In internet cafes, DHCP services are often used, such as the DHCP service provided by diskless system servers or the DHCP service on routers. First, network administrators need to understand DHCP protocol messages. DHCP is a protocol designed by the IETF to enable automatic IP configuration. The types of DHCP protocol messages are as follows.
(1) DHCPDISCOVER (0×01): This is the first message sent when a client begins the DHCP process.
(2) DHCPOFFER (0×02): This is the server’s response to the DHCPDISCOVER message.
(3) DHCPREQUEST (0×03): This message is the client’s response to the server’s DHCPOFFER message during the initial DHCP process, or a message sent when the client needs to renew its IP address lease.
(4) DHCPDECLINE (0×04): When the client discovers that the IP address assigned by the server cannot be used, such as in the case of an IP address conflict, it sends this message to notify the server to stop using that IP address.
(5) DHCPACK (0×05): This is the server’s acknowledgment response to the client’s DHCPREQUEST message. Only after the client receives this message does it truly obtain the IP address and related configuration information.
(6) DHCPNAK (0×06): This is the server’s rejection response to the client’s DHCPREQUEST message. After receiving this message, the client usually restarts a new DHCP process.
(7) DHCPRELEASE (0×07): This message is sent by the client to actively release the IP address assigned to it by the server. When the server receives this message, it can reclaim the IP address and assign it to another client.
(8) DHCPINFORM (0×08): This message is sent when the client has already obtained an IP address and only needs to request other network configuration information from the DHCP server, such as route IP, DNS IP, etc. The use of this type of message is very rare.
DHCP can automatically assign IP addresses, subnet masks, default gateways, DNS server IP