The reason of broadcasting storm from the principle of switch

Internet café Industry competition intensifies, there are some large scale of internet cafes. At present in the Internet café industry, more than hundred of Internet cafes have been everywhere. As Internet cafes in the network construction, the lack of professional network technology support, the network of Internet cafes frequent failures. In the network fault of Internet cafes, the network fault caused by the network broadcast storm accounted for more than 90% of the network fault of Internet cafes. How did the network broadcast storm actually form?

To understand the exact meaning of the broadcast storm, we must understand how the network devices working in the network work. At present, the network equipment that works in the net Bar network, basically all is the switch. For the switch, you don't really understand how it works.

First, the basic knowledge of the switch

1, the definition of the switch: The switch is based on the MAC (network card hardware address) recognition, can complete the package forwarding packet function network equipment. The switch can "learn" the MAC address and store it in an internal address table, by establishing a temporary exchange path between the originator of the data frame and the target receiver, so that the data frame is reached at the destination directly from the source address.

Now, the switch has replaced our more familiar network device hub, also known as the hub. But that doesn't mean we don't need to know the basics of the hub.

2, the definition of the hub: hub (hub) is a data communication system in the basic equipment, it and twisted-pair transmission media, such as, is a need for any software support or only little management software management hardware equipment. It is widely used in various situations. Hubs work in a local area network (LAN) environment, which, like a network adapter, is applied to the first layer of the OSI Reference Model and is therefore called a physical layer device. The interior of the hub adopts the interconnection of electrical appliances, and when maintaining the LAN environment is a logical bus or ring-type structure, it is possible to establish a physical star or tree network structure with a hub. In this respect, the hub acts as a repeater for multiport ports. In fact, the hub is actually a repeater, the difference is only the hub can provide more port services, so the hub is also called the multiple mouth relay.

The difference between the switch and the hub

Now, we often have such a technical misunderstanding, we are using the switch, the data are all point-to-point forwarding, why will generate a broadcast storm? After we have fully understood the difference between the switch and the hub, we will understand why there is a broadcast storm when you use the switch as a network device.

1. The essential difference between the switch and the hub: A network of hubs is called a shared network, while a network of switches is called a switched network. The main problem with shared Ethernet is that all users share the bandwidth, and the actual available bandwidth per user decreases with the increase in the number of network users. This is because when the information is busy, multiple users may simultaneously "contention" a channel, and a channel at a certain time only allow a user to occupy, so a large number of users are often in the monitoring waiting state, resulting in signal transmission jitter, stagnation or distortion, seriously affecting the performance of the network.

2. In switched Ethernet, the switch provides a dedicated information channel for each user, unless two source ports attempt to simultaneously send information to the same destination port, otherwise multiple source ports and destination ports can communicate without conflict. It is experimentally measured that in a multi server LAN, the actual maximum transmission speed of switched Ethernet in Half-duplex mode is 1.7 times times of that of shared network, while the actual maximum transmission speed of switched Ethernet in Full-duplex state can reach 3.8 times times of that of shared network. The switch is only in the way of working with the hub, and other such as connection, speed, etc. and the same as the hub, the current switch also from the speed of 10M, 100M and 1000M several, the number of ports provided for 8, 16 and 24 mouth several. Switches are mainly used in LAN to connect workstations, Hub, servers, or decentralized backbone networks.

Iii. causes of the broadcast storm

Through the understanding of the above network equipment, we can simply analyze, the network produces the cause of the broadcast storm. Under normal circumstances, the cause of the network broadcast storm, there are mainly the following:

1, network equipment reasons: We often have such a misunderstanding, the switch is point-to-point forwarding, will not produce a broadcast storm. When we buy the network settings, the switch, usually the smart hub, is sold by profiteers as a switch. In this way, when the network is a little busy, it will certainly produce a broadcast storm.

2, NIC Damage: If the network machine card damage, the same will generate broadcast storm. The corrupted network card, which sends a large number of packets to the switch, produces a lot of useless packets and generates a broadcast storm. Because the network card physical damage caused by the broadcast storm, the fault is more difficult to eliminate, due to the damage of the network card generally can also be connected to the Internet, we generally borrow sniffer LAN management software, view the network data flow, to determine the location of the fault point.

3, the network loop: once in a network troubleshooting, found a very ridiculous error, a twisted pair of cables, both ends of the same switch in the same port, resulting in a rapid decline in network performance, open the Web page is very difficult. The fault is a typical network loop. The generation of network loops is generally due to the two ends of a physical network line, which is connected to a network device.

4, Network virus: At present, some more popular network virus, Funlove, concussion wave, RPC and other viruses, once the machine poisoning, will immediately spread through the network. Network virus spread, will lose a lot of network bandwidth, causing network congestion, causing broadcast storm.

5, the use of hacker software: At present, some Internet users, often using network law enforcement officers, network scissors, such as hacker software, internet cafes to attack the internal network, because of the use of these software, the network may also cause radio storms.

In order to achieve rapid fault diagnosis, good solid basic knowledge, is indispensable. Therefore, in the future study, do not neglect the basic knowledge of the study!