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 any IP address can only be used by one DHCP client at a time.

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

3.DHCP should be able to be stored with hosts that have obtained IP addresses by other methods (for example, hosts with manually configured 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.

The format of DHCP message is based on BOOTP(Bootstrap Protocol) message format, which requires the device to have the function of BOOTP relay agent and be able to interact with BOOTP client and DHCP server. The function of BOOTP relay agent makes it unnecessary to deploy DHCP server on every physical network. RFC 95 1 and RFC 1542 describe the BOOTP protocol in detail.

Setting method of wireless router dhcp:

Enter the router setup interface and select "DHCp server"-"DHCP service" on the left to open the setup interface. Here is a brief talk about DHCP service. DHCP service refers to the service that the server automatically assigns IP addresses and subnet masks to clients connected to the server.

First, we click Enable to start the DHCP service. Let's look at several important parameters in DHCP, such as the starting address of the address pool, the ending address of the address pool, and the lease term of the address.

The ip address range in the address pool determines the ip address range that the client can automatically obtain. The ip address range available here is192.168.100-192.168.199. By looking at the list of clients, we can clearly see the ip addresses of the assigned clients.

Regarding the lease term of ip address, the default here is 120 minutes, which means that the ip address in the address pool will be re-acquired every 120 minutes from the time when the client obtains it. Under normal circumstances, if the client stays connected, it will get the same ip address. If the client disconnects, it will be released, and it is possible that other accessed clients will use this ip address.

We are currently using the DHCP service of the router, so the default settings are selected for settings such as gateway and dns.