Introduction to DHCP protocol

DHCP is the acronym for Dynamic Host Configuration Protocol, which is formerly a BOOTP. BOOTP was originally used for diskless host-connected networks: Network hosts use the BOOT ROM instead of disk to start and connect to the Internet, BOOTP can automatically set the TCP/IP environment for those hosts. But BOOTP has a disadvantage: you need to obtain prior to the client's hard address, and the corresponding IP is static. In other words, BOOTP is very lack of "dynamic", if in a limited IP resource environment, BOOTP one-to-one corresponding will cause a very considerable waste.

DHCP can be said to be the enhanced version of BOOTP, it is divided into two parts: one is the server side, and the other is the client. All IP network settings are centrally managed by the DHCP server and are responsible for handling the DHCP requirements of the client, while the client uses the IP environment data that is assigned from the server. Compared to BOOTP, DHCP through the concept of "lease", efficient and dynamic allocation of client TCP/IP settings, and, as a compatibility consideration, DHCP also fully take care of the requirements of BOOTP client.

Allocation form of DHCP

First, there must be at least one DHCP job on the network, which listens for DHCP requests on the network and with the client rubbing the TCP/IP settings environment. It provides two types of IP positioning:

Automatic allocation is automatically assigned, in the case that once the DHCP client successfully leases the IP address from the DHCP server side, it is always used.

Dynamic allocation is dynamically allocated and is not permanently used after DHCP first leased to an IP address from the HDCP server, and the client has to release this IP address for use by other workstations as long as the lease expires. Of course, clients can have a higher priority than other hosts to extend (renew) leases, or lease other IP addresses.

Dynamic allocation is obviously more flexible than automatic allocation, especially if your actual IP address is not sufficient, for example, you are an ISP that can only provide 200 IP addresses to dial-up customers, but does not mean that your customer can only have 200. Because to know, your customers can not all the same time on the Internet, in addition to their different behavior habits, it may be the phone line restrictions. In this way, you can use the 200 addresses, in turn, to hire the incoming customers. That's why when you look at an IP address, it's a different reason for each call (unless you're applying for a fixed IP, the usual ISP can meet that requirement, which may cost you another fee). Of course, ISPs do not necessarily use DHCP to allocate addresses, but this concept is the same as the principle of using IP Pool.

DHCP In addition to dynamically set IP address, you can also retain some of the IP to some special use of the machine, it can be fixed at the hard address of the allocation of IP address, which can give you a larger design space. At the same time, DHCP can also help clients to specify Router﹑netmask﹑dns Server﹑wins Server﹑, and so on, you on the client, in addition to the DHCP option tick, almost no need to do any IP environment settings.