H3C S3100-52P Manuale utente

Operation Manual – QoS

H3C S3100-52P Ethernet Switch Table of Contents

Table of Contents

Chapter 1 QoS Configuration.......................................................................................................1-1

1.1 Overview............................................................................................................................1-1

1.1.1 Traffic ......................................................................................................................1-1

1.1.2 Traffic Classification................................................................................................ 1-1

1.1.3 Precedence.............................................................................................................1-1

1.1.4 Priority of Protocol Packets.....................................................................................1-5

1.1.5 Port Rate Limit.........................................................................................................1-5

1.1.6 Queue Scheduling Configuration Synchronization on Aggregated Ports............... 1-5

1.1.7 Queue Scheduling...................................................................................................1-6

1.2 QoS Supported by S3100-52P..........................................................................................1-7

1.3 Configuring the Mapping between 802.1p Priority and Queues........................................1-8

1.4 Setting to Use the Port Priority or Packet Priority..............................................................1-9

1.5 Setting the Precedence of Protocol Packet.....................................................................1-10

1.5.1 Configuration Prerequisites...................................................................................1-10

1.5.2 Configuration Procedure.......................................................................................1-10

1.5.3 Configuration Example.......................................................................................... 1-11

1.6 Configuring Port Rate Limit..............................................................................................1-11

1.6.1 Configuration Prerequisites...................................................................................1-11

1.6.2 Configuration Procedure.......................................................................................1-11

1.6.3 Configuration Example.......................................................................................... 1-12

1.7 Configuring Queue-Scheduling........................................................................................ 1-12

1.7.1 Configuration Prerequisites...................................................................................1-12

1.7.2 Configuration Procedure.......................................................................................1-13

1.7.3 Configuration Example.......................................................................................... 1-14

1.8 Displaying QOS Configuration.........................................................................................1-15

Operation Manual – QoS

H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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Chapter 1 QoS Configuration

1.1 Overview

QoS (Quality of Service) is a concept generally existing in occasions with service

supply and demand. It evaluates the ability to meet the need of the customers in

service. Generally, the evaluation is not to grade precisely. Its purpose is to analyze the

conditions where the service is the best and the conditions where the service still needs

improvement and then to make improvements in the specified aspects.

In an internet, QoS evaluates the ability of the network to deliver packets. The

evaluation on QoS can be based on different aspects because the network provides

various services. Generally speaking, QoS is the evaluation on the service ability to

support the core requirements such as delay, jitter, and packet loss ratio in the packet

delivery.

1.1.1 Traffic

Traffic means service traffic; that is, all the packets passing the switch.

1.1.2 Traffic Classification

Traffic classification means identifying packets that conform to certain characteristics

according to certain rules.

Aclassification rule is a filter rule configured to meet your management requirements. It

can be very simple. For example, you can use a classification rule to identify traffic with

different priorities according to the ToS field in the IP packet header. It can be very

complicated too. For example, you can use a classification rule to identify the packets

according to the combination of link layer (Layer 2), network layer (Layer 3), and

transport layer (Layer 4) information including MAC addresses, IP protocols, source

addresses, destination addresses, port numbers of applications, and so on.

Classification is generally based on the information in the packet header and rarely

based on the packet contents.

1.1.3 Precedence

1) IP precedence, ToS precedence, and DSCP precedence

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H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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Figure 1-1 DS field and TOS byte

The TOS field in an IP header contains eight bits:

zThe first three bits indicate IP precedence in the range of 0 to 7.

zBit 3 to bit 6 indicate ToS precedence in the range of 0 to 15.

zRFC2474 re-defines the ToS field in the IP packet header, which is called the DS

field. The first six (bit 0 to bit 5) bits of the DS field indicate DSCP precedence in

the range of 0 to 63. The first three bits in DSCP precedence are class selector

codepoints, bit 4 and bit 5 indicate drop precedence, and bit 6 is zero indicating

that the device sets the service class with the DS model. The last two bits (bit 6

and bit 7) are reserved bits.

The precedence values of the IP packet indicate eight different service classes.

Table 1-1 Description on 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

The Diff-Serv network defines four traffic classes:

zExpedited Forwarding (EF) class: In this class, packets can be forwarded

regardless of link share of other traffic. The class is suitable for preferential

services with low delay, low packet loss ratio, low jitter, and assured bandwidth

(such as virtual leased line);

zAssured forwarding (AF) class: This class is further divided into four subclasses

(AF1/2/3/4) and a subclass is further divided into three drop priorities, so the AF

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H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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service level can be segmented. The QoS rank of the AF class is lower than that of

the EF class;

zClass selector (CS) class: This class comes from the IP TOS field and includes

eight classes;

zBest Effort (BE) class: This class is a special class without any assurance in the

CS class. The AF class can be degraded to the BE class if it exceeds the limit.

Current IP network traffic belongs to this class by default.

Table 1-2 Description on 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 default (be)

2) 802.1p priority

802.1p priority lies in Layer 2 packet headers and is applicable to occasions where the

Layer 3 packet header does not need analysis but QoS must be assured at Layer 2.

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H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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Figure 1-2 An Ethernet frame with an 802.1Q tag header

As shown in the figure above, each host supporting 802.1Q protocol adds a 4-byte

802.1Q tag header after the source address of the former Ethernet frame header when

sending packets.

The 4-byte 802.1Q tag header contains a 2-byte Tag Protocol Identifier (TPID) whose

value is 8100 and a 2-byte Tag Control Information (TCI). TPID is a new class defined

by IEEE to indicate a packet with an 802.1Q tag. Figure 1-3 describes the detailed

contents of an 802.1Q tag header.

Figure 1-3 802.1Q tag headers

In the figure above, the 3-bit priority field in TCI is 802.1p priority in the range of 0 to 7.

These three bits specify the precedence of the frame. Eight classes of precedence are

used to determine which packet is sent preferentially when congestion occurs.

Table 1-3 Description on 802.1p priority

CoS (decimal) CoS (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

The precedence is called 802.1p priority because the related applications of this

precedence are defined in detail in the 802.1p specifications.

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H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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1.1.4 Priority of Protocol Packets

Protocol packets carry their own priority. You can perform QoS actions on protocol

packets by setting their priorities.

1.1.5 Port Rate Limit

Port rate limit is port-based rate limit. It limits the total rate of outbound packets on a

port.

1.1.6 Queue Scheduling Configuration Synchronization on Aggregated

Ports

The feature of queue scheduling configuration synchronization on aggregated ports

makes the queue scheduling configuration synchronous on each port of an aggregation

group.

zSupporting the feature of queue scheduling configuration synchronization on the

ports in an aggregation group

When you modify or delete the queue scheduling mode in Ethernet port view, the

queue scheduling modes of all the ports in the aggregation group are modified or

deleted if this port belongs to an aggregation group; only the queue scheduling mode of

this port is modified or deleted if this port does not belong to any aggregation group.

zDynamic aggregation supported by queue scheduling modes on ports

If the queue scheduling configuration information of some LACP-enabled ports in up

state is the same, these ports can be aggregated into the same aggregation group.

zStatic aggregation or manual aggregation supported by queue scheduling modes

on ports

You can add a queue-scheduling-enabled port into a specific static or manual

aggregation group. This operation can be performed not only on the local device but

also across devices in an intelligent resilient framework (IRF).

zYou can use the copy command to copy the queue scheduling configuration of a

port.

Note:

For the introduction to the copy command, refer to the Basic Port Configuration Module

in this manual.

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H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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1.1.7 Queue Scheduling

When the network is congested, the problem that many packets compete for resources

must be solved, usually through queue scheduling.

In the following section, strict priority (SP) queueing and weighted round robin (WRR)

queueing are introduced.

1) SP queueing

Packets sent via this

interface

high priority

Low priority

Classify

Packets sent

Sending queueDequeue

queue 7

queue 6

queue 5

queue 4

queue 3

queue 2

queue 1

queue 0

Packets sent via this

interface

high priority

Low priority

Classify

Packets sent

Sending queueDequeue

queue 7

Packets sent via this

interface Packets sent

Sending queueDequeue

queue 7

queue 6

queue 5

queue 4

queue 3

queue 2

queue 1

queue 0

Packets sent via this

interface

high priority

Low priority

Classify

Packets sent

Sending queueDequeue

queue 7

Packets sent via this

interface

high priority

Low priority

Classify

Packets sent

Sending queueDequeue

queue 7

queue 6

queue 5

queue 4

queue 3

queue 2

queue 1

queue 0

Packets sent via this

interface

high priority

Low priority

Classify

Packets sent

Sending queueDequeue

queue 7

Packets sent via this

interface Packets sent

Sending queueDequeue

queue 7

queue 6

queue 5

queue 4

queue 3

queue 2

queue 1

queue 0

Figure 1-4 Diagram for SP queueing

SP queue-scheduling algorithm is specially designed for critical service applications.

An important feature of critical services is that they demand preferential service in

congestion in order to reduce the response delay. Assume that there are eight output

queues on the port and the preferential queue classifies the eight output queues on the

port into eight classes, which are queue7, queue6, queue5, queue4, queue3, queue2,

queue1, and queue0. Their priorities decrease in order.

In queue scheduling, SP sends packets in the queue with higher priority strictly

following the priority order from high to low. When the queue with higher priority is

empty, packets in the queue with lower priority are sent. You can put critical service

packets into the queueswith higher priority and put non-criticalservice (such as e-mail)

packets into the queues with lower priority. In this case, critical service packets are sent

preferentially and non-critical service packets are sent when critical service groups are

not sent.

The disadvantage of SP queue is that: if there are packets in the queues with higher

priority for a long time in congestion, thepackets in the queueswith lower priority will be

“starved” because they are not served.

2) WRR queueing

Operation Manual – QoS

H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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Figure 1-5 Diagram for WRR

WRR queue-scheduling algorithm schedules all the queues in turn and every queue

can be assured of a certain service time. Assume there are eight priority queues on a

port. WRR configures a weight value for each queue, which is w7, w6, w5, w4, w3, w2,

w1, and w0. The weight value indicates the proportion of obtaining resources. On a 100

M port, configure the weight value of WRR queue-scheduling algorithm to 50, 50, 30,

30, 10, 10, 10, and 10 (corresponding to w7, w6, w5, w4, w3, w2, w1, and w0 in order).

In this way, the queue with the lowest priority can get 5 Mbps bandwidth at least, and

the disadvantage of SP queue-scheduling that the packets in queues with lower priority

may not get service for a long time is avoided. Another advantage of WRR queue is that:

though the queues are scheduled in order, the service time for each queue is not fixed;

that is to say, if a queue is empty, the next queue will be scheduled. In this way, the

bandwidth resources are made full use.

1.2 QoS Supported by S3100-52P

Table 1-4 QoS functions supported by S3100-52P and related commands

QoS Specification Related command

Priority mapping Support only the mapping

between 802.1p priority and

local queues

qos

cos-local-precedence-map

Port priority Supported priority priority-level

priority trust

Queue

scheduling

Support SP and WRR

Support queue scheduling

configuration synchronization

on aggregated ports

queue-scheduler

Operation Manual – QoS

H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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QoS Specification Related command

Set the priority of

protocol packets Supported protocol-priority

Set port rate limit Supported line-rate

1.3 Configuring the Mapping between 802.1p Priority and

Queues

The mapping between the local precedence and the outbound queue is one-to-one.

You can modify the mapping between the 802.1p priority and the outbound queue by

modifying the mapping between the 802.1p priority and the local precedence.

I. Configuration prerequisites

You have understood the mapping between the 802.1p priority and the local

precedence and the default mapping table.

II. Configuration procedure

Table 1-5 Configure the mapping table

Operation Command Description

Enter system view system-view —

Configure the

COS-to-local-precedence

mapping table

qos

cos-local-precedence-map

cos0-map-local-prec

cos1-map-local-prec

cos2-map-local-prec

cos3-map-local-prec

cos4-map-local-prec

cos5-map-local-prec

cos6-map-local-prec

cos7-map-local-prec

Optional

Display the mapping table display qos

cos-local-precedence-map

Optional

You can execute the

display command in

any view

III. Configuration example

zConfigure the following 802.1p priority-to-local precedence mappings: 0 to 2, 1 to

3, 2 to 4, 3 to 1, 4 to 7, 5 to 0, 6 to 5, and 7 to 6.

zDisplay the configuration results.

Configuration procedure:

<H3C> system-view

Operation Manual – QoS

H3C S3100-52P Ethernet Switch Chapter 1 QoS Configuration

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System View: return to User View with Ctrl+Z.

[H3C] qos cos-local-precedence-map 2 3 4 1 7 0 5 6

[H3C] dis qos cos-local-precedence-map

cos-local-precedence-map:

cos(802.1p) : 0 1 2 3 4 5 6 7

--------------------------------------------------------------------------

local precedence(queue) : 2 3 4 1 7 0 5 6

1.4 Setting to Use the Port Priority or Packet Priority

By default, the switch replaces the 802.1p priority of the received packet with the

priority of the inbound interface, and then assigns local precedence to the packet

according to the priority. In this case, you can set the port priority.

In addition, you can specify the switch to use the packet priority.

I. Configuration prerequisites

zThe priority trust mode is specified

zThe port whose priority is to be configured is specified

zThe priority value of the specified port is specified

II. Configuration procedure

Table 1-6 Set to use the port priority

Operation Command Description

Enter system view system-view —

Enter Ethernet port

view interface interface-type

interface-number —

Set the port priority priority priority-level Optional

By default, the port

priority is 0

Table 1-7 Set to use the packet priority

Operation Command Description

Enter system view system-view —

Enter Ethernet port

view interface interface-type

interface-number —

Set the switch to use

the packet priority priority trust

Through this

configuration, the switch

uses the packet priority

instead of the port priority

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