Duplicate IP Address Detection for IPv4
Duplicate address detection is important . When the adapter is first initialized, gratuitous ARP requests are broadcast for the IP addresses of the local host. Windows Embedded CE sends three ARP requests. Windows Embedded CE does not support the ArpRetryCount registry parameter. If another host replies to any of these requests, the IP address is already in use. When this happens, the Windows Embedded CE-based device will still boot. However, the IP address is not registered with the TCP/IP stack, and an error message is displayed. If Windows Embedded CE detects another computer transmitting an ARP reply for the IP address that the Windows Embedded CE-based computer is using, an error message is displayed, but the interface continues to operate. After transmitting the ARP reply, the defending system again broadcasts an ARP request for its own address so that other hosts on the network will maintain the correct mapping for the address in their ARP caches.
A computer using a duplicate IP address can be started while it is not attached to the network, in which case no conflict would be detected. However, if it is then plugged into the network, the first time that it sends an ARP request for another IP address, any Windows-based computer with a conflicting address detects the conflict. The device detecting the conflict displays an error message.
DHCP-enabled clients will inform the DHCP server if an IPv4 address conflict is detected, and instead of invalidating the stack, they will request a new address from the DHCP server and request that the server flag the conflicting address as bad for the administrator. This capability is commonly known as DHCP Decline support.