Dynamic DNS
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Dynamic DNS

Dynamic DNS (DDNS) is a method of automatically updating a name server in the Domain Name System (DNS), often in real time, with the active DDNS configuration of its configured hostnames, addresses or other information.

The term is used to describe two different concepts. The first is "dynamic DNS updating" which refers to systems that are used to update traditional DNS records without manual editing. These mechanisms use TSIG to provide security. The second kind of dynamic DNS permits lightweight and immediate updates often using an update client, which do not use the RFC 2136 standard for updating DNS records. These clients provide a persistent addressing method for devices that change their location, configuration or IP address frequently.

In the initial stages of the Internet (ARPANET), addressing of hosts on the network was achieved by static translation tables that mapped hostnames to IP addresses. The tables were maintained manually in form of the host file. The Domain Name System brought a method of distributing the same address information automatically online through recursive queries to remote databases configured for each network, or domain. Even this DNS facility still used static lookup tables at each participating node. IP addresses, once assigned to a particular host, rarely changed and the mechanism was initially sufficient. However, the rapid growth of the Internet and the proliferation of personal computers in the workplace and in homes created the substantial burden for administrators of keeping track of assigned IP addresses and managing their address space. The Dynamic Host Configuration Protocol (DHCP) allowed enterprises and Internet service providers (ISPs) to assign addresses to computers automatically as they powered up. In addition, this helped conserve the address space available, since not all devices might be actively used at all times and addresses could be assigned as needed. This feature required that DNS servers be kept current automatically as well. The first implementations of DDNS fulfilled this purpose: Host computers gained the feature to notify their respective DNS server of the address they had received from a DHCP server or through self-configuration. This protocol-based DNS update method was documented and standardized in IETF publication in 1997 and has become a standard part of the DNS protocol (see also nsupdate program).

The explosive growth and proliferation of the Internet into homes brought a growing shortage of available IP addresses. DHCP became an important tool for ISPs as well to manage their address spaces for connecting home and small-business end-users with a single IP address each by implementing network address translation (NAT) at the customer-premises router. The private network behind these routers uses address space set aside for these purposes, masqueraded by the NAT device. This, however, broke the end-to-end principle of Internet architecture and methods were required to allow private networks, with frequently changing external IP addresses, to discover their public address and insert it into the Domain Name System in order to participate in Internet communications properly. Today, numerous providers, called Dynamic DNS service providers, offer such technology and services on the Internet.

DNS is based on a distributed database that takes some time to update globally. When DNS was first introduced, the database was small and could be easily maintained by hand. As the system grew this task became difficult for any one site to handle, and a new management structure was introduced to spread out the updates among many domain name registrars. Registrars today offer end-user updating to their account information, typically using a web-based form, and the registrar then pushes out update information to other DNS servers.

Due to the distributed nature of the domain name systems and its registrars, updates to the global DNS may take hours to distribute. Thus DNS is only suitable for services that do not change their IP address very often, as is the case for most large services like Wikipedia. Smaller services, however, are generally much more likely to move from host to host over shorter periods of time. Servers being run on certain types of Internet service provider, cable modems in particular, are likely to change their IP address over very short periods of time, on the order of days or hours. DDNS is a system that addresses the problem of rapid updates.

The term DDNS is used in two ways, which, while technically similar, have very different purposes and user populations. The first is standards-based DDNS, which uses an extension of the DNS protocol to ask for an update; this is often used for company laptops to register their address. The second is proprietary DDNS, usually a web-based protocol, normally a single HTTP fetch with username and password which then updates some DNS records (by some unspecified method); this is commonly used for a domestic computer to register itself by a publicly known name in order to be found by a wider group, for example as a games server or webcam.

End users of Internet access receive an allocation of IP addresses, often only a single address, by their Internet service provider. The assigned addresses may either be fixed (i.e. static), or may change from time to time, a situation called dynamic. Dynamic addresses are generally given only to residential customers and small businesses, as most enterprises specifically require static addresses.

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