Table of contents
1. What is a local area network?
Tip: The following is the text of this article. The following cases are for reference.
1. What is a local area network?
The concept of data link layer refers to a network that is reachable at Layer 2 (that is, a network that can be reached without Layer 3 equipment);
2. What is a network segment?
The definition of the physical layer is that part that can communicate directly using the same physical layer equipment (transmission media, repeaters, hubs, etc.) ;
(1) Why do network segments use physical layer equipment for communication? Isn’t it a network layer concept?
The network segment itself is indeed a network layer concept, but the same physical layer device can only connect to the same network segment. When devices in different network segments communicate, they first need to transmit data to the gateway (router) before they can continue;
(2) For example, can the hub connected to 192.168.1.0/24 and 192.168.2.0/24 communicate directly ?
When the hub is connected to 192.168.1.0/24 and 192.168.2.0/24, when host A (192.168.1.1) transmits to host B (192.168.2.1) on another network segment, it cannot be directly encapsulated into frames and transmitted transparently, because through The subnet mask and the target address are combined, and it is found that host B is not in the same network segment, and the data needs to be transmitted to the gateway (router) before proceeding; if there is no router, the transmission fails and the data is unreachable;
3. What is a subnet?
The definition of the network layer : When the number of hosts in the same network segment is too large, the broadcast domain is too large, which greatly affects the transmission efficiency. Therefore, segmentation makes the broadcast domain smaller, so that hosts in different network segments need routing to communicate.
(1) Is the network segment necessarily equal to the subnet?
In a general vague sense, a subnet is a network segment, such as 10.0.1.0/24 and 10.0.2.0/24, two network segments, two subnets;
However, if we discuss the overall network, we can say that the two subnets are on the same network segment 10.0.0.0/16. At this time, the network segment includes 2 subnets;
Summarize
(1) When the subnet is not divided, the network segment = subnet, because it is directly a subnet;
(2) When dividing subnets, one subnet = (small) network segment, one network = (large) network segment = multiple subnets;
(3) LAN generally refers to a network reachable by layer 2 devices. Now it is usually used mixed with private networks. For example, two private subnets 192.168.1.0/24 and 192.168.2.0/24 communicate through a router. Sometimes Some people may also call it a local area network, but this is incorrect;