Learning notes-conflicting domains, conflicting, broadcast domains, broadcast

Conflict domain (physical segment): a collection of All workstations connected to the same wire, or a collection of all nodes on the same physical network segment or nodes competing for the same bandwidth over Ethernet. This domain represents the region in which conflicts occur and spread. This region can be considered as a shared segment. In the OSI model, the conflicting domain is regarded as the first layer. devices connected to the same conflicting domain have hub, reperter, or other devices that perform simple replication signals. That is to say, all nodes connected with hub or repeater can be considered to be in the same conflicting domain and will not be divided into conflicting domains. The second-layer devices (bridges, switches) and third-layer devices (routers) can be divided into conflicting domains. Of course, they can also be connected to different conflicting domains. Simply put, repeater and so on can be considered as a cable, while bridge and so on can be considered as a bunch of cables.

Broadcast domain: a collection of nodes that receive the same broadcast message. For example, if a broadcast frame is transmitted to any node in the Set, all other nodes that can receive the frame are considered to be part of the broadcast frame. Because many devices are prone to broadcast, without maintenance, a large amount of bandwidth will be consumed, reducing network efficiency. Because the broadcast domain is regarded as the L2 concept in OSI, nodes connected to the L2 device, such as the hub and switch, are considered to be in the same broadcast domain. Vrouters and layer-3 vswitches can divide broadcast domains, that is, they can connect to different broadcast domains.

Note: a VLAN is a broadcast domain, which can isolate broadcast. One of the purposes of VLAN division is to isolate broadcast.

The following is an excerpt from "image metaphor helps you understand network devices" by bigh.

Below I will give a common analogy to these three network devices:

A lan is like a building. Each person (like a host) has his/her own room (the room is like a nic, and the room number is the physical address, that is, the MAC address). The person (host) in the room has a walkie talkie, because the work is on the same channel, one person can speak and others can hear it. This is broadcast (send information packets to all hosts), and only the target will respond, even though others have heard it, they ignore (discard packets), and all these walkie talkie devices that can hear the broadcast can become a broadcast domain. These walkie talkie are hubs. Every walkie talkie is like a port on the hub. We all know that walkie talkie cannot be listened to when talking. You must release the walkie talkie key to listen, this work mode can only receive or send at the same time is half duplex. In addition, only one person can speak on the walkie talkie at the same time. If two or more people talk together, there will be conflicts and no one can hear clearly. Therefore, this constitutes a domain of conflict.

Broadcast domain: a set of devices in the network. That is, all devices that the same broadcast package can reach become a broadcast domain. When one of these devices sends a broadcast, all other devices can receive the broadcast frame. All the ports of the hub and switch are in one broadcast domain. Each port on the router has its own broadcast domain.

One day, people in the building could not stand this low-efficiency communication, so they upgraded the device and changed it to an internal phone number (switch, each phone number is equivalent to a port on the switch ), each person has an internal number (logical address is the IP address ). (Here we will talk about the problem of IP address and MAC address translation. A common layer-2 switch only recognizes MAC addresses. It has a built-in MAC address table and keeps maintaining and updating it, to determine which port corresponds to the MAC address of the host, and the communication software we use is based on IP, IP address and MAC address conversion, it is done by the ARP Address Resolution Protocol .) At the beginning, no one knows which number corresponds to, so to call someone, you must first broadcast: "XXX, what is your number ?" "My number is XXXX ". In this way, you have the target number. All the internal numbers are added to the phone book in this way (the MAC address table of the switch ), next time, you can directly dial his extension number without broadcasting. As we all know, the phone number is a point-to-point communication device and will not affect others. The conflict will only be restricted to the local device. The line of a phone number is equivalent to a conflicting domain. Only when the extension is connected in series, there will be a conflict between the extension and the host. This conflict will not affect other calls outside. The telephone number is like the port number on the vswitch. That is to say, each port on the vswitch has a conflict domain. Therefore, the entire large conflict domain is divided into several small conflict domains. In addition, the call can be answered at the same time, and the work mode is full duplex. This is one of the reasons why vswitches have better performance than hubs.

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