Many friends have repeatedly asked what is the gateway, dns, subnet mask, what role does it have, indeed, we always talk about the gateway in the network, but rarely really understand it.
What is a gateway?
Gateway concept
Gateway (Gateway) is also known as the network gateway, protocol converter. The gateway is on the transport layer to implement network interconnection. It is a complex network interconnection device and is only used for different network interconnections of two high-level protocols.
How to understand the gateway
Everyone knows that going from one room to another is bound to go through a door. Similarly, sending information from one network to another requires a “gatewayâ€, which is the gateway. As the name suggests, a gateway is a "gateway" in which a network connects to another network.
According to different classification standards, there are many kinds of gateways. Gateways in the TCP/IP protocol are commonly used. The "gateway" we refer to here refers to the gateway under the TCP/IP protocol.
Gateway ip address
So what exactly is the gateway? The gateway is essentially an IP address that the network leads to other networks. The gateway selects one of the available ips in the network segment. However, the first and last ones are generally used.
E.g
For example, there are network A and network B:
Network A: The IP address range is "192.168.1.1~192. 168.1.254", and the subnet mask is 255.255.255.0.
If you need to communicate with other network segments, its gateway can be set to 192.168.1.1, of course, it can also be set to another ip address in the network segment.
Network B: The IP address range is "192.168.2.1~192.168.2.254" and the subnet mask is 255.255.255.0.
If you need to communicate with other network segments, its gateway can be set to 192.168.2.1, of course, it can also be set to another ip address in the network segment.
How does the gateway implement communication?
In the absence of a router, TCP/IP communication cannot be performed between two different networks. Even if two networks are connected on the same switch (or hub), the TCP/IP protocol will be based on the subnet mask. (255.255.255.0) Determines that the hosts in the two networks are in different networks. To achieve communication between the two networks, you need to go through the gateway.
If the host in network A finds that the destination host of the data packet is not in the local network, it forwards the data packet to its own gateway, and then the gateway forwards it to the gateway of network B, and the gateway of network B forwards it to some network B. Host (as shown in the figure). The process by which network B forwards packets to network A.
Therefore, only by setting the IP address of the gateway, the TCP/IP protocol can realize mutual communication between different networks.
What is the default gateway?
If you figure out what the gateway is, the default gateway will understand. Just like a room can have multiple doors, a host can have multiple gateways. The default gateway means that if a host cannot find an available gateway, it will send the packet to the default gateway, which will process the packet. The gateway used by the host now generally refers to the default gateway.
What is DNS?
DNS is a Domain Name System, which is a server that turns a URL into an IP address.
DNS is said to be a translation of a domain name into an IP address. Here is an example, and everyone can easily understand it.
For example, when we enter in the browser, the machine needs to communicate with a website. The machine needs to send data packets to the outside. The data package must write the IP address of the server. We don't know what the IP address is, then we need the host. Ask the DNS server, the DNS server will automatically translate this domain name into an IP address of 61.135.169.105. Then write to the destination IP address of the packet to communicate.
Just like we write a letter, you have to write a recipient's address post office to send it to you, you write to foreign countries, you write Chinese address post office does not know, you need this one to help you translate into English. This is the role of DNS, so you can browse the webpage by writing DNS in the local connection. If you do not set DNS, you cannot access the webpage normally.
MAC address
Speaking of the MAC address, you have to mention the ip address, here by the way the ip address is also said.
IP and MAC
Although ipv6 is now available, most of us basically use the ipv4 protocol. The so-called ip is the number of your computer's entire network. Other computers need this number when they want to access the computer. But this number has been changing in many cases. The only constant is your MAC address: physical address.
The MAC is the unique network address used to identify the NIC device in the network. It is uniformly distributed by the relevant hardware manufacturers, and the MAC address of each computer is unique.
To make a metaphor, you often move, you have not moved once, you have an address, XX cell XX unit XX, this is IP. But your name does not change, this is the MAC, the difference is that our MAC does not allow duplicate names.
Our IP is divided into two parts: the above picture is divided into the network part and the host part. The network part is like you are in the town of XX in the XX city of XX province. This is fixed by the state. However, the XX unit XX unit XX number is determined by the developer himself. The two numbers add up to your ip. The difference is that the length of the two numbers is fixed in reality. The ip addresses of A, B, C, and D on the network are changed. This was mentioned in detail the day before yesterday.
Subnet mask
The subnet mask is to distinguish between network bits and host bits. As we mentioned above, an ip address is determined by the network part and the host part. Just as a person's name consists of a first name and a last name.
Then we can compare the IP address to a person's name, then the subnet mask is like a list, you can quickly know those people with the same surname, those people with different surnames, the same surname people in a group, let them before Can communicate with each other.
example
There is a network segment of 192.168.1.0-192.1.254, this network segment is like a village, it is called security village, this network segment has an ip address is 192.168.1.1, we call him security one, another One person is called Security II. Its ip address is 192.168.1.2. When we look at them, we know that they are in the same village.
There is also a network segment, which is 192.168.0.0-192.168.255.254. We call it Ancun. There is also two ip addresses 192.168.1.1 and 192.168.1.2 in the village. It is also called Security One, Security II. Then the problem comes. ? At this time, how do you distinguish them from the village?
At this time, you need a subnet mask to judge that they belong to that network segment. You need to bring security one and security two to the village to recognize them. You know that they belong to the village. The security village's network segment is 255.255. 255.0, Ancun's network segment is 255.255.0.0.
There will also be ip addresses similar to "same name" and "same name" in the network. How to distinguish them from the network segment depends on the subnet mask.
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