What Is Automatic Private IP Addressing?

What Is Automatic Private IP Addressing?

The Windows 10 implementation of TCP/IP supports automatic assignment of IP addresses for simple LAN-based network configurations. This addressing mechanism is an extension of dynamic IP address assignment for LAN adapters, enabling configuration of IP addresses Without using static IP address assignment or using a DHCP server. Automatic Private IP Addressing (APIPA) is enabled by default in Windows 10 so that home users and small business users can create a functioning, single-subnet, TCP/IP-based network without having to configure the TCP/IP protocol manually or set up a DHCP server.

The IANA has reserved 169.254.0.0 through 169.254.255.255 for APlPA. As a result, APIPA provides an address that is guaranteed not to conflict with routable addresses.

APIPA assigns an IP address and subnet mask only, and configures no additional parameters. This service is very useful in smaller, single-network environments in Which there is no need for connectivity to other networks. APIPA provides a very pie way to configure TCP/IP; the network administrator does not need any know of the necessary configuration parameters. However, if connectivity to other networks is required, or if the client requires name-resolution services, APIPA is not sufficient. APIPA does not provide a default gateway or name server address to the client.

The process for the APIPA feature,  is explained in the folk»Mn steps:

1. Windows 10 TCP/IP attempts to find a DHCP server on the anached network to obtain a dynamically assigned IP address.

2. In the absence of a DHCP server during startup (for example, if the server is down for maintenance or repairs), the client cannot obtain an IP address.

3. APIPA generates an IP address in the form of 169.254.x.y (where x.y is the client‘s randomly generated unique identifier) and a subnet mask of 255.255.0.0.



After the computer generates the address, it broadcasts to this address, and then assigns the address to itself if no other computer responds. The computer continues to use this address until it detects and receives configuration information from a DHCP sewer. This allows two computers to be plugged into a LAN hub to restart without any IP address configuration and to use TCP/IP for local network access.

If the computer is a DHCP client that has previously obtained a lease from a DHCP server and the lease has not expired at boot time, the sequence of events is slightly different. The client tries to renew its lease With the DHCP server. If the client cannot locate a DHCP server during the renewal attempt, it attempts to ping the default gateway listed in the lease.

1f pinging the default gateway succeeds, the DHCP client assumes that it is still on the same network in which it obtained its current lease, so it continues to use the lease. By default, the client attempts to renew its lease when 50 percent of its assigned lease time has expired. If pinging the default gateway fails, the client assumes that it has been moved to a network that has no DHCP services currently available and it autoconfigures itself, as previously described. After being automatically configured, the client continues to try to locate a DHCP server every five minutes.

APIPA can assign a TCP/IP address to DHCP clients automatically. However, APIPA does not generate all the information that typically is provided by DHCP, such as the address of a default gateway. Consequently, computers enabled with APIPA can communicate only with computers on the same subnet that also have addresses of the form 169.254.x.y.

If you are troubleshooting a network problem and discover that a client computer has an IP address on the 169.254.0.0 network, the computer has assigned itself that address using APIPA because the computer could not locate a DHCP server.

By default, the APIPA feature is enabled. However, you can disable it by specifying an alternate configuration to use if a DHCP server cannot be located in the alternate configurations on internet protocol properties