IPv6 specifies the Fragment Header, which is employed for the
fragmentation and reassembly mechanisms. The Fragment Header
contains an "Identification" field which, together with the IPv6
Source Address and the IPv6 Destination Address of the packet,
identifies fragments that correspond to the same original datagram,
such that they can be reassembled together at the receiving host.
The only requirement for setting the "Identification" value is that
it must be different than that of any other fragmented packet sent
recently with the same Source Address and Destination Address. Some
implementations simply use a global counter for setting the Fragment
Identification field, thus leading to predictable values. This
document analyzes the security implications of predictable
Identification values, and updates RFC 2460 specifying additional
requirements for setting the Fragment Identification, such that the
aforementioned security implications are mitigated.