Cisco Systems The Prefix Information Option in the IPv6 Neighbor Discovery Router Advertisement defines an 8-bit flag field with two flags defined and the remaining 6 bits reservered (Reserved1). RFC 6275 has defined a new flag from this field without creating a IANA registry or updating RFC 4861. The purpose of this document is to request IANA to create a new registry for the PIO flags to avoid potential conflict in the use of these flags.