“ 127.0.0.1 ” redirects here. For the use of this address on Flickroom, see User:127.0.0.1 In computer network, localhost is a hostname that refers to the current device used to access it. It is used to access the network services that are running on the host via the loopback network interface. Using the loopback interface bypasses any local net interface hardware .
The local loopback mechanism may be used to run a network service on a horde without requiring a physical network interface, or without making the service accessible from the networks the computer may be connected to. For exercise, a locally installed web site may be accessed from a Web browser by the URL http://localhost to display its home page.
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The list localhost normally resolves to the IPv4 loopback cover 127.0.0.1, and to the IPv6 loopback address ::1. [ 1 ]
IPv4 network standards reserve the stallion address freeze 127.0.0.0/8 ( more than 16 million addresses ) for loopback purposes. [ 2 ] That means any mailboat sent to any of those addresses is looped back. The address 127.0.0.1 is the standard address for IPv4 loopback dealings ; the remainder are not supported by all operate systems. however, they can be used to set up multiple server applications on the server, all listening on the lapp port act. The IPv6 standard assigns only a single address for loopback : ::1. The resolution of the name localhost to one or more information science addresses is normally configured by the watch lines in the manoeuver system ‘s hosts file :
127.0.0.1 localhost ::1 localhost
The name may besides be resolved by Domain Name System ( DNS ) servers, but queries for this name should be resolved locally, and should not be forwarded to remote name servers. In addition to the map of localhost to the loopback addresses ( 127.0.0.1 and ::1 ), localhost may besides be mapped to other IPv4 ( loopback ) addresses and it is besides possible to assign other, or extra, names to any loopback address. The map of localhost to addresses early than the delegate loopback address range in the hosts file or in DNS is not guaranteed to have the hope effect, as applications may map the identify internally. In the Domain Name System, the name localhost is reserved as a top-level domain name, originally set away to avoid confusion with the hostname used for loopback purposes. [ 3 ] IETF standards forbid domain mention registrars from assigning the list localhost.
The mention localhost is reserved for loopback purposes by RFC 6761 ( Special-Use Domain Names ), [ 4 ] which achieved the Proposed Standard maturity level in February 2013. The standard sets forth a number of special considerations governing the use of the appoint in the Domain Name System :
- An IPv4 or IPv6 address query for the name localhost must always resolve to the respective loopback address, which is specified in a separate standard.
- 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.
- DNS registrars are precluded from delegating domain names in the top-level domain localhost.
- When authoritative name servers receive queries for ‘localhost’ in spite of the provisions mentioned resolve them appropriately.
The IPv4 loopback addresses are reserved within the IPv4 address outer space by the IETF “ Special Use IPv4 Addresses ” standard ( RFC 5735 ). [ 5 ] The reservation can be traced back to the November 1986 “ delegate Numbers ” standard ( RFC 990 ). In contrast, the IETF “ IP Version 6 Addressing Architecture ” standard ( RFC 4291 ) reserves the single IPv6 loopback address ::1 within the IPv6 address outer space. The standard precludes the grant of that address to any physical interface, arsenic well as its use as the beginning or address savoir-faire in any package sent to remote hosts. Any such packet that is mistakenly transmitted is not supposed to be routed, and should be dropped by all routers or hosts that receive it .
The process of any packet sent to a loopback address is implemented in the connection layer of the TCP/IP batch. such packets are never passed to any network interface control ( NIC ) or hardware device driver and must not appear outside of a computer science system or be routed by any router. This permits software testing and local anesthetic services in the absence of any hardware network interfaces. Looped-back packets are distinguished from any early packets traversing the TCP/IP stack only by the special IP address they were addressed to. frankincense, the services that ultimately receive them respond according to the specified finish. For case, an HTTP service could route packets addressed to 127.0.0.99:80 and 127.0.0.100:80 to different Web servers, or to a single server that returns different web pages. To simplify such test, the hosts file may be configured to provide appropriate names for each savoir-faire.
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Packets received on a non-loopback interface with a loopback reference or destination address must be dropped. such packets are sometimes referred to as martian packets. [ 6 ] As with any other bogus packets, they may be malicious and any problems they might cause can be avoided by applying bogon filter .
The releases of the MySQL database differentiate between the manipulation of the hostname localhost and the use of the addresses 127.0.0.1 and ::1. [ 7 ] When using localhost as the destination in a node connection interface of an application, the MySQL application programming interface connects to the database using a Unix knowledge domain socket, while a TCP connection via the loopback interface requires the lineal use of the denotative address. One noteworthy exception to the use of the 127.0.0.0/8 addresses is their use in Multiprotocol Label Switching ( MPLS ) traceroute error detection, in which their place of not being routable provides a convenient means to avoid rescue of faulty packets to end users .