Network Management Development History-IP Address allocation planning Part 1

When planning IP addresses, we already know that IP addresses include public and private IP addresses, at present, enterprises mainly provide one or several Class C addresses provided by ISPs, while private IP addresses include A, B, and C, in addition, it is the 169.254.0.0 -- 169.254.255.255) CIDR block address reserved by APIPA for Microsoft Windows. Next we will talk about the allocation of these IP addresses in the enterprise LAN.

I. How to allocate IP addresses that can be globally routed to the public network

There is no doubt that every computer in the Internet needs an IP address. However, it is impossible to obtain enough IP addresses from an Internet access provider when IP Address resources are scarce. If every enterprise user can only get 1-10 public IP addresses, even if it has hundreds of computers in the LAN, you should consider how to properly use the limited IP address.

1. static IP Address Allocation

That is, assign a fixed public IP address to each computer. If each computer in the network adopts a static allocation scheme, it is likely that the IP address is not enough. Therefore, this solution is generally used only in the following two cases:

The number of IP addresses is greater than the number of computers on the network.

There are special computers in the network, such as computers and servers used as routers.

2. dynamically allocate IP addresses

If there are many computers in the network and not all computers are using them at the same time, you may wish to use dynamic IP Address allocation.

What is dynamic IP Address Allocation? For example, the company has a total of 10 computers, but 15 people need to use the computer. Obviously, one computer is impossible for each person. If they are not used at the same time, we should consider whether they can adopt this strategy: to centralize management of all computers and wait until someone makes a request to use them, assign one of the computers to Him, and revoke the right to use them after they are used up. This ensures that all people have the opportunity to use the computer without causing "waste" on the computer ".

The principle of dynamic IP Address allocation is the same as in the above example. As long as the number of computers simultaneously opened is less than or equal to the IP address available for allocation, each computer will automatically obtain an IP address, and connect to the Internet. Of course, if too many computers are opened, the computers that follow will not be able to obtain the IP address. However, dynamic IP Address allocation is not always available. When the number of computers in the network reaches hundreds, several dynamic IP addresses are obviously insufficient. What should I do? This should be solved using the following method.

3. Use the NATNetwork Address Translation method.

Since a network without access to the Internet can use any private IP address, can there be such a solution, that is, using a private IP address inside the network and using a public IP address when connecting to the Internet, what is the conversion relationship between public and private addresses? Based on this idea, NAT network address translation is generated ).

It can convert a private IP address such as 10. x to an IPv4 address that can be globally routed. That is to say, for a LAN, no matter how many computers there are, you only need an IP address that can be globally routed. This method not only saves IP addresses but also satisfies the Internet access needs of multiple users at the same time. It is the first choice for networking.

NAT can be divided into three types: static NAT), NAT pool pooled NAT), and port NATPAT ). Figure 1, Figure 2, and figure 3. Static NAT is the easiest to set. Each host in the internal network is permanently mapped to a valid address in the external network.

Figure 1

The NAT pool defines a series of valid addresses in the external network and maps them to the internal network using dynamic allocation. PAT maps internal addresses to different ports of an IP address of an external network.

Figure 2

Figure 3

Based on different needs, various NAT solutions will have advantages and disadvantages. The following describes how to use a NAT pool.

Using a NAT pool, you can provide externally accessed services in an address space that has never been registered, or access an external network from an internal network, you do not need to reconfigure the IP addresses of each machine in the internal network.

Using a NAT pool means that many internal users can be defined in the Intranet, and a few external IP addresses can be shared through dynamic allocation. Static NAT can only form a one-to-one fixed ing mode. It should be noted that after all the external IP addresses dynamically allocated in the NAT pool are occupied, the subsequent nat ip address translation application will fail. However, many vrouters with the NAT Function have the timeout configuration function, which can be configured based on the connection time to alleviate the problem caused by the lack of IP addresses.

In addition to hardware devices such as routers, ADSL, and cable modem gateways, "Internet Connection Sharing" in Windows XP/2000/Me/98 can also be used for NAT, it can also be widely applied to various types of Internet access methods.

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