Automatic Private IP Addressing (APIPA) is a DHCP fail-safe that protects a computer system from failure. It invokes a standby mechanism for local Internet Protocol version 4 (IPv4) networks supported by Microsoft Windows. APIPA allows DHCP clients to obtain IP addresses even when DHCP servers are not functioning. APIPA exists in all modern versions of Windows, including Windows 10.
APIPA Explained – Automatic Private IP Addressing
Networks set up for dynamic addressing rely on a DHCP server to manage the pool of available local IP addresses. When a Windows client device attempts to join the local network, it contacts the DHCP server to request its IP address. If the DHCP server stops functioning or a network outage disrupts the request, this process may fail.
If the DHCP process fails, Windows automatically assigns an IP address from the private range, which is 169.254.0.1 through 169.254.254.255. Using Address Resolution Protocol (ARP), clients verify that the chosen APIPA address is unique on the network before using it. Clients then check with the DHCP server at regular intervals, typically every five minutes, and automatically update their addresses when the DHCP server can process requests.
For example, when you start a computer with Windows 10 installed, it waits a few seconds for a DHCP server before using an IP from the APIPA range. Previous versions of Windows search for a DHCP server for up to three minutes.
