The working group creates documents to enable NATs to function in as deterministic a fashion as possible. To support deployments where communicating hosts require using different address families (IPv4 or IPv6), address family translation is needed to establish communication. In BEHAVE's specification work on this topic it will coordinate with the V6ops WG on requirements and operational considerations. "An IPv4 network" or "an IPv6 network" in the descriptions below refer to a network with a clearly identifiable administrative domain (e.g., an enterprise campus network, a mobile operator's cellular network, a residential subscriber network, etc.). It will also be that network that deploys the necessary equipment for translation. BEHAVE will adopt additional work items to finish four scenarios: An IPv6 network to IPv4 Internet, IPv6 Internet to an IPv4 network, An IPv6 network to an IPv4 network, and An IPv4 network to an IPv6 network. These additional work items include suggestions to application developers to improve application interactions with those translation scenarios. The following scenario remains in scope for discussion, and new milestones can be created to address this scenario: * An IPv4 application running on an IPv6-only connected host to the IPv6 Internet, i.e. perform translation between IPv4 and IPv6 for packets in uni- or bi-directional flows that are initiated from an IPv4 host towards an IPv6 host. The translator function is embedded in the IPv4 host. The following scenarios remain in scope for discussion, but creating new milestones will require re-chartering: * An IPv4 network to IPv6 Internet, i.e. perform translation between IPv4 and IPv6 for packets in uni- or bi-directional flows that are initiated from an IPv4 host towards an IPv6 host. The translator function is intended to service a specific IPv4 network using either public or private IPv4 address space. * IPv4 Internet to an IPv6 network, i.e. perform translation between IPv4 and IPv6 for packets in uni- or bi-directional flows that are initiated from an IPv4 host towards an IPv6 host. The translator function is intended to service a specific IPv6 network where selected IPv6 hosts and services are to be reachable. * multicast translation, including control traffic (IGMP and MLD), Single Source Multicast (SSM) and Any Source Multicast (ASM). All translation solutions shall be capable of handling flows using TCP, UDP, DCCP, and SCTP, unless they prevent a timely completion of the work item. The parts of ICMP that can be translated are also required to work across a translation solution. Additional protocols directly on top of IP may be supported. Translation mechanisms must handle IP fragmentation. Translation mechanisms cannot transparently support protocols that embed network addresses within their protocol messages without application level gateways (ALGs). Because ALGs have security issues (like blocking usage of TLS), are error prone and brittle, and hinder application development, the usage of ALGs in the defined translators should be avoided. Instead application developers will need to be aware and use mechanisms that handle the address family translation. ALGs may be considered only for the most crucial of legacy applications. Solutions may solve more than one of the cases, however timely delivery is more important than a unified solution.