The reason of slow network speed 1. Problems with the network itself. The server you want to connect to the target website has insufficient bandwidth or is overloaded. The solution is simple, please change the time or change the target website.
Second, the network cable problem caused the network speed to slow down. As we know, twisted-pair wires are tightly twisted together by four pairs of wires according to strict regulations to reduce the influence of crosstalk and background noise. Meanwhile, in T568A standard and T568B standard, only four wires of twisted pair 1 2 and 3,6 are used, in which 1 2 is used for transmission, 3,6 is used for reception, 1 2 must come from one winding pair, and 3,6 must come from one winding pair. In this way, crosstalk can be avoided to the maximum extent and data transmission can be guaranteed. In practice, I found that the network cable not made according to the correct standards (T586A, T586B) has great hidden dangers.
The performance is as follows: in one case, the network speed is very slow when it is first used; In another case, the network speed was normal at first, but after a while, the network speed slowed down. The latter situation is very obvious on desktop computers, but it is normal to check the network speed with laptop computers. After years of practice, I found that the slow network speed caused by the network cable not made according to the correct standard is also related to the quality of the network card. Generally, the network card performance of desktop computers is not as good as that of notebook computers. Therefore, when using the switching method to troubleshoot, using a laptop to detect the normal network speed cannot rule out the problem that the network cable is not made according to the standard. We now require all network cables to be suppressed according to T586A and T586B standards, and notebook computers cannot be used instead of desktop computers for fault detection.
Third, the existence of loop in the network leads to the slow speed of the network. When the number of nodes involved in the network is small and the structure is not very complicated, this phenomenon rarely occurs. However, in some complex networks, there are often redundant spare lines, which will form a loop if they are inadvertently connected. For example, the network cable is connected from the network center to the computer room 1, and then from the computer room 1 to the computer room 2. At the same time, there is a backup line directly connected to the computer room from the network center. If these lines are connected at the same time, it will form a loop, constantly sending and checking packets, thus affecting the overall network speed. This situation is hard to find. In order to avoid this situation, we are required to develop good habits when laying network cables: the network cables should be clearly marked, and records should be made where there are spare cables. When this kind of fault is suspected, the method of partition step by step is generally adopted.
Fourth, the broadcast storm caused by the hardware failure of network equipment leads to the slow network speed. As the main means of discovering unknown devices, broadcasting plays a very important role in the network. However, with the increase of the number of computers in the network, the number of broadcast packets will increase dramatically. When the number of broadcast packets reaches 30%, the transmission efficiency of the network will decrease obviously. When the network card or network equipment is damaged, broadcast packets will be sent continuously, which will lead to a broadcast storm and paralyze network communication. Therefore, when the hardware of the network equipment fails, the network speed will also slow down. When this kind of fault is suspected, the hub or switch can be replaced by replacement method to eliminate the fault of hub equipment. If these devices are not faulty, turn off the power of the hub or switch, and then use DOS? Ping? Command to test the involved computers one by one, find the computer with faulty network card, replace the new network card and restore the normal network speed. Network cards, hubs and switches are the most prone to failure and slow down the network.
Verb (the abbreviation of verb) A port in the network has formed a bottleneck, which causes the network speed to slow down. In fact, router WAN port and LAN port, switch port, hub port and server network card may all become network bottlenecks. When the network speed is slow, we can use network management software to check the data flow of routers, switches and server ports during the peak period of network use; You can also use the Netstat command to count the data traffic of each port. On this basis, the location of network data circulation bottleneck is determined, and its bandwidth is managed to increase. There are many specific methods, such as changing the server network card to 100M or 1000M, installing multiple network cards, dividing multiple VLAN, changing the router configuration to increase bandwidth and so on. , which can effectively alleviate the network bottleneck and maximize the data transmission speed.
6. The influence of worms causes the network speed to slow down. Worms spread by e-mail have a more and more serious impact on network speed, which is extremely harmful. This virus causes infected users to keep sending emails as soon as they get online. The virus randomly selects documents from the user's personal computer and attaches them to random addresses in the user's computer address book to send emails. Hundreds of such junk mails were sent out in line, and some of them were returned in batches and piled up on the server. As a result, individual backbone Internet appears obvious congestion, and the network speed obviously slows down, which makes the local area network almost paralyzed. So be sure to upgrade antivirus software in time; Computers should also upgrade and install system patches in time, uninstall unnecessary services, and close unnecessary ports to improve the security and reliability of the system.
Seven, excessive use of firewalls Excessive use of firewalls will also lead to slower network speed. Needless to say, there is only one firewall powerful enough to uninstall unnecessary firewall.
Eight, the system resources are insufficient. You may have loaded too many applications running in the background. Please load the software reasonably or delete useless programs and files to release resources, so as to improve the network speed.
Nine, cpu, CPU is very busy, which will directly affect the speed of the network and computer. So it is necessary to check the operation of CPU when the network speed is slow.
Ten, the system has been used for a long time, and the network speed suddenly slows down for a long time. You may want to restart to see if it can solve the problem.
XI。 The reason why the server network virus attacks the server is often to slow down or paralyze the network. However, solving this problem is not a user's business.
12. The quality of the telephone line is very poor.
Reference: Reasons for the slow speed of ADSL Internet access and its rapid elimination; ADSL technology requires high quality telephone lines. At present, ADSL is a kind of RADSL (Rate Adaptive ADSL). If the telephone line between the telephone office and users is disturbed by external factors within a certain period of time, RADSL will dynamically adjust the access speed of users according to the line quality and transmission distance. If you visit a foreign site, the speed will be affected by the export bandwidth, the line and equipment configuration of the other site, and it needs the cooperation of the whole network. The main problems existing in this line are: because the construction standards are not followed during construction, there are hidden quality problems, such as rats biting off the line without plastic casing; Poor jumper contact due to quality problems of distribution frame or other materials; When decorating, the indoor lines hidden by users are damaged.
The solution of slow network speed 1. The network speed is slow due to the connection mode and quality of network cable.
(1) factor analysis
The installation of LAN starts with cable, which is the foundation of the whole network system. I roughly estimated that about 50%-70% of network failures are related to cables. The quality of cables and the installation method of cables directly affect the healthy operation of the network. As we all know, twisted pair is made up of four wires tightly twisted together according to strict regulations to reduce crosstalk.
And background noise. . Meanwhile, in T568A standard and T568B standard, only four wires of twisted pair 1 2 and 3,6 are used, in which 1 2 is used for transmission, 3,6 is used for reception, 1 2 must come from one winding pair, and 3,6 must come from one winding pair. In this way, crosstalk can be avoided to the maximum extent and data transmission can be guaranteed. In a lot of practice, it is found that there are great hidden dangers in network cables that are not made according to the correct standards (T586A, T586B). The performance is as follows: in one case, the network speed is very slow when it is first used; In another case, the network speed was normal at first, but after a while, the network speed slowed down. The latter situation is very obvious on desktop computers, but it is normal to check the network speed with laptop computers.
(2) Debugging scheme
For this problem, after many times of practice, it is found that the slow network speed caused by the network cable that is not made according to the standard is also related to the quality of the network card. The broom performance of general desktop computers is not as good as that of notebook computers. Therefore, when using the switching method to troubleshoot, the laptop is used to check that the network speed is normal, and the problem that the network cable is not made according to the standard cannot be ruled out. Therefore, in practical use, JK network cable should be made in strict accordance with the standards of F586A or T586B, and notebook computer and desktop computer should be used together when detecting cable failure.
2. There is a loop in the network, which causes the network speed to slow down.
(1) factor analysis
When the number of nodes involved in the network is insufficient and the structure is complex, this phenomenon rarely occurs. However, in some complex networks, there are often redundant spare lines, which will form a loop if they are accidentally connected; Or the uplink port of the switch generally uses the same physical channel as 1/24 port * *, and if 1/ uplink or 24/ uplink is connected to the client at the same time, it will also cause an exception. For example, the network cable of a hospital is connected from the network center to the outpatient building, and then from the outpatient building to the general affairs department. At the same time, there is a backup line directly connected to the general affairs department from the network center. If these lines are connected at the same time, a loop will be formed, and data packets will be sent and checked continuously, thus affecting the overall network speed. This situation is hard to find.
(2) Solutions
In order to avoid this situation, it is required to develop good habits when laying network cables: the network cables are clearly marked, and records should be made where there are spare cables. When this kind of fault is suspected, the method of partition, segmentation and step-by-step elimination is generally adopted.
3. The broadcast storm caused by the hardware failure of network equipment causes the network speed to slow down.
(1) factor analysis
As the main means of discovering unknown devices, broadcasting plays a very important role in the network. However, with the increase of the number of computers in the network, the number of broadcast packets will increase dramatically. When the number of broadcast packets reaches 30%, the transmission efficiency of the network will decrease obviously. When the network or network equipment is destroyed, broadcast packets will be sent continuously, which will lead to a broadcast storm and paralyze network communication. Therefore, when the hardware of the network equipment fails, the network speed will also slow down.
(2) Debugging scheme
When this kind of fault is suspected, the hub or switch can be replaced by replacement method to eliminate the fault of hub equipment. If these are not ready and there is no fault, turn off the power of the hub or switch and use it at the command line? Ping? Command to test the involved computers one by one, find the computer with faulty network card, and replace it with a new network card to restore the network speed to normal. Network cards, hubs and switches are the most prone to failure and slow down the network.
4. A port in the network has formed a bottleneck, which leads to the slow network speed.
(1) factor analysis
In fact, router WAN port and LAN port, switch port, hub port and server network card may all become network bottlenecks. The main reasons are port locking, port failure and port mode mismatch.
(2) Debugging scheme
When the network speed is slow, we can use network management software to check the data flow of routers, switches and server ports during the peak period of network use. You can also use the Netstat command to count the data traffic of each port. On this basis, the location of network data circulation bottleneck is determined, and its bandwidth is managed to increase. There are many specific methods, such as changing the server network card to lOOM or 1000M, installing multiple network cards, dividing multiple VLAN, changing the router configuration to increase bandwidth and so on. In order to effectively alleviate the network bottleneck and maximize the data transmission speed.
5. The influence of worms and other viruses causes the network to slow down.
(1) factor analysis
Worms spread by mail have a more and more serious impact on the network speed, which is extremely harmful. This virus causes infected users to keep sending emails as soon as they get online. This virus randomly selects files from users' personal computers and attaches them to users.
Send mail to any address in the computer address book. Hundreds of such junk mails were sent out in line, and some of them were returned in batches and piled up on the server. As a result, individual backbone Internet appears obvious congestion, and the network speed obviously slows down, which makes the local area network almost paralyzed.
(2) Solutions
Administrators must upgrade the antivirus software used by intranet computers in time, and the operating system should also upgrade and install system patches in time, while uninstalling unnecessary services and closing unnecessary ports to improve the security and reliability of the system.
6. Relevant debugging cases
In order to have a perceptual understanding of the troubleshooting of LAN connectivity, I will give a case.
(1) fault status
The network of a company suddenly appears serious congestion, the data between hosts is frequently interrupted, the collaborative office can not be carried out normally, and the online video system is often disconnected. In addition, uploading and downloading files from the file server are extremely slow, and sometimes they are interrupted due to timeout.
(2) Fault diagnosis
Test the connectivity of the gateway with the ping command on the host, and enter the command? Ping192.168.2.1-n1000? Send 1000 Ping packet to test the gateway. The test results can ping the gateway, but it is found that the packet loss phenomenon is very serious. There are 720 packets lost out of 1000 packets, with a packet loss rate of 72% and a long continuous packet loss time. Run the arp -a command and find that the gateway IP and gateway MAC address are pointing correctly. Through the above tests, network setup errors and ARP spoofing are basically eliminated.
Next, mirror the core switch and monitor the whole intranet with Sniffer. After monitoring, it was found that the network utilization rate reached 97%, which was very abnormal. Based on the company's network scale and daily business volume, the network utilization rate should be between 20% and 30%, so it can be concluded that the root cause of network packet loss should be that abnormal traffic takes up a lot of network bandwidth.
Further analysis shows that the host with MAC 00-0A-E6-98-84-B7 accounts for 57.87% of the total network traffic, which was originally targeted at this host. Further analysis did not find a large number of broadcast packets, thus completely eliminating the impact of broadcast storms. Find 00-0A-E6-98-84-B7 and analyze this host. The network activity of this host was found to be very suspicious. Only more than 700 packets enter this host, and hundreds of thousands of packets leave it in just 10 minutes, which is extremely abnormal.
(3) Troubleshooting