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The name localhost is a commonly defined hostname for the loopback interface in most TCP/IP systems, resolving to the IP addresses 127.0.0.1 in IPv4 and ::1 for IPv6.As a top-level domain, the name has traditionally been defined statically in host DNS implementations with address records (A and AAAA) pointing to the same loopback addresses.
127.0.0.1 localhost ::1 localhost The name may also be resolved by Domain Name System (DNS) servers, but there are special considerations [ 1 ] governing the use of this name: An IPv4 or IPv6 address query for the name localhost must always resolve to the respective loopback address.
Special address blocks Address block Address range Number of addresses Scope Description 0.0.0.0/8 0.0.0.0–0.255.255.255 16 777 216: Software Current (local, "this") network [1]
127.0.0.1 localhost loopback ::1 localhost This example only contains entries for the loopback addresses of the system and their host names, a typical default content of the hosts file. The example illustrates that an IP address may have multiple host names ( localhost and loopback ), and that a host name may be mapped to both IPv4 and IPv6 IP ...
RFC 1122 refers to 0.0.0.0 using the notation {0,0}. It prohibits this as a destination address in IPv4 and only allows it as a source address under specific circumstances. A host may use 0.0.0.0 as its own source address in IP when it has not yet been assigned an address, such as when sending the initial DHCPDISCOVER packet when using DHCP .
Then, if hostname is given (not NULL), a call to gethostbyname() resolves it, or otherwise the address 0.0.0.0 is used, if hints->ai_flags is set to AI_PASSIVE, and 127.0.0.1 otherwise. It allocated a new addrinfo structure filled with the appropriate sockaddr_in in one of these conditions and also adds the port retrieved at the beginning to it
The default route in Internet Protocol Version 4 (IPv4) is designated as the zero address, 0.0.0.0 / 0 in CIDR notation. [2] Similarly, in IPv6, the default route is specified by :: / 0. The subnet mask is specified as / 0, which effectively specifies all networks and is the shortest match possible. A route lookup that does not match any other ...
The most common IPv4 address used is 127.0.0.1. Commonly these loopback addresses are mapped to the hostnames localhost or loopback. MPLS One ...