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What is the IP address used for?

One of a handful of special-purpose addresses, has several applications in networking. It stands in as a placeholder address, identifies a default route and more.

The IP address number is a nonroutable IPv4 address with several uses, primarily as a default or placeholder...

address. Even though has several uses on computer networks, it is not a general-purpose device address.

The Internet Engineering Task Force defines the IP address as a reserved, special-purpose address for "this host, this network." Its IPv6 equivalent is expressed as ::/0. Although is valid address syntax, a client device using it as a source IP address cannot communicate on a network.

IPv4 address numbers start with and go up to

What is used for?

One use of is during system initialization, when a device adopts it before being assigned a usable IP address. Similarly, it can also manifest as a result of a Dynamic Host Configuration Protocol (DHCP) error. A Windows client that experiences this error and supports Automatic Private IP Addressing will assign itself an IP address within the range of through It will use as the gateway address.

Other ways to use the IP address include:

  • As a default static route -- when used with a subnet mask of, it matches any address; when used with a mask, it matches none;
  • As a source address in IPv4 broadcasting within a local area network;
  • On servers, to designate a service may bind to all interfaces; and
  • On PCs and client devices, a address indicates that the client isn't connected to a TCP/IP network, and a device may give itself a address when it is offline.
IP address classes
IPv4 address classes

What is the difference between and

Both and are considered special-purpose addresses that are used by hosts for self-identification. The key difference is is reserved for loopback traffic -- that is, communications within a single host. Addresses within the block do not appear on a network. The IPv6 equivalent of is ::1. It is typically used for testing and troubleshooting purposes, typically using the hostname localhost.

Troubleshooting IPv4 addresses

If a computer shows for an address and is configured for TCP/IP networking, the following troubleshooting steps can be taken to try to obtain a valid IP address:

  • Release and renew the computer's IP address networks with dynamic address assignment support. Failures with DHCP assignment can happen repeatedly or intermittently. If valid IP address failures continue, check the DHCP server configuration, because a common cause of failure includes having no available addresses in the DHCP pool.
  • For networks that require static IP addresses, a valid IP address can be configured on the computer.

Next Steps

Solving IP address management headaches

Learn how to calculate subnet masks

Expert information on how IPv6 changes subnetting

This was last published in May 2017

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