Basic network knowledge: hubs, bridges, and switches

Hub

HUB). It is a device that works on the physical layer. Because it only works on the physical layer, it does not care about or care about the layers involved in the OSI, its working process is: when a packet is received from a port, the packet is forwarded once on another port, because it does not know and it is impossible to know who the package is sent to. The physical layer device only cares about the physical concepts of voltage ), it can only broadcast to everyone (here it is different from the meaning of the word broadcast mentioned below and the broadcast at ARP request.

The broadcast here means that the broadcast caused by the use of physical layer forwarding devices, such as the HUB, can be said that this broadcast is forced because of device problems! It is a broadcast caused by a device forwarding packet! The ARP request broadcast is self-requested and active, because the IP address of the ARP request packet is 255.255.255.255, but the ARP request broadcast involves the knowledge of the IP layer, it is not in the scope of this article, so the broadcast mentioned here, unless otherwise stated, is the first meaning, that is, "broadcast caused by device packet forwarding "), let them handle it by themselves.

As a result, there will be a lot of problems. The data you send has been received by others, and private hiding does not exist! You can listen to your information as needed! Therefore, in those years, session hijacking was quite easy to remember when I first came into contact with the concept of session hijacking, which was 2001 ~ 2002. At that time, hubs were still quite common ).

Another serious problem is that if a large local area network, such as 500 machines, is connected to all the HUB machines, what will happen ?? Very slow, with poor network efficiency! Why? If 500 machines send a packet, each machine needs to receive about 499 useless packets... and if you need a response ...... useless data packets will flood the entire LAN. This is the legendary broadcast storm!

To reduce broadcast storms,BridgeNote that "decrease" is used here, not "stop", but "decrease! If we only use a bridge to prevent the broadcast storm, I think it is still not accurate. LaterVswitchThe emergence of broadcast storm can be said to completely prevent the occurrence )!

Before introducing the bridge, I would like to briefly introduce another physical layer device: "Repeater", which is used to enlarge the signal transmitted by the physical layer. Due to the long-distance transmission, there will be a certain amount of loss in the signal. This is the main solution of this kind of equipment. The difference between it and HUB is that the HUB is mainly used to forward data on the physical layer, so it does not care about the voltage value or enlarge the physical signal; the purpose of the repeater is to enlarge the signal. SO .....

Bridge:

A Bridge, also known as a Bridge, is a data link layer device. It is also a device that forwards data packets, but unlike the HUB, it works on the data link layer, and the HUB can only understand what is on the physical layer, such as a physical signal ), the bridge can understand some frame information on the Link Layer. After encapsulating the data transmitted above, the encapsulated data is the frame, however, here I use a wildcard like "data packet" to replace the term "frame ).

On the LAN constructed by Ethernet, the final addressing is identified by the MAC address of the data link layer (that is, a unique machine can be found on the LAN Using the MAC address ), the bridge can extract MAC information from the sent packets and forward the packets purposefully Based on the MAC information, instead of broadcasting, which can reduce the appearance of broadcast storms, to improve the efficiency of the entire network, I would like to introduce the switch before I elaborate on the Net Bridge.

Vswitch:

This is one of the most familiar devices.

 

Switch, a data link layer device that forwards data packets. Like a bridge, it also recognizes the MAC address in the frame and then forwards the specified port. For the differences between the vswitch and the bridge, see:

Working principles and differences between bridges and Switches Based on Network