Dynamic DNS

Dynamic DNS

Dynamic DNS is a method/protocol/network service that provides the capability for a networked device, such as a router or computer system using the Internet Protocol Suite, to notify a Domain Name System (DNS) name server to change, in real time, the active DNS configuration of its configured hostnames, addresses or other information.

A popular application of dynamic DNS is to provide a residential user's Internet gateway that has a variable, often changing, IP address with a well known hostname resolvable through standard DNS queries. This kind of dynamic DNS is commonly referred to as 'DynDNS', after a popular internet service of that name. It is accomplished via queries to especially formatted http/https URLs. Neither the format of these URLs nor the returned response codes is standardized. It is almost exclusively used on public networks, i.e. the internet, and does not require a user to run their own nameservers.

The standardized method of dynamically updating nameserver records is prescribed by RFC 2136, commonly known as 'Dynamic DNS Update' or 'DDNS'. Unlike the DynDNS-type updates, RFC 2136 is a protocol in its own right, with its own security mechanisms, and for use with managed nameservers. While RFC 2136 supports all DNS record types (including zone and user), it is most commonly used for dynamic hosts. In this form it is used primarily as an extension of the DHCP system, and in which the authorized DHCP servers register the clients' records with the nameserver(s) (Windows servers are an exception: by default, Windows servers only register 'A' records and the DHCP clients are expected to register the reverse pointers). This form of support for RFC 2136 is provided by a plethora of client and server software, including those that are components of most current operating systems. Support for RFC 2136 is also an integral part of many directory services, including LDAP and Windows' Active Directory domains.



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 hosts 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 dynamic DNS 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 RFC 2136 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 people's 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 premise router. The private network behind these routers uses address space set aside for these purposes (RFC 1918), 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 more fully. Today, numerous providers, called Dynamic DNS service providers, offer such technology and services on the Internet.


Dynamic DNS providers offer a software client program that automates the discovery and registration of client's public IP addresses. The client program is executed on a computer or device in the private network. It connects to the service provider's systems and causes those systems to link the discovered public IP address of the home network with a hostname in the domain name system. Depending on the provider, the hostname is registered within a domain owned by the provider or the customer's own domain name. These services can function by a number of mechanisms. Often they use an HTTP service request since even restrictive environments usually allow HTTP service. This group of services is commonly also referred to by the term Dynamic DNS, although it is not the standards-based DNS Update method. However, the latter might be involved in the providers systems.

Most home networking routers today have this feature already built into their firmware. One of the early routers to support Dynamic DNS was the UMAX UGate-3000 in 1999, which supported the TZO.COM dynamic DNS service.[1]

An example is residential users who wish to access their personal computer at home while traveling. If the home computer has a fixed static IP address, the user can connect directly using this address, but many provider networks force frequent changes to the IP address configured in their customers' equipment. With dynamic DNS, the home computer can automatically associate its current IP address with a domain name. As a result the remote user can resolve the host name used for the dynamic DNS service entry to the current address of the home computer with a DNS query. If a remote control program such as VNC server may be kept running on a host in the private network, the user can connect to the home network with a VNC client program.

In Microsoft Windows networks, dynamic DNS is an integral part of Active Directory, because domain controllers register their network service types in DNS so that other computers in the Domain (or Forest) can access them.

Increasing efforts to secure Internet communications today involve encryption of all dynamic updates via the public Internet, as these public dynamic DNS services have been abused increasingly to design security breaches. Standards-based methods within the DNSSEC protocol suite, such as TSIG, have been developed to secure DNS updates, but are not widely in use. Microsoft developed alternative technology (GSS-TSIG) based on Kerberos authentication.


See also

External links

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