Network Working Group                                      M. Kuehlewind
Internet-Draft                                               B. Trammell
Intended status: Informational                                ETH Zurich
Expires: January 3, 2019                                   July 02, 2018

              Manageability of the QUIC Transport Protocol


   This document discusses manageability of the QUIC transport protocol,
   focusing on caveats impacting network operations involving QUIC
   traffic.  Its intended audience is network operators, as well as
   content providers that rely on the use of QUIC-aware middleboxes,
   e.g. for load balancing.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 3, 2019.

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   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Features of the QUIC Wire Image . . . . . . . . . . . . . . .   3
     2.1.  QUIC Packet Header Structure  . . . . . . . . . . . . . .   4
     2.2.  Coalesced Packets . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Integrity Protection of the Wire Image  . . . . . . . . .   5
     2.4.  Connection ID and Rebinding . . . . . . . . . . . . . . .   5
     2.5.  Packet Numbers  . . . . . . . . . . . . . . . . . . . . .   6
     2.6.  Version Negotiation and Greasing  . . . . . . . . . . . .   6
   3.  Network-visible information about QUIC flows  . . . . . . . .   6
     3.1.  Identifying QUIC traffic  . . . . . . . . . . . . . . . .   6
       3.1.1.  Identifying Negotiated Version  . . . . . . . . . . .   7
       3.1.2.  Rejection of Garbage Traffic  . . . . . . . . . . . .   7
     3.2.  Connection confirmation . . . . . . . . . . . . . . . . .   7
     3.3.  Application Identification  . . . . . . . . . . . . . . .   7
     3.4.  Flow association  . . . . . . . . . . . . . . . . . . . .   8
     3.5.  Flow teardown . . . . . . . . . . . . . . . . . . . . . .   8
     3.6.  Round-trip time measurement . . . . . . . . . . . . . . .   8
     3.7.  Flow symmetry measurement . . . . . . . . . . . . . . . .  10
   4.  Specific Network Management Tasks . . . . . . . . . . . . . .  10
     4.1.  Stateful treatment of QUIC traffic  . . . . . . . . . . .  10
     4.2.  Passive network performance measurement and
           troubleshooting . . . . . . . . . . . . . . . . . . . . .  10
     4.3.  Server cooperation with load balancers  . . . . . . . . .  10
     4.4.  DDoS Detection and Mitigation . . . . . . . . . . . . . .  11
     4.5.  QoS support and ECMP  . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   QUIC [QUIC-TRANSPORT] is a new transport protocol currently under
   development in the IETF quic working group, focusing on support of
   semantics as needed for HTTP/2 [QUIC-HTTP].  Based on current
   deployment practices, QUIC is encapsulated in UDP and encrypted by
   default.  The current version of QUIC integrates TLS [QUIC-TLS] to
   encrypt all payload data and most control information.  Given QUIC is
   an end-to-end transport protocol, all information in the protocol
   header, even that which can be inspected, is is not meant to be

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   mutable by the network, and is therefore integrity-protected to the
   extent possible.

   This document provides guidance for network operation on the
   management of QUIC traffic.  This includes guidance on how to
   interpret and utilize information that is exposed by QUIC to the
   network as well as explaining requirement and assumptions that the
   QUIC protocol design takes toward the expected network treatment.  It
   also discusses how common network management practices will be
   impacted by QUIC.

   Of course, network management is not a one-size-fits-all endeavour:
   practices considered necessary or even mandatory within enterprise
   networks with certain compliance requirements, for example, would be
   impermissible on other networks without those requirements.  This
   document therefore does not make any specific recommendations as to
   which practices should or should not be applied; for each practice,
   it describes what is and is not possible with the QUIC transport
   protocol as defined.

   QUIC is at the moment very much a moving target.  This document
   refers the state of the QUIC working group drafts as well as to
   changes under discussion, via issues and pull requests in GitHub
   current as of the time of writing.

1.1.  Notational Conventions

   The words "MUST", "MUST NOT", "SHOULD", and "MAY" are used in this
   document.  It's not shouting; when these words are capitalized, they
   have a special meaning as defined in [RFC2119].

2.  Features of the QUIC Wire Image

   In this section, we discusses those aspects of the QUIC transport
   protocol that have an impact on the design and operation of devices
   that forward QUIC packets.  Here, we are concerned primarily with
   QUIC's unencrypted wire image [WIRE-IMAGE], which we define as the
   information available in the packet header in each QUIC packet, and
   the dynamics of that information.  Since QUIC is a versioned
   protocol, the wire image of the header format can also change from
   version to version.  However, at least the mechanism by which a
   receiver can determine which version is used and the meaning and
   location of fields used in the version negotiation process is
   invariant [QUIC-INVARIANTS].

   This document is focused on the protocol as presently defined in
   [QUIC-TRANSPORT] and [QUIC-TLS], and will change to track those

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2.1.  QUIC Packet Header Structure

   QUIC packets may have either a long header, or a short header.  The
   first bit of the QUIC header indicates which type of header is

   The long header exposes more information.  It is used during
   connection establishment, including version negotiation, server
   retry, and 0-RTT data.  It contains a version number, as well as
   source and destination connection IDs for grouping packets belonging
   to the same flow.  The definition and location of these fields in the
   QUIC long header are invariant for future versions of QUIC, although
   future versions of QUIC may provide additional fields in the long
   header [QUIC-INVARIANTS].

   Short headers are used after connection establishment.  The only
   information they contain for inspection on the path is an optional,
   variable-length destination connection ID.

   As of draft version 13 of the QUIC transport document, the following
   information may be exposed in QUIC packet headers:

   o  header type: the long header has a 7-bit packet type field
      following the Header Form bit.  Header types correspond to stages
      of the handshake; see Section 4.1 of [QUIC-TRANSPORT].

   o  version number: The version number is present in the long header,
      and identifies the version used for that packet.  Note that during
      Version Negotiation (see Section 2.6, and Section 4.3 of
      [QUIC-TRANSPORT], the version number field has a special value
      (0x00000000) that identifies the packet as a Version Negotiation

   o  source and destination connection ID: The source and destination
      connection IDs are variable-length fields that can be used to
      identify the connection associated with a QUIC packet, for load-
      balancing and NAT rebinding purposes; see Section 4.3 and
      Section 2.4.  The source connection ID corresponds to the
      destination connection ID the source would like to have on packets
      sent to it, and is only present on long packet headers.  The
      destination connection ID, if present, is present on both long and
      short header packets.  On long header packets, the length of the
      connection IDs is also present; on short header packets, the
      length of the destination connection ID is implicit.

   o  length: the length of the remaining quic packet after the length
      field, present on long headers.  This field is used to implement
      coalesced packets during the handshake (see Section 2.2).

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   o  packet number: Every packet has an associated packet number;
      however, this packet number is encrypted, and therefore not of use
      to on-path observers.  This packet number has a fixed location and
      length in long headers, and an implicit location and encrypted
      variable length in short headers.

   o  key phase: The Key Phase bit, present in short headers identifies
      the key used to encrypt the packet during key rotation.

2.2.  Coalesced Packets

   Multiple QUIC packets may be coalesced into a UDP datagram, with a
   datagram carrying one or more long header packets followed by zero or
   one short header packets.  When packets are coalesced, the Length
   fields in the long headers are used to separate QUIC packets.  The
   length header field is variable length and its position in the header
   is also variable depending on the length of the source and
   destionation connection ID.  See Section 4.6 of [QUIC-TRANSPORT].

2.3.  Integrity Protection of the Wire Image

   As soon as the cryptographic context is established, all information
   in the QUIC header, including those exposed in the packet header, is
   integrity protected.  Further, information that were sent and exposed
   in previous packets when the cryptographic context was established
   yet, e.g. for the cryptographic initial handshake itself, will be
   validated later during the cryptographic handshake.  Therefore,
   devices on path MUST NOT change any information or bits in QUIC
   packet headers, since alteration of header information will lead to a
   failed integrity check at the receiver, and can even lead to
   connection termination.

2.4.  Connection ID and Rebinding

   The connection ID in the QUIC packet headers allows routing of QUIC
   packets at load balancers on other than five-tuple information,
   ensuring that related flows are appropriately balanced together; and
   to allow rebinding of a connection after one of the endpoint's
   addresses changes - usually the client's, in the case of the HTTP
   binding.  Client and server negotiate connection IDs during the
   handshake; typically, however, only the server will request a
   connection ID for the lifetime of the connection.  Connection IDs for
   either endpoint may change during the lifetime of a connection, with
   the new connection ID being negotiated via encrypted frames.  See
   Section 6.1 of [QUIC-TRANSPORT].

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2.5.  Packet Numbers

   The packet number field is always present in the QUIC packet header;
   however, it is always encrypted.  The encryption key for packet
   number protection on handshake packets sent before cryptographic
   context establishment is specific to the QUIC version, while packet
   number protection on subsequent packets uses secrets derived from the
   end-to-end cryptographic context.  Packet numbers are therefore not
   part of the wire image that is useful to on-path observers.

2.6.  Version Negotiation and Greasing

   Version negotiation is not protected, given the used protection
   mechanism can change with the version.  However, the choices provided
   in the list of version in the Version Negotiation packet will be
   validated as soon as the cryptographic context has been established.
   Therefore any manipulation of this list will be detected and will
   cause the endpoints to terminate the connection.

   Also note that the list of versions in the Version Negotiation packet
   may contain reserved versions.  This mechanism is used to avoid
   ossification in the implementation on the selection mechanism.
   Further, a client may send a Initial Client packet with a reserved
   version number to trigger version negotiation.  In the Version
   Negotiation packet the connection ID and packet number of the Client
   Initial packet are reflected to provide a proof of return-
   routability.  Therefore changing these information will also cause
   the connection to fail.

3.  Network-visible information about QUIC flows

   This section addresses the different kinds of observations and
   inferences that can be made about QUIC flows by a passive observer in
   the network based on the wire image in Section 2.  Here we assume a
   bidirectional observer (one that can see packets in both directions
   in the sequence in which they are carried on the wire) unless noted.

3.1.  Identifying QUIC traffic

   The QUIC wire image is not specifically designed to be
   distinguishable from other UDP traffic.

   The only application binding currently defined for QUIC is HTTP
   [QUIC-HTTP].  HTTP over QUIC uses UDP port 443 by default, although
   URLs referring to resources available over HTTP over QUIC may specify
   alternate port numbers.  Simple assumptions about whether a given
   flow is using QUIC based upon a UDP port number may therefore not
   hold; see also [RFC7605] section 5.

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3.1.1.  Identifying Negotiated Version

   An in-network observer assuming that a set of packets belongs to a
   QUIC flow can infer the version number in use by observing the
   handshake: an Initial packet with a given version from a client to
   which a server responds with an Initial packet with the same version
   implies acceptance of that version.

   Negotiated version cannot be identified for flows for which a
   handshake is not observed, such as in the case of NAT rebinding;
   however, these flows can be associated with flows for which a version
   has been identified; see Section 3.4.

   In the rest of this section, we discuss only packets belonging to
   Version 1 QUIC flows, and assume that these packets have been
   identified as such through the observation of a version negotiation.

3.1.2.  Rejection of Garbage Traffic

   A related question is whether a first packet of a given flow on known
   QUIC-associated port is a valid QUIC packet, in order to support in-
   network filtering of garbage UDP packets (reflection attacks, random
   backscatter).  While heuristics based on the first byte of the packet
   (packet type) could be used to separate valid from invalid first
   packet types, the deployment of such heuristics is not recommended,
   as packet types may have different meanings in future versions of the

3.2.  Connection confirmation

   Connection establishment uses Initial, Handshake, and Retry packets
   containing a TLS handshake on Stream 0.  Connection establishment can
   therefore be detected using heuristics similar to those used to
   detect TLS over TCP.  A client using 0-RTT connection may also send
   data packets in 0-RTT Protected packets directly after the Initial
   packet containing the TLS Client Hello.  Since these packets may be
   reordered in the network, note that 0-RTT Protected data packets may
   be seen before the Initial packet.  Note that only clients send
   Initial packets, so the sides of a connection can be distinguished by
   QUIC packet type in the handshake.

3.3.  Application Identification

   The cleartext TLS handshake may contain Server Name Indication (SNI)
   [RFC6066], by which the client reveals the name of the server it
   intends to connect to, in order to allow the server to present a
   certificate based on that name.  It may also contain information from
   Application-Layer Protocol Negotiation (ALPN) [RFC7301], by which the

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   client exposes the names of application-layer protocols it supports;
   an observer can deduce that one of those protocols will be used if
   the connection continues.

   Work is currently underway in the TLS working group to encrypt the
   SNI in TLS 1.3 [TLS-ENCRYPT-SNI], reducing the information available
   in the SNI to the name of a fronting service, which can generally be
   identified by the IP address of the server anyway.  If used with
   QUIC, this would make SNI-based application identification impossible
   through passive measurement.

3.4.  Flow association

   The QUIC Connection ID (see Section 2.4) is designed to allow an on-
   path device such as a load-balancer to associate two flows as
   identified by five-tuple when the address and port of one of the
   endpoints changes; e.g. due to NAT rebinding or server IP address
   migration.  An observer keeping flow state can associate a connection
   ID with a given flow, and can associate a known flow with a new flow
   when when observing a packet sharing a connection ID and one endpoint
   address (IP address and port) with the known flow.

   The connection ID to be used for a long-running flow is chosen by the
   server (see [QUIC-TRANSPORT] section 5.6) during the handshake.  This
   value should be treated as opaque; see Section 4.3 for caveats
   regarding connection ID selection at servers.

3.5.  Flow teardown

   The QUIC does not expose the end of a connection; the only indication
   to on-path devices that a flow has ended is that packets are no
   longer observed.  Stateful devices on path such as NATs and firewalls
   must therefore use idle timeouts to determine when to drop state for
   QUIC flows.

   Changes to this behavior have been discussed in the working group,
   but there is no current proposal to implement these changes: see

3.6.  Round-trip time measurement

   Round-trip time of QUIC flows can be inferred by observation once per
   flow, during the handshake, as in passive TCP measurement; this
   requires parsing of the QUIC packet header and the cleartext TLS
   handshake on stream 0.

   In the common case, the delay between the Initial packet containing
   the TLS Client Hello and the Handshake packet containing the TLS

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   Server Hello represents the RTT component on the path between the
   observer and the server.  The delay between the TLS Server Hello and
   the Handshake packet containing the TLS Finished message sent by the
   client represents the RTT component on the path between the observer
   and the client.  While the client may send 0-RTT Protected packets
   after the Initial packet during 0-RTT connection re-establishment,
   these can be ignored for RTT measurement purposes.

   Handshake RTT can be measured by adding the client-to-observer and
   observer-to-server RTT components together.  This measurement
   necessarily includes any transport and application layer delay at
   both sides.

   The spin bit experiment, detailed in [QUIC-SPIN], provides an
   additional method to measure intraflow per-flow RTT.  When a QUIC
   flow is sending at full rate (i.e., neither application nor flow
   control limited), the latency spin bit described in that document
   changes value once per round-trip time (RTT).  An on-path observer
   can observe the time difference between edges in the spin bit signal
   in a single direction to measure one sample of end-to-end RTT.  Note
   that this measurement, as with passive RTT measurement for TCP,
   includes any transport protocol delay (e.g., delayed sending of
   acknowledgements) and/or application layer delay (e.g., waiting for a
   request to complete).  It therefore provides devices on path a good
   instantaneous estimate of the RTT as experienced by the application.
   A simple linear smoothing or moving minimum filter can be applied to
   the stream of RTT information to get a more stable estimate.

   An on-path observer that can see traffic in both directions (from
   client to server and from server to client) can also use the spin bit
   to measure "upstream" and "downstream" component RTT; i.e, the
   component of the end-to-end RTT attributable to the paths between the
   observer and the server and the observer and the client,
   respectively.  It does this by measuring the delay between a spin
   edge observed in the upstream direction and that observed in the
   downstream direction, and vice versa.

   Application-limited and flow-control-limited senders can have
   application and transport layer delay, respectively, that are much
   greater than network RTT.  Therefore, the spin bit provides network
   latency information only when the sender is neither application nor
   flow control limited.  When the sender is application-limited by
   periodic application traffic, where that period is longer than the
   RTT, measuring the spin bit provides information about the
   application period, not the RTT.  Simple heuristics based on the
   observed data rate per flow or changes in the RTT series can be used
   to reject bad RTT samples due to application or flow control

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   Since the spin bit logic at each endpoint considers only samples on
   packets that advance the largest packet number seen, signal
   generation itself is resistant to reordering.  However, reordering
   can cause problems at an observer by causing spurious edge detection
   and therefore low RTT estimates, if reordering occurs across a spin
   bit flip in the stream.  This can be probabilistically mitigated by
   the observer also tracking the low-order bits of the packet number,
   and rejecting edges that appear out-of-order [RFC4737].

3.7.  Flow symmetry measurement

   QUIC explicitly exposes which side of a connection is a client and
   which side is a server during the handshake.  In addition, the
   symmerty of a flow (whether primarily client-to-server, primarily
   server-to-client, or roughly bidirectional, as input to basic traffic
   classification techniques) can be inferred through the measurement of
   data rate in each direction.  While QUIC traffic is protected and
   ACKS may be padded, padding is not required.

4.  Specific Network Management Tasks

   In this section, we address specific network management and
   measurement techniques and how QUIC's design impacts them.

4.1.  Stateful treatment of QUIC traffic

   Stateful treatment of QUIC traffic is possible through QUIC traffic
   and version identification (Section 3.1) and observation of the
   handshake for connection confirmation (Section 3.2).  The lack of any
   visible end-of-flow signal (Section 3.5) means that this state must
   be purged either through timers or through least-recently-used
   eviction, depending on application requirements.

4.2.  Passive network performance measurement and troubleshooting

   Limited RTT measurement is possible by passive observation of QUIC
   traffic; see Section 3.6.  No passive measurement of loss is possible
   with the present wire image.  Extremely limited observation of
   upstream congestion may be possible via the observation of CE
   markings on ECN-enabled QUIC traffic.

4.3.  Server cooperation with load balancers

   In the case of content distribution networking architectures
   including load balancers, the connection ID provides a way for the
   server to signal information about the desired treatment of a flow to
   the load balancers.

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   Server-generated Connection IDs must not encode any information other
   that that needed to route packets to the appropriate backend
   server(s): typically the identity of the backend server or pool of
   servers, if the data-center's load balancing system keeps "local"
   state of all flows itself.  Care must be exercised to ensure that the
   information encoded in the Connection ID is not sufficient to
   identify unique end users.  Note that by encoding routing information
   in the Connection ID, load balancers open up a new attack vector that
   allows bad actors to direct traffic at a specific backend server or
   pool.  It is therefore recommended that Server-Generated Connection
   ID includes a cryptographic MAC that the load balancer pool server
   are able to identify and discard packets featuring an invalid MAC.

4.4.  DDoS Detection and Mitigation

   Current practices in detection and mitigation of Distributed Denial
   of Service (DDoS) attacks generally involve passive measurement using
   network flow data [RFC7011], classification of traffic into "good"
   (productive) and "bad" (DoS) flows, and filtering of these bad flows
   in a "scrubbing" environment.  Key to successful DDoS mitigation is
   efficient classification of this traffic.

   Limited first-packet garbage detection as in Section 3.1.2 and
   stateful tracking of QUIC traffic as in Section 4.1 above can be used
   in this classification step.

   Note that the use of a connection ID to support connection migration
   renders 5-tuple based filtering insufficient, and requires more state
   to be maintained by DDoS defense systems, and linkability resistance
   in connection ID update mechanisms means that a connection ID aware
   DDoS defense system must have the same information about flows as the
   load balancer.

   However, it is questionable if connection migrations needs to be
   supported in a DDOS attack.  If the connection migration is not
   visible to the network that performs the DDoS detection, an active,
   migrated QUIC connection may be blocked by such a system under
   attack.  However, a defense system might simply rely on the fast
   resumption mechanism provided by QUIC.

4.5.  QoS support and ECMP

   [EDITOR'S NOTE: this is a bit speculative; keep?]

   QUIC does not provide any additional information on requirements on
   Quality of Service (QoS) provided from the network.  QUIC assumes
   that all packets with the same 5-tuple {dest addr, source addr,
   protocol, dest port, source port} will receive similar network

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   treatment.  That means all stream that are multiplexed over the same
   QUIC connection require the same network treatment and are handled by
   the same congestion controller.  If differential network treatment is
   desired, multiple QUIC connections to the same server might be used,
   given that establishing a new connection using 0-RTT support is cheap
   and fast.

   QoS mechanisms in the network MAY also use the connection ID for
   service differentiation, as a change of connection ID is bound to a
   change of address which anyway is likely to lead to a re-route on a
   different path with different network characteristics.

   Given that QUIC is more tolerant of packet re-ordering than TCP (see
   Section 2.5), Equal-cost multi-path routing (ECMP) does not
   necessarily need to be flow based.  However, 5-tuple (plus eventually
   connection ID if present) matching is still beneficial for QoS given
   all packets are handled by the same congestion controller.

5.  IANA Considerations

   This document has no actions for IANA.

6.  Security Considerations

   Supporting manageability of QUIC traffic inherently involves
   tradeoffs with the confidentiality of QUIC's control information;
   this entire document is therefore security-relevant.

   Some of the properties of the QUIC header used in network management
   are irrelevant to application-layer protocol operation and/or user
   privacy.  For example, packet number exposure (and echo, as proposed
   in this document), as well as connection establishment exposure for
   1-RTT establishment, make no additional information about user
   traffic available to devices on path.

   At the other extreme, supporting current traffic classification
   methods that operate through the deep packet inspection (DPI) of
   application-layer headers are directly antithetical to QUIC's goal to
   provide confidentiality to its application-layer protocol(s); in
   these cases, alternatives must be found.

7.  Contributors

   Dan Druta contributed text to Section 4.4.  Igor Lubashev contributed
   text to Section 4.3 on the use of the connection ID for load
   balancing.  Marcus Ilhar contributed text to Section 3.6 on the use
   of the spin bit.

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8.  Acknowledgments

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement no. 688421 Measurement and Architecture
   for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
   for Education, Research, and Innovation under contract no. 15.0268.
   This support does not imply endorsement.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997, <

9.2.  Informative References

              Ding, H. and M. Rabinovich, "TCP Stretch Acknowledgments
              and Timestamps - Findings and Impliciations for Passive
              RTT Measurement (ACM Computer Communication Review)", July
              2015, <

   [IPIM]     Allman, M., Beverly, R., and B. Trammell, "In-Protocol
              Internet Measurement (arXiv preprint 1612.02902)",
              December 2016, <>.

              Bishop, M., "Hypertext Transfer Protocol (HTTP) over
              QUIC", draft-ietf-quic-http-13 (work in progress), June

              Thomson, M., "Version-Independent Properties of QUIC",
              draft-ietf-quic-invariants-01 (work in progress), March

              Trammell, B. and M. Kuehlewind, "The QUIC Latency Spin
              Bit", draft-ietf-quic-spin-exp-00 (work in progress),
              April 2018.

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              Thomson, M. and S. Turner, "Using Transport Layer Security
              (TLS) to Secure QUIC", draft-ietf-quic-tls-13 (work in
              progress), June 2018.

              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-13 (work
              in progress), June 2018.

   [RFC4737]  Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
              S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
              DOI 10.17487/RFC4737, November 2006, <https://www.rfc-

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066, DOI
              10.17487/RFC6066, January 2011, <https://www.rfc-

   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
              "Specification of the IP Flow Information Export (IPFIX)
              Protocol for the Exchange of Flow Information", STD 77,
              RFC 7011, DOI 10.17487/RFC7011, September 2013,

   [RFC7301]  Friedl, S., Popov, A., Langley, A., and E. Stephan,
              "Transport Layer Security (TLS) Application-Layer Protocol
              Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
              July 2014, <>.

   [RFC7605]  Touch, J., "Recommendations on Using Assigned Transport
              Port Numbers", BCP 165, RFC 7605, DOI 10.17487/RFC7605,
              August 2015, <>.

              Huitema, C. and E. Rescorla, "Issues and Requirements for
              SNI Encryption in TLS", draft-ietf-tls-sni-encryption-03
              (work in progress), May 2018.

              Trammell, B. and M. Kuehlewind, "The Wire Image of a
              Network Protocol", draft-trammell-wire-image-04 (work in
              progress), April 2018.

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Authors' Addresses

   Mirja Kuehlewind
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


   Brian Trammell
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


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