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 © 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.

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.

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 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" (see Section 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 (see Section 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.

4.1. 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 (see Section 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 (see Section 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.

6. References

6.1. 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.

Author's Address

   Carlos Pignataro
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709
   US
   
   EMail:  cpignata@cisco.com