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DNS resolvers have several advantages over letting each Internet host query directly nameservers. Firstly, regular Internet hosts do not need to maintain the up-to-date list of the addresses of the root servers. Secondly, regular Internet hosts do not need to send queries to nameservers all over the Internet. Furthermore, as a DNS resolver serves a large number of hosts, it can cache the received answers. This allows the resolver to quickly return answers for popular DNS queries and reduces the load on all DNS servers [JSBM2002]_.
Benefits of names
In addition to being more human friendly, using names instead of addresses inside applications has several important benefits. To understand them, let us consider a popular application that provides information stored on servers. This application involves clients and servers. The server provides information upon requests from client processes. A first deployment of this application would be to rely only on addresses. In this case, the server process would be installed on one host and the clients would connect to this server to retrieve information. Such a deployment has several drawbacks :
if the server process moves to another physical server, all clients must be informed about the new server address
if there are many concurrent clients, the load of the server will increase without any possibility of adding another server without changing the server addresses used by the clients
Using names solves these problems and provides additional benefits. If the clients are configured with the name of the server, they will query the name service before contacting the server. The name service will resolve the name into the corresponding address. If a server process needs to move from one physical server to another, it suffices to update the name to address mapping on the name service to allow all clients to connect to the new server. The name service also enables the servers to better sustain the load. Assume a very popular server which is accessed by millions of users. This service cannot be provided by a single physical server due to performance limitations. Thanks to the utilization of names, it is possible to scale this service by mapping a given name to a set of addresses. When a client queries the name service for the server's name, the name service returns one of the addresses in the set. Various strategies can be used to select one particular address inside the set of addresses. A first strategy is to select a random address in the set. A second strategy is to maintain information about the load on the servers and return the address of the less loaded server. Note that the list of server addresses does not need to remain fixed. It is possible to add and remove addresses from the list to cope with load fluctuations. Another strategy is to infer the location of the client from the name request and return the address of the closest server.
Mapping a single name onto a set of addresses allows popular servers to dynamically scale. There are also benefits in mapping multiple names, possibly a large number of them, onto a single address. Consider the case of information servers run by individuals or SMEs. Some of these servers attract only a few clients per day. Using a single physical server for each of these services would be a waste of resources. A better approach is to use a single server for a set of services that are all identified by different names. This enables service providers to support a large number of servers processes, identified by different names, onto a single physical server. If one of these server processes becomes very popular, it will be possible to map its name onto a set of addresses to be able to sustain the load. There are some deployments where this mapping is done dynamically in function of the load.
Names provide a lot of flexibility compared to addresses. For the network, they play a similar role as variables in programming languages. No programmer using a high-level programming language would consider using hardcoded values instead of variables. For the same reasons, all networked applications should depend on names and avoid dealing with addresses as much as possible.
Footnotes
The :term:`hosts.txt` file is not maintained anymore. A historical snapshot from April 1984 is available from http://ftp.univie.ac.at/netinfo/netinfo/hosts.txt
See http://www.donelan.com/dnstimeline.html for a time line of DNS related developments.
This specification evolved later to support domain names written by using other character sets than us-ASCII :rfc:`5890`. This extension is important to support languages other than English, but a detailed discussion is outside the scope of this document.
The official list of top-level domain names is maintained by :term:`IANA` at http://data.iana.org/TLD/tlds-alpha-by-domain.txt Additional information about these domains may be found at http://en.wikipedia.org/wiki/List_of_Internet_top-level_domains
It is interesting to note that to prevent any homograph attack, Google Inc. registered the `g00gle.com` domain name but does not apparently use it.
A copy of the information maintained by each root nameserver is available at http://www.internic.net/zones/root.zone
Until February 2008, the root DNS servers only had IPv4 addresses. IPv6 addresses were slowly added to the root DNS servers to avoid creating problems as discussed in http://www.icann.org/en/committees/security/sac018.pdf As of February 2021, there remain a few DNS root servers that are still not reachable using IPv6. The full list is available at http://www.root-servers.org/

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cnp3-ebook / principles/naming — English

Until February 2008, the root DNS servers only had IPv4 addresses. IPv6 addresses were slowly added to the root DNS servers to avoid creating problems as discussed in http://www.icann.org/en/committees/security/sac018.pdf As of February 2021, there remain a few DNS root servers that are still not reachable using IPv6. The full list is available at http://www.root-servers.org/
Until February 2008, the root DNS servers only had IPv4 addresses. IPv6 addresses were slowly added to the root DNS servers to avoid creating problems as discussed in http://www.icann.org/en/committees/security/sac018.pdf As of February 2021, there remain a few DNS root servers that are still not reachable using IPv6. The full list is available at http://www.root-servers.org/
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../../principles/naming.rst:154
String age
2 years ago
Source string age
2 years ago
Translation file
locale/pot/principles/naming.pot, string 38