The shim6 protocol defines a header that contains a "context tag" that
identifies packets as belonging to a certain shim6 context that exists
between two hosts. It has been suggested that this shim6 header is
inserted between the IPv6 header and the upper layer protocol such as
TCP in all packets where the shim layer has rewritten the source
and/or
destination address. This document considers the suppression of this
header in situations where packets can be successfully
demultiplexed by
the receiver without it.