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The address 127.0.0.1 is the standard address for IPv4 loopback traffic; the rest are not supported by all operating systems. However, they can be used to set up multiple server applications on the host, all listening on the same port number. In the IPv6 addressing architecture [3] there is only a single address assigned for loopback: ::1. The ...
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.
127.0.0.0/8 127.0.0.0–127.255.255.255 16 777 216: Host Used for loopback addresses to the local host [1] 169.254.0.0/16 169.254.0.0–169.254.255.255 65 536: Subnet Used for link-local addresses [5] between two hosts on a single link when no IP address is otherwise specified, such as would have normally been retrieved from a DHCP server 172 ...
Various Internet Engineering Task Force (IETF) standards reserve the IPv4 address block 127.0.0.0 / 8, in CIDR notation and the IPv6 address ::1 / 128 for this purpose. The most common IPv4 address used is 127.0.0.1. Commonly these loopback addresses are mapped to the hostnames localhost or loopback.
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 ...
This is useful for determining the efficiency of a certain route from two points in a network. In this example, it is more efficient to communicate with the computer itself through the use of address 127.0.0.1 (called localhost) than it would be through 192.168.0.100 (the IP address of the local network card).
This means that 256 /8 address blocks fit into the entire IPv4 space. As IPv4 address exhaustion has advanced to its final stages, some organizations, such as Stanford University, formerly using 36.0.0.0 / 8, have returned their allocated blocks (in this case to APNIC) to assist in the delay of the exhaustion date.
If an ISP deploys a CGN and uses private Internet address space [2] (networks 10.0.0.0 / 8, 172.16.0.0 / 12, 192.168.0.0 / 16) to connect their customers, there is a risk that customer equipment using an internal network in the same range will stop working.