Cisco Systems Cisco Systems RFC 2461 [ND] describes host data forwarding and address resolution. However, nine years after the ND protocol became an RFC, IPv6 hosts still do not fully comply with RFC 2461 [ND]. In particular, hosts incorrectly implement on- vs. off-link data forwarding. This document clarifies host behavior and associated router behavior to define explicitly address resolution and data forwarding models. The set of new requirements beyond what has been specified in RFC 2461 [ND] and RFC 2462 [ADDRCONF] is restricted to clarifications deemed necessary to facilitate correct implementation. The intention of this document is to incorporate normative changes into draft-ietf-ipv6-rfc2461bis-11 [NDbis] and draft-ietf-ipv6-rfc2462bis-08 [ADDRCONFbis]. After this has been accomplished, this document will be on track to become an Informational RFC. Following the same model as RFC 2525 [TCPProb], a section of this document collects known IPv6 ND implementation problems.