DHCP (Dynamic Host Configuration Protocol) is a local area network protocol, which works with UDP protocol. It has two main purposes: automatically assigning IP addresses to internal networks or network service providers, and providing users or internal network administrators with the means to centrally manage all computers. It is described in detail in RFC 2 13 1. DHCP has three ports, of which UDP67 and UDP68 are normal DHCP service ports, serving as DHCP server and DHCP client respectively. Port 546 is used for DHCPv6 clients, but not for DHCPv4. It is used for DHCP failover, which is a service that needs to be started specially. DHCP failover is used for "hot standby".

DHCP protocol adopts client/server mode, and the dynamic allocation of host addresses is driven by network hosts. When the DHCP server receives the address application information of the network host, it will send the related address configuration information to the network host, so as to realize the dynamic configuration of the address information of the network host. DHCP has the following functions:

1. Ensure that only one DHCP client can use any IP address at a time.

2.DHCP should be able to assign permanent and fixed IP addresses to users.

3.DHCP should be able to coexist with hosts that use other methods to obtain IP addresses (such as hosts that manually configure IP addresses).

4.DHCP server should provide services for existing BOOTP clients.

DHCP has three mechanisms for assigning IP addresses:

1). The DHCP server assigns a permanent IP address to the host. Once the DHCP client successfully rents the IP address from the DHCP server for the first time, it can use the address permanently.

2) Dynamic allocation: DHCP server allocates a time-limited IP address to the host, and when the time expires or the host explicitly abandons the address, other hosts can use the address.

3) Manual allocation. The IP address of the client is specified by the network administrator, and the DHCP server only tells the IP address specified by the client host.

Among the three address allocation methods, only dynamic allocation can reuse addresses that clients no longer need.