- Why This IP Address Means Trouble

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IP address numbers in Internet Protocol (IP) version 4 (IPv4) range from up to The IP address has several special meanings on computer networks. It cannot be used as a general-purpose device address, however.

IPv6 networks have a similar concept of an all-zeros network address. on Clients

PCs and other client devices normally show an address of when they are not connected to a TCP/IP network.

A device may give itself this address by default whenever they are offline. It may also be automatically assigned by DHCP in case of address assignment failures.  When set with this address, a device cannot communicate with any other devices on that network over IP. can also theoretically set as a device's network (subnet) mask rather than its IP address. However, a subnet mask with this value has no practical purpose. Both the IP address and network maskare typically assigned as on a client together.

Software Application and Server Uses of

Some devices, particularly network servers, possess more than one IP network interface. TCP/IP software applications use as a programming technique to monitor network traffic across all of the IP addresses currently assigned to the interfaces on that multi-homed device.

While connected computers do not use this address, messages carried over IP sometimes include inside the protocol header when the source of the message is unknown.

The Use of vs. on Local Networks

Students of computer networks sometimes confuse the usages of and on IP networks. Whereas has several defined uses as described above, has the one very specific purpose of allowing a device to send messages to itself.

Troubleshooting IP Address Problems with

If a computer is properly configured for TCP/IP networking yet still shows for an address, try the following to troubleshoot this problem and obtain a valid address:

  • On networks with dynamic address asssignment support, release and renew the computer's IP address. Failures with DHCP assignment can be intermittent or persistent. If the failures persist, troubleshoot the DHCP server configuration: Common causes of failure include having no available addresses in the DHCP pool.
  • For networks that require static IP addressing, configure a valid IP address on the computer

See also: Working With IP Addresses