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Reusing the IPv4 Identification Field in Atomic Packets

Document Type Expired Internet-Draft (individual)
Expired & archived
Author Bob Briscoe
Last updated 2014-08-18 (Latest revision 2014-02-14)
RFC stream (None)
Intended RFC status (None)
Stream Stream state (No stream defined)
Consensus boilerplate Unknown
RFC Editor Note (None)
IESG IESG state Expired
Telechat date (None)
Responsible AD (None)
Send notices to (None)

This Internet-Draft is no longer active. A copy of the expired Internet-Draft is available in these formats:


This specification takes a new approach to extensibility that is both principled and a hack. It builds on recent moves to formalise the increasingly common practice where fragmentation in IPv4 more closely matches that of IPv6. The large majority of IPv4 packets are now 'atomic', meaning indivisible. In such packets, the 16 bits of the IPv4 Identification (IPv4 ID) field are redundant and could be freed up for the Internet community to put to other uses, at least within the constraints imposed by their original use for reassembly. This specification defines the process for redefining the semantics of these bits. It uses the previously reserved control flag in the IPv4 header to indicate that these 16 bits have new semantics. Great care is taken throughout to ease incremental deployment, even in the presence of middleboxes that incorrectly discard or normalise packets that have the reserved control flag set.


Bob Briscoe

(Note: The e-mail addresses provided for the authors of this Internet-Draft may no longer be valid.)