DNS Delete-Confirm Mechanism with Multi-DHCP-Servers

[I-D.ietf-dhc-addr-registration] specifies how a host register its self-generated addresses in DNS through DHCPv6 server. [RFC3315] allows multiple DHCPv6 servers working in an administrative domain. There exists a scenario that the client may register its addresses in multiple servers for some reasons such as higher availability and etc. This document defines a mechanism to ensure the multiple servers could work properly during updating DNS.