Dynamic Domain Name System record or Dynamic DNS or DynDNS or DDNS is a system of information technology, in which real-time domain name entries can be updated. The term Dynamic DNS can have multiple network services which can refer to a DNS service that offers an update mechanism for host names via the web interface (often called DynDNS) or a DNS service to a mechanism for updating DNS records according to RFC 2136. Practical usage of Dynamic DNS can be found as hyper-links on our previous article on Cloud DNS.
Dynamic DNS and DynDNS
Despite changing the IP address a server or computer can be under a constant domain name on the web. The DynDNS provider ensures that the current (changing) IP address of the server or computer giving everyone to access over the Internet. Constantly changing entries in the domain name system is not actually provided. To save the network resources DNS entries are cached as long as possible, for several hours or even days. Nevertheless, in order to enable dynamic DNS entries, one can reduce the maximum time (TTL = time to live) of the DNS records (for example, 60 seconds). One who uses DynDNS, tests whether the use of the name server reflects the storage time (TTL) correctly. On Unix, this goes with dig domainname. In the Answer section the storage time is displayed. The example can be the usage on Platform on a Service like Heroku Cloud.
To update a DynDNS entry in the name servers of the operator, usually a DynDNS client installed. This is a program that connects automatically when IP changes with the DynDNS server and sends the new IP address of the computer. Most current DSL router have already incorporated such a client that can be used alternatively. DynDNS can not replace a static IP address.
Dynamic DNS and DDNS
The nsupdate program is a part of the BIND package that allows the client-side updates of DNS records. Additionally, there is the possibility of authentication, optionally using TSIG or SIG (0). TSIG works on RFC 2845 and uses two symmetric keys, whose only HMAC-MD5 hashing algorithm to time exists. SIG (0) ( RFC 3535 and RFC 2931 ) is supported since BIND 9.3 and has the advantage of asymmetric keys that support almost any hash algorithm (RSAMD5, RSASHA1, DSA, etc.).