Editing Localhost (section)

==Name resolution==
{{Anchor|Name resolution}} <!--Old name of this section - in case somebody linked to it-->
The name ''localhost'' normally resolves to the [[IPv4]] loopback [[IP address|address]] {{IPaddr|127.0.0.1}}, and to the [[IPv6]] loopback address {{IPaddr|::1}}.

This resolution is normally configured by the following lines in the operating system's [[hosts (file)|hosts file]]:
<pre>
127.0.0.1    localhost
::1          localhost
</pre>
The name may also be resolved by [[Domain Name System]] (DNS) servers, but there are special considerations{{Ref RFC|6761}} governing the use of this name:

* An [[IPv4]] or [[IPv6]] address query for the name localhost must always resolve to the respective loopback address.
* Applications may resolve the name to a loopback address themselves, or pass it to the local name resolver mechanisms.
* When a name resolver receives an address (A or AAAA) query for ''localhost'', it should return the appropriate loopback addresses, and negative responses for any other requested record types. Queries for ''localhost'' should not be sent to caching name servers.
* To avoid burdening the [[Domain Name System]] root servers with traffic, caching name servers should never request name server records for ''localhost'', or forward resolution to authoritative name servers.
* When authoritative name servers receive queries for 'localhost' in spite of the provisions mentioned above, they should resolve them appropriately.
In addition to the mapping of ''localhost'' to the loopback addresses ({{IPaddr|127.0.0.1}} and {{IPaddr|::1}}), ''localhost'' may also be mapped to other IPv4 (loopback) addresses and it is also possible to assign other, or additional, names to any loopback address. The mapping of ''localhost'' to addresses other than the designated loopback address range in the hosts file or in DNS is not guaranteed to have the desired effect, as applications may map the name internally.

In the Domain Name System, the name ''[[.localhost]]'' is reserved as a [[top-level domain|top-level]] [[domain name]], originally set aside to avoid confusion with the <u>hostname</u> ''localhost''.{{Ref RFC|2606}} Domain name registrars are precluded from delegating domain names in the top-level ''.localhost'' domain.{{Ref RFC|6761}}