During the development of a network application, it can be useful to run multiple instances of the application using the same transport layer protocol port on the same development host, while also having network access to the application instances limited to the local host. Under IPv4, this has been possible by using different loopback addresses within 127/8. It is not possible under IPv6, as the loopback prefix of ::1/128 only provides a single loopback address. This memo proposes a new larger loopback prefix that will provide many loopback IPv6 addresses.