However, it may be used in a manner similar to RFC 1918 private address space on routing equipment that is able to do address translation across router interfaces when the addresses are identical on two different interfaces. Details are provided in the text of this document. This document details the allocation of an additional special-use IPv4 address block and updates RFC 5735. Status of This Memo This memo documents an Internet Best Current Practice. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6598. Weil, et al.

Enterprise network administrators worldwide are in various stages of preparing for or deploying IPv6 into their networks. The administrators face different challenges than operators of Internet access providers and have reasons for different priorities. The overall problem for many administrators will be to offer Internetfacing services over IPv6 while continuing to support IPv4, and while introducing IPv6 access within the enterprise IT network. The overall transition will take most networks from an IPv4-only environment to a dual-stack network environment and eventually an

6to4Provider Managed Tunnels (6to4-PMT) provide a framework that can help manage 6to4 tunnels operating in an anycast configuration. The 6to4-PMT framework is intended to serve as an option for operators to help improve the experience of 6to4 operation when conditions of the network may provide sub-optimal performance or break normal 6to4 operation. 6to4-PMT supplies a stable provider prefix and forwarding environment by utilizing existing 6to4 relays with an added function of IPv6 Prefix Translation. This operation may be particularly important in NAT444 infrastructures where a customer endpoint may be assigned a non-RFC1918 address, thus breaking the return path for anycast-based 6to4 operation. 6to4-PMT has been successfully used in a production network, implemented as open source code, and implemented by a major routing vendor.

NAT444 is an IPv4 extension technology being considered by Service Providers as a means to continue offering IPv4 service to customers while transitioning to IPv6. This technology adds an extra CarrierGrade NAT (CGN) in the Service Provider network, often resulting in two NATs. CableLabs, Time Warner Cable, and Rogers Communications independently tested the impacts of NAT444 on many popular Internet services using a variety of test scenarios, network topologies, and vendor equipment. This document identifies areas where adding a second layer of NAT disrupts the communication channel for common Internet applications. This document was updated to include the Dual-Stack Lite (DS-Lite) impacts also.

Operators worldwide are in various stages of preparing for or deploying IPv6 in their networks. These operators often face difficult challenges related