When IP Addresses Conflict

Q: Every now and then, I get a pop-up on my work computer that reads, “There is an IP address conflict with another system on the network.” This happens at times when I need my network the most, but, in order to recover, a reboot is required. So far I have been unable to find out what is causing it.

A: An IP address conflict is a network problem that is caused by having two network devices (computers, printers, routers, firewalls, etc.) with the same IP address on the same broadcast domain, local area network (LAN) or virtual local area network (VLAN) at the same time.

The IP protocol, version 4, requires every network device to have a unique identifier — an IP address — in order to function properly. When two network devices have the same identifier, the traffic that needs to get to them will be inconsistent. It might be that all the traffic will end up in only one of them, or that one packet will go to one and another will go to the other. This is unacceptable and can cause major disruption in the transferred information, and therefore network devices that implement the IP protocol are programmed to detect and avoid those conflicting conditions.

The detection mechanism is usually based on a probe address resolution protocol (ARP), where the host sends a broadcast ARP probe packet upon the interface configuration — either manual or dynamic addressing network (DHCP). At this point, a host with a…



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