Resolving routers cannot assign IP addresses

In today's life, routers play a lot of role, part-time more server functions, such planning is indeed convenient for the management and maintenance, but also for the security of the network, stable operation buried hidden dangers, once the network failure, the entire local area network impact is almost devastating, this article describes how to troubleshoot routers can not allocate IP addresses.

First, if found that most of the client can not log in, can not get IP after login or very slow, another department also reflects the large area of network, in the operating system command prompt in the use of Network command ipconfig, found that the client machine can not obtain IP address.

So this is definitely the reason for the inability to access the network, restart the computer failure is still, prove that the problem is not out on the client, to see the switch LED display status is normal, no blocking caused by the phenomenon, then the problem can only be out of the router.

Second, to understand the reason that causes the DHCP server to slow down, it is necessary to understand the work process of the DHCP service. If a DHCP server is deployed on a local area network and the client is set to obtain an IP address automatically, the DHCP client will issue a DHCP Discover packet to the network when it first logs on to the network, when the client discovers that there are no IP data settings on the computer. Because the client still does not know which network they belong to, so the packet's source address will be 0.0.0.0, and the destination address is 255.255.255.255, and then attach the DHCP Discover information, broadcast to the network.

By default for Windows, the DHCP Discover wait time is preset to 1 seconds, which means that the second DHCP Discover broadcast occurs after the client sends the first DHCP Discover packet without a response within 1 seconds.

If there is no response, the client will have four DHCP Discover broadcasts (including the first time). In addition to waiting 1 seconds for the first time, the remaining three wait times are 9, 13, and 16 seconds, respectively.

If you do not receive a response from the DHCP server, the client displays an error message declaring the DHCP discover failed. After that, based on the user's choice, the system will continue to repeat the DHCP Discover process after 5 minutes;

When a DHCP server receives DHCP Discover information that is broadcast by a DHCP client, it sends DHCP client offer information, including a leased IP address. 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 client cannot obtain the IP address that the DHCP server does not respond to, or the DHCP server makes a sound but the client does not receive DHCP offer information from the DHCP server.

After testing the network cable first, excluding the client from the DHCP server because of the hardware causes, the reason is that the DHCP server does not respond properly.

Five, the client and the server has a large number of data interaction, which occupies a large number of system resources and network bandwidth, resulting in a corresponding slow DHCP server. This goes into a vicious circle, and in the network is filled with a large number of duplicate requests, which occupy a large number of bandwidth, the formation of a network storm, the server needs to carry out a large number of data transmission, which makes the server network and bus overload, Not only does the operating system process fail to respond to DHCP requests from clients in a timely manner, but none of the three departments work properly.

Six, it is clear that the overburdened DHCP service has resulted in a series of failures in three sectors. To fundamentally solve the problem, only by upgrading the server or increase the number of servers to do their own duties, so as to avoid overloading the server. That is, deploying specialized DHCP servers for departmental IP services, deploying specialized database servers to serve the online exam system, deploying specialized file servers to provide file servers, and providing network cloning services. In this way, although additional input is required, this is necessary.

Vii. the acquisition of specialized servers is not realistic for institutions such as schools, LAN is a complete logical system it has its own characteristics, the server as the core of the network function to ensure that its normal work, over the normal use of the limit and the scope of some or the entire network will bring unintended consequences.

From the above, we understand the root cause of the failure, mainly because the DHCP function is beyond the limit, this is what we need to deploy the local area network special attention, otherwise it will be like the above router strike.