Shulou(Shulou.com)06/01 Report--

Concept:

Dynamic Host configuration Protocol (Dynamic Host Configuration)

Protocol, DHCP) is a network protocol of a local area network, which uses UDP protocol to work. It has two main uses: automatically assigning IP addresses to internal networks or network service providers, and giving users or internal network administrators as a means of central management of all computers.

Action:

DHCP is a broadcast-based protocol, which can be divided into four stages: IP lease request, IP lease offer, IP lease selection, and IP lease confirmation.

IP lease request: at any time, if the client computer is set to obtain the IP address automatically, it will check whether it currently leases an IP address when it is powered on. If not, it requests a lease from DCHP. Because the client computer does not know the address of the DHCP server, it will use 255.255.255.255 as the destination address, and the source address will use 0.0.0.0. Broadcast an DHCPDISCOVER message on the network containing the media access control (MAC) address of the client computer (the built-in hardware address on the network card) and its NetBIOS name.

IP lease provision: when a DHCP server receives an IP lease request from a customer, it reserves an IP address for the customer according to its scoped address pool and broadcasts one on the network. The message includes the customer's MAC address, the IP address that the server can provide, the subnet mask, the lease period, and the IP address of the leased DHCP server itself. IP lease choice: if there are other DHCP servers in the subnet, after receiving a DHCPOFFER message from a DHCP server, the client broadcasts a DHCPREQUEST message containing the IP address of the server providing the lease, notifying all other DHCP servers in the subnet that it has accepted an address, and the other DHCP servers will revoke the lease provided to the customer after receiving this message. The leased address assigned to the customer is then returned to the address pool, and the address can be re-provided to other computers as a valid address. IP lease confirmation: when the DHCP server receives a DHCPREQUEST message from the customer, it begins the last stage of the configuration process, in which the DHCP server sends a DHCPACK packet to the customer, which includes a lease period and all other configuration information requested by the customer. At this point, the TCP/IP configuration is completed.

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