IP address allocation sequence

A DHCP server assigns an IP address to a client according to the following sequence:

  1. The IP address statically bound to the client's MAC address or ID.

  2. The IP address that was ever assigned to the client.

  3. The IP address designated by the Option 50 field in a DHCP-DISCOVER message. Option 50 is the requested IP address field in DHCP-DISCOVER messages. It is padded by the client to specify the IP address that the client wants to obtain. The contents to be padded depend on the client.

  4. The first assignable IP address found in an extended or common address pool.

  5. The IP address that was a conflict or passed its lease duration.

If no IP address is assignable, the server will not respond.