The Quantum Bug
RFC 8774

Document Type RFC - Informational (April 2020; Errata)
Last updated 2020-04-03
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Independent Submission                                          M. Welzl
Request for Comments: 8774                            University of Oslo
Category: Informational                                     1 April 2020
ISSN: 2070-1721

                            The Quantum Bug


   The age of quantum networking is upon us, and with it comes
   "entanglement": a procedure in which a state (i.e., a bit) can be
   transferred instantly, with no measurable delay between peers.  This
   will lead to a perceived round-trip time of zero seconds on some
   Internet paths, a capability which was not predicted and so not
   included as a possibility in many protocol specifications.  Worse
   than the millennium bug, this unexpected value is bound to cause
   serious Internet failures unless the specifications are fixed in

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 candidates for any level of Internet Standard;
   see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2020 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
   ( 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.  Protocols and Protocol Mechanisms That Will Fail
     2.1.  LEDBAT
     2.2.  Multipath TCP (MPTCP)
     2.3.  RTP Circuit Breakers
   3.  What can be done?
   4.  Conclusion
   5.  IANA Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Author's Address

1.  Introduction

   [RFC6921] discusses faster-than-light communication, where packets
   arrive before they are sent.  While it is amusing to entertain the
   possibility of time travel, we have to accept the cold facts: time
   travel will never work (or it would already have been used).  Quantum
   networking, however, is an entirely different matter -- commercial
   products are already available, and quantum networks will without a
   doubt become the prevalent Internet link-layer technology across the
   globe within the next five to ten years.

   With the help of entanglement, implemented in quantum repeaters,
   quantum networks can transfer information faster than ever before: a
   state can be transmitted over a long distance instantly, with no
   delay.  This is so cool that it is also called (and, by some,
   mistaken for) teleportation.  If a path between a sender and a
   receiver is fully quantum-ized, the measured one-way delay (OWD) will
   be zero.  What's more, assuming that there are blazing fast quantum
   computers involved on both ends, the processing time will be well
   below anything measurable; hence, even the round-trip time (RTT) will
   be zero in these scenarios.

   In today's Internet, only very few protocols are prepared for such
   "0-RTT" situations (e.g., TCP with "TCP Fast Open" (TFO) [RFC7413],
   TLS 1.3 [RFC8446], and QUIC [QUIC-TRANS]).  Many others will fail in
   interesting ways; we coin the term "Quantum Bug" for such failures.
   In the following section, we will discuss some examples of Quantum

2.  Protocols and Protocol Mechanisms That Will Fail

   The number of protocols and protocol mechanisms that will fail in the
   face of a zero RTT is too large to report here; we are truly heading
   towards something close to an Internet meltdown.  We can only provide
   some guidance to those who hunt for the Quantum Bug, by discussing
   examples of specification mistakes that will need to be fixed.

2.1.  LEDBAT

   The Low Extra Delay Background Transfer (LEDBAT) congestion control
   mechanism [RFC6817] is a very interesting failure case: designed to
   "get out of the way" of other traffic; it will end up sending as fast
   as possible.  Specifically, when the algorithm described in
   Section 2.4.2 of [RFC6817] obtains a delay sample, it updates a list
   of base delays that will all become 0 and current delays that will
   also all become 0.  It calculates a queuing delay as the difference
   between the current delay and the base delay (resulting in 0) and
   keeps increasing the Congestion Window (cwnd) until the queuing delay
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