ipconfig (internet protocol configuration) in Microsoft Windows is a console application that displays all current TCP/IP network configuration values and can modify Dynamic Host Configuration Protocol DHCP and Domain Name System DNS settings.
Forced release and renew
An important additional feature of ipconfig is to allow system admins to force refreshing of the DHCP IP address of the host computer to request a different IP address. This is done using two commands in sequence. First, ipconfig /release is executed to force the client to immediately give up its lease by sending the server a DHCP release notification which updates the server's status information and marks the old client's IP address as "Available". Then, the command ipconfig /renew is executed to request a new IP address. Where a computer is connected to a cable or DSL modem, it may have to be plugged directly into the modem network port to bypass the router, before using ipconfig /release and turning off the power for a period of time, to ensure that the old IP address is taken by another computer.
For ISP's that don't allow a user to request a new IP address using ipconfig /release and /renew, a good alternative is to use a DD-WRT hardware router setup with a VPN service. With this setup it's possible to get a new VPN IP address simply by cycling the power on the router...
Mac OS X ipconfig
ipconfig in Mac OS X serves as a wrapper to the IPConfiguration agent, and can be used to control the BootP and DHCP client from the command line interface. Like most UNIX-based operating systems, Mac OS X also uses ifconfig for more direct control over network interfaces, such as configuring static IP addresses.