The TCP protocol creates a channel using the IP addresses of machines. When you type a URL in the browser, it usually does not contain IP numbers. It contains machine names. The name is converted to IP numbers using a distributed database called Domain Name System (DNS). This database is distributed, and when a program needs to convert a name to an address, it sends DNS request to one of the DNS servers it knows. These servers query each other or tell the client whom to ask, until the client knows the IP address assigned to the name. The servers and the client also cache the recently requested names, so answering is fast. On the other hand, when the IP address of a server changes this name, not all clients will immediately see the address assignment over the globe. The DNS lookup can be easily programmed, and there are classes and methods in JDK that support this, but usually we need not care about that; when we program, it is done automatically in web programming.