Dynamic DNS is a system for allowing an Internet domain name to be assigned to a varying IP address. This makes it possible for other sites on the Internet to establish connections to the machine without needing to track the IP address themselves. A common use is for running server software on a computer that has a dynamic IP address (e.g., a dialup connection where a new address is assigned at each connection, or a DSL service where the address is changed by the ISP occasionally.)
To implement dynamic DNS it is necessary to set the maximum caching time of the domain to an unusually short period (typically a few minutes). This prevents other sites on the Internet from retaining the old address in their cache, so that they will typically contact the name server of the domain for each new connection.
Dynamic DNS service is provided on a large scale by various organisations, which retain the current addresses in a database and provide a means for the user to update it as required. Some providers of dynamic DNS are: