SI6 Networks This document describes a method for selecting IPv6 Interface Identifiers that can be employed by Dynamic Host Configuration Protocol for IPv6 (DHCPv6) servers when leasing non-temporary IPv6 addresses to DHCPv6 clients. This method is a DHCPv6 server-side algorithm that does not require any updates to the existing DHCPv6 specifications. The aforementioned method results in stable addresses within each subnet, even in the presence of multiple DHCPv6 servers or DHCPv6 server reinstallments. It is a DHCPv6 variant of the method specified in RFC 7217 for IPv6 Stateless Address Autoconfiguration (SLAAC).