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.
Server running the DHCP Service is unavailable
2No IP address returned
1Request
3Automatic Private IP AddressingIP address
F13us04
Figure 13-4 APIPA assigns IP addresses automatically.
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
server. 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 dif-
ferent. 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 gate-
way listed in the lease.
