In IPv6, optional internet-layer information is encoded in separate
headers that may be placed between the IPv6 header and the transport-layer
header. There are a small number of such extension headers
currently defined. This document describes the issues that can arise
when defining new extension headers and discusses the alternate
extension mechanisms in IPv6. It also provides a common format for
defining any new IPv6 extension headers, if they are needed.
[STANDARDS-TRACK]