Record an intranet DHCP fault

I. symptom

The Intranet router is a DHCP server by default and provides the DHCP service. There are five network segments below. Suddenly, the IP addresses obtained by the hosts in the four network segments one day are not the IP address segments allocated by the Intranet route, as a result, hosts with 4 CIDR blocks accessing the Internet through DHCP cannot automatically obtain reasonable IP addresses.

Ii. Solution

(1) static address binding for all devices

The disadvantage is that it is troublesome. In this network, the PC is a static address, and a Wireless AP provides an IP address for the wireless device. If it is changed to static binding, it is troublesome to bind a static IP address to each mobile phone, the problem cannot be completely solved.

(2) locate the pseudo DHCP server and disable its service.

A. Capture packets from Wireshark and view the source IP address and source MAC address in the broadcast packet that responds to the DHCP request. For example

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B. Configure the local IP address and the pseudo DHCP server in the same network segment. Ping the IP address of the pseudo DHCP server and check the TTL value to determine the system type (64 is generally a Linux system, 128 is generally for Windows, 255 is generally for UNIX), and Mac Scanning

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C. Based on the Mac scan results, find the host name of the pseudo DHCP server, and then find the host to close its service (if it is a network administrator, it is important to register the host ), this is the result of the failure to shut down the pppoe server set up by a colleague during the test. Fortunately, its virtual machine also has an obvious host name. Otherwise, you can find the host one by one...

This article from the "Flying Pig" blog, please be sure to keep this source http://thinkpig007.blog.51cto.com/971471/1553159

Record an intranet DHCP fault