Configuring congestion management
Overview
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 12 shows two typical congestion scenarios.
Figure 12 Traffic congestion scenarios
100M
100M 10M 100M 10M
100M > 10M
(1)
50M
(100M + 10M + 50M) > 100M
(2)
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 uses queuing and scheduling algorithms to classify and sort traffic leaving a port.
The switch supports the following queuing mechanisms.
SP queuing
SP queuing is designed for mission-critical applications that require preferential service to reduce the response delay when congestion occurs.
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Figure 13 SP queuing
Queue 7
High priority
Packets to be sent through this port
Queue 6 Sent packets
Interface
……
Queue 1
Packet classification
Queue scheduling
Sending queue
Queue 0
Low priority
In Figure 13 , 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 14 .
Figure 14 WRR queuing
Queue 0 Weight 1
Packets to be sent through this port Queue 1 Weight 2 Sent packets
Interface
……
Queue N-2 Weight N-1
Packet classification
Queue N-1 Weight N
Queue scheduling
Sending queue
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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.
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.
Only group-based WRR queuing is supported in the current software version, and only WRR group 1 is supported.
WFQ queuing
Figure 15 WFQ queuing
Queue 0 Weight 1
Packets to be sent through this port Queue 1 Weight 2 Sent packets
Interface
……
Queue N-2 Weight N-1
Packet classification
Queue N-1 Weight N
Queue scheduling
Sending queue
WFQ is similar to WRR. The difference is that WFQ enables you to set guaranteed bandwidth that a
WFQ queue can get during congestion.
On an interface with WFQ queuing enabled, 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 WFQ groups.
Configuration task list
Both Layer 2 and Layer 3 Ethernet interfaces support the congestion management feature. The term
"interface" in this section collectively refers to these two types of interfaces. You can use the port
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link-mode command to configure an Ethernet port as a Layer 2 or Layer 3 interface (see Layer
2—LAN Switching Configuration Guide ).
To achieve congestion management, perform the following tasks:
Tasks at a glance
(Required.) Perform one of the following tasks to configure congestion management:
•
Configuring SP queuing
•
Configuring WRR queuing
•
Configuring WFQ queuing
•
Configuring SP+WRR queuing
•
Configuring SP+WFQ queuing
Configuring SP queuing
Step
1. Enter system view.
Command system-view
Remarks
N/A
2. Enter interface view. interface interface-type interface-number N/A
3. Configure SP queuing. qos sp
By default, byte-count WRR queuing is used on an interface.
Configuring WRR queuing
Step Command
1. Enter system view. system-view
2. Enter interface view.
Remarks
N/A
interface interface-type interface-number N/A
3. Enable WRR queuing. qos wrr { byte-count | weight }
By default, byte-count WRR queuing is used on an interface.
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, queues 0 through 7 are in
WRR group 1 and have a weight of
1, 2, 3, 4, 5, 9, 13, and 15, respectively.
Select byte-count or weight according to the WRR type
(byte-count or packet-based) you have enabled.
Configuring WFQ queuing
With a WFQ queue configured, an interface has WFQ enabled. Other queues on the interface use the default WFQ scheduling value.
To configure WFQ queuing:
Step
1. Enter system view.
Command system-view
Remarks
N/A
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Step
2. Enter interface view.
3. Enable WFQ queuing.
Command Remarks interface interface-type interface-number N/A qos wfq { byte-count | weight }
By default, byte-count WRR queuing is used on an interface.
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 are in
WFQ group 1 and have a weight of 1.
Select byte-count or weight according to the WFQ type
(byte-count or packet-based) you have enabled.
5. (Optional.) Set the minimum guaranteed bandwidth for a WFQ queue.
qos bandwidth queue queue-id
min bandwidth-value
The default setting is 64 kbps.
Configuring SP+WRR queuing
Configuration procedure
To configure SP+WRR queuing:
Step
1. Enter system view.
Command system-view
Remarks
N/A
2. Enter interface view.
interface interface-type interface-number
N/A
3. Enable byte-count or packet-based WRR queuing.
4. Assign a queue to the SP group. qos wrr { byte-count
| weight } qos
wrr queue-id group sp
By default, byte-count WRR queuing is used on an interface.
By default, all queues on a WRR-enabled interface are in WRR group 1.
5. Assign a queue to the 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 are in WRR group 1, and the scheduling values of queues 0 through 7 are
1, 2, 3, 4, 5, 9, 13, and 15, respectively.
Select byte-count or weight according to the WRR type (byte-count or packet-based) you have enabled.
Configuration example
1. Network requirements
Configure SP+WRR queuing on HundredGigE 1/0/1, and use packet-based WRR.
Assign queues 4 through 7 on HundredGigE 1/0/1 to the SP group.
Assign queues 0 through 3 on HundredGigE 1/0/1 to WRR group 1, with their weights as 1,
2, 1, and 3, respectively.
2. Configuration procedure
# Enter system view.
<Sysname> system-view
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# Configure SP+WRR queuing on HundredGigE 1/0/1.
[Sysname] interface hundredgige 1/0/1
[Sysname-HundredGigE1/0/1] qos wrr weight
[Sysname-HundredGigE1/0/1] qos wrr 4 group sp
[Sysname-HundredGigE1/0/1] qos wrr 5 group sp
[Sysname-HundredGigE1/0/1] qos wrr 6 group sp
[Sysname-HundredGigE1/0/1] qos wrr 7 group sp
[Sysname-HundredGigE1/0/1] qos wrr 0 group 1 weight 1
[Sysname-HundredGigE1/0/1] qos wrr 1 group 1 weight 2
[Sysname-HundredGigE1/0/1] qos wrr 2 group 1 weight 1
[Sysname-HundredGigE1/0/1] qos wrr 3 group 1 weight 3
Configuring SP+WFQ queuing
Configuration procedure
To configure SP+WFQ queuing:
Step
1. Enter system view.
2. Enter interface view.
Command system-view
interface interface-type
interface-number
Remarks
N/A
N/A
3. Enable byte-count or packet-based WFQ queuing. qos wfq { byte-count | weight }
By default, byte-count WRR queuing is used on an interface.
4. Assign a queue to the SP group.
qos wfq queue-id group sp
By default, all queues on a
WFQ-enabled interface are in WFQ group 1.
5. Assign a queue to the
WFQ 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 are in WFQ group 1 and have a scheduling value of 1.
Select byte-count or weight according to the WFQ type
(byte-count or packet-based) you have enabled.
6. (Optional.) Set the minimum guaranteed bandwidth for a queue.
Configuration example
qos bandwidth queue queue-id
min bandwidth-value
The default setting is 64 kbps.
1. Network requirements
Configure SP+WFQ queuing on HundredGigE 1/0/1, and use packet-based WFQ.
Assign queues 4 through 7 to the SP group.
Assign queues 0 through 3 to WFQ group 1, with their weights as 1, 2, 1, and 3, respectively.
Set the minimum guaranteed bandwidth to 128 Mbps for each of the four WFQ queues.
2. Configuration procedure
# Enter system view.
<Sysname> system-view
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# Configure SP+WFQ queuing on HundredGigE 1/0/1.
[Sysname] interface hundredgige 1/0/1
[Sysname-HundredGigE1/0/1] qos wfq weight
[Sysname-HundredGigE1/0/1] qos wfq 4 group sp
[Sysname-HundredGigE1/0/1] qos wfq 5 group sp
[Sysname-HundredGigE1/0/1] qos wfq 6 group sp
[Sysname-HundredGigE1/0/1] qos wfq 7 group sp
[Sysname-HundredGigE1/0/1] qos wfq 0 group 1 weight 1
[Sysname-HundredGigE1/0/1] qos bandwidth queue 4 min 128000
[Sysname-HundredGigE1/0/1] qos wfq 1 group 1 weight 2
[Sysname-HundredGigE1/0/1] qos bandwidth queue 5 min 128000
[Sysname-HundredGigE1/0/1] qos wfq 2 group 1 weight 1
[Sysname-HundredGigE1/0/1] qos bandwidth queue 6 min 128000
[Sysname-HundredGigE1/0/1] qos wfq 3 group 1 weight 3
[Sysname-HundredGigE1/0/1] qos bandwidth queue 7 min 128000
Displaying and maintaining congestion management
Execute display commands in any view and reset commands in user view.
Task
Display SP queuing configuration.
Display WRR queuing configuration.
Display WFQ queuing configuration.
Display queue-based outgoing traffic statistics for interfaces.
Clear interface statistics.
Command display qos queue sp interface [ interface-type interface-number ] display qos queue wrr interface [ interface-type interface-number ] display qos queue wfq interface [ interface-type interface-number ] display qos queue-statistics interface [ interface-type interface-number ] outbound reset counters interface [ interface-type
[ interface-number | interface-number.subnumber
] ]
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