The control of IP address distribution is performed by a suite of tools that is known as DDI. The DDI acronym stands for DNS, DHCP, and IPAM. The DHCP server allocates an IP address to a device that connects to the network. The settings of that server restrict the range of available IP addresses. IP addresses are allocated for a limited period, then, if the device is still connected, the address allocation is extended or the device is allocated a new IP address. An IP address manager scans the network to discover which addresses are in use. If an address that has been allocated is not detected, that device must have disconnected from the network, so the IP address is flagged as available for reuse. The allocation of addresses to devices needs to be cross-referenced to hostnames and this lookup table is held in a DNS server.