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QoS Configuration

Priority Mapping

Section titled “Priority Mapping”

Networks typically face various types of traffic, each with different performance and service requirements. Therefore, to meet the needs of different applications and services and ensure the performance of critical applications while improving the overall network performance, users can use different QoS priorities in different networks. This involves mapping the priority carried by the packet to the local priority processed by the device, providing differentiated QoS services based on the local priority.

The priority carried by the packet is called packet priority, for example: VLAN packets use 802.1p, and IP packets use DSCP.

The local priority, also known as TC (traffic class), corresponds to the eight queues at the egress by default. Differentiated services for packets of different priorities are implemented based on the scheduling methods of different egress queues.

Queue Scheduling

Section titled “Queue Scheduling”

Queue scheduling algorithms are one of the core mechanisms for implementing network QoS control and an important part of network resource management. It controls the use of link bandwidth by different types of packets to provide different levels of service to different data streams.

Each interface of the device in the outbound direction is configured with 8 queues. They are identified by queue IDs from 0 to 7. Packets are assigned to different egress queues based on the mapping from local priority to egress queues, and then processed according to the configured queue scheduling method.

Strict Scheduling

Strict priority scheduling. The scheduling is strictly based on the priority of the egress queue, and only when the high-priority queue is empty will the low-priority queue be scheduled. Users can put high-priority business packets into high-priority queues and non-critical business packets into low-priority queues to ensure that high-priority business can be scheduled first during congestion, ensuring business stability. The priority scheduling order for queues is: Queue7> Queue6> Queue5> Queue4> Queue3> Queue2> Queue1> Queue0. It is worth noting that this scheduling method may cause packets in low-priority queues to be scheduled late, leading to queue starvation.

DWRR Scheduling

Weighted Round Robin scheduling. Queues are scheduled in a round-robin manner according to their weights. The device supports a mixed scheduling mode of STRICT and DWRR for different queues under the same interface. Queues configured with STRICT scheduling mode are given priority. When there are no packets in queues scheduled by the STRICT mode, queues are scheduled according to the weights in the DWRR mode. By default, the scheduling mode for queues is DWRR, with a weight of 100 for each queue.

Traffic Shaping

Section titled “Traffic Shaping”

When the transmission rate of packets exceeds the reception rate, or when the downstream device interface speed is lower than that of the upstream device, it can lead to network congestion. Without restricting the size of user-generated traffic, a continuous burst of business data from numerous users can further congest the network. To ensure that limited network resources are effectively utilized to serve users, it’s necessary to impose limits on user-generated traffic. Typically, traffic specifications are evaluated using token buckets.

A token bucket can be envisioned as a container that holds a certain number of tokens. The device deposits tokens into the bucket at a predetermined rate. When the bucket is full, any excess tokens overflow, and no more tokens are added to the bucket. The token bucket is merely a method for measuring traffic and does not filter or take any action on the traffic, such as discarding packets; these operations are performed by other functionalities.

QoS Priority Configuration

Section titled “QoS Priority Configuration”
Configure TasksInstructions
Configure priority mapping relationshipRequired
Bind priority mapping relationshipRequired

Configuring Priority Mapping Relationship

Section titled “Configuring Priority Mapping Relationship”

By default, the mapping from the DSCP/802.1p priority carried in the packet to the local priority is as follows: all mapped to priority 0. The mapping from local priority to the egress queue is as follows: tc 0—queue 0, tc 1—queue 1, tc 2—queue 2, tc 3—queue 3, tc 4—queue 4, tc 5—queue 5, tc 6—queue 6, tc 7—queue 7.

OperationCommandDescription
Enter the system configuration viewconfigure terminal
Configure priority mapping relationshipqos map {dot1p_to_tc|dscp_to_tc|tc_to_queue} profile_name in_value valuedot1p_to_tc: Mapping from 802.1p priority to local priority.
dscp_to_tc: Mapping from DSCP priority to local priority.
tc_to_queue: Mapping from local priority to egress queue.
in_value: Input priority (priority carried in the packet). value: Local priority.

Section titled “”
OperationCommandDescription
Enter the system configuration viewconfigure terminal
Bind the specified mapping relationship between local priority and queue globallyqos-map-all bind tc_to_queue profile name
Enter the interface viewinterface ethernet ID
Bind the QoS map to the specified interfaceqos-map bind type profile_nametype: QoS map type, which includes dot1p_to_tc and dscp_to_tc

Section titled “”

The device supports a hybrid scheduling mode of STRICT and DWRR for different queues under the same interface. Queues configured with STRICT mode for priority scheduling are given priority, and when there are no packets in the STRICT mode queues, DWRR queues are scheduled according to their weights. By default, the scheduling mode for queues is DWRR, with weights all set to 1.

OperationCommandDescription
Enter the interface configuration viewinterface ethernet<interface_num>
Configure the queue scheduling mode for the interfaceuc-tx-queue scheduler queue_id mode STRICT
uc-tx-queue scheduler queue_id mode DWRR [ weight value ]

Section titled “”
Configure TasksInstructions
Configure traffic shaping based on the interfaceOptional
Configure queue rate limitingRequired
Configure traffic shaping based on flowsRequired

Section titled “”
OperationCommandDescription
Enter the interface configuration viewinterface ethernet interface_num
Traffic Shaping Configuration Based on Interfaceport-shaper enable pir pbsThe PIR unit is kbit/s.
The PBS unit is bytes.
Traffic shaping can be directly configured based on the interface, and it takes effect in the outbound direction of the interface.

Section titled “”
OperationCommandDescription
Enter the interface configuration viewinterface ethernet interface_num
Configure queue rate limitinguc-tx-queue scheduler queue_id { pir|pbs }pir: Maximum allowable rate, measured in bytes per second (byte/s).
pbs: Peak Burst Size, measured in bytes

Section titled “”
Configure TasksInstructions
Create a traffic behaviorRequired
Configure a CAR (Committed Access Rate) templateRequired
Bind the traffic behavior to the interfaceRequired

Section titled “”
OperationCommandDescription
Enter the system configuration viewconfigure terminal
Create a traffic behaviortraffic-behavior traffic-behavior-name>

Section titled “”

Single bucket single rate (SBSR) mode is a traffic control mechanism that uses a token bucket to regulate the forwarding rate of packets, aiming to control the average rate of traffic to ensure that the traffic on the network does not exceed a specific rate limit. When evaluating traffic, the parameters of the token bucket include:

CIR (Committed Information Rate): The rate at which tokens are added to the token bucket, default unit is KBps.

CBS (Committed Burst Size): The capacity of the token bucket, default unit is bytes, representing the size of the burst that can be accommodated by the token bucket.

In single bucket single rate mode, when the device receives a packet, it compares the number of tokens in the bucket. If there are enough tokens, the packet is forwarded. If there are not enough tokens, the packet is either dropped or buffered. Let Tc represent the number of tokens in the bucket, and Tc is initialized to CBS.

If the length of the packet does not exceed the number of tokens Tc in the bucket, the packet is marked as green, and Tc is decremented by the size of the packet (Tc = Tc - B).

If the length of the packet exceeds the number of tokens Tc in the bucket, the packet is marked as red, and Tc remains unchanged.

Dual token bucket dual rate (TBDR) mode uses two token buckets to control packet transmission, each defining the “CBS (Committed Burst Size)” and “PBS (Peak Burst Size)” respectively.

CIR: Committed Information Rate, expressed in default units of KBps, represents the rate at which tokens are added to the C bucket.

CBS: Committed Burst Size, expressed in default units of bytes, represents the maximum amount of data that can be transmitted from the C bucket.

PIR: Peak Information Rate, expressed in default units of KBps, represents the rate at which tokens are added to the P bucket. PIR is greater than CIR.

PBS: Peak Burst Size, expressed in default units of bytes, represents the maximum amount of data that can be transmitted from the P bucket.

Token addition method: Tokens are added to the C and P buckets at rates of CIR and PIR respectively. Since these two token buckets are independent, if one bucket runs out of tokens, incoming packets to that bucket will be discarded while the other bucket remains unaffected and continues to receive tokens. Tc and Tp represent the token counts in the C and P buckets respectively, with both initialized to CBS and PBS.

  • If the length of the packet exceeds the token count in the P bucket (Tp), the packet is marked as red, and Tc and Tp remain unchanged.
  • If the length of the packet is greater than Tc but less than Tp, the packet is marked as yellow, and Tp is decreased by the token count (B) while Tc remains unchanged.
  • If the length of the packet does not exceed the token count in the C bucket (Tc), the packet is marked as green, and both Tp and Tc are decreased by the token count (B).

The Dual Token Bucket Dual Rate (TBDR) mode allows for more granular control over different types of traffic, enabling marking and management based on rate requirements and congestion conditions. It facilitates the implementation of more sophisticated QoS policies to ensure that different traffic classes receive appropriate treatment, thereby maintaining network stability and service quality.

OperationCommandDescription
Enter Traffic behavior configuration viewtraffic-behavior
Configure CAR templatecar {sr-tcm|tr-tcm} [meter-type {bytes|packets}] cir cir [cbs cbs ] [pirpir**] [pbs** pbs] [yellow-packet-action {DROP|FORWARD|REMARK}] [red-packet-action {DROP|FORWARD|REMARK}] [remark-dot1p] value [remark-dscp value ] [remark-tc value ]cir: Committed Information Rate, which represents the guaranteed rate of traffic that can pass through.
cbs: Committed Burst Size, indicating the amount of committed burst traffic that can be passed through instantly.
pir: Peak Information Rate, which represents the maximum rate of traffic that can pass through.
pbs: Peak Burst Size, indicating the amount of peak burst traffic that can be passed through instantly.

Section titled “”

By configuring a CAR (Committed Access Rate) template and binding it with an ACL (Access Control List), users can finely control which traffic needs to be rate-limited. This approach helps in managing bandwidth usage for specific types or sources of traffic, preventing certain flows from excessively consuming network resources and thereby balancing the overall network utilization.

OperationCommandDescription
Enter ACL configuration viewaccess-list L3 name egress
Bind the CAR template with the ACLrule id traffic-behavior traffic-behavior-name
Enter interface configuration viewinterface ethernet interface-id
Bind the behavior to the interfaceacl name

Section titled “”
OperationCommand
View QoS map configurationshow qos map{all|dot1p_to_tc|dscp_to_tc| tc_to_queue}
View the interface mapping tableshow interface qos-map-bind
View outbound queue statisticsshow queue counters [ interface-name ]
View interface queue scheduling modeshow interface uc-tx-queue
View interface-based traffic shaping rulesshow interface port-shaper
View configured behaviors and CAR policiesshow traffic-behavior rule
View behavior hit statisticsshow traffic-behavior counters

Section titled “”

In a certain data center network structure as shown in the diagram below, there are three types of traffic accessing the Internet: HTTP, FTP, and Email, with corresponding DSCP values of 33, 35, and 27.

The current requirement is to configure the packet transmission priorities on the switch as follows: HTTP > FTP > Email. In case of congestion, ensure the priority transmission of HTTP packets. HTTP data must be transmitted first before sending other data, and the ratio of FTP to Email traffic should be controlled at 2:1.

  1. Assign IP Addresses to Interfaces for Network Access
  2. Configure DSCP-to-Priority Mapping
sonic(config)# qos map dscp_to_tc profile1 33 4
sonic(config)# qos map dscp_to_tc profile1 35 3
sonic(config)# qos map dscp_to_tc profile1 27 2
sonic(config)# port-group ethernet 1-48
sonic(config-port-group-1-48)# qos-map bind dscp_to_tc profile1
  1. Configure mapping from local priority to egress queue
sonic(config)# qos map tc_to_queue test 0 0
sonic(config)# qos map tc_to_queue test 1 1
sonic(config)# qos map tc_to_queue test 2 2
sonic(config)# qos map tc_to_queue test 3 3
sonic(config)# qos map tc_to_queue test 4 4
sonic(config)# qos map tc_to_queue test 5 5
sonic(config)# qos map tc_to_queue test 6 6
sonic(config)# qos map tc_to_queue test 7 7
sonic(config)# qos-map-all bind tc_to_queue
  1. Configure DWRR Scheduling on Ethernet1
sonic(config)# interface ethernet 1
sonic(config-if-1)# uc-tx-queue scheduler 4 -m STRICT
sonic(config-if-1)# uc-tx-queue scheduler 3 -m DWRR -w 2
sonic(config-if-1)# uc-tx-queue scheduler 2 -m DWRR -w 1
sonic# show qos map dscp_to_tc
{
  "profile1":{
    "27":"2",
    "33":"4",
    "35":"3"
  }
}


sonic# show interface qos-map-bind
{
  "Ethernet1":{
    "dscp_to_tc_map":"[DSCP_TO_TC_MAP|profile1]"
  }
}


sonic# show interface uc-tx-queue
{
  "Ethernet1|4":{
    "SCHEDULER|scheduler.Ethernet1_2":{
      "type":"STRICT"
    }
  }


  "Ethernet1|3":{
    "SCHEDULER|scheduler.Ethernet1_3":{
      "type":"DWRR"
    }
  }


  "Ethernet1|2":{
    "SCHEDULER|scheduler.Ethernet1_4":{
      "type":"DWRR"
    }
  }
}

When congestion occurs, queue2 should be prioritized, and there should be no packet drops in queue2. This means that the packets from the HTTP traffic (DSCP 33) in queue2 should be serviced without any drops.

Section titled “”

A data center network structure is shown below, the services from the network side of the network are data, voice and video, carrying 802.1p priorities of 2, 3 and 4 respectively.

Bandwidth jitter may occur because the traffic rate on the ingress side of the Device is greater than the rate on the egress side. To reduce bandwidth jitter while ensuring bandwidth requirements for various services, it is required that:

Device egress bandwidth is limited to 1000Mbit/s;

Data bandwidth limited to 200Mbit/s;

Voice bandwidth is limited to 300Mbit/s;

Video bandwidth limited to 500Mbit/s;

  1. Configure each interface IP to enable users to access the network through the Device.
  2. Configure priority mapping for dot1p_to_tc.
sonic(config)# qos map dot1p_to_tc profile1 2 2
sonic(config)# qos map dot1p_to_tc profile1 3 3
sonic(config)# qos map dot1p_to_tc profile1 4 4
sonic(config)# interface ethernet 1
sonic(config-if-1)# qos-map bind dot1p_to_tc profile1
  1. Configure port traffic shaping on Ethernet1 of the Device, set pir=12500000 byte/s, pbs=1280000 byte.
sonic(config)# interface ethernet 1
sonic(config-if-1)# port-shaper enable 12500000 1280000
  1. Configure queue traffic shaping policies.
sonic(config)# interface ethernet 1
sonic(config-if-1)# uc-tx-queue scheduler 2 -m STRICT -p 200000000
sonic(config-if-1)# uc-tx-queue scheduler 3 -m STRICT -p 300000000
sonic(config-if-1)# uc-tx-queue scheduler 4 -m STRICT -p 500000000
  1. Configuration Verification
sonic# show qos map dot1p_to_tc
sonic# show interfaces ethernet qos_map_bind
sonic# show interfaces ethernet port-shaper
  1. Streaming verification After successful configuration, check the port count through the command show interfaces counters and check the queue reception through the command show queue counters Ethernet1 on the Switch, both meet the requirements.