This document specifies the Internet Protocol version 6 (IPv6), also known as IP Next Generation or IPng. It outlines the changes from IPv4, including expanded addressing capabilities, simplified header format, improved support for extensions and options, and the addition of flow labeling capability. The document covers the IPv6 header format, extension headers (such as Hop-by-Hop Options, Routing, Fragment, and Destination Options headers), packet size issues, flow labels, traffic classes, and upper-layer protocol issues. It also discusses the security features of IPv6 and provides guidelines for designing new options. The document is intended for discussion and suggestions from the Internet community.This document specifies the Internet Protocol version 6 (IPv6), also known as IP Next Generation or IPng. It outlines the changes from IPv4, including expanded addressing capabilities, simplified header format, improved support for extensions and options, and the addition of flow labeling capability. The document covers the IPv6 header format, extension headers (such as Hop-by-Hop Options, Routing, Fragment, and Destination Options headers), packet size issues, flow labels, traffic classes, and upper-layer protocol issues. It also discusses the security features of IPv6 and provides guidelines for designing new options. The document is intended for discussion and suggestions from the Internet community.