This IP address is structured like a regular one (it has four places for numbers). However, it’s a placeholder address or one that’s used to describe that there isn’t a normal address assigned—neither public nor private. For example, instead of putting no IP address into the network area of a program, 0.0.0.0 can be used to mean anything from accept all IP addresses or block all IP addresses to the default route. It’s easy to confuse 0.0.0.0 and 127.0.0.1. An address with four zeros has several defined uses (as described below), while 127.0.0.1 has one specific purpose of allowing a device to send messages to itself.
What 0.0.0.0 Means
In short, 0.0.0.0 is a non-routable address that describes an invalid or unknown target. However, it means something different depending on whether it’s seen on a client device like a computer or on a server machine.
On Client Computers
PCs and other client devices normally show an address of 0.0.0.0 when not connected to a TCP/IP network. A device might give itself this address by default whenever it is offline. It might also be automatically assigned by DHCP in the case of address assignment failures. When set with this address, a device cannot communicate with any other devices on that network. 0.0.0.0 can also theoretically be set as a device’s subnet mask rather than its IP address. However, a subnet mask with this value has no practical purpose. Both the IP address and network mask are typically assigned 0.0.0.0 on a client. Depending on the way it’s used, firewall or router software might use 0.0.0.0 to indicate that every IP address should be blocked (or allowed).
On Software Applications and Servers
Some devices, particularly network servers, possess more than one network interface. TCP/IP software applications use 0.0.0.0 as a programming technique to monitor network traffic across all 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 0.0.0.0 inside the protocol header when the source of the message is unknown.
What to Do When You See the 0.0.0.0 IP Address
If a computer is properly configured for TCP/IP networking but shows 0.0.0.0 for an address, try the following to troubleshoot this problem and obtain a valid address:
On networks with dynamic address assignment 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.
