With the widespread use of x-DSL and cable-modem technologies, many home users now host Web sites on their own desktop computers. As their IP addresses are dynamically assigned by their Internet service providers (ISPs), users must update their DNS records every time their IP addresses change (it’s usually done by some computer software on the user machine that automatically contacts the name server to update the corresponding data whenever the assigned IP address changes). This service is usually called Dynamic DNS. However, in order for these updates to work as expected, there’s one field of each resource record that must be set to a quite different value from the typical ones. Which one, and why?