Dynamic Host Configuration Protocol ( DHCP )

Dynamic Host Configuration Protocol ( DHCP ) is a network protocol, UDP protocol, there are two main purposes: to the internal network or a network service provider automatically assigned IP address to the user to the internal network administrators as to all computer for central management method.

Introduction of structure

DHCP Dynamic Host Configuration Protocol abbreviation, it is the predecessor of the BOOTP. BOOTP was used without disk host connected network above: network host using BOOT ROM rather than disk starting and connect to the network, BOOTP can automatically for the host set TCP / IP environment. But BOOTP has a drawback: you set before prior to obtaining client hardware address, and IP, and the corresponding static. In other words, BOOTP is the lack of" dynamic", if in a limited resource environment in IP, BOOTP one-to-one correspondence can cause very serious waste of resources. DHCP is an enhanced version of the BOOTP, it is divided into two parts: one is the server-side, and another is the client. All of the IP network data set by DHCP server centralized management, and is responsible for processing the client DHCP request; and the client will use distributed from the server to the IP environment data. Compared to BOOTP, DHCP through the " lease " concept, effective and dynamic allocation of the client's TCP / IP settings, and, as the compatibility, DHCP BOOTP Client complete care needs. The distribution of DHCP form above all, must have at least one DHCP work in the network above, it will monitor the network DHCP request, and with the client consultations TCP / IP setting environment. It offers three IP positioning method:

Address assignment

Manual Allocation

Network administrator for a few specific Host binding to a fixed IP address, and the address will never expire

Automatic Allocation

Automatic allocation, the situation is: once the DHCP client first successful from the DHCP server rental IP address, will use this address.

Dynamic Allocation

Dynamic allocation, when a DHCP client first from the DHCP server rental IP address, not a permanent use of the address, as long as the lease expires, the client must release ( release ) the IP address, in order to give other workstation. Of course, the client can host more than other priority update ( renew ) lease, or rent the other IP address. Dynamic distribution than the automatic assignment of more flexible, especially when your real IP address is not enough, for example: you are a ISP, can only provide 200 IP address used to dial the customer, but does not mean that your customers can have up to 200. As you know, your customers may not all at the same time online, in addition to their respective behavioral habits are different, there may be a telephone line limit. In this way, you can put the 200 address, in turn leased to customers using a dial up. That is why when you view the IP address, because each dial and different reason ( unless you apply for a fixed IP, ISP usually can satisfy the requirement that, perhaps to the other charges ). Of course, ISP must not use DHCP to assign address, but the concept and use of the principle is the same as IP Pool. DHCP can dynamically set the IP address, can also be some IP retained for some special purpose machine is used, it can be in accordance with the hardware address fixed allocation of IP address, it can give you a larger design space. At the same time, DHCP can also help a client to specify router, netmask, DNS Server, WINS Server, and so on, your client, in addition to the DHCP option ticked away, almost without any IP environment settings.