In modern life, routers play a very important role and often double as multiple server functions. While this design does facilitate management and maintenance, it also plants hidden risks for network security and stable operation. Once a network fault occurs, its impact on the entire LAN can be devastating. This article explains how to fix a router that fails to assign IP addresses.
1. If you find that most clients cannot log in, cannot obtain an IP address after logging in, or the speed is extremely slow, and another department also reports widespread network outages, use the ipconfig network command in the operating system’s command prompt. You will discover that the client machines cannot obtain an IP address.
Therefore, it can be confirmed that this is the reason for the network access failure. Restarting the computers does not fix the problem, proving the issue is not on the clients. Checking the switch indicator lights shows normal status, with no crash caused by congestion, so the problem must lie with the router.
2. To understand why the DHCP server response becomes slow, it is necessary to understand the DHCP service workflow. If a DHCP server is deployed on the LAN and clients are set to obtain IP addresses automatically, then when a DHCP client logs into the network for the first time鈥攎eaning the client finds no existing IP data settings on the machine鈥攊t sends out a DHCP discover packet to the network. Because the client does not yet know which network it belongs to, the source address of the packet will be 0.0.0.0, and the destination address will be 255.255.255.255, with the DHCP discover information attached, broadcasting to the network.
In the default Windows preset, the waiting time for DHCP discover is preset to 1 second. That is, if the client does not receive a response within 1 second after sending the first DHCP discover packet, it will perform a second DHCP discover broadcast.
3. If no response is received continuously, the client will make a total of four DHCP discover broadcasts (including the first one). Except for the first time which waits 1 second, the waiting times for the remaining three times are 9, 13, and 16 seconds respectively.
If no response is received from the DHCP server after all attempts, the client will display an error message, declaring the DHCP discover a failure. Afterwards, based on the user’s choice, the system will repeat the DHCP discover process again after 5 minutes;
When the DHCP server receives the DHCP discover information broadcast by the DHCP client, it sends a DHCP offer message to the DHCP client, which includes a leasable IP address. Once the client receives the DHCP offer message, it will use the IP address provided by the server.
4. Analyzing from the DHCP workflow, the client’s inability to obtain an IP address should be because the DHCP server did not respond, or because the DHCP server responded but the client did not receive the DHCP offer message from the DHCP server.
After testing the network cables, the possibility that the client could not receive the DHCP server’s response due to network hardware reasons was first ruled out, leading to the judgment that the DHCP server did not respond normally.
5. There is a large amount of data interaction between the clients and the server. This data consumes significant system resources and network bandwidth, thus causing the DHCP server to respond slowly. This creates a vicious cycle, where the network is flooded with massive duplicate requests. This junk information consumes a large amount of bandwidth, forming a network storm. The server needs to perform massive data transmission, overloading the server’s network interface and bus. Consequently, not only can the operating system process not respond to the DHCP requests from clients in time, but all three departments are unable to work normally.
6. Clearly, the overloaded DHCP service caused a series of failures across the three departments. To fundamentally solve the problem, the only way is to upgrade the server or increase the number of servers