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Independent Submission                                      C. PignataroRequest for Comments: 6592                                        CiscoCategory: Informational                                     1 April 2012ISSN:  2070-1721The Null PacketAbstract   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; seeSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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 2012Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  The Null Packet . . . . . . . . . . . . . . . . . . . . . . . .22.1.  Formal Definition . . . . . . . . . . . . . . . . . . . . .32.2.  Faux Amis . . . . . . . . . . . . . . . . . . . . . . . . .33.  Performance Metrics Considerations  . . . . . . . . . . . . . .34.  Security Considerations . . . . . . . . . . . . . . . . . . . .34.1.  The Paradoxical Firewall  . . . . . . . . . . . . . . . . .44.2.  The Null Packet is Good . . . . . . . . . . . . . . . . . .44.3.  Just Encrypt It, Carefully  . . . . . . . . . . . . . . . .44.4.  Denial of Denial of Service . . . . . . . . . . . . . . . .45.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .46.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .56.1.  Normative References  . . . . . . . . . . . . . . . . . . .56.2.  Informative References  . . . . . . . . . . . . . . . . . .51.  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 "" (seeSection 2.1).   An IPv6 Next Header value of 59 (No Next Header) (seeSection 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 20122.1.  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   the behavior is similar to that of input streams reading from /dev/   null (i.e., "nothing is returned").3.  Performance Metrics Considerations   A protocol sending Null Packets effectively sends packets of zero   length.  One characteristic of flow streams of Null Packet traffic is   that increasing the rate at which Null Packets are sent does not   increase the bit rate of the Null Packet traffic.  The bit rate   continues being unequivocally null, unless an infinite number of Null   Packets per unit of time could be sent.  Similarly, should a user   stop sending Null Packets, the bit rate of Null Packets would not   vary.  Traditional traffic performance metrics are not well suited to   qualify Null Packet traffic; this fact argues for the creation of new   sets of performance metrics that test positive for "usefulness" (seeSection 5.2 of [RFC6390]).4.  Security Considerations   When used in a Multiprotocol Label Switching (MPLS) environment, the   Null Packet can only use an Implicit NULL label (seeSection 4.1.5 of   [RFC3031].  The Implicit NULL label is a label that can be   distributed, but which never actually appears in the encapsulation.   The Nil FEC is not used.   The security considerations for the Null Packet are undefined, as   hereby described.  The "good" nature of Null Packets is quite   useless, and the "bad" nature of Null Packets is rather inefficient.Pignataro                     Informational                     [Page 3]

RFC 6592                     The Null Packet                1 April 20124.1.  The Paradoxical Firewall   Many firewalls and other security devices have trouble identifying   the Null Packet.  Others claim to filter out Null Packets quite   effectively and effortlessly.  Interestingly, or not, both might be   correct, which begs the omnipotence paradox:  Can a firewall create a   rule to filter out the Null Packet coming from the "outside", and not   see Null Packets being allowed on the "inside"?4.2.  The Null Packet is Good   The Null Packet cannot have the Evil Bit ("E") [RFC3514] set, by   definition (seeSection 2.1).  Consequently, it is rather clear and   undeniable that the Null Packet is harmless, having no evil intent.4.3.  Just Encrypt It, Carefully   A commonly accepted practice for Security Considerations sections is   to wrap a blanket "encrypt around foo" statement, for almost any   value of "foo".  This document is no exception.  However, surgical   care must be taken to not apply NULL encryption [RFC2410] to the Null   Packet; such a careless act can bring discontinuities and "Oops" more   epic than dividing by zero or Googling the word "Google" (it has been   rumored that such action can break the Internet, although this can be   easily disproved by reductio ad absurdum.)4.4.  Denial of Denial of Service   Even when sysadmins, netadmins, secadmins, and other NOC engineers   are faced with the undisputed inability to block Null Packets (seeSection 4.1), attacks leveraging Null Packets are not quite so common   in the wild and are not seen in the seek^Wsecurity news.  Perhaps   because these unusual packets are hard to spoof in the data plane, or   because their Time to Live (TTL) or Hop Limit cannot be altered since   it does not exist [RFC5082], the fact is that Null Packets present a   denial of denial of service (DoDoS).   An important corollary is that dropping Null Packets does not   generate packets.5.  IANA Considerations   This document explicitly and emphatically, yet very humbly, requests   IANA to not create an empty registry for the Null Packet.Pignataro                     Informational                     [Page 4]

RFC 6592                     The Null Packet                1 April 20126.  References6.1.  Normative References   [NULL]     "".   [RFC1144]  Jacobson, V., "Compressing TCP/IP headers for low-speed              serial links",RFC 1144, February 1990.   [RFC1925]  Callon, R., "The Twelve Networking Truths",RFC 1925,              April 1996.   [RFC3514]  Bellovin, S., "The Security Flag in the IPv4 Header",RFC 3514, April 1 2003.6.2.  Informative References   [RFC2410]  Glenn, R. and S. Kent, "The NULL Encryption Algorithm and              Its Use With IPsec",RFC 2410, November 1998.   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6              (IPv6) Specification",RFC 2460, December 1998.   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol              Label Switching Architecture",RFC 3031, January 2001.   [RFC4259]  Montpetit, M., Fairhurst, G., Clausen, H., Collini-Nocker,              B., and H. Linder, "A Framework for Transmission of IP              Datagrams over MPEG-2 Networks",RFC 4259, November 2005.   [RFC4571]  Lazzaro, J., "Framing Real-time Transport Protocol (RTP)              and RTP Control Protocol (RTCP) Packets over Connection-              Oriented Transport",RFC 4571, July 2006.   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., and C.              Pignataro, "The Generalized TTL Security Mechanism              (GTSM)",RFC 5082, October 2007.   [RFC5320]  Templin, F., "The Subnetwork Encapsulation and Adaptation              Layer (SEAL)",RFC 5320, February 2010.   [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New              Performance Metric Development",BCP 170,RFC 6390,              October 2011.Pignataro                     Informational                     [Page 5]

RFC 6592                     The Null Packet                1 April 2012Author's Address   Carlos Pignataro   Cisco Systems, Inc.   7200-12 Kit Creek Road   Research Triangle Park, NC  27709   US   EMail:  cpignata@cisco.comPignataro                     Informational                     [Page 6]