Deep Analysis of slow network speed: Interview

Surfing the Internet has become an indispensable way of work and leisure in our daily life. However, in our daily work, we often encounter questions such as "why is the network speed slow and how to do with the network speed slow. To solve these problems, we should first understand some concepts.

I. Some basic concepts about network speed

1. network speed and bandwidth

The network speed usually refers to the actual network access speed of the user, and the theoretical network speed is usually expressed by bandwidth. As we often call it a 1 mbps bandwidth, that is, 1024 kbps (kilo bit per second kilobytes per second ). The so-called network speed, that is, the transmission speed per second, that is, the upload speed and download speed, expressed in BPS, that is, the number of bytes that can be transmitted per second.

Another representation is kb/s (kilo byte per second kilobytes per second). Because 1 byte is 8 bit, 1 mbps bandwidth can also be expressed as kb/s, this is our common form of download or upload speed.

2. Why is there a network speed limit?

Due to the impact of network transmission media and technical level, the network speed will be limited. For example, we used to use a modem to dial up the Internet over a telephone line at a speed of 54 kbps. Now most users access the Internet through ADSL, the network speed is usually 1-3 Mbps (related to the services provided by the local carrier). The fiber optic access can reach 10 m or 100 m.

3. What is traffic?

Traffic refers to the sum of data transmitted within the specified time. Traffic is calculated on a monthly basis. The calculation method is: webpage size (or file download) × browsing times = total traffic. For example, if a 10 Kbyte web page views 1000 times in a month, the traffic is 10 Kbyte × 1000 = 20.kb = 9.77 MB

Ii. Why does the Internet access speed become slower?

There are many reasons for slow Internet access, including computer problems, transmission media, routers, and servers. I have summarized some common cases for your reference.

1. Analysis of slow network speed when accessing a single machine

Currently, the common single-host internet access is through ADSL Moden and other methods. A computer occupies the internet. If you find that the speed of the Internet connection is slow, it is common to be caused by the following reasons.

1) slow network speed caused by a worm attack

After your computer is connected to the network, the worm keeps sending emails via e-mail, which causes network congestion and slow network speed. If it is a LAN user, it will also cause LAN paralysis. Therefore, you can promptly upgrade the anti-virus software, update operating system patches, uninstall unnecessary services, and disable unnecessary ports to improve system security and reliability and Prevent Worms.

2) Too many firewalls cause slow network speeds

For security purposes, some users often have two or more firewall software installed on the system. But they do not know that the firewall will check each transmitted or received packet on the network. Multiple firewalls consume resources, and may cause conflicts between software. You only need to keep a powerful firewall.

3) slow network speed due to insufficient system resources

Because too many applications are loadedProgram, Resulting in insufficient system resources, affecting system performance, resulting in slow access speed. You can try to close useless programs or leave enough cache space for the system disk.

4) slow network speed caused by ADSL moden overheating or other faults

This situation is not very good judgment, if the network speed is slow after a long period of time, you can try to turn off the moden power for a few seconds and then re-open the power, or another moden test.

5) Too many residential broadband users, leading to slow network speeds during peak hours

Some users actually use shared optical fiber access for the residential area. The entire residential area shares this optical fiber. When there are not many users, the network speed is very fast. However, if there are too many users in the residential area, during peak hours, the network speed becomes slower.

2. Reasons for slow LAN access speed

The LAN is complex because of its network structure. If the network speed slows down, you must check the network effectively, such as the network cable status, network cable connector, hub, and nic, and drivers and other hardware devices may cause the enterprise lan network speed to slow down.

1) network speed slows down due to network cable problems

The network cable cannot be too long. The 802.3u twisted pair Wires transmit about 150 meters in theory, but it is best not to exceed 100 meters. If it is too long, it may cause signal attenuation or even failure to connect to the network.

To ensure the quality, it is best to make the network cable cabling concise and do not wrap it around. In addition, twisted pair wires do not pass through electrical appliances such as televisions to avoid interference and cause unnecessary packet loss. We recommend that you use a network cable with shielding function.

2) poor contact with the crystal head causes slow network speed

Poor contact with the crystal head may cause packet loss between network transmission, resulting in slow network speed.

3) network speed slows down due to too many protocols bound to the NIC

This situation is common among LAN users. If many protocols are bound to the network card, when the data passes through the network card, the computer will spend a lot of time to determine which protocol is used for transmission of the data, then the user will feel slow. Solution: Use a network card to only bind the pppoe protocol to connect to ADSL to provide external connections to the Internet, and use another network card to bind other protocols to the LAN, so as to do their jobs and improve performance, in this way, the client's Internet access speed will increase.

4) slow network speed caused by poor heat dissipation of ADSL, routers, and other devices

The heat usage of ADSL equipment is relatively high during work, so you should pay attention to the heat dissipation at ordinary times. Many users pile ADSL devices together with routers and hubs, which is not conducive to heat dissipation and affects normal operations of ADSL. ADSL and other equipment need to be placed separately, and there is a ventilation and heat dissipation channel between the equipment. If it is in the data room, it is best to achieve constant temperature, the General Ambient temperature should be controlled at 10 ~ 30 deg C.

5) network speed slows down due to loops in the Network

This phenomenon rarely occurs when the number of nodes involved in the network is not large and the structure is not complex. However, in some complex networks, there are often redundant backup lines. A loop may be formed when a connection is accidentally established. When laying a network cable, you must develop a good habit: The network cable must be clearly labeled and recorded where there is a backup line. When such a fault is suspected, the partitioning and segmentation method is generally used.

6) broadcast storm caused by hardware failure of network equipment, resulting in slow network speed

As the main means to discover unknown devices, broadcast plays a very important role in the network. However, as the number of computers in the network increases, the number of broadcast packets increases dramatically. When the number of broadcast packets reaches 30%, the network transmission efficiency will be significantly reduced. When the network adapter or network device is damaged, it will send broadcast packets continuously, resulting in broadcast storms and network communication paralysis. Therefore, when the hardware of the network device fails, the network speed may also slow down. If such a fault is suspected, replace the hub or switch with the replacement method to eliminate the fault of the collector line equipment. If these devices are not faulty, after the power of the hub or switch is turned off, run the "ping" command in DOS to test the involved Computers one by one and find the computers with the faulty Nic, the network speed can be restored after a new Nic is changed. NICs, hubs, and switches are the most vulnerable devices to slow network speeds.

7) a port in the network forms a bottleneck, leading to slow speed.

Vro WAN ports, LAN ports, switch ports, hub ports, and server NICs may all become network bottlenecks. When the network speed slows down, we can use the network management software to view the data traffic of routers, switches, and server ports during peak hours. We can also use the netstat command to count the data traffic of each port. Based on this, identify the network data flow bottleneck and try to increase its bandwidth. There are many specific methods, such as replacing the server NIC with 1000 m or M, installing multiple NICs, dividing multiple VLANs, and changing the vro configuration to increase bandwidth, which can effectively alleviate network bottlenecks, it can increase the data transmission speed to the maximum extent.

3. Slow Internet access on the server

1) the response speed of the target website is slow due to insufficient server bandwidth or heavy load. In this case, you can use the ping command to check the packet loss and then use tracert to analyze the route. Ping Command explanation http://www.linkwan.com/gb/broadmeter/article/pinghelp.htm

Tracert recommends that you directly use the Chinese route analysis tool provided by the World Network to visually display the route direction at http://www.linkwan.com/gb/broadmeter/tracemap/traceroute.aspthrough a map.

2) DNS fails to explain the IP address of the website, or it may be during peak hours. Many users can access the same hotspot website because the website server cannot handle the problem, or if the bandwidth is narrow, the network speed is slow and the web page cannot be opened for a long time. You 'd better avoid surfing the internet or accessing other sites during peak hours.

3) due to an Internet node failure, the network system automatically routes back to the target server, resulting in slow network speed. In this case, you can reflect the situation to the broadband provider and wait patiently for system repair.

There are many reasons for slow network speeds. In addition to some of the above factors, we also need to consider vswitches, routes, lines, interference, bandwidth restrictions, operating system or hardware problems, etc, you need to analyze specific issues and consider them comprehensively. For example, when the broadcast storm of A vswitch is large, the performance of the vswitch will decrease. On the same route, attacks on other VLAN segments will lead to a decline in the routing performance, so you will also be affected; the longer the line distance of the target server to access, the more nodes that pass by, the slower the transmission speed.