Shulou(Shulou.com)06/01 Report--

With the development of the network, the Internet traffic increases rapidly, the network produces congestion, the delay increases, and sometimes it causes packet loss, which leads to the decline of service quality. When the network is congested, how to ensure that the bandwidth and real-time data of important data can be quickly forwarded?

QOS application requirements

Overview of 1.QOS

With the rapid development of the network, more and more users are connected to the network, and the network provides more and more services. The popularity of the network and the diversification of services make the network traffic increase rapidly, resulting in the network bandwidth can not meet the needs of the network, then there is the phenomenon of network congestion.

Network congestion leads to unexpected transmission of messages, delay jitter, packet loss and other phenomena, which will lead to the decline of service quality or even unusability. In order to deal with the network congestion, the most direct way is to expand the network bandwidth, but due to technical or economic limitations, sometimes it can not be solved by increasing the bandwidth. At this time, we need a technology that can ensure the bandwidth of the message in the limited bandwidth to avoid delay and packet loss. This technology is QOS technology.

two。 Network congestion

1) the generation of network congestion

Data enters the device from the high-speed port and is forwarded out the low-speed port.

Traffic converges, traffic enters the device through multiple ports, forwards out one port, and the sum of the rates entering the device port is greater than the rate of the forwarding interface.

2) the influence of network congestion

When the network is congested, it may have the following effects on the network

Message transmission delay, delay jitter and packet loss rate increase

High delay and packet loss lead to packet retransmission, which increases the burden on the network.

Due to network congestion, packet retransmission reduces the effective throughput of the network.

3) the solution of network congestion

In the case of unable to improve the network bandwidth, the effective way to solve the network congestion is to make rational use of the network bandwidth. When the network congestion occurs, the existing bandwidth is allocated reasonably by using QOS technology according to the nature and needs of the business, so as to reduce the impact of network congestion. QOS service model

There are three service models of QOS in the network.

1) Best-effort service: best-effort service model

Mode working model, first come, forward first, then forward later, do not prioritize

2) Integrated service: integrated Services Model, abbreviated as Intserv

The bandwidth resources need to be reserved in advance, the configuration is complex and flexible, and the reserved resources cannot be returned after the bandwidth is used up.

3) Differentiated service: DiffServ model, referred to as Diffserv

Do not need to reserve bandwidth resources, can identify the source and destination protocol IP address port number, automatically set the priority of data packets, high priority to the device priority forwarding. QOS operation model

QOS involves four major components, namely, classification and marking, × × and supervision, congestion avoidance, and congestion management.

1. Classification and marking

QOS is an overall design framework, which is not limited to one device, but the devices in the whole network cooperate with each other to achieve the goal of traffic optimization. The core of QOS is to ensure that important traffic passes through the network device first. By default, network devices treat any message equally, in order that any device can identify important traffic at the boundary of the network. That is, any traffic entering the network should be classified according to the degree of importance and marked differently, based on which subsequent devices can identify which traffic is relatively important.

classification

Flow classification is the basis for distinguishing services. Flow classification can use the priority of messages to identify traffic with different priority characteristics, and it can also use information such as source address, destination address, MAC address, protocol or port to identify different traffic. flow classification is completely defined by network managers, and the importance of traffic varies with different networks. for example, HTTP traffic may be more important for small companies. For large companies, voice traffic is more important, it is relatively important, any traffic should pass through the network, QOS only gives priority to ensure important traffic, and flow classification must be associated with some kind of traffic control or bandwidth allocation action. Flow classification generally distinguishes different traffic through ACL, especially extended ACL, which basically defines most of the traffic. The following command defines all HTTP traffic in the network.

R1 (config) # access-list 101 permit tcp any any eq 80

Marking

In the diffserv service model of QOS technology, DSCP is used as the QOS priority description for the DS field in the IP message.

The DS field has a total of eight bits, and the first eight bits of DS, that is, DS0~DS5, define a total of 64 priorities in Diffserv. QOS can also use the IP priority in the DS field, using the first three bits of DS IP, with a total of eight priority levels, where 0 indicates normal traffic and follows the best-effort principle.

By default, in actual network communication, if nothing is set, the normal data priority is 0, while for messages such as RIP or OSPF, the default priority is 6. 5.

1) define matching classes

Define matching traffic through class map, which is equivalent to an enhanced ACL. First, define class map to match a traffic or protocol

Where class-map-name is the name of the class map created, match-all means to match all the conditions defined by class-map, which is the default configuration, and match-any means to match at least one condition defined by class-map

2) define flow control policy

Call class map through policy map, and then configure policies for each class map separately

First, define policy map and call class map, with the following command

Then, configure the policy in the called class map, which includes tagging traffic, traffic × × ×, CAR, etc., and use the set command to mark the priority of the traffic, as follows

3) apply policies on interfaces

4) View configuration

You can use the show policy-map [policy-map-name] command to view the policy configuration

Use the show policy-map interface [interface-type interface-number] command to view port policy application and traffic information. × × and supervision

In order to avoid the emergence of network congestion, we can control the traffic, by using a certain strategy to control the size of traffic, in order to reduce the emergence of network congestion, the main traffic management technology is × × and supervision.

In order to make better use of network resources and avoid network congestion caused by sudden traffic generated by a large number of users, it is necessary to limit the speed of users in the network. When the port receives a traffic exceeding the limit, it is necessary to take certain measures (reduce priority or discard). For example, limit the bandwidth of each user and take measures to discard when the user generates burst traffic, which can avoid network congestion caused by too much burst traffic.

Generally speaking, three parameters can be set when monitoring the traffic, namely, the average rate, the burst and the extra burst.

Committed average rate: the average rate at which traffic is allowed to pass

Burst: the amount of traffic that is allowed to be generated by the burst, which must be greater than the maximum message length.

Extra burst: indicates the amount of traffic that can be forwarded after the burst is exceeded.

1) Traffic policy

Forwarding: you can set the policy to forward for both compliance and violation traffic

Discard: you can set the policy to discard for both compliance and violation traffic

Tag: marks the priority of the message, for example, setting the IP priority of the compliance traffic message to 5 and the IP priority of the violation traffic message to 0.

Enter the next-level traffic policy: the traffic policy can be processed at multiple levels, and the traffic can be submitted to the next-level traffic policy for control.

2) × × and supervision

Traffic × × is a measure to adjust the output rate, which uses buffers to forward traffic evenly. When the traffic enters the device for classification, there is no need to forward the × × traffic directly through the device. The × × × traffic is divided into compliance traffic and illegal traffic according to the configuration. When the traffic rate exceeds the setting, the device caches the excess traffic to the GTS queue, and then forwards the message evenly according to the configured CIR to ensure stable network traffic.

CIR for speed, Bc and Be for size

The configuration of Bc and Be values specified in different devices and technical manuals may be different. It is generally recommended to use the following formula: Bc=2 X RTT X CIR/8, where RTT represents the round-trip time of traffic, can be tested using the ping command. Be traffic is generally equal to Bc. Congestion management

Congestion management technology

FIFP: FIFO queue

Default network usage

PQ: priority queu

Post-transmit data with high priority and low priority

CQ: custom queu

Need to manage and configure ACL to capture the specified traffic

WFQ weighted fair queue

Traffic is differentiated according to source-destination IP addresses and evenly distributed according to traffic

CBWFQ: a Class-based weighted Fair queue

The administrator specifies specific traffic priority, which can only be applied in the out direction.

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