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.
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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.
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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.
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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.
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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.
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Author's Address
Carlos Pignataro
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
US
EMail: cpignata@cisco.com
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RFC, FYI, BCP