The Null Packet
RFC 6592

Document Type RFC - Informational (April 2012; No errata)
Last updated 2013-07-23
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Independent Submission                                      C. Pignataro
Request for Comments: 6592                                        Cisco
Category: Informational                                     1 April 2012
ISSN:  2070-1721

                            The Null Packet

Abstract

   The ever-elusive Null Packet received numerous mentions in documents
   in the RFC series, but it has never been explicitly defined.  This
   memo corrects that omission.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6592.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Pignataro                     Informational                     [Page 1]
RFC 6592                     The Null Packet                1 April 2012

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2.  The Null Packet . . . . . . . . . . . . . . . . . . . . . . . . 2
     2.1.  Formal Definition . . . . . . . . . . . . . . . . . . . . . 3
     2.2.  Faux Amis . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Performance Metrics Considerations  . . . . . . . . . . . . . . 3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 3
     4.1.  The Paradoxical Firewall  . . . . . . . . . . . . . . . . . 4
     4.2.  The Null Packet is Good . . . . . . . . . . . . . . . . . . 4
     4.3.  Just Encrypt It, Carefully  . . . . . . . . . . . . . . . . 4
     4.4.  Denial of Denial of Service . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 5

1.  Introduction

   Null Packets are neither sent nor acknowledged when not received.
   They are perfect in their simplicity and they are very true, as they
   extrapolate from the twelfth Truth of networking [RFC1925]:  there is
   *literally* nothing left to take away.

   An early mention of the Null Packet is attributed to Van Jacobson in
   the context of TCP/IP Header Compression [RFC1144].  Mind you, the
   Null Packet is not created by compressing a packet until it
   disappears into nothingness.  Such a compression scheme might not be
   reversible; instead, Section 3.2.4 of [RFC1144] describes an explicit
   lack of response as "Nothing (a null packet) is returned".

   Many documents attempt to define in-the-wire code points and protocol
   identifiers (PIDs) for a Null Packet [RFC4259] [RFC4571] [RFC5320].
   However, such an exercise is futile.  This memo postulates that a
   Null Packet cannot have a PID, as the existence of a protocol
   construct or value would null the null; this includes the inability
   to use 0x0, 0x0000, or even 0x00000000, but excludes the restriction
   to use "" (see Section 2.1).

   An IPv6 Next Header value of 59 (No Next Header) (see Section 4.7 of
   [RFC2460]) does not create a Null Packet.

2.  The Null Packet

   The Null Packet is a zero-dimensional packet.  The Null Packet exists
   since it is non-self-contradictorily definable.

Pignataro                     Informational                     [Page 2]
RFC 6592                     The Null Packet                1 April 2012

2.1.  Formal Definition

   [This section is intentionally left blank, see also Section 0 of
   [NULL].]

2.2.  Faux Amis

   Many experts naively confuse the Null Packet with an Imaginary
   Packet, in a rationalization attempt when faced with the inability to
   prove the existence of the Null Packet.  For reference, an Imaginary
   Packet contains the IP Version of 4i or 6i.  However, protocol
   purists are not fooled and quickly plea with experts to get real.

   The Null Packet's qualities should not be confused with the bit-
   bucket blackhole nature of the null device, since the Null Packet
   does not discard packets.  Confusion might stem from the fact that
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