Avoid overloading the DHCP server

The school room is a Windows NT network, configured separately as a subnet, connected through the hub with the upper level switch, and then through the router to achieve access to the Internet.

The server is used as a DHCP server, responsible for assigning IP addresses, and also as a file server backup room of various related materials, such as drivers, exercise, mirror files and so on. Because the student machine does not have the optical drive, the floppy drive and no hard disk protection card, in order to facilitate maintenance system, so configured the remote boot function, and the server did a mirrored backup of the system, so once the system was destroyed by the students, can easily be restored through the network cloning.

Failure phenomenon

In a student on the machine class, the students can not get the IP address, the system prompts the DHCP server is not available, unable to obtain the IP address, which can not access the Internet, restart the computer failure is still.

Cause analysis

Because it is a DHCP error, the cause of the failure is of course related to DHCP. The process of DHCP is this: The client initiates a broadcast of DHCP discover information to obtain the IP address of the DHCP server, and then the DHCP server receives the DHCP Discover information broadcast by the DHCP client. It sends DHCP client offer information, including a leased IP address, to DHCP clients. If the DHCP server does not respond to a client request, the initialization fails, the client automatically assigns itself an IP address and sends four DHCP discover messages every 5 minutes in the background until the DHCP solicitation information is received. Once the client receives the DHCP offer information, it will use the IP address provided by the server.

From the working process of DHCP, the student computer cannot obtain the IP address that the DHCP server did not respond to, or that the student computer did not receive a response from the DHCP server. After testing the network cable, the problem that the student machine does not receive the DHCP server response is first excluded, thus the DHCP server does not make a normal response, but why does the DHCP server not respond? After investigation, there are several systems in the computer room was destroyed by students in the network cloning recovery, The server needs to do a lot of data transfer, which makes the server overburdened, unable to respond to the student's DHCP request in time, resulting in the customer's inability to access the Internet due to the IP address.

The author waits until the network cloning process is complete, restarts the client, the client really has obtained the IP address smoothly, the problem solves.

However, such problems can be solved only by upgrading the server to avoid overloading the server