DDNS (Dynamic DNS) is a service that maps Internet domain names to IP addresses. DDNS serves a similar purpose to the Internet's Domain Name System (DNS): DDNS allows anyone hosting a Web or FTP server to advertise a public name to prospective users.

Unlike DNS that only works with static IP addresses, DDNS is designed to also support dynamic IP addresses, such as those assigned by a DHCP server. That makes DDNS a good fit for home networks, which normally receive dynamic public IP addresses from their Internet provider that occasionally change.

To use DDNS, one simply signs up with a Dynamic DNS provider and installs network software on their host to monitor its IP address. Several online providers offer free DDNS subscription services that support Windows, Mac or Linux computers including FreeDNS Afraid (freedns.afraid.org) and NoIP (noip.com). Google Domains also includes dynamic DNS support. Other providers offer paid services including Dyn (dyn.com).

Compared to ordinary DNS, the disadvantage of DDNS is that additional host software, a new potential failure point on the network, often must be maintained.