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| Title | Size | Download |
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Contents
QoS processing flow in a device
Restrictions and guidelines for applying a QoS policy
Applying the QoS policy to an interface
Applying the QoS policy globally
Applying the QoS policy to a control plane
Display and maintenance commands for QoS policies
Priority mapping configuration methods
Priority mapping tasks at a glance
Configuring a port to trust packet priority for priority mapping
Changing the port priority of an interface
Changing the port priority of an interface
Display and maintenance commands for priority mapping
Priority mapping configuration examples
Example: Configuring a priority trust mode
Example: Configuring priority mapping tables and priority marking
Configuring traffic policing, GTS, and rate limit
About traffic policing, GTS, and rate limit
Traffic evaluation and token buckets
Configuring the rate limit for an interface
Display and maintenance commands for traffic policing, GTS, and rate limit
Configuring congestion management
Cause, negative results, and countermeasure of congestion
Congestion management tasks at a glance
Configuring queuing on an interface
Display and maintenance commands for congestion management
Configuring congestion avoidance
Relationship between WRED and queuing mechanisms
Configuring and applying a queue-based WRED table
Example: Configuring and applying a queue-based WRED table
Display and maintenance commands for WRED
Restrictions and guidelines: Traffic filtering configuration
Traffic filtering configuration examples
Example: Configuring traffic filtering
Configuring protocol packet rate limiting
About protocol packet rate limiting
Protocol packet rate limiting configuration examples
Example: Configuring protocol packet rate limiting
Priority marking configuration examples
Example: Configuring priority marking
Display and maintenance commands for global CAR
Global CAR configuration examples
Example: Configuring multi-level CAR
Configuring queue-based accounting
Configuring interface queue-based accounting
About interface queue-based accounting
Display and maintenance commands for queue-based accounting
Appendix B Default priority maps
Appendix C Introduction to packet precedence
QoS overview
In data communications, Quality of Service (QoS) provides differentiated service guarantees for diversified traffic in terms of bandwidth, delay, jitter, and drop rate, all of which can affect QoS.
QoS manages network resources and prioritizes traffic to balance system resources.
The following section describes typical QoS service models and widely used QoS techniques.
QoS service models
This section describes several typical QoS service models.
Best-effort service model
The best-effort model is a single-service model. The best-effort model is not as reliable as other models and does not guarantee delay-free delivery.
The best-effort service model is the default model for the Internet and applies to most network applications. It uses the First In First Out (FIFO) queuing mechanism.
IntServ model
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. For more information about RSVP, see MPLS Configuration Guide.
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.
· Traffic shaping.
· Rate limit.
· Congestion management.
· Congestion avoidance.
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
As shown in Figure 1, traffic classification, traffic shaping, traffic policing, congestion management, and congestion avoidance 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.
· Traffic shaping—Adapts the output rate of traffic to the network resources available on the downstream device to eliminate packet drops. Traffic shaping usually applies to the outgoing traffic of a port.
· Congestion management—Provides a resource scheduling policy to determine the packet forwarding sequence when congestion occurs. Congestion management usually applies to the outgoing traffic of a port.
· Congestion avoidance—Monitors the network resource usage. It is usually applied to the outgoing traffic of a port. When congestion worsens, congestion avoidance reduces the queue length by dropping packets.
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 the QoS module to perform the following operations:
¡ Traffic policing for incoming traffic.
¡ Traffic shaping for outgoing traffic.
¡ Congestion avoidance before congestion occurs.
¡ Congestion management when congestion occurs.
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:
2. Defining a traffic behavior
¡ Applying the QoS policy to an interface
¡ Applying the QoS policy globally
¡ Applying the QoS policy to a control plane
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. (Optional.) Configure a description for the traffic class.
description text
By default, no description is configured.
4. Configure a match criterion.
if-match 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.
You can configure multiple actions in a traffic behavior.
For more information about configuring an action, see the subsequent chapters for traffic policing, traffic filtering, priority marking, class-based accounting, and so on.
Defining a QoS policy
Restrictions and guidelines
A QoS policy can contain multiple class-behavior associations. The device matches a packet against the class-behavior associations in their configuration order. When a match is found, the device stops the match process and takes the actions in the matching class-behavior association.
Procedure
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.
|
Parameter |
Description |
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.
· Globally—The QoS policy takes effect on the traffic sent or received on all ports.
· Control plane—The QoS policy takes effect on the traffic received on the control plane.
To use a traffic class to match MPLS packet, you must configure an MPLS EXP match criterion or an Layer 2 ACL match criterion with the Ethernet type as 0x8847.
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.
If an action in a traffic behavior cannot take effect, all other actions in the traffic behavior do not take effect.
Applying the QoS policy to an interface
Restrictions and guidelines
A QoS policy can be applied to multiple interfaces.
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, routing, LDP, RSVP, 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.
Restrictions and guidelines
· If the hardware resources of an interface card are insufficient, applying a QoS policy globally might fail on the interface card. The system does not automatically roll back the QoS policy configuration already applied to other interface cards. 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.
Display and maintenance commands for QoS policies
Execute display commands in any view and reset commands in user view.
|
Task |
Command |
|
Display traffic class configuration. |
display traffic classifier user-defined [ classifier-name ] [ slot slot-number ] |
|
Display traffic behavior configuration. |
display traffic behavior user-defined [ behavior-name ] [ slot slot-number ] |
|
Display QoS policy configuration. |
display qos policy user-defined [ policy-name [ classifier classifier-name ] ] [ slot slot-number ] |
|
Display information about QoS policies applied to interfaces. |
display qos policy interface [ interface-type interface-number ] [ slot slot-number | all ] [ inbound | outbound ] |
|
Display information about QoS policies applied globally. |
display qos policy global [ slot slot-number ] [ inbound | outbound ] |
|
Display information about QoS policies applied to a control plane. |
display qos policy control-plane slot slot-number |
|
Display information about the predefined QoS policy applied to the control plane. |
display qos policy control-plane pre-defined [ slot slot-number ] |
|
Clear the statistics for a QoS policy applied globally. |
reset qos policy global [ inbound | outbound ] |
|
Clear the statistics for the QoS policy applied to a control plane. |
reset qos policy control-plane slot slot-number |
Configuring priority mapping
About priority mapping
When a packet arrives, a device assigns a set of QoS priority parameters to the packet based on either of the following:
· A priority field carried in the packet.
· The port priority of the incoming port.
This process is called priority mapping. During this process, the device can modify the priority of the packet according to the priority mapping rules. The set of QoS priority parameters decides the scheduling priority and forwarding priority of the packet.
Priority mapping is implemented with priority maps and involves the following priorities:
· 802.11e priority.
· 802.1p priority.
· DSCP.
· EXP.
· IP precedence.
· Local precedence.
· Drop priority.
About priorities
Priorities include the following types: priorities carried in packets, and priorities locally assigned for scheduling only.
Packet-carried priorities include 802.1p priority, DSCP precedence, IP precedence, and EXP. These priorities have global significance and affect the forwarding priority of packets across the network. For more information about these priorities, see "Appendixes."
Locally assigned priorities only have local significance. They are assigned by the device only for scheduling. These priorities include the local precedence, drop priority, and user priority, as follows:
· Local precedence—Used for queuing. A local precedence value corresponds to an output queue. A packet with higher local precedence is assigned to a higher priority output queue to be preferentially scheduled.
· Drop priority—Used for making packet drop decisions. Packets with the highest drop priority are dropped preferentially.
· User priority—Precedence that the device automatically extracts from a priority field of the packet according to its forwarding path. It is a parameter for determining the scheduling priority and forwarding priority of the packet. The user priority represents the following items:
¡ The 802.1p priority for Layer 2 packets.
¡ The IP precedence for Layer 3 packets.
¡ The EXP for MPLS packets.
Priority maps
The device provides various types of priority maps. By looking through a priority map, the device decides which priority value to assign to a packet for subsequent packet processing.
The default priority maps (as shown in Appendix B Default priority maps) are available for priority mapping. They are adequate in most cases. If a default priority map cannot meet your requirements, you can modify the priority map as required.
Priority mapping configuration methods
You can configure priority mapping by using any of the following methods.
Configuring priority trust mode
In this method, you can configure a port to look up a trusted priority type (802.1p, for example) in incoming packets in the priority maps. Then, the system maps the trusted priority to the target priority types and values.
Changing port priority
If no packet priority is trusted, the port priority of the incoming port is used. By changing the port priority of a port, you change the priority of the incoming packets on the port.
Priority mapping process
On receiving an Ethernet packet on a port, the switch marks the scheduling priorities (local precedence and drop precedence) for the Ethernet packet. This procedure is done according to the priority trust mode of the receiving port and the 802.1Q tagging status of the packet, as shown in Figure 3.
Figure 3 Priority mapping process for an Ethernet packet
The switch marks a received MPLS packet with a scheduling priority based on the priority trust mode and the packet EXP value, as shown in Figure 4.
Figure 4 Priority mapping process for an MPLS packet
For information about priority marking, see "Configuring priority marking."
Priority mapping tasks at a glance
To configure priority mapping, perform the following tasks:
1. (Optional.) Configuring a priority map
2. configure a priority mapping method:
¡ Configuring a port to trust packet priority for priority mapping
¡ Changing the port priority of an interface
Configuring a priority map
About priority maps
_Ref89094948 shows the priority maps provided by the device.
|
Priority map |
Description |
|
dot1p-lp |
802.1p-local priority map. |
|
dscp -lp |
DSCP-local priority map. |
|
exp-dscp |
EXP-DSCP priority map. |
Configuring a priority map
1. Enter system view.
system-view
2. Enter priority map view.
qos map-table { dot1p-lp | dscp-lp | exp-dscp }
3. Configure mappings for the priority map.
import import-value-list export export-value
By default, the default priority maps are used. For more information, see "Appendix B Default priority maps."
If you execute this command multiple times, the most recent configuration takes effect.
Configuring a port to trust packet priority for priority mapping
About this task
You can configure the device to trust a particular priority field carried in packets for priority mapping on ports or globally.
When you configure the trusted packet priority type on an interface, use the following available keywords:
· dot1p—Uses the 802.1p priority of received packets for mapping.
· dscp—Uses the DSCP precedence of received IP packets for mapping.
Procedure
1. Enter system view.
system-view
2. Enter interface view.
interface interface-type interface-number
3. Configure the trusted packet priority type.
qos trust { dot1p | dscp }
By default, an interface trusts the port priority.
Changing the port priority of an interface
Changing the port priority of an interface
About this task
If an interface does not trust any packet priority, the device uses its port priority to look for priority parameters for the incoming packets. By changing port priority, you can prioritize traffic received on different interfaces.
Procedure
1. Enter system view.
system-view
2. Enter interface view.
interface interface-type interface-number
3. Set the port priority of the interface.
qos priority priority-value
The default setting is 0.
Display and maintenance commands for priority mapping
Execute display commands in any view.
|
Task |
Command |
|
Display priority map configuration. |
display qos map-table [ dot1p-dp | dot1p-exp | dot1p-lp | dscp-dot1p| dscp-dp | dscp-dscp | dscp-exp | dscp-lp | exp-dot1p | exp-dscp ] |
|
Display the trusted packet priority type on a port. |
display qos trust interface [ interface-type interface-number ] |
Priority mapping configuration examples
Example: Configuring a priority trust mode
Network configuration
As shown in Figure 5:
· The 802.1p priority of traffic from Device A to Device C is 3.
· The 802.1p priority of traffic from Device B to Device C is 1.
Configure Device C to preferentially process packets from Device A to the server when Ten-GigabitEthernet 2/0/2 of Device C is congested.
Procedure
(Method 1) Configure Device C to trust packet priority
# Configure Ten-GigabitEthernet 2/0/0 and Ten-GigabitEthernet 2/0/1 to trust 802.1p priority for priority mapping.
<DeviceC> system-view
[DeviceC] interface ten-gigabitethernet 2/0/0
[DeviceC-Ten-GigabitEthernet2/0/0] qos trust dot1p
[DeviceC-Ten-GigabitEthernet2/0/0] quit
[DeviceC] interface ten-gigabitethernet 2/0/1
[DeviceC-Ten-GigabitEthernet2/0/1] qos trust dot1p
[DeviceC-Ten-GigabitEthernet2/0/1] quit
(Method 2) Configure Device C to trust port priority
# Assign port priority to Ten-GigabitEthernet 2/0/0 and Ten-GigabitEthernet 2/0/1. Make sure the following requirements are met:
· The priority of Ten-GigabitEthernet 2/0/0 is higher than that of Ten-GigabitEthernet 2/0/1.
· No trusted packet priority type is configured on Ten-GigabitEthernet 2/0/0 or Ten-GigabitEthernet 2/0/1.
<DeviceC> system-view
[DeviceC] interface ten-gigabitethernet 2/0/0
[DeviceC-Ten-GigabitEthernet2/0/0] qos priority 3
[DeviceC-Ten-GigabitEthernet2/0/0] quit
[DeviceC] interface ten-gigabitethernet 2/0/1
[DeviceC-Ten-GigabitEthernet2/0/1] qos priority 1
[DeviceC-Ten-GigabitEthernet2/0/1] quit
Example: Configuring priority mapping tables and priority marking
Network configuration
As shown in Figure 6:
· The Marketing department connects to Ten-GigabitEthernet 2/0/0 of Device, which sets the 802.1p priority of traffic from the Marketing department to 3.
· The R&D department connects to Ten-GigabitEthernet 2/0/1 of Device, which sets the 802.1p priority of traffic from the R&D department to 4.
· The Management department connects to Ten-GigabitEthernet 2/0/2 of Device, which sets the 802.1p priority of traffic from the Management department to 5.
Configure port priority, 802.1p-to-local mapping table, and priority marking to implement the plan as described in Table 2.
|
Traffic destination |
Traffic priority order |
Queuing plan |
||
|
Traffic source |
Output queue |
Queue priority |
||
|
Public servers |
R&D department > Management department > Marketing department |
R&D department |
6 |
High |
|
Management department |
4 |
Medium |
||
|
Marketing department |
2 |
Low |
||
|
Internet |
Management department > Marketing department > R&D department |
R&D department |
2 |
Low |
|
Management department |
6 |
High |
||
|
Marketing department |
3 |
Medium |
||
Procedure
1. Configure trusting port priority:
# Set the port priority of Ten-GigabitEthernet 2/0/0 to 3.
<Device> system-view
[Device] interface ten-gigabitethernet 2/0/0
[Device-Ten-GigabitEthernet2/0/0] qos priority 3
[Device-Ten-GigabitEthernet2/0/0] quit
# Set the port priority of Ten-GigabitEthernet 2/0/1 to 4.
[Device] interface ten-gigabitethernet 2/0/1
[Device-Ten-GigabitEthernet2/0/1] qos priority 4
[Device-Ten-GigabitEthernet2/0/1] quit
# Set the port priority of Ten-GigabitEthernet 2/0/2 to 5.
[Device] interface ten-gigabitethernet 2/0/2
[Device-Ten-GigabitEthernet2/0/2] qos priority 5
[Device-Ten-GigabitEthernet2/0/2] quit
2. Configure the 802.1p-to-local mapping table to map 802.1p priority values 3, 4, and 5 to local precedence values 2, 6, and 4.
This guarantees the R&D department, Management department, and Marketing department decreased priorities to access the public servers.
[Device] qos map-table dot1p-lp
[Device-maptbl-dot1p-lp] import 3 export 2
[Device-maptbl-dot1p-lp] import 4 export 6
[Device-maptbl-dot1p-lp] import 5 export 4
[Device-maptbl-dot1p-lp] quit
3. Map the local precedence values 6 and 2 to local precedence values 2 and 3 and keep local precedence value 4 unchanged.
This guarantees the Management department, Marketing department, and R&D department decreased priorities to access the Internet.
[Device] traffic classifier rd
[Device-classifier-rd] if-match local-precedence 6
[Device-classifier-rd] quit
[Device] traffic classifier market
[Device-classifier-market] if-match local-precedence 2
[Device-classifier-market] quit
[Device] traffic behavior rd
[Device-behavior-rd] remark local-precedence 2
[Device-behavior-rd] quit
[Device] traffic behavior market
[Device-behavior-market] remark local-precedence 3
[Device-behavior-market] quit
[Device] qos policy policy1
[Device-qospolicy-policy1] classifier rd behavior rd
[Device-qospolicy-policy1] classifier market behavior market
[Device-qospolicy-policy1] quit
[Device] interface ten-gigabitethernet 2/0/4
[Device-Ten-GigabitEthernet2/0/4] qos apply policy policy1 outbound
Configuring traffic policing, GTS, and rate limit
About traffic policing, GTS, 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, Generic Traffic Shaping (GTS), and rate limit control 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
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 re-set the priority of the packets. Figure 7 shows an example of policing outbound traffic on an interface.
Traffic policing can classify the policed traffic and take predefined policing actions on each packet depending on the evaluation result:
· Forwarding the packet.
· Dropping the packet.
· Forwarding the packet with its precedence re-marked.
· Delivering the packet to next-level traffic policing with its precedence re-marked.
GTS
GTS limits the traffic rate by buffering exceeding traffic. You can use GTS to adapt the traffic output rate on a device to the input traffic rate of its connected device to avoid packet loss.
The differences between traffic policing and GTS are as follows:
· Packets to be dropped with traffic policing are retained in a buffer or queue with GTS, as shown in Figure 8. When enough tokens are in the token bucket, the buffered packets are sent at an even rate.
· GTS can result in additional delay and traffic policing does not.
For example, in Figure 9, Device B performs traffic policing on packets from Device A and drops packets exceeding the limit. To avoid packet loss, you can perform GTS on the outgoing interface of Device A so that packets exceeding the limit are cached in Device A. Once resources are released, GTS takes out the cached packets and sends them out.
Rate limit
The rate limit of an interface specifies the maximum rate for forwarding packets (excluding critical packets).
Rate limit also uses token buckets for traffic control. When rate limit is configured on an interface, a token bucket handles all packets to be sent through the interface for rate limiting. If enough tokens are in the token bucket, packets can be forwarded. Otherwise, packets are put into QoS queues for congestion management. In this way, the traffic passing the interface is controlled.
Figure 10 Rate limit implementation
The token bucket mechanism limits traffic rate when accommodating bursts. It allows bursty traffic to be transmitted if enough tokens are available. If tokens are scarce, packets cannot be transmitted until efficient tokens are generated in the token bucket. It restricts the traffic rate to the rate for generating tokens.
Rate limit controls the total rate of all packets on an interface or PW. It is easier to use than traffic policing and GTS in controlling the total traffic rate.
Configuring traffic policing
Configuring traffic policing
Restrictions and guidelines
The device supports the following application destinations for traffic policing:
· Interface.
· Globally.
· 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 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.
¡ 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 ] *
By default, no traffic policing action is 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 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 GTS
Configuring queue-based GTS
Restrictions and guidelines
Queue-based GTS takes effect only on outbound traffic.
Procedure
1. Enter system view.
system-view
2. Enter interface view.
interface interface-type interface-number
3. Configure GTS for a queue.
¡ qos gts queue queue-id cir committed-information-rate [ cbs committed-burst-size ]
By default, GTS is not configured on an interface.
Configuring the rate limit
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 ]
By default, no rate limit is configured on an interface.
Display and maintenance commands for traffic policing, GTS, and rate limit
Execute display commands in any view and reset commands in user view.
|
Task |
Command |
|
Display traffic behavior configuration. |
display traffic behavior user-defined [ behavior-name ] |
|
Display GTS configuration and statistics for interfaces. |
display qos gts interface [ interface-type interface-number ] |
|
Display rate limit configuration and statistics for interfaces or PWs. |
display qos lr interface [ interface-type interface-number ] |
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 11 shows two typical congestion scenarios.
Figure 11 Traffic congestion scenarios
Congestion produces 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 even system breakdown.
Congestion is unavoidable in switched networks and multiuser application environments. To improve the service performance of your network, take measures to manage and control it.
The key to congestion management is defining a resource dispatching policy to prioritize packets for forwarding when congestion occurs.
Congestion management methods
Congestion management uses queuing and scheduling algorithms to classify and sort traffic leaving a port.
· SP.
· WRR.
· WFQ.
SP queuing
SP queuing is designed for mission-critical applications that require preferential service to reduce the response delay when congestion occurs.
In Figure 12, SP queuing classifies eight queues on a port into eight classes, numbered 7 to 0 in descending priority order.
SP queuing schedules the eight queues in the descending order of priority. SP queuing 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, and so on. You can assign mission-critical packets to a high priority queue to make sure they are always served first. Common service packets can be assigned to low priority queues to be transmitted when high priority queues are empty.
The disadvantage of SP queuing is that packets in the lower priority queues cannot be transmitted if packets exist in the higher priority queues. In the worst case, lower priority traffic might never get serviced.
WRR queuing
WRR queuing schedules all the queues in turn to ensure that every queue is served for a certain time, as shown in Figure 13.
Assume a port provides eight output queues. WRR assigns each queue a weight value (represented by w7, w6, w5, w4, w3, w2, w1, or w0). The weight value of a queue decides the proportion of resources assigned to the queue. On a 100 Mbps port, you can set the weight values to 50, 30, 10, 10, 50, 30, 10, and 10 for w7 through w0. In this way, the queue with the lowest priority can get a minimum of 5 Mbps of bandwidth. WRR solves the problem that SP queuing might fail to serve packets in low-priority queues for a long time.
Another advantage of WRR queuing is that when the queues are scheduled in turn, the service time for each queue is not fixed. If a queue is empty, the next queue will be scheduled immediately. This improves bandwidth resource use efficiency.
WRR queuing includes the following types:
· Basic WRR queuing—Contains multiple queues. You can set the weight for each queue, and WRR schedules these queues based on the user-defined parameters in a round robin manner.
· Group-based WRR queuing—All the queues are scheduled by WRR. You can divide output queues to WRR priority queue group 1 and WRR priority queue group 2. Round robin queue scheduling is performed for group 1 first. If group 1 is empty, round robin queue scheduling is performed for group 2.
Only WRR group 1 is supported in the current software version.
On an interface enabled with group-based WRR queuing, you can assign queues to the SP group. Queues in the SP group are scheduled with SP. The SP group has higher scheduling priority than the WRR groups.
WFQ queuing
Figure 14 WFQ queuing
WFQ is similar to WRR. WFQ queuing includes basic WFQ queuing and group-based WFQ queuing. Only WFQ group 1 is supported in the current software version.
On an interface with group-based WFQ queuing enabled, you can also assign queues to the SP group. Queues in the SP group are scheduled with SP. The difference is that WFQ enables you to set guaranteed bandwidth that a WFQ queue can get during congestion.
SP+WFQ queuing schedules traffic in the following order:
1. Schedules the queues in the SP group based on their priorities.
2. Schedules the traffic conforming to the minimum guaranteed bandwidth of each queue in the WFQ group when all queues in the SP group are empty.
3. Schedules the traffic in each queue in the WFQ group according to the configured weights.
Congestion management tasks at a glance
To configure hardware congestion management, perform the following tasks:
· Configuring queuing on an interface
· Configuring queuing on an interface
¡ Configuring SP queuing
¡ Configuring WRR queuing
¡ Configuring WFQ queuing
Configuring queuing on an interface
Configuring SP queuing
1. Enter system view.
system-view
2. Enter interface view.
interface interface-type interface-number
3. Configure SP queuing.
qos sp
By default, an interface uses SP queuing.
Configuring WRR queuing
Configuring group-based WRR queuing
1. Enter system view.
system-view
2. Enter interface view.
interface interface-type interface-number
3. Enable WRR queuing.
qos wrr { byte-count | weight }
By default, an interface uses SP queuing.
4. Assign a queue to a WRR group, and configure scheduling parameters for the queue.
qos wrr queue-id group 1 { byte-count | weight } schedule-value
By default, all queues on a WRR-enabled interface belong to WRR group 1, and the scheduling weight of a queue is its queue ID plus 1.
Configuring WFQ queuing
Configuring grouped WFQ queues
1. Enter system view.
system-view
2. Enter interface view.
interface interface-type interface-number
3. Enable WFQ queuing.
qos wfq { byte-count | weight }
By default, an interface uses SP queuing.
4. Assign a queue to a WFQ group, and configure scheduling parameters for the queue.
qos wfq queue-id group 1 { byte-count | weight } schedule-value
By default, all queues on a WFQ-enabled interface belong to WFQ group 1, and the scheduling weight of a queue is its queue ID plus 1.
Configuring SP+WRR queuing
Restrictions and guidelines
To configure the scheduling weight, you must specify the same scheduling unit as specified when enabling WRR queuing.
Procedure
1. Enter system view.
system-view
2. Enter interface view.
interface interface-type interface-number
3. Enable byte-count or packet-count WRR queuing.
qos wrr { byte-count | weight }
By default, an interface uses SP queuing.
4. Assign a queue to the SP group.
qos wrr queue-id group sp
By default, all queues on a WRR-enabled interface belong to WRR group 1, and the scheduling weight of a queue is its queue ID plus 1.
5. Assign a queue to a WRR group, and configure a scheduling weight for the queue.
qos wrr queue-id group 1 { byte-count | weight } schedule-value
By default, all queues on a WRR-enabled interface belong to WRR group 1, and the scheduling weight of a queue is its queue ID plus 1.
Configuring SP+WFQ queuing
Restrictions and guidelines
To configure the scheduling weight, you must specify the same scheduling unit as specified when enabling WFQ queuing.
Procedure
1. Enter system view.
system-view
2. Enter interface view.
interface interface-type interface-number
3. Enable byte-count or packet-count WFQ queuing.
qos wfq { byte-count | weight }
By default, an interface uses SP queuing.
4. Assign a queue to the SP group.
qos wfq queue-id group sp
By default, all queues on a WFQ-enabled interface belong to WFQ group 1, and the scheduling weight of a queue is its queue ID plus 1.
5. Assign a queue to a WFQ queue scheduling group, and configure a scheduling weight for the queue.
qos wfq queue-id group 1 { byte-count | weight } schedule-value
By default, all queues on a WFQ-enabled interface belong to WFQ group 1, and the scheduling weight of a queue is its queue ID plus 1.
Display and maintenance commands for congestion management
Execute display commands in any view.
|
Task |
Command |
|
Display SP queuing configuration. |
display qos queue sp interface [ interface-type interface-number ] |
|
Display WRR queuing configuration. |
display qos queue wrr interface [ interface-type interface-number ] |
|
Display WFQ queuing configuration. |
display qos queue wfq interface [ interface-type interface-number ] |
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 15 Relationship between WRED and queuing mechanisms
· 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 a WRED table in system view and then apply the WRED table to an interface.
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.
· Drop probability—Drop probability in percentage. The greater the value, the higher the drop probability. (Applicable when you configure a WRED table.)
Configuring and applying a queue-based WRED table
Restrictions and guidelines
One WRED table can be applied to multiple interfaces. You can modify the parameters of a WRED table applied to an interface, but you cannot delete the WRED table.
Procedure
1. Enter system view.
system-view
2. Create a WRED table and enter its view.
qos wred queue table table-name
3. (Optional.) Set the WRED exponent for average queue size calculation.
queue queue-id weighting-constant exponent
The default setting is 9.
4. (Optional.) Configure the other WRED parameters.
queue queue-id [ drop-level drop-level ] low-limit low-limit high-limit high-limit [ discard-probability discard-prob ]
By default, no WRED parameters are configured.
5. Return to system view.
quit
6. Enter interface view.
interface interface-type interface-number
7. Apply the WRED table to the interface.
qos wred apply [ table-name ]
By default, no WRED table is applied to an interface, and tail drop is used on an interface.
Example: Configuring and applying a queue-based WRED table
Network configuration
Apply a WRED table to Ten-GigabitEthernet 2/0/1, so that the packets are dropped as follows when congestion occurs:
· For the interface to preferentially forward higher-priority traffic, set a lower drop probability for a queue with a greater queue number. Set different drop parameters for queue 0, queue 3, and queue 7.
· Drop packets according to their colors.
¡ In queue 0, set the drop probability to 25%, 50%, and 75% for green, yellow, and red packets, respectively.
¡ In queue 3, set the drop probability to 5%, 10%, and 25% for green, yellow, and red packets, respectively.
¡ In queue 7, set the drop probability to 1%, 5%, and 10% for green, yellow, and red packets, respectively.
Procedure
# Configure a queue-based WRED table, and set different drop parameters for packets with different drop levels in different queues.
<Sysname> system-view
[Sysname] qos wred queue table queue-table1
[Sysname-wred-table-queue-table1] queue 0 drop-level 0 low-limit 128 high-limit 512 discard-probability 25
[Sysname-wred-table-queue-table1] queue 0 drop-level 1 low-limit 128 high-limit 512 discard-probability 50
[Sysname-wred-table-queue-table1] queue 0 drop-level 2 low-limit 128 high-limit 512 discard-probability 75
[Sysname-wred-table-queue-table1] queue 3 drop-level 0 low-limit 256 high-limit 640 discard-probability 5
[Sysname-wred-table-queue-table1] queue 3 drop-level 1 low-limit 256 high-limit 640 discard-probability 10
[Sysname-wred-table-queue-table1] queue 3 drop-level 2 low-limit 256 high-limit 640 discard-probability 25
[Sysname-wred-table-queue-table1] queue 7 drop-level 0 low-limit 512 high-limit 1024 discard-probability 1
[Sysname-wred-table-queue-table1] queue 7 drop-level 1 low-limit 512 high-limit 1024 discard-probability 5
[Sysname-wred-table-queue-table1] queue 7 drop-level 2 low-limit 512 high-limit 1024 discard-probability 10
[Sysname-wred-table-queue-table1] quit
# Apply the queue-based WRED table to Ten-GigabitEthernet 2/0/1.
[Sysname] interface ten-gigabitethernet 2/0/1
[Sysname-Ten-GigabitEthernet2/0/1] qos wred apply queue-table1
[Sysname-Ten-GigabitEthernet2/0/1] quit
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 ] |
|
Display the configuration of a WRED table or all WRED tables. |
display qos wred table [ name table-name ] [ slot slot-number ] |
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 the following application destinations for traffic filtering:
· Interface.
· Globally.
· 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 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.
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 ]
This command is available in any view.
Traffic filtering configuration examples
Example: Configuring traffic filtering
Network configuration
As shown in Figure 16, configure traffic filtering on Ten-GigabitEthernet 2/0/0 to deny the incoming packets with destination port number 21.
Procedure
# Create advanced ACL 3000, and configure a rule to match packets with destination port number 21.
<Device> system-view
[Device] acl advanced 3000
[Device-acl-ipv4-adv-3000] rule 0 permit tcp destination-port eq 21
[Device-acl-ipv4-adv-3000] quit
# Create a traffic class named classifier_1, and use ACL 3000 as the match criterion in the traffic class.
[Device] traffic classifier classifier_1
[Device-classifier-classifier_1] if-match acl 3000
[Device-classifier-classifier_1] quit
# Create a traffic behavior named behavior_1, and configure the traffic filtering action to drop packets.
[Device] traffic behavior behavior_1
[Device-behavior-behavior_1] filter deny
[Device-behavior-behavior_1] quit
# Create a QoS policy named policy, and associate traffic class classifier_1 with traffic behavior behavior_1 in the QoS policy.
[Device] qos policy policy
[Device-qospolicy-policy] classifier classifier_1 behavior behavior_1
[Device-qospolicy-policy] quit
# Apply QoS policy policy to the incoming traffic of Ten-GigabitEthernet 2/0/0.
[Device] interface ten-gigabitethernet 2/0/0
[Device-Ten-GigabitEthernet2/0/0] qos apply policy policy inbound
Configuring protocol packet rate limiting
About protocol packet rate limiting
The protocol packet processing rate of a CPU is limited. When a large number of protocol packets are sent to the CPU, the CPU might be occupied by the protocol packets and cannot process other tasks. The protocol packet rate limiting feature limits the rate of protocol packets sent to the CPU, and it guarantees the normal operation of the CPU.
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 match-criteria
By default, no match criteria are configured.
For more information, see the if-match command in 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 protocol packet rate limiting.
packet-rate value
By default, protocol packet rate limiting 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 the class with the traffic behavior in the QoS policy.
classifier classifier-name behavior behavior-name
By default, a class is not associated with any behavior.
c. Return to system view.
quit
5. Apply the QoS policy to a control plane.
For more information, see "Applying the QoS policy to a control plane."
By default, no QoS policy is applied to a control plane.
6. (Optional.) Display the protocol packet rate limiting configuration.
display traffic behavior user-defined [ behavior-name ]
This command is available in any view.
Protocol packet rate limiting configuration examples
Example: Configuring protocol packet rate limiting
Network configuration
As shown in Figure 17, limit the rate of DHCP protocol packets sent to the CPU of the device to 500 pps.
Procedure
# Create a traffic class named classifier_1 and configure the class to match DHCP protocol packets.
<Device> system-view
[Device] traffic classifier classifier_1
[Device-classifier-classifier_1] if-match control-plane protocol dhcp
[Device-classifier-classifier_1] quit
# Create a traffic behavior named behavior_1 and configure the behavior to limit the packet rate to 500 pps.
[Device] traffic behavior behavior_1
[Device-behavior-behavior_1] packet-rate 500
[Device-behavior-behavior_1] quit
# Create a QoS policy named and associate class classifier_1 with behavior behavior_1 in the policy.
[Device] qos policy policy
[Device-qospolicy-policy] classifier classifier_1 behavior behavior_1
[Device-qospolicy-policy] quit
# Apply QoS policy policy to the control plane.
[Device] control-plane slot 1
[Device-cp] qos apply policy policy inbound
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.
1. Configure a traffic behavior with a priority marking action.
2. Associate the traffic class with the traffic behavior.
Priority marking can be used together with priority mapping. For more information, see "Configuring priority mapping."
Configuring priority marking
Restrictions and guidelines
The device supports the following application destinations for priority marking:
· Interface.
· Globally.
· 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 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 ]
This command is available in any view.
Priority marking configuration examples
Example: Configuring priority marking
Network configuration
As shown in Figure 18, configure priority marking on the device to meet the following requirements:
|
Traffic source |
Destination |
Processing priority |
|
Host A, B |
Data server |
High |
|
Host A, B |
Mail server |
Medium |
|
Host A, B |
File server |
Low |
Procedure
# Create advanced ACL 3000, and configure a rule to match packets with destination IP address 192.168.0.1.
<Device> system-view
[Device] acl advanced 3000
[Device-acl-ipv4-adv-3000] rule permit ip destination 192.168.0.1 0
[Device-acl-ipv4-adv-3000] quit
# Create advanced ACL 3001, and configure a rule to match packets with destination IP address 192.168.0.2.
[Device] acl advanced 3001
[Device-acl-ipv4-adv-3001] rule permit ip destination 192.168.0.2 0
[Device-acl-ipv4-adv-3001] quit
# Create advanced ACL 3002, and configure a rule to match packets with destination IP address 192.168.0.3.
[Device] acl advanced 3002
[Device-acl-ipv4-adv-3002] rule permit ip destination 192.168.0.3 0
[Device-acl-ipv4-adv-3002] quit
# Create a traffic class named classifier_dbserver, and use ACL 3000 as the match criterion in the traffic class.
[Device] traffic classifier classifier_dbserver
[Device-classifier-classifier_dbserver] if-match acl 3000
[Device-classifier-classifier_dbserver] quit
# Create a traffic class named classifier_mserver, and use ACL 3001 as the match criterion in the traffic class.
[Device] traffic classifier classifier_mserver
[Device-classifier-classifier_mserver] if-match acl 3001
[Device-classifier-classifier_mserver] quit
# Create a traffic class named classifier_fserver, and use ACL 3002 as the match criterion in the traffic class.
[Device] traffic classifier classifier_fserver
[Device-classifier-classifier_fserver] if-match acl 3002
[Device-classifier-classifier_fserver] quit
# Create a traffic behavior named behavior_dbserver, and configure the action of setting the local precedence value to 4.
[Device] traffic behavior behavior_dbserver
[Device-behavior-behavior_dbserver] remark local-precedence 4
[Device-behavior-behavior_dbserver] quit
# Create a traffic behavior named behavior_mserver, and configure the action of setting the local precedence value to 3.
[Device] traffic behavior behavior_mserver
[Device-behavior-behavior_mserver] remark local-precedence 3
[Device-behavior-behavior_mserver] quit
# Create a traffic behavior named behavior_fserver, and configure the action of setting the local precedence value to 2.
[Device] traffic behavior behavior_fserver
[Device-behavior-behavior_fserver] remark local-precedence 2
[Device-behavior-behavior_fserver] quit
# Create a QoS policy named policy_server, and associate traffic classes with traffic behaviors in the QoS policy.
[Device] qos policy policy_server
[Device-qospolicy-policy_server] classifier classifier_dbserver behavior behavior_dbserver
[Device-qospolicy-policy_server] classifier classifier_mserver behavior behavior_mserver
[Device-qospolicy-policy_server] classifier classifier_fserver behavior behavior_fserver
[Device-qospolicy-policy_server] quit
# Apply QoS policy policy_server to the incoming traffic of Ten-GigabitEthernet 2/0/0.
[Device] interface ten-gigabitethernet 2/0/0
[Device-Ten-GigabitEthernet2/0/0] qos apply policy policy_server inbound
[Device-Ten-GigabitEthernet2/0/0] quit
Configuring global CAR
About global CAR
Global CAR provides the following CAR actions: aggregate CAR and multi-level CAR.
Aggregate CAR
An aggregate CAR action is created globally. It can be directly applied to interfaces or used in the traffic behaviors associated with different traffic classes to police multiple traffic flows as a whole. The total rate of the traffic flows must conform to the traffic policing specifications set in the aggregate CAR action.
Multi-level CAR
Multi-level CAR is implemented through a QoS policy. In the QoS policy, you associate different traffic classes with different-level CAR statements of a multi-level CAR action. When congestion occurs, the traffic class associated with a lower-level CAR statement receives preferential treatment over the traffic class associated with a higher-level CAR statement.
Configuring aggregate CAR
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 match-criteria
By default, no match criterion is configured.
For configurable match criteria, see the if-match command in ACL and QoS Command Reference.
c. Return to system view.
quit
3. Configure an aggregate CAR action.
qos car car-name aggregative cir committed-information-rate [ cbs committed-burst-size [ ebs excess-burst-size ] ] [ green action | red action | yellow action ] *
qos car car-name aggregative 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 aggregate CAR action is configured.
4. Define a traffic behavior.
a. Enter traffic behavior view.
traffic behavior behavior-name
b. Use the aggregate CAR in the traffic behavior.
car name car-name
By default, no aggregate CAR action is used in a traffic behavior.
5. 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
6. Apply the QoS policy.
For more information, see "Applying the QoS policy."
By default, no QoS policy is applied.
Configuring multi-level CAR
1. Enter system view.
system-view
2. Create a multi-level CAR action.
qos car car-name cascade
3. Configure the multi-level CAR action.
level level-value cir committed-information-rate [ cbs committed-burst-size [ ebs excess-burst-size ] ] [ max cir committed-information-rate ]
level level-value cir committed-information-rate [ cbs committed-burst-size ] pir peak-information-rate [ ebs excess-burst-size ] [ max cir committed-information-rate max pir peak-information-rate ]
By default, a multi-level CAR action is not configured.
4. 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 match-criteria
By default, no match criterion is configured.
For configurable match criteria, see the if-match command in ACL and QoS Command Reference.
c. Return to system view.
quit
By default, no multi-level CAR action is configured.
5. Define a traffic behavior.
a. Enter traffic behavior view.
traffic behavior behavior-name
b. Use the multi-level CAR in the traffic behavior.
car name car-name cascade level level-value
c. Return to system view.
quit
By default, no multi-level CAR action is used in a traffic behavior.
6. 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
7. Apply the QoS policy.
For more information, see "Applying the QoS policy."
By default, no QoS policy is applied.
Display and maintenance commands for global CAR
Execute display commands in any view and reset commands in user view.
|
Task |
Command |
|
Display statistics for global CAR actions. |
display qos car name [ car-name ] |
|
Clear statistics for global CAR actions. |
reset qos car name [ car-name ] |
Global CAR configuration examples
Example: Configuring multi-level CAR
Network configuration
As shown in 错误!未找到引用源。, configure multi-level CAR on Ten-GigabitEthernet 2/0/0 to meet the following requirements:
· The traffic from 192.168.0.2 and and 192.168.0.3 is limited to 240 kbps and 120 kbps, respectively.
· When the available interface bandwidth is less than 240 kbps, some of the traffic from 192.168.0.2 is dropped and all the traffic from 192.168.0.3 is dropped.
· When the available interface bandwidth is between 240 kbps and 360 kbps, all the traffic from 192.168.0.2 is forwarded and some of the traffic from 192.168.0.3 is dropped.
· When the available interface bandwidth is greater than 360 kbps, the traffic from both 192.168.0.2 and 192.168.0.3 is forwarded.
Figure 19 Network diagram
Procedure
# Configure a multi-level CAR action named ccar according to the rate limit requirements.
<Device> system-view
[Device] qos car ccar cascade
[Device-qos-cascade-car-ccar] level 1 cir 240
[Device-qos-cascade-car-ccar] level 2 cir 120
[Device-qos-cascade-car-ccar] quit
# Configure ACL 2000 to match packets sourced from 192.168.0.2.
[Device] acl basic 2000
[Device-acl-ipv4-basic-2000] rule permit source 192.168.0.2 0.0.0.0
[Device-acl-ipv4-basic-2000] quit
# Create traffic class 1, and use ACL 2000 as the match criterion.
[Device] traffic classifier 1
[Device-classifier-1] if-match acl 2000
[Device-classifier-1] quit
# Create traffic behavior 1, and use CAR action ccar for level-1 rate limiting.
[Device] traffic behavior 1
[Device-behavior-1] car name ccar cascade level 1
[Device-behavior-1] quit
# Configure ACL 2001 to match packets sourced from 192.168.0.3.
[Device] acl basic 2001
[Device-acl-ipv4-basic-2001] rule permit source 192.168.0.3 0.0.0.0
[Device-acl-ipv4-basic-2001] quit
# Create traffic class 2, and use ACL 2001 as the match criterion.
[Device] traffic classifier 2
[Device-classifier-2] if-match acl 2001
[Device-classifier-2] quit
# Create traffic behavior 2, and use CAR action ccar for level-2 rate limiting.
[Device] traffic behavior 2
[Device-behavior-2] car name ccar cascade level 2
[Device-behavior-2] quit
# Create a QoS policy named cascadecar, and associate traffic class 1 with traffic behavior 1 and traffic class 2 with traffic behavior 2 in the QoS policy.
[Device] qos policy cascadecar
[Device-qospolicy-cascadecar] classifier 1 behavior 1
[Device-qospolicy-cascadecar] classifier 2 behavior 2
[Device-qospolicy-cascadecar] quit
# Apply QoS policy cascadecar to the incoming traffic of Ten-GigabitEthernet 2/0/0.
[Device] interface ten-gigabitethernet 2/0/0
[Device-Ten-GigabitEthernet2/0/0] qos apply policy cascadecar inbound
Configuring queue-based accounting
Configuring interface queue-based accounting
About interface queue-based accounting
Queue-based accounting collects queue-based traffic statistics for interfaces, such as:
· The total length of a queue.
· The current queue length.
· The total number of packets forwarded.
· The number of per-color packets forwarded.
Procedure
1. Enter system view.
system-view
2. Set the packet counting mode to queue.
statistic mode queue
The default packet counting mode is vsi.
Display and maintenance commands for queue-based accounting
Execute display commands in any view and reset commands in user view.
|
Task |
Command |
|
Display queue-based traffic statistics for interfaces. |
display qos queue-statistics interface [ interface-type interface-number ] outbound |
|
Display the packet counting mode. |
display statistic mode |
|
Clear queue-based traffic statistics for interfaces. |
reset qos queue-statistics interface [ interface-type interface-number ] outbound |
|
Clear queue-based traffic statistics for interfaces (see Interface Command Reference). |
reset counters interface [ interface-type [ interface-number | interface-number.subnumber ] ] |
Appendixes
Appendix A Acronyms
Table 3 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 |
|
PHB |
Per Hop Behavior |
|
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 Default priority maps
For the default dot1p-exp and dscp-dscp priority maps, an input value yields a target value equal to it.
Table 4 Default dot1p-lp and dot1p-dp priority maps
|
Input priority value |
dot1p-lp map |
dot1p-dp map |
|
dot1p |
lp |
dp |
|
0 |
2 |
0 |
|
1 |
0 |
0 |
|
2 |
1 |
0 |
|
3 |
3 |
0 |
|
4 |
4 |
0 |
|
5 |
5 |
0 |
|
6 |
6 |
0 |
|
7 |
7 |
0 |
Table 5 Default dscp-lp, dscp-dp, dscp-dot1p, and dscp-exp priority maps
|
Input priority value |
dscp-lp map |
dscp-dp map |
dscp-dot1p map |
dscp-exp map |
|
dscp |
lp |
dp |
dot1p |
exp |
|
0 to 7 |
0 |
0 |
0 |
0 |
|
8 to 15 |
1 |
0 |
1 |
1 |
|
16 to 23 |
2 |
0 |
2 |
2 |
|
24 to 31 |
3 |
0 |
3 |
3 |
|
32 to 39 |
4 |
0 |
4 |
4 |
|
40 to 47 |
5 |
0 |
5 |
5 |
|
48 to 55 |
6 |
0 |
6 |
6 |
|
56 to 63 |
7 |
0 |
7 |
7 |
Table 6 Default exp-dscp priority map
|
Input priority value |
exp-dscp map |
|
EXP value |
dscp |
|
0 |
0 |
|
1 |
8 |
|
2 |
16 |
|
3 |
24 |
|
4 |
32 |
|
5 |
40 |
|
6 |
48 |
|
7 |
56 |
Table 7 Default port priority-local priority map
|
Port priority |
Local precedence |
|
0 |
0 |
|
1 |
1 |
|
2 |
2 |
|
3 |
3 |
|
4 |
4 |
|
5 |
5 |
|
6 |
6 |
|
7 |
7 |
Appendix C Introduction to packet precedence
IP precedence and DSCP values
As shown in Figure 20, 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 8 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 9 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 21 An Ethernet frame with an 802.1Q tag header
As shown in Figure 21, 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 22 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 10 shows the values for 802.1p priority.
Table 10 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 |
802.11e priority
To provide QoS services on WLAN, the 802.11e standard was developed. IEEE 802.11e is a MAC-layer enhancement to IEEE 802.11. IEEE 802.11e adds a 2-byte QoS control field to the 802.11e MAC frame header. The 3-bit QoS control field represents the 802.11e priority in the range of 0 to 7.
Figure 23 802.11e frame structure
EXP values
The EXP field is in MPLS labels for MPLS QoS purposes. As shown in Figure 24, the EXP field is 3-bit long and is in the range of 0 to 7.
Figure 24 MPLS label structure
