The basic protocol for sending data over the Internet network and many other computer networks is the
Internet Protocol (IP). The protocol specifies that each IP packet must have a
header which contains (among other things) the IP address of the sender of the packet. The source IP address is normally the address that the packet was sent from, but the sender's address in the header can be altered, so that to the recipient it appears that the packet came from another source.
The protocol requires the receiving computer to send back a response to the source IP address, so that spoofing is mainly used when the sender can anticipate the network response or does not care about the response.
The source IP address provides only limited information about the sender. It may provide general information on the region, city and town when on the packet was sent. It does not provide information on the identity of the sender or the computer being used.