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Routers and switches are increasingly used in LANs. Here I will analyze some faults related to such devices in the local area network (we take a typical local area network for example).
Phenomenon 1. The terminal users in the local area network visit each other normally, but the rate of access to the external network is low or even there is a lot of packet loss. According to the fault phenomenon, it can be known that the communication between the switch and each user is normal? The phenomenon is serious. After logging in to the router through the console port, it is found that the router's CPU utilization rate is very high, lasting about 99%. Use the SHOW IP ARP command to learn that the CPU consumption caused by the number of IP resolutions reaches about 30%. Normally, it should be Less than 10%. I found an interesting phenomenon after using the SHOW ARP command? That is, a large amount of source data regularly accesses external network addresses one by one, which can be concluded that the router is under attack by a virus in the network? The user address infected with the virus is found through the SNIFFER software, and the router The access control list command access list prohibits infected users from accessing the LAN, and then grants access to the network after the end user has disinfected the virus, so that the network can resume normal work.
Phenomenon 2 Intermittent inter-user access in the local area network The inter-access between end users is mainly carried out through the MAC table of the switch, that is, the TCP layer 2 protocol, so such a failure should be checked first. There are generally two reasons for blocking access to each port of the switch:
1. Network broadcast storm. The causes of such failures are usually: â‘ Due to the unreasonable allocation of private network addresses in the network, for example, the entire Class B address is not subdivided and directly assigned to a switch; There is no reasonable separation. The above two situations are generally solved by adjusting the network topology and adjusting the distribution structure to avoid the existence of the topology loop.
2. There are a lot of invalid IP packets in the network. There are many reasons for this phenomenon, for example, a user in a network has a certain network virus or the quality of the switch used for connection between network users is not good. What the author wants to explain here is another kind of fault that is easily overlooked, that is, the fault that the switch is blocked due to the short circuit of the end user's network cable. We know that most of the switches on the market currently use storage and forwarding technology. Its working principle is to analyze and identify a certain data packet and address it, and forward it. It is stored in the buffer of the switch before it is sent out. When the network cable occurs When a short circuit occurs, the switch will receive a large number of packets that do not conform to the packaging principle, causing the switch processor to be busy, which will cause the packet to be too late to be forwarded, which will result in a buffer overflow and packet loss. To deal with such faults, you generally need to check the switch port traffic or close the ports one by one.