- Data travels across networks in a structure called a packet. The data lies in the packet body, and the networking software adds headers on the front of this. The headers contain data about the data in the packet body and also addresses for the packet. The Internet Protocol dictates the format of an IP address, which identifies a computer on a network. The IP header goes on the front of the data packet. Behind this comes the transport header. The transport protocol creates the packet and puts its header on the front of the data. This header contains the address of the destination application for the packet. Application addresses are called port numbers, and the association between applications and port numbers is administered by the Internet Assigned Numbers Authority, or IANA. IANA assigned port 43 to the Whois application.
- The format of a data packet is dictated by a transport protocol. The two possible transport protocols are the Transmission Control Protocol, called TCP, and the User Datagram Protocol, or UDP. Only one or the other acts on a data packet, never both. TCP forms a connection between the two ports in a transmission. This enables a series of packets to be exchanged in the context of a "session." UDP sends packets as one complete transaction. It puts the source and destination port numbers in its packet header, but makes no attempt to relate packets together and has no procedures for lost packets. A port is identified by its port number and the transport protocol it serves. Hence, there is a UDP port 43 and a TCP port 43. These two are not the same port. Whois only uses TCP port 43. It doesn't use the UDP port, even though that port is assigned to it.
- Whois is the name of a protocol and an application. It enables outsiders to query a database containing data on domain name, or IP address, ownership. The client sends an IP address or a domain name, such as "www.example.com," and the Whois server returns the details of the registered contact for the owners of that domain.
- Originally, all domain names and IP addresses were distributed by one global authority. However, the registration of IP address and Web domains is now distributed among many different authorities. This means that a client needs to know which registry to visit to present a Whois query.
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