Classic network failures and solutions The problem of binding IP and MAC Q: My computer originally used a fixed IP address on the public network. In order to avoid being misappropriated by others, the "arp -s ip mac" command is used to bind the MAC address and the IP address. Later, for some reason, the "arp -d ip mac" command was used to cancel the binding. However, the strange thing is that after canceling the binding, the IP address cannot be used on other computers, but only on my own computer. It should be noted that my computer is not a proxy server. Agricultural Drone,Crop Sprayer Drone,Drone Crop Sprayer,Agricultural Sprayer Drone Xuzhou Jitian Intelligent Equipment Co. Ltd , https://www.jitianintelligent.com
Answer: Although in the TCP / IP network, the computer often needs to set the IP address to communicate, however, in fact, the communication between computers is not through the IP address, but through the MAC address of the network card. The IP address is only used to query the MAC address of the computer to be communicated with.
The ARP protocol is used to notify each other's computers and network equipment of the MAC address corresponding to their IP. The computer's ARP cache contains one or more tables for storing IP addresses and their resolved Ethernet MAC addresses. After a computer communicates with another computer with an IP address, the corresponding MAC address is retained in the ARP cache. Therefore, the next time you communicate with a computer with the same IP address, you will no longer query the MAC address, but directly reference the MAC address in the cache. In addition, it should be noted that items added through the "-s" parameter are static items and will not cause the ARP cache to time out. These items will be deleted only after the TCP / IP protocol is terminated and then started. Therefore, even if you cancel the binding, other computers will still think that you are using the original IP address within a short time.
In a switched network, the switch also maintains a MAC address table and sends data to the destination computer based on the MAC address. After binding the IP and MAC addresses, the switch will record the MAC address as long as it has communicated with the switch. In this way, even if someone uses the same IP address later, they will still not be able to communicate with the gateway, and will not be able to connect to the outside unless the switch is restarted, the MAC table is cleared, or the MAC address table exceeds the specified aging time.
Why is the network often paralyzed? Q: Internet cafes have more than 70 computers, and the network is paralyzed one to three times a day. Under normal circumstances, you only need to unplug all the network cables of the first-level switch and then connect it to return to normal, and sometimes you have to restart the switch. After replacing the original 10Mbps network card with a 10 / 100Mbps network card, the network has not been down for almost a week. However, these days the network has started to malfunction again. The hub equipment uses 16-port and 24-port 10 / 100Mbps switches, and the proxy server uses Windows 2000 ICS (Windows Connection Sharing). What is the reason for this phenomenon?
Answer: After excluding the possibility of viruses sending packets to the network crazy? It can be considered that this is a typical network paralysis caused by broadcast storms. After the outbreak of the broadcast storm, all the packets transmitted on the network were broadcast packets, and all the computers processed were broadcast packets. Normal data packets could not be forwarded and processed. After unplugging the network cable or turning off the switch, the broadcast storm is curbed and normal communication resumes.
Broadcasting can be understood as a person speaking to everyone present. The advantage of this is that the call efficiency is high, the information can be passed to all the computers in the network at once. Even if no user sends broadcast frames artificially, a certain number of broadcast frames will appear on the network. It should be noted that broadcasting not only takes up a lot of network bandwidth, but also takes up a lot of CPU processing time of the computer. A broadcast storm means that the network is occupied by a large number of broadcast packets for a long time, which prevents normal peer-to-peer communication from proceeding normally. The external manifestation is that the network speed is extremely slow, and even the network is paralyzed.
There are many reasons for the broadcast storm. A faulty network card or a faulty port may cause a broadcast storm.
It should be noted that the switch can only isolate the collision domain, but not the broadcast domain. In fact, when the number of broadcast packets accounts for 30% of the total communication volume, the transmission efficiency of the network will drop significantly.
Normally, in a network using multiple communication protocols, there should be no more than 100 computers, and in a network using one communication protocol, there should be no more than 150 computers. If the number of computers is large, the network should be separated by dividing the VLAN, and the large broadcast domain is divided into several small broadcast domains to reduce the possible damage caused by the broadcast storm.
Visiting My Network Places is very slow Q: There is a small local area network, the server is Windows NT operating system, and the workstations are Windows 98. In the past, the local area network has been working normally. Later, after reinstalling Windows 98 on a workstation, the speed at which this computer browses other computers through Network Neighborhood is very slow, and only a part of the computers can be seen. Everything is normal. Check that the IP address and subnet mask are correct, and the domain name and workgroup are the same. I do not know what the reason is, what should I do?
A: Through the user description, we can draw the following conclusions:
First, since you can see some computers, it means that the network connection is normal, and the network card driver and network communication protocol are correctly installed; second, since there is no error in the IP address and subnet mask, it means that the IP address information is set correctly; third Since the domain name is the same as the workgroup, it should be able to find other users in the same workgroup very quickly.
However, in fact, the connection speed between computers is not only very slow, but only some of them can be found, which is the key to the problem.
The cause and solution of the fault are as follows. First, the NetBEUI protocol is not installed. TCP / IP is an inefficient protocol. Therefore, in small local area networks, the NetBEUI protocol that takes up less system resources and is more efficient is usually used. In addition, only Windows 98 computers with TCP / IP protocol installed must join the NetBEUI protocol to join the Windows NT domain. Second, the network card driver is defective. Although many network cards use the same chipset, the drivers are not exactly the same. Although a defective driver does not necessarily cause communication failure, it often reduces the transmission efficiency. Therefore, you should confirm that the selection and installation of the network card driver are correct. Third, because Windows NT does not have the function of Active Directory, it cannot quickly and efficiently organize network resources. Therefore, computers that have not been visited may not appear in My Network Places. Try to use the "Find" function on the server, using the computer name or IP address to find a computer that cannot be displayed in My Network Places. Normally, the found computer will be automatically displayed in My Network Places.