In the
Internet Protocol Version 4
Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...
, the address is a non-routable meta-address used to designate an invalid, unknown or non-applicable target. This address is assigned specific meanings in a number of contexts, such as on
clients or on
servers.
As a host address
Uses include:
* A way to specify "any IPv4 address at all". It is used in this way when configuring servers (i.e. when binding listening sockets). This is known to TCP programmers as INADDR_ANY. (bind(2) binds to addresses, not interfaces.)
* The address a host claims as its own when it has not yet been assigned an address. Such as when sending the initial ''DHCPDISCOVER'' packet when using
DHCP
The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a cli ...
.
* The address a host assigns to itself when address request via DHCP has failed, provided the host's IP stack supports this. This usage has been replaced with the
APIPA
In computer networking, a link-local address is a unicast network address that is valid only for communications within the subnetwork that the host is connected to. Link-local addresses are most often assigned automatically with a process known as ...
mechanism in modern operating systems.
* A way to explicitly specify that the target is unavailable.
*A way to route a request to a nonexistent target instead of the original target. Often used for adblocking purposes.
In the context of servers, can mean "all IPv4 addresses on the local machine". If a host has two IP addresses, and , and a server running on the host is configured to listen on , it will be reachable at both of those IP addresses.
Routing
In the context of
routing tables
In computer networking, a routing table, or routing information base (RIB), is a data table stored in a router or a network host that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with th ...
, a network destination of is used with a network mask of 0 to depict the
default route
In computer networking, the default route is a configuration of the Internet Protocol (IP) that establishes a forwarding rule for packets when no specific address of a next-hop host is available from the routing table or other routing mechanisms ...
as a destination
subnet
A subnetwork or subnet is a logical subdivision of an IP network. Updated by RFC 6918. The practice of dividing a network into two or more networks is called subnetting.
Computers that belong to the same subnet are addressed with an identical ...
. This destination is expressed as in
CIDR notation. It matches all addresses in the IPv4 address space and is present on most hosts, directed towards a local router.
In routing tables, can also appear in the gateway column. This indicates that the gateway to reach the corresponding destination subnet is unspecified. This generally means that no intermediate routing hops are necessary because the system is directly connected to the destination.
In IPv6
In
IPv6
Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv ...
, the all-zeros address is typically represented by (two colons), which is the short notation of .
The IPv6 variant serves the same purpose as its IPv4 counterpart.
See also
*
Reserved IP addresses
*
localhost
References
* In the notation "" is used to designate 0.0.0.0/x (x being anything from 0 to 32). Quote: " This host on this network. MUST NOT be sent, except as a source address as part of an initialization procedure by which the host learns its own IP address."
External links
*
Routing
IP addresses
0 (number)
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