What is the difference and connection between LAN, WAN, and Internet?

Local area network

English is LAN (Local Area Network), Local, local, local. For example, someone in Shanghai asks: Are you a local? Subtext: Are you born and raised in Shanghai? This is a regional concept, so the local area network is also a regional concept. For example, the home network is a small local area network, which generally includes a free optical cat sent by telecommunications. Because the wireless signal of the optical cat is not good, users will connect the LAN port of the optical cat Wireless router, then there is a small home LAN, schematic diagram:

PC --- wireless router ---- (LAN) optical cat (WAN) --- ISP --- InternetGW --- Internet

Although this diagram is simple, it includes all three of LAN, WAN, and Internet. The wireless router connects computers, mobile phones and other devices to the local area network LAN, and assigns an IP address, that is, a private IP. We can call it LAN_IP, where LAN_IP can walk, called LAN routing domain.

Light cat is a border, there are borders between countries, and there are borders between networks. Light cat is the border between local area network LAN and wide area network WAN. The local area network LAN_IP can roam in the local area network LAN, but when it reaches the border, that is, the optical cat here, it is not so free. LAN_IP is the IP assigned by the optical cat, and it enters the WAN across the border. The WAN is the operator ’s territory. The WAN has Own IP, WAN_IP, form a WAN routing domain.

Guangmao dialed up through PPPoE and got WAN_IP from the ISP. This is a special pass for the WAN routing domain. All Internet traffic on the local area network must be at the Guangmao. LAN_IP

The IP packet holding the WAN_IP successfully reaches the next border, Internet Gateway, which is the last level to the Internet, the border. On the left is the WAN routing domain, and on the right is the Internet routing domain. If the operator is rich, WAN_IP is all GlobalIP assigned by IANA (the only one in the world that can access this IP anywhere in the world), then these IP packets carrying WAN_IP directly enter the Internet.

If the operator's WAN_IP is also private, you also need to do WAN_IP and Global_IP address translation, and then use the Global_IP global pass to travel the Internet.

What is the Internet?

If the local area network is a stream, many streams will converge into a large main stream, such as the Yangtze River and the Yellow River. The main stream is the wide area network, and then flows into the sea, and the sea is the Internet.

The Internet is composed of countless local area networks, which are aggregated to operators through WAN lines, and then the operators are interconnected to form the Internet.

The Internet is open and interconnected. If the LAN of a company or organization is not connected to the Internet, then the LAN will not belong to the Internet.

The concept of company LAN, WAN, Internet

The concept of LAN and Internet is the same as above, nothing more than the company LAN adds some switches, APs, firewalls, and there is no real difference from the home LAN. But here we talk more about WAN.

One company is headquartered in Beijing and its branch is in Shanghai. The headquarters is a local area network, and the branch is also a local area network.

Company headquarters LAN1 --- Gateway 1 --- Internet

Branch LAN2 --- Gateway 2 --- Internet

Since the company headquarters and branches are connected to the Internet, can the computers in LAN1 communicate directly with the computers in LAN2? It is very difficult. You need to do static NAT mapping on gateways 1 and 2. Everyone can use global IP to communicate. This solution is not scalable, and no company will use it.

Wouldn't it be fine to pull a wire between gateways 1 and 2?

Company headquarters LAN1 --- Internet gateway 1 --- 1 root line --- Internet gateway 2 --- branch office LAN2

Of course, but the price is expensive. If you pull a fiber from Beijing for more than 1,000 kilometers, the price will not be cheap. But this is also a solution. This line and its interface are WAN.

Is there a cheaper one, not to pull the line, the operator has taken the package, there are Layer 2 MPLS VPN, Layer 3 MPLS VPN, although the price is expensive, but the bite is acceptable, the network between Gateway 1 to Gateway 2 is a wide area network .

Company headquarters LAN1 --- Internet gateway 1 --- MPLS VPN --- Internet gateway 2 --- branch office LAN2

However, there are still some small and medium-sized enterprises that still feel expensive. Engineers work overtime between two gateways overnight, relying on existing Internet lines, and configure an encrypted VPN. Schematic diagram:

Company headquarters LAN1 --- Internet gateway 1 --- encrypted VPN (run on the Internet) --- Internet gateway 2 --- branch LAN2

The network between the two gateways is also a wide area network.

As long as you pay attention, you will find that I mentioned three terms, LAN routing domain, WAN routing domain, and Internet routing domain.

At the same time, I also mentioned three terms: LAN_IP, WAN_IP, and Global_IP, which are the IP of the home LAN, the internal IP of the operator, and the public IP of the Internet.

Global_IP can reach any corner of the world, including home LAN:

Global_IP: LAN routing domain + WAN routing domain + Internet routing domain

WAN_IP: LAN routing domain + WAN routing domain

LAN_IP: LAN routing domain

Since LAN_IP is only legal in the LAN routing domain, is it necessary to change to a legal identity if entering the WAN routing domain?

Similarly, if WAN_IP is not legal in the Internet routing domain, you must do identity conversion. These tasks are the basic responsibilities of NAT, and this content is no longer described.

The company's WAN interconnection based on Internet lines

The company has an internet line, and does not want to pay for a dedicated line to meet the interconnection between the branch and the headquarters. You can establish a secure VPN between these two sites. This is a secure tunnel. The content is encrypted and flows through the public Internet routing domain. The third party cannot be tampered with or peeped, and the security is high.

From the perspective of routing technology, the LAN_IP traffic is encapsulated in a Global_IP car, Global_IP is in the outer layer, LAN_IP is in the inner layer, and it traverses the Internet as a Global_IP legal identity to reach the end of the tunnel (another branch of the company) and then remove The external Global_IP continues to walk in the company's LAN routing domain as LAN_IP.

Who is Global_IP? Who is responsible for encryption, who is responsible for encryption, then where does this special car go? Of course it is another site of the company. When the special car arrives, it needs to be decrypted, get off the car (remove the outer Global_IP), and then walk (LAN_IP) to enter the company.

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