaviors for these traffic classes as required. You can use the display qos policy control-plane pre-defined command to display predefined control plane QoS policies.

Procedure

1. Enter system view.

system-view

2. Enter control plane view.

control-plane slot slot-number

3. Apply the QoS policy to the control plane.

qos apply policy policy-name inbound

By default, no QoS policy is applied to a control plane.

Applying the QoS policy in control-plane management view

About this task

If the rate of packets from the management interface to the control plane exceeds the processing capability, the control plane will fail to handle the packets correctly or timely. As a result, protocol performance is affected.

This feature allows you to rate limit the packets sent from the management interface to the control plane. This ensures that the control plane can correctly receive, transmit, and process packets from the management interface.

By default, a predefined QoS policy is applied in control-plane management view. To display the predefined QoS policy, use the display qos policy control-plane management pre-defined command. The predefined QoS policy uses the protocol type or protocol group type to identify the type of packets sent from the management interface to the control plane. You can use protocol types or protocol group types in if-match commands in traffic class view for traffic classification. Then, you can reconfigure traffic behaviors for these traffic classes as required.

Procedure

1. Enter system view.

system-view

2. Enter control-plane management view.

control-plane management

3. Apply the QoS policy.

qos apply policy policy-name inbound

By default, no QoS policy is applied in control-plane management view.

Setting the QoS policy-based traffic rate statistics collection period for an interface

About this task

You can enable collection of per-class traffic statistics over a period of time, including the average forwarding rate and drop rate. For example, if you set the statistics collection period to n minutes, the system performs the following operations:

· Collects traffic statistics for the most recent n minutes.

· Refreshes the statistics every n/5 minutes.

You can use the display qos policy interface command to view the collected traffic rate statistics.

A subinterface uses the statistics collection period configured on the main interface.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Set the traffic rate statistics collection period for the interface.

qos flow-interval interval

The default setting is 5 minutes.

Display and maintenance commands for QoS policies

Execute display commands in any view and reset commands in user view.

Task	Command
Display QoS policy configuration.	display qos policy { system-defined \| user-defined } [ policy-name [ classifier classifier-name ] ] [ slot slot-number ]
Display information about QoS policies applied to the control plane.	display qos policy control-plane slot slot-number
Display information about the predefined QoS policy applied in control-plane management view.	display qos policy control-plane management pre-defined
Display information about the predefined QoS policy applied to the control plane.	display qos policy control-plane pre-defined [ slot slot-number ]
Display information about QoS policies applied to interfaces.	display qos policy interface [ interface-type interface-number ] [ slot slot-number ] [ inbound \| outbound ]
Display traffic behavior configuration.	display traffic behavior { system-defined \| user-defined } [ behavior-name ] [ slot slot-number ]
Display traffic class configuration.	display traffic classifier { system-defined \| user-defined } [ classifier-name ] [ slot slot-number ]
Clear the statistics for the QoS policy applied to the control plane.	reset qos policy control-plane slot slot-number

Configuring traffic policing and rate limit

About traffic policing and rate limit

Traffic limit helps assign network resources (including bandwidth) and increase network performance. For example, you can configure a flow to use only the resources committed to it in a certain time range. This avoids network congestion caused by burst traffic.

Traffic policing controls the traffic rate and resource usage according to traffic specifications. You can use token buckets for evaluating traffic specifications.

Traffic evaluation and token buckets

Token bucket features

A token bucket is analogous to a container that holds a certain number of tokens. Each token represents a certain forwarding capacity. The system puts tokens into the bucket at a constant rate. When the token bucket is full, the extra tokens cause the token bucket to overflow.

Evaluating traffic with the token bucket

A token bucket mechanism evaluates traffic by looking at the number of tokens in the bucket. If the number of tokens in the bucket is enough for forwarding the packets:

· The traffic conforms to the specification (called conforming traffic).

· The corresponding tokens are taken away from the bucket.

Otherwise, the traffic does not conform to the specification (called excess traffic).

A token bucket has the following configurable parameters:

· Mean rate at which tokens are put into the bucket, which is the permitted average rate of traffic. It is usually set to the committed information rate (CIR).

· Burst size or the capacity of the token bucket. It is the maximum traffic size permitted in each burst. It is usually set to the committed burst size (CBS). The set burst size must be greater than the maximum packet size.

Each arriving packet is evaluated.

Complicated evaluation

You can set two token buckets, bucket C and bucket E, to evaluate traffic in a more complicated environment and achieve more policing flexibility. The following are main mechanisms used for complicated evaluation:

· Single rate two color—Uses one token bucket and the following parameters:

¡ CIR—Rate at which tokens are put into bucket C. It sets the average packet transmission or forwarding rate allowed by bucket C.

¡ CBS—Size of bucket C, which specifies the transient burst of traffic that bucket C can forward.

When a packet arrives, the following rules apply:

¡ If bucket C has enough tokens to forward the packet, the packet is colored green.

¡ Otherwise, the packet is colored red.

· Single rate three color—Uses two token buckets and the following parameters:

¡ CIR—Rate at which tokens are put into bucket C. It sets the average packet transmission or forwarding rate allowed by bucket C.

¡ CBS—Size of bucket C, which specifies the transient burst of traffic that bucket C can forward.

¡ EBS—Size of bucket E minus size of bucket C, which specifies the transient burst of traffic that bucket E can forward. The EBS cannot be 0. The size of E bucket is the sum of the CBS and EBS.

When a packet arrives, the following rules apply:

¡ If bucket C has enough tokens, the packet is colored green.

¡ If bucket C does not have enough tokens but bucket E has enough tokens, the packet is colored yellow.

¡ If neither bucket C nor bucket E has sufficient tokens, the packet is colored red.

· Two rate three color—Uses two token buckets and the following parameters:

¡ CIR—Rate at which tokens are put into bucket C. It sets the average packet transmission or forwarding rate allowed by bucket C.

¡ CBS—Size of bucket C, which specifies the transient burst of traffic that bucket C can forward.

¡ PIR—Rate at which tokens are put into bucket E, which specifies the average packet transmission or forwarding rate allowed by bucket E.

¡ EBS—Size of bucket E, which specifies the transient burst of traffic that bucket E can forward.

When a packet arrives, the following rules apply:

¡ If bucket C has enough tokens, the packet is colored green.

¡ If bucket C does not have enough tokens but bucket E has enough tokens, the packet is colored yellow.

¡ If neither bucket C nor bucket E has sufficient tokens, the packet is colored red.

Traffic policing

Traffic policing supports policing the inbound traffic and the outbound traffic.

A typical application of traffic policing is to supervise the specification of traffic entering a network and limit it within a reasonable range. Another application is to "discipline" the extra traffic to prevent aggressive use of network resources by an application. For example, you can limit bandwidth for HTTP packets to less than 50% of the total. If the traffic of a session exceeds the limit, traffic policing can drop the packets or reset the IP precedence of the packets. Figure 3 shows an example of policing outbound traffic on an interface.

Figure 3 Traffic policing

Traffic policing is widely used in policing traffic entering the ISP networks. It can classify the policed traffic and take predefined policing actions on each packet depending on the evaluation result:

· Forwarding the packet if the evaluation result is "conforming."

· Dropping the packet if the evaluation result is "excess."

· Forwarding the packet with its precedence re-marked if the evaluation result is "conforming."

· Delivering the packet to next-level traffic policing with its precedence re-marked if the evaluation result is "conforming."

· Entering the next-level policing (you can set multiple traffic policing levels, each focused on objects at different levels).

Configuring traffic policing

Traffic policing configuration approaches

You can configure traffic policing by using the MQC approach or the non-MQC approach. If both approaches are used, the MQC configuration takes effect.

You can configure the following types of traffic policing by using the non-MQC approach:

· CAR-list-based traffic policing.

· ACL-based traffic policing.

· Traffic policing for all traffic.

If traffic policing is configured by using both the MQC approach and non-MQC approach, the configuration in MQC approach takes effect.

Configuring traffic policing by using the MQC approach

Restrictions and guidelines

The device supports the following application destinations for traffic policing:

· Interface.

· Control plane.

· Control-plane management view.

Procedure

1. Enter system view.

system-view

2. Define a traffic class.

a. Create a traffic class and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

b. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information about the if-match command, see ACL and QoS Command Reference.

c. Return to system view.

quit

3. Define a traffic behavior.

a. Create a traffic behavior and enter traffic behavior view.

traffic behavior behavior-name

b. Configure a traffic policing action.

¡ In absolute value:

car cir committed-information-rate [ cbs committed-burst-size [ ebs excess-burst-size ] ] [ green action | red action | yellow action ] *

car cir committed-information-rate [ cbs committed-burst-size ] pir peak-information-rate [ ebs excess-burst-size ] [ green action | red action | yellow action ] *

¡ In percentage:

car cir percent cir-percent [ cbs cbs-time [ ebs ebs-time ] ] [ green action | red action | yellow action ] *

car cir percent cir-percent [ cbs cbs-time ] pir percent pir-percent [ ebs ebs-time ] [ green action | red action | yellow action ] *

By default, no traffic policing action is configured.

Support for this command depends on the device model. For more information, see the command reference.

c. Return to system view.

quit

4. Define a QoS policy.

a. Create a QoS policy and enter QoS policy view.

qos policy policy-name

b. Associate the traffic class with the traffic behavior in the QoS policy.

classifier classifier-name behavior behavior-name

By default, a traffic class is not associated with a traffic behavior.

c. Return to system view.

quit

5. Apply the QoS policy.

For more information, see "Applying the QoS policy."

By default, no QoS policy is applied.

Configuring CAR-list-based traffic policing

1. Enter system view.

system-view

2. Configure a CAR list.

qos carl carl-index { dscp dscp-list | mac mac-address | mpls-exp mpls-exp-value | precedence precedence-value | { destination-ip-address | source-ip-address } { range start-ip-address to end-ip-address | subnet ip-address mask-length } [ per-address [ shared-bandwidth ] ] }

3. Enter interface view.

interface interface-type interface-number

4. Apply a CAR-list-based CAR policy to the interface.

qos car { inbound | outbound } carl carl-index cir committed-information-rate [ cbs committed-burst-size [ ebs excess-burst-size ] ] [ green action | red action | yellow action ] *

qos car { inbound | outbound } carl carl-index cir committed-information-rate [ cbs committed-burst-size ] pir peak-information-rate [ ebs excess-burst-size ] [ green action | red action | yellow action ] *

By default, no CAR policy is applied to an interface.

Configuring ACL-based traffic policing

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure an ACL-based CAR policy on the interface.

qos car { inbound | outbound } acl [ ipv6 ] acl-number cir committed-information-rate [ cbs committed-burst-size [ ebs excess-burst-size ] ] [ green action | red action | yellow action ] *

qos car { inbound | outbound } acl [ ipv6 ] acl-number cir committed-information-rate [ cbs committed-burst-size ] pir peak-information-rate [ ebs excess-burst-size ] [ green action | red action | yellow action ] *

By default, no CAR policy is configured on an interface.

Configuring traffic policing for all traffic

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure a CAR policy for all traffic on the interface.

qos car { inbound | outbound } any cir committed-information-rate [ cbs committed-burst-size [ ebs excess-burst-size ] ] [ green action | red action | yellow action ] *

qos car { inbound | outbound } any cir committed-information-rate [ cbs committed-burst-size ] pir peak-information-rate [ ebs excess-burst-size ] [ green action | red action | yellow action ] *

By default, no CAR policy is configured on an interface.

Configuring the rate limit

Hardware compatibility with rate limit

Hardware	Feature compatibility
F5010, F5020, F5020-GM, F5030, F5030-6GW, F5040, F5060, F5080, F5000-AI-20, F5000-AI-40, F5000-V30, F5000-C, F5000-S, F5000-M, F5000-A	No
F1000-AI-20, F1000-AI-30, F1000-AI-50, F1000-AI-60, F1000-AI-70, F1000-AI-80, F1000-AI-90	No
F1003-L, F1005-L, F1010-L	No
F1005, F1010	No
F1020, F1020-GM, F1030, F1030-GM, F1050, F1060, F1070, F1070-GM, F1070-GM-L, F1080, F1090, F1000-V70	No
F1000-AK1110, F1000-AK1120, F1000-AK1130, F1000-AK1140	No
F1000-AK1212, F1000-AK1222, F1000-AK1232, F1000-AK1312, F1000-AK1322, F1000-AK1332	No
F1000-AK1414, F1000-AK1424, F1000-AK1434, F1000-AK1514, F1000-AK1524, F1000-AK1534, F1000-AK1614	No
F1000-AK108, F1000-AK109, F1000-AK110, F1000-AK115, F1000-AK120, F1000-AK125, F1000-AK710	No
F1000-AK130, F1000-AK135, F1000-AK140, F1000-AK145, F1000-AK150, F1000-AK155, F1000-AK160, F1000-AK165, F1000-AK170, F1000-AK175, F1000-AK180, F1000-AK185, F1000-GM-AK370, F1000-GM-AK380, F1000-AK711	No
LSU3FWCEA0, LSUM1FWCEAB0, LSX1FWCEA1	No
LSXM1FWDF1, LSUM1FWDEC0, IM-NGFWX-IV, LSQM1FWDSC0, LSWM1FWD0, LSPM6FWD, LSQM2FWDSC0	No
vFW1000, vFW2000	Yes

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Configuring the rate limit for an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure the rate limit for the interface.

qos lr { inbound | outbound } cir committed-information-rate [ cbs committed-burst-size [ ebs excess-burst-size ] ]

By default, no rate limit is configured on an interface.

Display and maintenance commands for traffic policing and rate limit

Execute display commands in any view.

Task	Command
Display CAR configuration and statistics on an interface.	display qos car interface [ interface-type interface-number ]
Display CAR list information.	display qos carl [ carl-index ] [ slot slot-number ]
Display traffic behavior configuration.	display traffic behavior user-defined [ behavior-name ] [ slot slot-number ]

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Configuring congestion management

About congestion management

Cause, negative results, and countermeasure of congestion

Congestion occurs on a link or node when traffic size exceeds the processing capability of the link or node. It is typical of a statistical multiplexing network and can be caused by link failures, insufficient resources, and various other causes. Figure 4 shows common congestion scenarios.

Figure 4 Traffic congestion causes

Congestion can introduce the following negative results:

· Increased delay and jitter during packet transmission.

· Decreased network throughput and resource use efficiency.

· Network resource (memory, in particular) exhaustion and system breakdown.

Congestion is unavoidable in switched networks or multiuser application environments. To improve the service performance of your network, implement congestion management policies.

For example, congestion management defines a resource dispatching policy to prioritize packets for forwarding when congestion occurs.

Congestion management methods

Congestion management involves queue creating, traffic classification, packet enqueuing, and queue scheduling.

Queuing is a common congestion management technique. It classifies traffic into queues and picks out packets from each queue by using an algorithm. Various queuing algorithms are available, and each addresses a particular network traffic problem. Your choice of algorithm significantly affects bandwidth assignment, delay, and jitter.

The device supports the following queuing mechanisms:

· FIFO.

· PQ.

· WFQ.

· CBQ.

· RTPQ.

FIFO

Figure 5 FIFO queuing

As shown in Figure 5, the first in first out (FIFO) uses a single queue and does not classify traffic or schedule queues. FIFO delivers packets in their arrival order. The packet that arrives earlier is scheduled first. The only concern of FIFO is queue length, which affects delay and packet loss rate. On a device, resources are assigned to packets depending on their arrival order and load status of the device. The best-effort service model uses FIFO queuing.

FIFO does not address congestion problems. If only one FIFO output/input queue exists on a port, you cannot ensure timely delivery of mission-critical or delay-sensitive traffic or smooth traffic jitter. If malicious traffic occupies bandwidth aggressively, the problems increase. To control congestion and prioritize forwarding of critical traffic, use other queue scheduling mechanisms, where multiple queues can be configured. Within each queue, FIFO is still used.

PQ

Figure 6 Priority queuing (PQ)

PQ is designed for mission-critical applications. Mission-critical applications require preferential treatment to reduce the response delay when congestion occurs. PQ can flexibly determine the order of forwarding packets by network protocol (for example, IP and IPX), incoming interface, packet length, source/destination address, and so on. Priority queuing classifies packets into four queues (top, middle, normal, and bottom queues, in descending priority order). By default, packets are assigned to the normal queue. Each of the four queues is a FIFO queue.

PQ schedules the four queues in descending order of priority. It sends packets in the queue with the highest priority first. When the queue with the highest priority is empty, it sends packets in the queue with the second highest priority. To make sure mission-critical packets are always served first, assign the mission-critical packets to the highest-priority queue. The common service packets that are assigned to the low-priority queues are transmitted when the high-priority queues are empty.

However, packets in the lower-priority queues cannot be transmitted when congestion occurs if packets exist in the higher-priority queues for a long time.

WFQ

Figure 7 Weighted fair queuing (WFQ)

FQ is designed to equally allocate network resources to reduce the delay and jitter of each traffic flow as much as possible. FQ follows these principles:

· Different queues have fair dispatching opportunities for delay balancing among flows.

· Short packets and long packets are equally scheduled. If long packets and short packets exist in queues, statistically the short packets are scheduled preferentially to reduce the jitter between packets.

WFQ considers weights when determining the queue scheduling order. Statistically, WFQ gives high-priority traffic more scheduling opportunities than low-priority traffic. To balance the delay of every traffic flow, WFQ performs the following operations:

· Automatically classifies traffic according to the "session" information of traffic.

· Attempts to provide as many queues as possible for traffic flows.

The session information of traffic includes the following information:

· Protocol type.

· TCP or UDP source/destination port numbers.

· Source/destination IP addresses.

· IP precedence bits in the ToS field.

When dequeuing packets, WFQ assigns the outgoing interface bandwidth to each traffic flow by precedence. The higher precedence value a traffic flow has, the more bandwidth it gets.

For example, five flows exist in the current interface with precedence 0, 1, 2, 3, and 4, respectively. The total bandwidth quota is the sum of all the (precedence value + 1)s, 1 + 2 + 3 + 4 + 5 = 15.

The bandwidth percentage assigned to each flow is (precedence value of the flow + 1)/total bandwidth quota. The bandwidth percentages for flows are 1/15, 2/15, 3/15, 4/15, and 5/15, respectively.

Because WFQ can balance the delay and jitter of each flow when congestion occurs, it is suitable for handling special situations. For example, WFQ is used in the assured forwarding (AF) services of the RSVP, and WFQ is used to schedule buffered packets in GTS.

CBQ

Figure 8 CBQ

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Class-based queuing (CBQ) extends WFQ by supporting user-defined classes. When network congestion occurs, CBQ uses user-defined traffic match criteria to enqueue packets. Before packets are enqueued, congestion avoidance actions, such as tail drop or WRED and bandwidth restriction check, are performed. When being dequeued, packets are scheduled by WFQ.

CBQ provides the following queues:

· Emergency queue—Enqueues emergent packets. The emergency queue is a FIFO queue without bandwidth restriction.

· Strict priority (SP) queuing—SP queuing is designed for mission-critical applications. Mission-critical applications require preferential treatment to reduce the response delay when congestion occurs. With SP queuing, CBQ can provide strict priority service. A maximum of 64 SP queues are supported.

· Low Latency Queuing (LLQ)—An EF queue. Because packets are fairly treated in CBQ, delay-sensitive flows like video and voice packets might not be transmitted timely. To solve this problem, LLQ combines PQ and CBQ to preferentially transmit delay-sensitive flows like voice packets. When defining traffic classes for LLQ, you can configure a class of packets to be preferentially transmitted. The packets of all priority classes are assigned to the same priority queue. Bandwidth restriction on each class of packets is checked before the packets are enqueued. During the dequeuing operation, packets in the priority queue are transmitted first. To reduce the delay of the other queues except the priority queue, LLQ assigns the maximum available bandwidth to each priority class. The bandwidth value polices traffic during congestion. When no congestion is present, a priority class can use more than the bandwidth assigned to it. During congestion, the packets of each priority class exceeding the assigned bandwidth are discarded.

· Bandwidth queuing (BQ)—An AF queue. The BQ provides guaranteed bandwidth for AF traffic, and schedules the AF classes proportionally. The system supports up to 64 AF queues.

· Default queue—A WFQ queue. The default queue transmits the BE traffic by using the remaining interface bandwidth.

The system matches packets with classification rules in the following order:

· Match packets with priority classes and then the other classes.

· Match packets with priority classes in the configuration order.

· Match packets with other classes in the configuration order.

· Match packets with classification rules in a class in the configuration order.

RTPQ

RTP queuing (RTPQ) is designed for delay-sensitive, real-time traffic (such as voice and video). You can assign voice or video packets to a high-priority queue by specifying a UDP port range as the match criterion. These packets are given strict priority service and are sent before packets in other queues are sent.

Figure 9 RTPQ

Congestion management technique comparison

Congestion management techniques offer different QoS capabilities to meet different application requirements, as explained in Table 1.

Table 1 Congestion management technique comparison

Type	Number of queues	Advantages	Disadvantages
FIFO	1	· No need to configure, easy to use. · Easy to operate, low delay.	· All packets are treated equally. The available bandwidth, delay and drop probability are determined by the arrival order of packets. · No restriction on traffic from connectionless protocols (protocols without any flow control mechanism, UDP, for example). This problem results in bandwidth loss for traffic of connection-oriented protocols (TCP, for example). · No delay guarantee for time-sensitive real-time applications, such as VoIP.
PQ	4	Provides strict priority service for mission-critical applications and guarantees low delay for real-time traffic, such as voice traffic.	· Need to configure, low processing speed. · If packets always exist in high-priority queues, packets in low-priority queues cannot be sent.
CQ	16	· Bandwidth assignment in percentages for different applications. · Bandwidth reassignment to increase bandwidth for each class when packets of certain classes are not present.	Need to configure, low processing speed.
WFQ	Configurable	· Easy to configure. · Bandwidth guarantee for packets from cooperative (interactive) sources (such as TCP packets). · Reduces jitter. · Reduces the delay for interactive applications with a small amount of data. · Bandwidth assignment based on traffic priority. · Automatic bandwidth reassignment to increase bandwidth for each class when the number of traffic classes decreases.	The processing speed is slower than FIFO.
CBQ	Configurable (0 to 64)	· Flexible traffic classification based on rules and differentiated queue scheduling mechanisms for EF, AF and BE services. · Highly precise bandwidth guarantee and queue scheduling on the basis of AF service weights for various AF services. · Absolute preferential queue scheduling for the EF service to meet the delay requirement of real-time data. · Overcomes the PQ disadvantage where some low-priority queues are not serviced by restricting the high-priority traffic. · WFQ scheduling for best-effort traffic (the default class).	The system overheads are large.
RTPQ	1	· Provides preferential treatment for real-time applications. · Performs traffic policing before enqueuing packets to prevent other queues from being starved.	Applicable only to delay-sensitive applications, such as voice and video.

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Restrictions: Hardware compatibility with congestion management

Hardware	Congestion management compatibility
F5010, F5020, F5020-GM, F5030, F5030-6GW, F5040, F5060, F5080, F5000-AI-20, F5000-AI-40, F5000-V30, F5000-C, F5000-S, F5000-M, F5000-A	No
F1000-AI-20, F1000-AI-30, F1000-AI-50, F1000-AI-60, F1000-AI-70, F1000-AI-80, F1000-AI-90	No
F1003-L, F1005-L, F1010-L	No
F1005, F1010	No
F1020, F1020-GM, F1030, F1030-GM, F1050, F1060, F1070, F1070-GM, F1070-GM-L, F1080, F1090, F1000-V70	No
F1000-AK1110, F1000-AK1120, F1000-AK1130, F1000-AK1140	No
F1000-AK1212, F1000-AK1222, F1000-AK1232, F1000-AK1312, F1000-AK1322, F1000-AK1332	No
F1000-AK1414, F1000-AK1424, F1000-AK1434, F1000-AK1514, F1000-AK1524, F1000-AK1534, F1000-AK1614	No
F1000-AK108, F1000-AK109, F1000-AK110, F1000-AK115, F1000-AK120, F1000-AK125, F1000-AK710	No
F1000-AK130, F1000-AK135, F1000-AK140, F1000-AK145, F1000-AK150, F1000-AK155, F1000-AK160, F1000-AK165, F1000-AK170, F1000-AK175, F1000-AK180, F1000-AK185, F1000-GM-AK370, F1000-GM-AK380, F1000-AK711	No
LSU3FWCEA0, LSUM1FWCEAB0, LSX1FWCEA1	No
LSXM1FWDF1, LSUM1FWDEC0, IM-NGFWX-IV, LSQM1FWDSC0, LSWM1FWD0, LSPM6FWD, LSQM2FWDSC0	No
vFW1000, vFW2000	Yes

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Setting the FIFO queue size

FIFO is the default queue scheduling mechanism for an interface, and the FIFO queue size is configurable. Queue length can affect delay and packet loss ratio.

Setting the FIFO queue size for an interface

Restrictions and guidelines

For the FIFO queuing feature to take effect on a subinterface, you must configure the rate limit on the subinterface.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Set the FIFO queue size for the interface.

qos fifo queue-length queue-length

The default setting is 75.

If the burst traffic is too heavy, increase the queue length to make queue scheduling more accurate.

Configuring PQ

About configuring PQ

You can define a set of assignment rules in a PQ list and then apply the PQ list to an interface. An assignment rule assigns a packet that meets a specific match criterion to a queue.

When a packet arrives, it is examined against match criteria in their configuration order.

· When a match is found, the packet is assigned to the corresponding queue, and the matching process ends.

· If no match is found, the packet is assigned to the default queue.

Restrictions and guidelines

· If you apply multiple PQ lists to an interface, the PQ list last applied takes effect.

· You must configure the rate limit for the PQ feature to take effect on the following interfaces:

¡ Tunnel interfaces.

¡ Subinterfaces.

¡ Layer 3 aggregate interfaces.

For information about the rate limit function, see "Configuring the rate limit."

Configuring PQ for an interface

1. Enter system view.

system-view

2. Configure a PQ list.

¡ Configure a protocol-based PQ list.

qos pql pql-index protocol { ip | ipv6 } [ queue-key key-value ] queue { bottom | middle | normal | top }

¡ Configure an interface-based PQ list.

qos pql pql-index inbound-interface interface-type interface-number queue { bottom | middle | normal | top }

¡ Configure a local-precedence-based PQ list.

qos pql pql-index local-precedence local-precedence-list queue { bottom | middle | normal | top }

3. (Optional.) Configure a queue as the default queue for the PQ list.

qos pql pql-index default-queue { bottom | middle | normal | top }

By default, the normal queue is the default queue.

The default queue enqueues packets that do not match any criteria in a PQ list.

4. (Optional.) Set the maximum queue length for a queue in the PQ list.

qos pql pql-index queue { bottom | middle | normal | top } queue-length queue-length

By default:

¡ The maximum top queue length is 20.

¡ The maximum middle queue length is 40.

¡ The maximum normal queue length is 60.

¡ The maximum bottom queue length is 80.

5. Enter interface view.

interface interface-type interface-number

6. Apply the PQ list to the interface.

qos pq pql pql-index

By default, FIFO is used.

Configuring WFQ

Restrictions and guidelines

· You must configure the rate limit for the WFQ feature to take effect on the following interfaces:

¡ Tunnel interfaces.

¡ Subinterfaces.

¡ Layer 3 aggregate interfaces.

For information about the rate limit function, see "Configuring the rate limit."

· On an interface that is not enabled with WFQ, the qos wfq command can enable WFQ and configure WFQ-related parameters. If WFQ has been enabled for the interface, the qos wfq command can modify the WFQ-related parameters.

Configuring WFQ for an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure WFQ for the interface.

qos wfq [ dscp | precedence ] [ queue-length max-queue-length | queue-number total-queue-number ] *

By default, WFQ is not configured for an interface.

Configuring CBQ

About CBQ

The system predefines the following classes, traffic behaviors, and policies:

Predefined classes

The system predefines some classes and defines general rules for the classes. You can use the following predefined classes when defining a policy:

· default-class—Matches the default traffic.

· ef, af1, af2, af3, af4—Matches IP DSCP value ef, af1, af2, af3, af4, respectively.

· ip-prec0, ip-prec1, …ip-prec7—Matches IP precedence value 0, 1, …7, respectively.

· mpls-exp0, mpls-exp1, …mpls-exp7—Matches MPLS EXP value 0, 1, …7, respectively.

Predefined traffic behaviors

The system predefines some traffic behaviors and defines QoS features for the behaviors.

· ef—Assigns a class of packets to the EF queue and assigns 20% of the available interface or PVC bandwidth to the class of packets.

· af—Assigns a class of packets to the AF queue and assigns 20% of the available interface or PVC bandwidth to the class of packets.

· be—Defines no features.

· be-flow-based—Assigns a class of packets to a WFQ queue and specifies the drop policy as WRED. By default, 256 WFQ queues exist, and WRED is an IP precedence-based drop policy.

Predefined QoS policy

The system predefines a QoS policy, specifies a predefined class for the policy and associates a predefined behavior with the class. The policy is named default, with the default CBQ action.

The policy default is defined as follows:

· Associates the predefined class ef with the predefined traffic behavior ef.

· Associates predefined classes af1 through af4 with the predefined traffic behavior af.

· Associates the predefined class default-class with the predefined traffic behavior be.

Restrictions and guidelines for CBQ configuration

When you configure CBQ, follow these restrictions and guidelines:

· Only one of the following queuing actions can be configured in the same behavior:

¡ AF.

¡ EF.

¡ SP.

¡ WFQ.

· To configure queue af for multiple classes of a policy, you must configure them in one of the following units:

¡ Bandwidth in kbps.

¡ Percentage of the available bandwidth.

¡ Percentage of the remaining bandwidth.

· In a QoS policy, if AF is configured in percentage of the remaining bandwidth, EF can be configured in absolute value or in percentage.

· In a QoS policy, if AF is configured in absolute value or in percentage, EF can be configured in absolute value or in percentage.

· You must configure the rate limit on a subinterface for the CBQ feature to take effect on the subinterface.

· The default class cannot be associated with a traffic behavior including EF or SP.

· You can associate the traffic behavior that contains a WFQ action only with the default class.

· RTPQ and CBQ are mutually exclusive. CBQ can use LLQ to provide priority service for real-time traffic.

Configure AF and the minimum guaranteed bandwidth

Restrictions and guidelines

· The undo queue af command also cancels the queue-length command configuration and all WRED-related settings.

· The wred and queue-length commands are mutually exclusive in a traffic behavior.

· The undo wred [ dscp | ip-precedence ] command also cancels all other WRED-related settings.

· A QoS policy that contains an AF action can only be applied to the outbound direction of an interface.

Procedure

1. Enter system view.

system-view

2. Define a traffic class.

a. Create a traffic class and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

b. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information about configuring match criteria, see ACL and QoS Command Reference.

c. Return to system view.

quit

3. Define a traffic behavior.

a. Create a traffic behavior and enter traffic behavior view.

traffic behavior behavior-name

b. Configure AF and the minimum guaranteed bandwidth.

queue af bandwidth { bandwidth | pct percentage | remaining-pct remaining-percentage }

By default, AF is not configured.

c. (Optional.) Set the maximum queue size.

queue-length queue-length

The default setting is 64 packets.

If the burst traffic is too heavy, increase the queue length to make queue scheduling more accurate.

d. Enable WRED.

wred [ dscp | ip-precedence ]

By default, WRED is not enabled.

e. Set the exponent for WRED to calculate the average queue size.

wred weighting-constant exponent

The default setting is 9.

f. Set the lower limit, upper limit, and drop probability denominator for a DSCP value in WRED

wred dscp dscp-value low-limit low-limit high-limit high-limit [ discard-probability discard-prob ]

By default, the lower limit is 10, the upper limit is 30, and the drop probability denominator is 10.

You must enable DSCP-based WRED by using the wred dscp command before you configure this command.

g. Set the lower limit, upper limit, and drop probability denominator for an IP precedence in WRED.

wred ip-precedence precedence low-limit low-limit high-limit high-limit [ discard-probability discard-prob ]

By default, the lower limit is 10, the upper limit is 30, and the drop probability denominator is 10.

h. Return to system view.

quit

4. Define a QoS policy.

a. Create a QoS policy and enter QoS policy view.

qos policy policy-name

b. Associate a traffic behavior with a class in the policy.

classifier classifier-name behavior behavior-name

By default, a class is not associated with a behavior.

c. Return to system view.

quit

5. Apply the QoS policy.

For more information, see "Applying the QoS policy."

By default, no QoS policy is applied.

Configuring EF and the maximum bandwidth

Restrictions and guidelines

· A QoS policy that contains an EF action can only be applied to the outbound direction of an interface.

Procedure

1. Enter system view.

system-view

2. Define a traffic class.

a. Create a traffic class and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

b. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information about configuring match criteria, see ACL and QoS Command Reference.

c. Return to system view.

quit

3. Define a traffic behavior.

a. Create a traffic behavior and enter traffic behavior view.

traffic behavior behavior-name

b. Configure EF and the maximum bandwidth.

queue ef bandwidth { bandwidth [ cbs burst ] | pct percentage [ cbs-ratio ratio] }

By default, EF is not configured.

c. (Optional.) Set the maximum queue size.

queue-length queue-length

The default setting is 64 packets.

If the burst traffic is too heavy, increase the queue length to make queue scheduling more accurate.

d. Return to system view.

quit

4. Define a QoS policy.

a. Create a QoS policy and enter QoS policy view.

qos policy policy-name

b. Associate a traffic behavior with a class in the policy.

classifier classifier-name behavior behavior-name

By default, a class is not associated with a behavior.

c. Return to system view.

quit

5. Apply the QoS policy.

For more information, see "Applying the QoS policy."

By default, no QoS policy is applied.

Configuring SP

Restrictions and guidelines

A QoS policy that contains an SP action can be applied to the outbound direction of an interface.

Procedure

1. Enter system view.

system-view

2. Define a traffic class.

a. Create a traffic class and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

b. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information about configuring match criteria, see ACL and QoS Command Reference.

c. Return to system view.

quit

3. Define a traffic behavior.

a. Create a traffic behavior and enter traffic behavior view.

traffic behavior behavior-name

b. Configure SP.

queue sp

By default, SP is not configured.

c. Return to system view.

quit

4. Define a QoS policy.

a. Create a QoS policy and enter QoS policy view.

qos policy policy-name

b. Associate a traffic behavior with a class in the policy.

classifier classifier-name behavior behavior-name

By default, a class is not associated with a behavior.

c. Return to system view.

quit

5. Apply the QoS policy.

For more information, see "Applying the QoS policy."

By default, no QoS policy is applied.

Configuring WFQ

Restrictions and guidelines

· The undo queue wfq command also cancels the queue-length command configuration and all WRED-related settings.

· The wred and queue-length commands are mutually exclusive in a traffic behavior.

· The undo wred [ dscp | ip-precedence ] command also cancels all other WRED-related settings.

· A QoS policy that contains a WFQ action can only be applied to the outbound direction of an interface.

Procedure

1. Enter system view.

system-view

2. Define a traffic class.

a. Create a traffic class and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

b. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information about configuring match criteria, see ACL and QoS Command Reference.

c. Return to system view.

quit

3. Define a traffic behavior.

a. Create a traffic behavior and enter traffic behavior view.

traffic behavior behavior-name

b. Configure WFQ.

queue wfq [ queue-number total-queue-number ]

By default, WFQ is not configured.

c. Set the maximum queue size.

queue-length queue-length

The default setting is 64 packets.

If the burst traffic is too heavy, increase the queue length to make queue scheduling more accurate.

d. Enable WRED.

wred [ dscp | ip-precedence ]

By default, WRED is not enabled.

e. Set the exponent for WRED to calculate the average queue size

wred weighting-constant exponent

The default setting is 9.

f. Set the lower limit, upper limit, and drop probability denominator for a DSCP value in WRED

wred dscp dscp-value low-limit low-limit high-limit high-limit [ discard-probability discard-prob ]

By default, the lower limit is 10, the upper limit is 30, and the drop probability denominator is 10.

g. Set the lower limit, upper limit, and drop probability denominator for an IP precedence in WRED.

wred ip-precedence precedence low-limit low-limit high-limit high-limit [ discard-probability discard-prob ]

By default, the lower limit is 10, the upper limit is 30, and the drop probability denominator is 10.

h. Return to system view.

quit

4. Define a QoS policy.

a. Create a QoS policy and enter QoS policy view.

qos policy policy-name

b. Associate a traffic behavior with a class in the policy.

classifier classifier-name behavior behavior-name

By default, a class is not associated with a behavior.

c. Return to system view.

quit

5. Apply the QoS policy.

For more information, see "Applying the QoS policy."

By default, no QoS policy is applied.

Setting the maximum available interface bandwidth

Restrictions and guidelines

· The maximum available interface bandwidth refers to the maximum interface bandwidth used for bandwidth check when CBQ enqueues packets. It is not the actual bandwidth of the physical interface.

· As a best practice, set the maximum available interface bandwidth to be smaller than the actual available bandwidth of the physical interface or logical link.

· On subinterfaces, you must configure the bandwidth command to provide base bandwidth for CBQ calculation.

¡ If no maximum available bandwidth is set for an interface, the following bandwidth is used for CBQ calculation:

¡ The actual baud rate or rate if the interface is a physical one.

¡ 0 kbps if the interface is a virtual interface, tunnel interface or Layer 3 aggregate interface.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Set the maximum available bandwidth of the interface.

bandwidth bandwidth-value

For more information about this command, see Interface Command Reference.

Setting the maximum reserved bandwidth as a percentage of available bandwidth for an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Set the maximum reserved bandwidth as a percentage of available bandwidth.

qos reserved-bandwidth pct percent

The default setting is 80.

Typically, the maximum reserved bandwidth should not be greater than 80% of available bandwidth. As a best practice, use the default setting.

Configuring RTPQ

Restrictions and guidelines

· RTPQ and CBQ are mutually exclusive.

· You must configure the rate limit for the RTPQ feature to take effect on the following interfaces:

¡ Tunnel interfaces.

¡ Subinterfaces.

¡ Layer 3 aggregate interfaces.

For information about the rate limit function, see "Configuring the rate limit."

Configuring RTPQ on an interface

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Configure RTPQ.

qos rtpq start-port first-rtp-port-number end-port last-rtp-port-number bandwidth bandwidth [ cbs cbs ]

By default, RTPQ is not configured.

Displaying and maintaining congestion management

Execute display commands in any view and reset commands in user view.

Task	Command
Display QoS policy configuration.	display qos policy { system-defined \| user-defined } [ policy-name [ classifier classifier-name ] ]
Display information about QoS policies applied to interfaces.	display qos policy interface [ interface-type interface-number ] [ slot slot-number ] [ inbound \| outbound ]
Display the configuration of PQ lists.	display qos pql [ pql-index ]
Display the CBQ configuration and statistics for interfaces.	display qos queue cbq interface [ interface-type interface-number ]
Display the FIFO configuration and statistics for interfaces.	display qos queue fifo interface [ interface-type interface-number ]
Display queuing configuration and statistics for interfaces.	display qos queue interface [ interface-type interface-number ]
Display the PQ configuration and statistics for interfaces.	display qos queue pq interface [ interface-type interface-number ]
Display RTPQ configuration and statistics for interfaces.	display qos queue rtpq interface [ interface-type interface-number ]
Display the WFQ configuration and statistics for interfaces.	display qos queue wfq { interface [ interface-type interface-number ] \| l2vpn-pw [ peer ip-address pw-id pw-id ] }
Display traffic behavior configuration.	display traffic behavior { system-defined \| user-defined } [ behavior-name ]
Display class configuration.	display traffic classifier { system-defined \| user-defined } [ classifier-name ]

Configuring congestion avoidance

About congestion avoidance

Avoiding congestion before it occurs is a proactive approach to improving network performance. As a flow control mechanism, congestion avoidance:

· Actively monitors network resources (such as queues and memory buffers).

· Drops packets when congestion is expected to occur or deteriorate.

When dropping packets from a source end, congestion avoidance cooperates with the flow control mechanism at the source end to regulate the network traffic size. The combination of the local packet drop policy and the source-end flow control mechanism implements the following functions:

· Maximizes throughput and network use efficiency.

· Minimizes packet loss and delay.

Tail drop

Congestion management techniques drop all packets that are arriving at a full queue. This tail drop mechanism results in global TCP synchronization. If packets from multiple TCP connections are dropped, these TCP connections go into the state of congestion avoidance and slow start to reduce traffic. However, traffic peak occurs later. Consequently, the network traffic jitters all the time.

RED and WRED

You can use Random Early Detection (RED) or Weighted Random Early Detection (WRED) to avoid global TCP synchronization.

Both RED and WRED avoid global TCP synchronization by randomly dropping packets. When the sending rates of some TCP sessions slow down after their packets are dropped, other TCP sessions remain at high sending rates. Link bandwidth is efficiently used, because TCP sessions at high sending rates always exist.

The RED or WRED algorithm sets an upper threshold and lower threshold for each queue, and processes the packets in a queue as follows:

· When the queue size is shorter than the lower threshold, no packet is dropped.

· When the queue size reaches the upper threshold, all subsequent packets are dropped.

· When the queue size is between the lower threshold and the upper threshold, the received packets are dropped at random. The drop probability in a queue increases along with the queue size under the maximum drop probability.

If the current queue size is compared with the upper threshold and lower threshold to determine the drop policy, burst traffic is not fairly treated. To solve this problem, WRED compares the average queue size with the upper threshold and lower threshold to determine the drop probability.

The average queue size reflects the queue size change trend but is not sensitive to burst queue size changes, and burst traffic can be fairly treated.

When WFQ queuing is used, you can set the following parameters for packets with different precedence values to provide differentiated drop policies:

· Exponent for average queue size calculation.

· Upper threshold.

· Lower threshold.

· Drop probability.

When FIFO, PQ, or CQ is used, you can set the following parameters for each queue to provide differentiated drop policies:

· Exponent for average queue size calculation.

· Upper threshold.

· Lower threshold.

· Drop probability.

Relationship between WRED and queuing mechanisms

Figure 10 Relationship between WRED and queuing mechanisms

Through combining WRED with WFQ, the flow-based WRED can be realized. Each flow has its own queue after classification.

· A flow with a smaller queue size has a lower packet drop probability.

· A flow with a larger queue size has a higher packet drop probability.

In this way, the benefits of the flow with a smaller queue size are protected.

WRED configuration approaches

You can configure WRED parameters on an interface and enable WRED.

WRED parameters

Determine the following parameters before configuring WRED:

· Upper threshold and lower threshold—When the average queue size is smaller than the lower threshold, packets are not dropped. When the average queue size is between the lower threshold and the upper threshold, the packets are dropped at random. The longer the queue, the higher the drop probability. When the average queue size exceeds the upper threshold, subsequent packets are dropped.

· Drop precedence—A parameter used for packet drop. The value 0 corresponds to green packets, the value 1 corresponds to yellow packets, and the value 2 corresponds to red packets. Red packets are dropped preferentially.

· Exponent for average queue size calculation—The greater the exponent, the less sensitive the average queue size is to real-time queue size changes. The formula for calculating the average queue size is:

Average queue size = ( previous average queue size x (1 – 2–n) ) + (current queue size x 2–n), where n is the exponent.

· Denominator for drop probability calculation—The greater the denominator, the smaller the calculated drop probability.

Configuring WRED parameters on an interface

Restrictions and guidelines

To enable WRED on an interface, you must first enable WFQ on the interface.

Procedure

1. Enter system view.

system-view

2. Enter interface view.

interface interface-type interface-number

3. Enable WRED.

qos wred [ dscp | ip-precedence ] enable

By default, tail drop is adopted.

4. (Optional.) Set the WRED exponent for average queue size calculation.

qos wred weighting-constant exponent

The default setting is 9.

5. (Optional.) Set the drop-related parameters for a precedence value.

qos wred { ip-precedence ip-precedence | dscp dscp-value } low-limit low-limit high-limit high-limit discard-probability discard-prob

By default, the lower limit is 10, the upper limit is 30, and the drop probability denominator is 10.

Repeat this command to configure more precedence values.

Restrictions: Hardware compatibility with congestion avoidance

Hardware	Congestion avoidance compatibility
F5010, F5020, F5020-GM, F5030, F5030-6GW, F5040, F5060, F5080, F5000-AI-20, F5000-AI-40, F5000-V30, F5000-C, F5000-S, F5000-M, F5000-A	No
F1000-AI-20, F1000-AI-30, F1000-AI-50, F1000-AI-60, F1000-AI-70, F1000-AI-80, F1000-AI-90	No
F1003-L, F1005-L, F1010-L	No
F1005, F1010	No
F1020, F1020-GM, F1030, F1030-GM, F1050, F1060, F1070, F1070-GM, F1070-GM-L, F1080, F1090, F1000-V70	No
F1000-AK1110, F1000-AK1120, F1000-AK1130, F1000-AK1140	No
F1000-AK1212, F1000-AK1222, F1000-AK1232, F1000-AK1312, F1000-AK1322, F1000-AK1332	No
F1000-AK1414, F1000-AK1424, F1000-AK1434, F1000-AK1514, F1000-AK1524, F1000-AK1534, F1000-AK1614	No
F1000-AK108, F1000-AK109, F1000-AK110, F1000-AK115, F1000-AK120, F1000-AK125, F1000-AK710	No
F1000-AK130, F1000-AK135, F1000-AK140, F1000-AK145, F1000-AK150, F1000-AK155, F1000-AK160, F1000-AK165, F1000-AK170, F1000-AK175, F1000-AK180, F1000-AK185, F1000-GM-AK370, F1000-GM-AK380, F1000-AK711	No
LSU3FWCEA0, LSUM1FWCEAB0, LSX1FWCEA1	No
LSXM1FWDF1, LSUM1FWDEC0, IM-NGFWX-IV, LSQM1FWDSC0, LSWM1FWD0, LSPM6FWD, LSQM2FWDSC0	No
vFW1000, vFW2000	Yes

‌

Display and maintenance commands for WRED

Execute display commands in any view.

Task	Command
Display WRED configuration and statistics for an interface.	display qos wred interface [ interface-type interface-number ]

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Configuring traffic filtering

About traffic filtering

You can filter in or filter out traffic of a class by associating the class with a traffic filtering action. For example, you can filter packets sourced from an IP address according to network status.

Restrictions and guidelines: Traffic filtering configuration

The device supports applying traffic filtering to an interface or control plane.

Procedure

1. Enter system view.

system-view

2. Define a traffic class.

a. Create a traffic class and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

b. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information about configuring match criteria, see ACL and QoS Command Reference.

c. Return to system view.

quit

3. Define a traffic behavior.

a. Create a traffic behavior and enter traffic behavior view.

traffic behavior behavior-name

b. Configure the traffic filtering action.

filter { deny | permit }

By default, no traffic filtering action is configured.

If a traffic behavior has the filter deny action, all other actions in the traffic behavior except class-based accounting do not take effect.

c. Return to system view.

quit

4. Define a QoS policy.

a. Create a QoS policy and enter QoS policy view.

qos policy policy-name

b. Associate the traffic class with the traffic behavior in the QoS policy.

classifier classifier-name behavior behavior-name

By default, a traffic class is not associated with a traffic behavior.

c. Return to system view.

quit

5. Apply the QoS policy.

For more information, see "Applying the QoS policy."

By default, no QoS policy is applied.

6. (Optional.) Display the traffic filtering configuration.

display traffic behavior user-defined [ behavior-name ] [ slot slot-number ]

This command is available in any view.

Configuring priority marking

About priority marking

Priority marking sets the priority fields or flag bits of packets to modify the priority of packets. For example, you can use priority marking to set IP precedence or DSCP for a class of IP packets to control the forwarding of these packets.

To configure priority marking to set the priority fields or flag bits for a class of packets, perform the following tasks:

1. Configure a traffic behavior with a priority marking action.

2. Associate the traffic class with the traffic behavior.

Configuring priority marking

Restrictions and guidelines

The device supports applying priority marking to an interface or control plane.

Procedure

1. Enter system view.

system-view

2. Define a traffic class.

a. Create a traffic class and enter traffic class view.

traffic classifier classifier-name [ operator { and | or } ]

b. Configure a match criterion.

if-match [ not ] match-criteria

By default, no match criterion is configured.

For more information about the if-match command, see ACL and QoS Command Reference.

c. Return to system view.

quit

3. Define a traffic behavior.

a. Create a traffic behavior and enter traffic behavior view.

traffic behavior behavior-name

b. Configure a priority marking action.

For configurable priority marking actions, see the remark commands in ACL and QoS Command Reference.

c. Return to system view.

quit

4. Define a QoS policy.

a. Create a QoS policy and enter QoS policy view.

qos policy policy-name

b. Associate the traffic class with the traffic behavior in the QoS policy.

classifier classifier-name behavior behavior-name

By default, a traffic class is not associated with a traffic behavior.

c. Return to system view.

quit

5. Apply the QoS policy.

For more information, see "Applying the QoS policy."

By default, no QoS policy is applied.

6. (Optional.) Display the priority marking configuration.

display traffic behavior user-defined [ behavior-name ] [ slot slot-number ]

This command is available in any view.

Appendixes

Appendix A Acronyms

Table 2 Appendix A Acronyms

Acronym	Full spelling
AF	Assured Forwarding
BE	Best Effort
BQ	Bandwidth Queuing
CAR	Committed Access Rate
CBS	Committed Burst Size
CBQ	Class Based Queuing
CE	Congestion Experienced
CIR	Committed Information Rate
CQ	Custom Queuing
DCBX	Data Center Bridging Exchange Protocol
DiffServ	Differentiated Service
DSCP	Differentiated Services Code Point
EBS	Excess Burst Size
ECN	Explicit Congestion Notification
EF	Expedited Forwarding
FIFO	First in First out
FQ	Fair Queuing
GMB	Guaranteed Minimum Bandwidth
GTS	Generic Traffic Shaping
IntServ	Integrated Service
ISP	Internet Service Provider
LLQ	Low Latency Queuing
LSP	Label Switched Path
MPLS	Multiprotocol Label Switching
PE	Provider Edge
PIR	Peak Information Rate
PQ	Priority Queuing
PW	Pseudowire
QoS	Quality of Service
QPPB	QoS Policy Propagation Through the Border Gateway Protocol
RED	Random Early Detection
RSVP	Resource Reservation Protocol
RTP	Real-Time Transport Protocol
SP	Strict Priority
ToS	Type of Service
VoIP	Voice over IP
VPN	Virtual Private Network
WFQ	Weighted Fair Queuing
WRED	Weighted Random Early Detection
WRR	Weighted Round Robin

Appendix B Introduction to packet precedence

IP precedence and DSCP values

Figure 11 ToS and DS fields

As shown in Figure 11, the ToS field in the IP header contains 8 bits. The first 3 bits (0 to 2) represent IP precedence from 0 to 7. According to RFC 2474, the ToS field is redefined as the differentiated services (DS) field. A DSCP value is represented by the first 6 bits (0 to 5) of the DS field and is in the range 0 to 63. The remaining 2 bits (6 and 7) are reserved.

Table 3 IP precedence

IP precedence (decimal)	IP precedence (binary)	Description
0	000	Routine
1	001	priority
2	010	immediate
3	011	flash
4	100	flash-override
5	101	critical
6	110	internet
7	111	network

Table 4 DSCP values

DSCP value (decimal)	DSCP value (binary)	Description
46	101110	ef
10	001010	af11
12	001100	af12
14	001110	af13
18	010010	af21
20	010100	af22
22	010110	af23
26	011010	af31
28	011100	af32
30	011110	af33
34	100010	af41
36	100100	af42
38	100110	af43
8	001000	cs1
16	010000	cs2
24	011000	cs3
32	100000	cs4
40	101000	cs5
48	110000	cs6
56	111000	cs7
0	000000	be (default)

802.1p priority

802.1p priority lies in the Layer 2 header. It applies to occasions where Layer 3 header analysis is not needed and QoS must be assured at Layer 2.

Figure 12 An Ethernet frame with an 802.1Q tag header

As shown in Figure 12, the 4-byte 802.1Q tag header contains the 2-byte tag protocol identifier (TPID) and the 2-byte tag control information (TCI). The value of the TPID is 0x8100. Figure 13 shows the format of the 802.1Q tag header. The Priority field in the 802.1Q tag header is called 802.1p priority, because its use is defined in IEEE 802.1p. Table 5 shows the values for 802.1p priority.

Figure 13 802.1Q tag header

Table 5 Description on 802.1p priority

802.1p priority (decimal)	802.1p priority (binary)	Description
0	000	best-effort
1	001	background
2	010	spare
3	011	excellent-effort
4	100	controlled-load
5	101	video
6	110	voice
7	111	network-management

15-ACL and QoS Configuration Guide

QoS techniques in a network

Defining a traffic class

Defining a traffic behavior

Defining a QoS policy

About this task

Prerequisites

Procedure

Restrictions and guidelines

Procedure

About this task

Hardware and feature compatibility

Restrictions and guidelines

Procedure

Applying the QoS policy to a control plane

About this task

Procedure

About this task

Procedure

About this task

Procedure

Traffic evaluation and token buckets

Token bucket features

Evaluating traffic with the token bucket

Complicated evaluation

Configuring traffic policing

Restrictions and guidelines

Procedure

Configuring CAR-list-based traffic policing

Configuring ACL-based traffic policing

Configuring the rate limit

Congestion management technique comparison

Setting the FIFO queue size

Restrictions and guidelines

Procedure

Predefined classes

Predefined traffic behaviors

Predefined QoS policy

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

Restrictions and guidelines

Procedure

Setting the maximum reserved bandwidth as a percentage of available bandwidth for an interface

Restrictions and guidelines

Procedure

Appendixes

Appendix A Acronyms

Cloud & AI

InterConnect

Intelligent Terminal Products

Product Support Services

Technical Service Solutions

Resource Center

Policy

Online Help

Become a Partner

Partner Resources

Partner Business Management

Company Information