An IP address is a unique identifying number assigned to an internet-capable device. Most devices have an IP address assigned using the IPv4 protocol. But as the supply of available IPv4 addresses dwindles, IPv6 was developed to allow for more addresses to be created — trillions of trillions of addresses — to meet the growing demand of internet-capable devices. Many devices support IPv6 addresses, but most websites currently do not, as the technology is relatively new and the cost of upgrading and adoption is high.