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QUIC                                                    A. Ferrieux, Ed.
Internet-Draft                                         I. Hamchaoui, Ed.
Intended status: Informational                               Orange Labs
Expires: July 19, 2020                                  I. Lubashev, Ed.
                                                     Akamai Technologies
                                                        D. Tikhonov, Ed.
                                                  LiteSpeed Technologies
                                                        January 16, 2020


             Packet Loss Signaling for Encrypted Protocols
                draft-ferrieuxhamchaoui-quic-lossbits-03

Abstract

   This document defines an extension to the QUIC transport protocol to
   allow endpoints to signal packet loss in a way that can be used by
   network devices to measure and locate the source of the loss.

   Discussion of this work is encouraged to happen on the QUIC IETF
   mailing list quic@ietf.org [1] or on the GitHub repository which
   contains the draft: https://github.com/igorlord/draft-
   ferrieuxhamchaoui-lossbits [2].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 19, 2020.

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



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   (https://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.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   3
   3.  Loss Bits . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Setting the sQuare Signal Bit on Outgoing Packets . . . .   4
       3.1.1.  Q Run Length Selection  . . . . . . . . . . . . . . .   4
     3.2.  Setting the Loss Event Bit on Outgoing Packets  . . . . .   4
   4.  Using Loss Bits for Passive Loss Measurement  . . . . . . . .   5
     4.1.  End-To-End Loss . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Upstream Loss . . . . . . . . . . . . . . . . . . . . . .   6
     4.3.  Correlating End-to-End and Upstream Loss  . . . . . . . .   6
     4.4.  Downstream Loss . . . . . . . . . . . . . . . . . . . . .   7
     4.5.  Observer Loss . . . . . . . . . . . . . . . . . . . . . .   7
   5.  QUIC v1 Implementation  . . . . . . . . . . . . . . . . . . .   7
     5.1.  Transport Parameter . . . . . . . . . . . . . . . . . . .   7
     5.2.  Short Packet Header . . . . . . . . . . . . . . . . . . .   8
     5.3.  Header Protection . . . . . . . . . . . . . . . . . . . .   8
   6.  Ossification Considerations . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     7.1.  Optimistic ACK Attack . . . . . . . . . . . . . . . . . .   9
   8.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   10. Change Log  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Since version 02 . . . . . . . . . . . . . . . . . . . .  10
     10.2.  Since version 01 . . . . . . . . . . . . . . . . . . . .  11
     10.3.  Since version 00 . . . . . . . . . . . . . . . . . . . .  11
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     12.2.  Informative References . . . . . . . . . . . . . . . . .  12
     12.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   Packet loss is a hard and pervasive problem of day-to-day network
   operation.  Proactively detecting, measuring, and locating it is
   crucial to maintaining high QoS and timely resolution of crippling
   end-to-end throughput issues.  To this effect, in a TCP-dominated



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   world, network operators have been heavily relying on information
   present in the clear in TCP headers: sequence and acknowledgment
   numbers, and SACK when enabled.  These allow for quantitative
   estimation of packet loss by passive on-path observation.
   Additionally, the lossy segment (upstream or downstream from the
   observation point) can be quickly identified by moving the passive
   observer around.

   With QUIC, the equivalent transport headers are encrypted and passive
   packet loss observation is not possible, as described in
   [TRANSPORT-ENCRYPT].

   Measuring TCP loss between similar endpoints cannot be relied upon to
   evaluate QUIC loss.  QUIC could be routed by the network differently
   and the fraction of Internet traffic delivered using QUIC is
   increasing every year.  It is imperative to measure packet loss
   experienced by QUIC users directly.

   Since explicit path signals are preferred by [RFC8558], two explicit
   loss bits in the clear portion of short headers are used to signal
   packet loss to on-path network devices.

   This draft adapts the general technique described in [LOSSBITS] for
   QUIC using reserved bits in QUIC v1 short header.

2.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Loss Bits

   The draft introduces two bits that are to be present in packets with
   a short header.  Therefore, only loss of short header packets is
   reported using loss bits.  Whenever this specification refers to
   packets, it is referring only to packets with short headers.

   -  Q: The "sQuare signal" bit is toggled every N outgoing packets as
      explained below in Section 3.1.

   -  L: The "Loss event" bit is set to 0 or 1 according to the
      Unreported Loss counter, as explained below in Section 3.2.

   Each endpoint maintains appropriate counters independently and
   separately for each connection 4-tuple and Destination Connection ID.
   Whenever this specification refers to connections, it is referring to
   packets sharing the same 4-tuple and Destination Connection ID.  A



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   "QUIC connection", however, refers to connections in the traditional
   QUIC sense.

3.1.  Setting the sQuare Signal Bit on Outgoing Packets

   The sQuare Value is initialized to the Initial Q Value (0 or 1) and
   is reflected in the Q bit of every outgoing packet.  The sQuare value
   is inverted after sending every N packets (a Q run).  Hence, Q Period
   is 2*N.  The Q bit represents "packet color" as defined by [RFC8321].

   Observation points can estimate upstream losses by counting the
   number of packets during one period of the square signal, as
   described in Section 4.

3.1.1.  Q Run Length Selection

   The sender is expected to choose N (Q run length) based on the
   expected amount of loss and reordering on the path.  The choice of N
   strikes a compromise - the observation could become too unreliable in
   case of packet reordering and/or severe loss if N is too small, while
   short connections may not yield a useful upstream loss measurement if
   N is too large (see Section 4.2).

   The value of N MUST be at least 64 and be a power of 2.  This
   requirement allows an Observer to infer the Q run length by observing
   one period of the square signal.  It also allows the Observer to
   identify flows that set the loss bits to arbitrary values (see
   Section 6).

   If the sender does not have sufficient information to make an
   informed decision about Q run length, the sender SHOULD use N=64,
   since this value has been extensively tried in large-scale field
   tests and yielded good results.  Alternatively, the sender MAY also
   choose a random N for each connection, increasing the chances of
   using a Q run length that gives the best signal for some connections.

   The sender MUST keep the value of N constant for a given connection.
   The sender can change the value of N during a QUIC connection by
   switching to a new Destination Connection ID, if one is available.

3.2.  Setting the Loss Event Bit on Outgoing Packets

   The Unreported Loss counter is initialized to 0, and the L bit of
   every outgoing packet indicates whether the Unreported Loss counter
   is positive (L=1 if the counter is positive, and L=0 otherwise).  The
   value of the Unreported Loss counter is decremented every time a
   packet with L=1 is sent.




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   The value of the Unreported Loss counter is incremented for every
   packet that the protocol declares lost, using QUIC's existing loss
   detection machinery.  If the implementation is able to rescind the
   loss determination later, a positive Unreported Loss counter MAY be
   decremented due to the rescission, but it SHOULD NOT become negative.

   This loss signaling is similar to loss signaling in [RFC7713], except
   the Loss Event bit is reporting the exact number of lost packets,
   whereas the Echo Loss bit in [RFC7713] is reporting an approximate
   number of lost bytes.

   Observation points can estimate the end-to-end loss, as determined by
   the upstream endpoint, by counting packets in this direction with the
   L bit equal to 1, as described in Section 4.

4.  Using Loss Bits for Passive Loss Measurement

   There are three sources of observable loss:

   -  _upstream loss_ - loss between the sender and the observation
      point (Section 4.2)

   -  _downstream loss_ - loss between the observation point and the
      destination (Section 4.4)

   -  _observer loss_ - loss by the observer itself that does not cause
      downstream loss (Section 4.5)

   The upstream and downstream loss together constitute _end-to-end
   loss_ (Section 4.1).

   The Q and L bits allow detection and measurement of all these types
   of loss.

4.1.  End-To-End Loss

   The Loss Event bit allows an observer to calculate the end-to-end
   loss rate by counting packets with the L bit value of 0 and 1 for a
   given connection.  The end-to-end loss rate is the fraction of
   packets with L=1.

   The assumption here is that upstream loss affects packets with L=0
   and L=1 equally.  If some loss is caused by tail-drop in a network
   device, this may be a simplification.  If the sender congestion
   controller reduces the packet send rate after loss, there may be a
   sufficient delay before sending packets with L=1 that they have a
   greater chance of arriving at the observer.




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4.2.  Upstream Loss

   Blocks of N (Q run length) consecutive packets are sent with the same
   value of the Q bit, followed by another block of N packets with an
   inverted value of the Q bit.  Hence, knowing the value of N, an on-
   path observer can estimate the amount of loss after observing at
   least N packets.  The upstream loss rate ("u") is one minus the
   average number of packets in a block of packets with the same Q value
   ("p") divided by N ("u=1-avg(p)/N").

   The observer needs to be able to tolerate packet reordering that can
   blur the edges of the square signal.

   The observer needs to differentiate packets as belonging to different
   connections, since they use independent counters.

4.3.  Correlating End-to-End and Upstream Loss

   Upstream loss is calculated by observing packets that did not suffer
   the upstream loss.  End-to-end loss, however, is calculated by
   observing subsequent packets after the sender's protocol detected the
   loss.  Hence, end-to-end loss is generally observed with a delay of
   between 1 RTT (loss declared due to multiple duplicate
   acknowledgments) and 1 RTO (loss declared due to a timeout) relative
   to the upstream loss.

   The connection RTT can sometimes be estimated by timing protocol
   handshake messages.  This RTT estimate can be greatly improved by
   observing a dedicated protocol mechanism for conveying RTT
   information, such as the Latency Spin bit of [QUIC-TRANSPORT].

   Whenever the observer needs to perform a computation that uses both
   upstream and end-to-end loss rate measurements, it SHOULD use
   upstream loss rate leading the end-to-end loss rate by approximately
   1 RTT.  If the observer is unable to estimate RTT of the connection,
   it should accumulate loss measurements over time periods of at least
   4 times the typical RTT for the observed connections.

   If the calculated upstream loss rate exceeds the end-to-end loss rate
   calculated in Section 4.1, then either the Q run length is too short
   for the amount of packet reordering or there is observer loss,
   described in Section 4.5.  If this happens, the observer SHOULD
   adjust the calculated upstream loss rate to match end-to-end loss
   rate.







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4.4.  Downstream Loss

   Because downstream loss affects only those packets that did not
   suffer upstream loss, the end-to-end loss rate ("e") relates to the
   upstream loss rate ("u") and downstream loss rate ("d") as
   "(1-u)(1-d)=1-e".  Hence, "d=(e-u)/(1-u)".

4.5.  Observer Loss

   A typical deployment of a passive observation system includes a
   network tap device that mirrors network packets of interest to a
   device that performs analysis and measurement on the mirrored
   packets.  The observer loss is the loss that occurs on the mirror
   path.

   Observer loss affects upstream loss rate measurement, since it causes
   the observer to account for fewer packets in a block of identical Q
   bit values (see {{upstreamloss)}).  The end-to-end loss rate
   measurement, however, is unaffected by the observer loss, since it is
   a measurement of the fraction of packets with the set L bit value,
   and the observer loss would affect all packets equally (see
   Section 4.1).

   The need to adjust the upstream loss rate down to match end-to-end
   loss rate as described in Section 4.3 is a strong indication of the
   observer loss, whose magnitude is between the amount of such
   adjustment and the entirety of the upstream loss measured in
   Section 4.2.  Alternatively, a high apparent upstream loss rate could
   be an indication of significant reordering, possibly due to packets
   belonging to a single connection being multiplexed over several
   upstream paths with different latency characteristics.

5.  QUIC v1 Implementation

5.1.  Transport Parameter

   The use of the loss bits is negotiated using a transport parameter:

   loss_bits (0x1057):  The loss bits transport parameter is an integer
      value, encoded as a variable-length integer, that can be set to 0
      or 1 indicating the level of loss bits support.

   When loss_bits parameter is present, the peer is allowed to use
   reserved bits in the short packet header as loss bits if the peer
   sends loss_bits=1.

   When loss_bits is set to 1, the sender will use reserved bits as loss
   bits if the peer includes the loss_bits transport parameter.



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   A client MUST NOT use remembered value of loss_bits for 0-RTT
   connections.

5.2.  Short Packet Header

   When sending loss bits has been negotiated, the reserved (R) bits are
   replaced by the loss (Q and L) bits in the short packet header (see
   Section 17.3 of [QUIC-TRANSPORT]).

       0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+
      |0|1|S|Q|L|K|P P|
      +-+-+-+-+-+-+-+-+

   sQuare Signal Bit (Q):  The fourth most significant bit (0x10) is the
      sQuare signal bit, set as described in Section 3.1.

   Loss Event Bit (L):  The fifth most significant bit (0x08) is the
      Loss event bit, set as described in Section 3.2.

5.3.  Header Protection

   Unlike the reserved (R) bits, the loss (Q and L) bits are not
   protected.  When sending loss bits has been negotiated, the first
   byte of the header protection mask used to protect short packet
   headers has its five most significant bits masked out instead of
   three.

   The algorithm specified in Section 5.4.1 of [QUIC-TLS] changes as
   follows:

      else:
         # Short header: 3 bits masked
         packet[0] ^= mask[0] & 0x07

6.  Ossification Considerations

   Accurate loss reporting signal is not critical for the operation QUIC
   protocol, though its presence in a sufficient number of connections
   is important for the operation of networks.

   The loss bits are amenable to "greasing" described in [GREASE] and
   MUST be greased.  The greasing should be accomplished similarly to
   the Latency Spin bit greasing in [QUIC-TRANSPORT].  Namely,
   implementations MUST NOT include loss_bits transport parameter for a
   random selection of at least one in every 16 QUIC connections.





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   It is possible to observe packet reordering near the edge of the
   square signal.  A middle box might observe the signal and try to fix
   packet reordering that it can identify, though only a small fraction
   of reordering can be fixed using this method.  Latency spin bit
   signal edge can be used for the same purpose.

7.  Security Considerations

   In the absence of packet loss, the Q bit signal does not provide any
   information that cannot be observed by simply counting packets
   transiting a network path.  The L bit signal discloses internal state
   of the protocol's loss detection machinery, but this state can often
   be gleamed by timing packets and observing congestion controller
   response.  Hence, loss bits do not provide a viable new mechanism to
   attack QUIC data integrity and secrecy.

7.1.  Optimistic ACK Attack

   A defense against an Optimistic ACK Attack [QUIC-TRANSPORT] involves
   a sender randomly skipping packet numbers to detect a receiver
   acknowledging packet numbers that have never been received.  The Q
   bit signal may inform the attacker which packet numbers were skipped
   on purpose and which had been actually lost (and are, therefore, safe
   for the attacker to acknowledge).  To use the Q bit for this purpose,
   the attacker must first receive at least an entire Q run of packets,
   which renders the attack ineffective against a delay-sensitive
   congestion controller.

   For QUIC v1 connections, if the attacker can make its peer transmit
   data using a single large stream, examining offsets in STREAM frames
   can reveal whether packet number skips are deliberate.  In that case,
   the Q bit signal provides no new information (but it does save the
   attacker the need to remove packet protection).  However, an endpoint
   that communicates using [DATAGRAM] and uses a loss-based congestion
   controller MAY shorten the current Q run by the number of skipped
   packets.  For example, skipping a single packet number will invert
   the sQuare signal one outgoing packet sooner.

8.  Privacy Considerations

   To minimize unintentional exposure of information, loss bits provide
   an explicit loss signal - a preferred way to share information per
   [RFC8558].

   [QUIC-TRANSPORT] allows changing connection IDs in the middle of a
   QUIC connection to reduce the likelihood of a passive observer
   linking old and new subflows to the same device.  Hence, a QUIC
   implementation would need to reset all counters when it changes



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   connection ID used for outgoing packets.  It would also need to avoid
   incrementing Unreported Loss counter for loss of packets sent with a
   different connection ID.

   Accurate loss information allows identification and correlation of
   network conditions upstream and downstream of the observer.  This
   could be a powerful tool to identify connections that attempt to hide
   their origin networks, if the adversary is able to affect network
   conditions in those origin networks.  Similar information can be
   obtained by packet timing and inferring congestion controller
   response to network events, but loss information provides a clearer
   signal.

   Implementations MUST allow administrators of clients and servers to
   disable loss reporting either globally or per QUIC connection.
   Additionally, as described in Section 6, loss reporting MUST be
   disabled for a certain fraction of all QUIC connections.

9.  IANA Considerations

   This document registers a new value in the QUIC Transport Parameter
   Registry:

   Value: 0x1057 (if this document is approved)

   Parameter Name: loss_bits

   Specification: Indicates that the endpoint supports loss bits.  An
   endpoint that advertises this transport parameter can receive loss
   bits.  An endpoint that advertises this transport parameter with
   value 1 can also send loss bits.

10.  Change Log

10.1.  Since version 02

   -  Add QUIC v1 negotiation using transport parameter, use short
      header reserved bits as loss bits, header protection change, IANA
      Considerations

   -  Add Optimistic ACK Attack Defense to Security Considerations

   -  Expand Privacy Considerations

   -  Clarify Q run length selection






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10.2.  Since version 01

   -  Add reference to RFC7713

10.3.  Since version 00

   -  Rewrote to base this draft on [LOSSBITS]

11.  Acknowledgments

   The sQuare signal bit was originally specified by Kazuho Oku in early
   proposals for loss measurement and is an instance of the "alternate
   marking" as defined in [RFC8321].

   Many thanks to Christian Huitema for pointing out the interaction of
   Q bit and Optimistic ACK Attack defence.

12.  References

12.1.  Normative References

   [QUIC-TLS]
              Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
              draft-ietf-quic-tls-24 (work in progress), November 2019.

   [QUIC-TRANSPORT]
              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-24 (work
              in progress), November 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8558]  Hardie, T., Ed., "Transport Protocol Path Signals",
              RFC 8558, DOI 10.17487/RFC8558, April 2019,
              <https://www.rfc-editor.org/info/rfc8558>.

   [TRANSPORT-ENCRYPT]
              Fairhurst, G. and C. Perkins, "Considerations around
              Transport Header Confidentiality, Network Operations, and
              the Evolution of Internet Transport Protocols", draft-
              ietf-tsvwg-transport-encrypt-10 (work in progress),
              January 2020.






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12.2.  Informative References

   [DATAGRAM]
              Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
              Datagram Extension to QUIC", draft-pauly-quic-datagram-05
              (work in progress), November 2019.

   [GREASE]   Benjamin, D., "Applying GREASE to TLS Extensibility",
              draft-ietf-tls-grease-04 (work in progress), August 2019.

   [LOSSBITS]
              Ferrieux, A., Hamchaoui, I., and I. Lubashev, "Packet Loss
              Signaling for Encrypted Protocols", draft-
              ferrieuxhamchaoui-tsvwg-lossbits-02 (work in progress),
              November 2019.

   [RFC7713]  Mathis, M. and B. Briscoe, "Congestion Exposure (ConEx)
              Concepts, Abstract Mechanism, and Requirements", RFC 7713,
              DOI 10.17487/RFC7713, December 2015,
              <https://www.rfc-editor.org/info/rfc7713>.

   [RFC8321]  Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
              L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate-Marking Method for Passive and Hybrid
              Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
              January 2018, <https://www.rfc-editor.org/info/rfc8321>.

12.3.  URIs

   [1] mailto:quic@ietf.org

   [2] https://github.com/igorlord/draft-ferrieuxhamchaoui-lossbits

Authors' Addresses

   Alexandre Ferrieux (editor)
   Orange Labs

   EMail: alexandre.ferrieux@orange.com


   Isabelle Hamchaoui (editor)
   Orange Labs

   EMail: isabelle.hamchaoui@orange.com






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   Igor Lubashev (editor)
   Akamai Technologies

   EMail: ilubashe@akamai.com


   Dmitri Tikhonov (editor)
   LiteSpeed Technologies

   EMail: dtikhonov@litespeedtech.com









































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