Network Working Group                                      M. Kuehlewind
Internet-Draft                                                  Ericsson
Intended status: Informational                               B. Trammell
Expires: January 6, 2020                                          Google
                                                           July 05, 2019

              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

   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
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   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 January 6, 2020.

Copyright Notice

   Copyright (c) 2019 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.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   4
   2.  Features of the QUIC Wire Image . . . . . . . . . . . . . . .   4
     2.1.  QUIC Packet Header Structure  . . . . . . . . . . . . . .   4
     2.2.  Coalesced Packets . . . . . . . . . . . . . . . . . . . .   6
     2.3.  Use of Port Numbers . . . . . . . . . . . . . . . . . . .   6
     2.4.  The QUIC handshake  . . . . . . . . . . . . . . . . . . .   6
     2.5.  Integrity Protection of the Wire Image  . . . . . . . . .  11
     2.6.  Connection ID and Rebinding . . . . . . . . . . . . . . .  11
     2.7.  Packet Numbers  . . . . . . . . . . . . . . . . . . . . .  11
     2.8.  Version Negotiation and Greasing  . . . . . . . . . . . .  11
   3.  Network-visible information about QUIC flows  . . . . . . . .  12
     3.1.  Identifying QUIC traffic  . . . . . . . . . . . . . . . .  12
       3.1.1.  Identifying Negotiated Version  . . . . . . . . . . .  12
       3.1.2.  Rejection of Garbage Traffic  . . . . . . . . . . . .  13
     3.2.  Connection confirmation . . . . . . . . . . . . . . . . .  13
     3.3.  Application Identification  . . . . . . . . . . . . . . .  13
     3.4.  Flow association  . . . . . . . . . . . . . . . . . . . .  14
     3.5.  Flow teardown . . . . . . . . . . . . . . . . . . . . . .  14
     3.6.  Flow symmetry measurement . . . . . . . . . . . . . . . .  14
     3.7.  Round-Trip Time (RTT) Measurement . . . . . . . . . . . .  14
       3.7.1.  Measuring initial RTT . . . . . . . . . . . . . . . .  15
       3.7.2.  Using the Spin Bit for Passive RTT Measurement  . . .  15
   4.  Specific Network Management Tasks . . . . . . . . . . . . . .  16
     4.1.  Stateful treatment of QUIC traffic  . . . . . . . . . . .  17
     4.2.  Passive network performance measurement and
           troubleshooting . . . . . . . . . . . . . . . . . . . . .  17
     4.3.  Server cooperation with load balancers  . . . . . . . . .  17
     4.4.  DDoS Detection and Mitigation . . . . . . . . . . . . . .  17
     4.5.  Distinguishing acknowledgment traffic . . . . . . . . . .  18
     4.6.  QoS support and ECMP  . . . . . . . . . . . . . . . . . .  18
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  19
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  19
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

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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 that QUIC is an end-to-end transport protocol, all information
   in the protocol header, even that which can be inspected, is not
   meant to be mutable by the network, and is therefore integrity-
   protected.  While less information is visible to the network than for
   TCP, integrity protection can also simplify troubleshooting because
   none of the nodes on the network path can modify the transport layer

   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.

   Since QUIC's wire image [WIRE-IMAGE] is integrity protected and not
   modifiable on path, in-network operations are not possible without
   terminating the QUIC connection, for instance using a back-to-back
   proxy.  Proxy operations are not in scope for this document.  QUIC
   proxies must be fully-fledged QUIC endpoints, implementing the
   transport as defined in [QUIC-TRANSPORT] and [QUIC-TLS] as well as
   proxy-relevant semantics for the application(s) running over QUIC
   (e.g.  HTTP/3 as defined in [QUIC-HTTP]).

   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.

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1.1.  Notational Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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 the
   unencrypted part of QUIC's 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

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, 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

   Short headers are used after connection establishment, and contain
   only an optional destination connection ID and the spin bit for RTT

   The following information is exposed in QUIC packet headers:

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   o  demux bit: the second most significant bit of the first octet
      every QUIC packet of the current version is set to 1, for
      demultiplexing with other UDP-encapsulated protocols.

   o  latency spin bit: the third most significant bit of first octet in
      the short packet header.  The spin bit is set by endpoints such
      that tracking edge transitions can be used to passively observe
      end-to-end RTT.  See Section 3.7.2 for further details.

   o  header type: the long header has a 2 bit packet type field
      following the Header Form bit.  Header types correspond to stages
      of the handshake; see Section 17.2 of [QUIC-TRANSPORT].

   o  version number: the version number present in the long header, and
      identifies the version used for that packet.  Note that during
      Version Negotiation (see Section 2.8, and Section 17.2.1 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: short and long packet
      headers carry a destination connection ID, a variable-length field
      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 2.6.  Long packet headers additionally
      carry a source connection ID.  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.  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).

   o  token: Initial packets may contain a token, a variable-length
      opaque value optionally sent from client to server, used for
      validating the client's address.  Retry packets also contain a
      token, which can be used by the client in an Initial packet on a
      subsequent connection attempt.  The length of the token is
      explicit in both cases.

   Retry and Version Negotiation packets are not encrypted or obfuscated
   in any way.  For other kinds of packets, other information in the
   packet headers is cryptographically obfuscated:

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   o  packet number: Most packets (with the exception of Version
      Negotiation and Retry packets) have an associated packet number;
      however, this packet number is encrypted, and therefore not of use
      to on-path observers.  The offset of the packet number is encoded
      in the header for packets with long headers, while it is implicit
      (depending on Destination Connection ID length) in short header
      packets.  The length of the packet number is cryptographically

   o  key phase: The Key Phase bit, present in short headers, specifies
      the keys used to encrypt the packet, supporting key rotation.  The
      Key Phase bit is cryptographically obfuscated.

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
   destination connection ID.  See Section 4.6 of [QUIC-TRANSPORT].

2.3.  Use of Port Numbers

   Applications that have a mapping for TCP as well as QUIC are expected
   to use the same port number for both services.  However, as with TCP-
   based services, especially when application layer information is
   encrypted, there is no guarantee that a specific application will use
   the registered port, or the used port is carrying traffic belonging
   to the respective registered service.  For example, [QUIC-TRANSPORT]
   specifies the use of Alt-Svc for discovery of QUIC/HTTP services on
   other ports.

   Further, as QUIC has a connection ID, it is also possible to maintain
   multiple QUIC connections over one 5-tuple.  However, if the
   connection ID is not present in the packet header, all packets of the
   5-tuple belong to the same QUIC connection.

2.4.  The QUIC handshake

   New QUIC connections are established using a handshake, which is
   distinguishable on the wire and contains some information that can be
   passively observed.

   To illustrate the information visible in the QUIC wire image during
   the handshake, we first show the general communication pattern

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   visible in the UDP datagrams containing the QUIC handshake, then
   examine each of the datagrams in detail.

   In the nominal case, the QUIC handshake can be recognized on the wire
   through at least four datagrams we'll call "QUIC Client Hello", "QUIC
   Server Hello", and "Initial Completion", and "Handshake Completion",
   for purposes of this illustration, as shown in Figure 1.

   Packets in the handshake belong to three separate cryptographic and
   transport contexts ("Initial", which contains observable payload, and
   "Handshake" and "1-RTT", which do not).  QUIC packets in separate
   contexts during the handshake are generally coalesced (see
   Section 2.2) in order to reduce the number of UDP datagrams sent
   during the handshake.

   As shown here, the client can send 0-RTT data as soon as it has sent
   its Client Hello, and the server can send 1-RTT data as soon as it
   has sent its Server Hello.

   Client                                    Server
     |                                          |
     +----QUIC Client Hello-------------------->|
     +----(zero or more 0RTT)------------------>|
     |                                          |
     |<--------------------QUIC Server Hello----+
     |<---------(1RTT encrypted data starts)----+
     |                                          |
     +----Initial Completion------------------->|
     +----(1RTT encrypted data starts)--------->|
     |                                          |
     |<-----------------Handshake Completion----+
     |                                          |

   Figure 1: General communication pattern visible in the QUIC handshake

   A typical handshake starts with the client sending of a QUIC Client
   Hello datagram as shown in Figure 2, which elicits a QUIC Server
   Hello datagram as shown in Figure 3 typically containing three
   packets: an Initial packet with the Server Hello, a Handshake packet
   with the rest of the server's side of the TLS handshake, and initial
   1-RTT data, if present.

   The content of QUIC Initial packets are encrypted using Initial
   Secrets, which are derived from a per-version constant and the
   client's destination connection ID; they are therefore observable by
   any on-path device that knows the per-version constant; we therefore
   consider these as visible in our illustration.  The content of QUIC

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   Handshake packets are encrypted using keys established during the
   initial handshake exchange, and are therefore not visible.

   Initial, Handshake, and the Short Header packets transmitted after
   the handshake belong to cryptographic and transport contexts.  The
   Initial Completion Figure 4 and the Handshake Completion Figure 5
   datagrams finish these first two contexts, by sending the final
   acknowledgment and finishing the transmission of CRYPTO frames.

   | UDP header (source and destination UDP ports)            |
   | QUIC long header (type = Initial, Version, DCID, SCID) (Length)
   +----------------------------------------------------------+  |
   | QUIC CRYPTO frame header                                 |  |
   +----------------------------------------------------------+  |
   | TLS Client Hello (incl. TLS SNI)                         |  |
   +----------------------------------------------------------+  |
   | QUIC PADDING frame                                       |  |

        Figure 2: Typical 1-RTT QUIC Client Hello datagram pattern

   The Client Hello datagram exposes version number, source and
   destination connection IDs, and information in the TLS Client Hello
   message, including any TLS Server Name Indication (SNI) present, in
   the clear.  The QUIC PADDING frame shown here may be present to
   ensure the Client Hello datagram has a minimum size of 1200 octets,
   to mitigate the possibility of handshake amplification.  Note that
   the location of PADDING is implementation-dependent, and PADDING
   frames may not appear in the Initial packet in a coalesced packet.

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   | UDP header (source and destination UDP ports)              |
   | QUIC long header (type = Initial, Version, DCID, SCID)   (Length)
   +------------------------------------------------------------+  |
   | QUIC CRYPTO frame header                                   |  |
   +------------------------------------------------------------+  |
   | TLS Server Hello                                           |  |
   +------------------------------------------------------------+  |
   | QUIC ACK frame (acknowledging client hello)                |  |
   | QUIC long header (type = Handshake, Version, DCID, SCID) (Length)
   +------------------------------------------------------------+  |
   | encrypted payload (presumably CRYPTO frames)               |  |
   | QUIC short header                                          |
   | 1-RTT encrypted payload                                    |

           Figure 3: Typical QUIC Server Hello datagram pattern

   The Server Hello datagram exposes version number, source and
   destination connection IDs, and information in the TLS Server Hello

   | UDP header (source and destination UDP ports)              |
   | QUIC long header (type = Initial, Version, DCID, SCID)   (Length)
   +------------------------------------------------------------+  |
   | QUIC ACK frame (acknowledging Server Hello Initial)        |  |
   | QUIC long header (type = Handshake, Version, DCID, SCID) (Length)
   +------------------------------------------------------------+  |
   | encrypted payload (presumably CRYPTO/ACK frames)           |  |
   | QUIC short header                                          |
   | 1-RTT encrypted payload                                    |

        Figure 4: Typical QUIC Initial Completion datagram pattern

   The Initial Completion datagram does not expose any additional
   information; however, recognizing it can be used to determine that a
   handshake has completed (see Section 3.2), and for three-way
   handshake RTT estimation as in Section 3.7.

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   | UDP header (source and destination UDP ports)              |
   | QUIC long header (type = Handshake, Version, DCID, SCID) (Length)
   +------------------------------------------------------------+  |
   | encrypted payload (presumably ACK frame)                   |  |
   | QUIC short header                                          |
   | 1-RTT encrypted payload                                    |

       Figure 5: Typical QUIC Handshake Completion datagram pattern

   Similar to Initial Completion, Handshake Completion also exposes no
   additional information; observing it serves only to determine that
   the handshake has completed.

   When the client uses 0-RTT connection resumption, 0-RTT data may also
   be seen in the QUIC Client Hello datagram, as shown in Figure 6.

   | UDP header (source and destination UDP ports)            |
   | QUIC long header (type = Initial, Version, DCID, SCID) (Length)
   +----------------------------------------------------------+  |
   | QUIC CRYPTO frame header                                 |  |
   +----------------------------------------------------------+  |
   | TLS Client Hello (incl. TLS SNI)                         |  |
   | QUIC long header (type = 0RTT, Version, DCID, SCID)    (Length)
   +----------------------------------------------------------+  |
   | 0-rtt encrypted payload                                  |  |

        Figure 6: Typical 0-RTT QUIC Client Hello datagram pattern

   In a 0-RTT QUIC Client Hello datagram, the PADDING frame is only
   present if necessary to increase the size of the datagram with 0RTT
   data to at least 1200 bytes.  Additional datagrams containing only
   0-RTT protected long header packets may be sent from the client to
   the server after the Client Hello datagram, containing the rest of
   the 0-RTT data.  The amount of 0-RTT protected data is limited by the
   initial congestion window, typically around 10 packets [RFC6928].

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2.5.  Integrity Protection of the Wire Image

   As soon as the cryptographic context is established, all information
   in the QUIC header, including information exposed in the packet
   header, is integrity protected.  Further, information that was sent
   and exposed in handshake packets sent before the cryptographic
   context was established are 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.

2.6.  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 5.1 of [QUIC-TRANSPORT].

2.7.  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 visible to on-path observers.

2.8.  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.

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   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.

   While the second most significant bit (0x40) of the first octet is
   always set to 1 in QUIC packets of the current version, this is not a
   recommended method of recognizing QUIC traffic, as it only provides
   one bit of information and is quite prone to collide with UDP-based
   protocols other than those that this static bit is meant to allow
   multiplexing with.

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 connection
   migration; however, these flows can be associated with flows for
   which a version has been identified; see Section 3.4.

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   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.  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 clients send Initial packets before servers do, servers
   send Handshake packets before clients do, and only clients send
   Initial packets with tokens, so the sides of a connection can be
   generally be confirmed by an on-path observer.  An attempted
   connection after Retry can be detected by correlating the token on
   the Retry with the token on the subsequent Initial packet.

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
   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-ESNI].  If used with QUIC, this would make SNI-
   based application identification impossible through passive

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3.4.  Flow association

   The QUIC Connection ID (see Section 2.6) 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.

   However, since the connection ID may change multiple times during the
   lifetime of a flow, and the negotiation of connection ID changes is
   encrypted, packets with the same 5-tuple but different connection IDs
   may or may not belong to the same connection.

   The connection ID value should be treated as opaque; see Section 4.3
   for caveats regarding connection ID selection at servers.

3.5.  Flow teardown

   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

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

3.6.  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
   symmetry 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.

3.7.  Round-Trip Time (RTT) 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 recognition of the
   handshake, as illustrated in Section 2.4.  It can also be inferred

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   during the flow's lifetime, if the endpoints use the spin bit
   facility described below and in [QUIC-TRANSPORT], section 17.3.1.

3.7.1.  Measuring initial RTT

   In the common case, the delay between the Initial packet containing
   the TLS Client Hello and the Handshake packet containing the TLS
   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 (the
   latter mainly caused by the asymmetric crypto operations associated
   with the TLS handshake) at both sides.

3.7.2.  Using the Spin Bit for Passive RTT Measurement

   The spin bit provides an additional method to measure per-flow RTT
   from observation points on the network path throughout the duration
   of a connection.  Endpoint participation in spin bit signaling is
   optional in QUIC.  That is, while its location is fixed in this
   version of QUIC, an endpoint can unilaterally choose to not support
   "spinning" the bit.  Use of the spin bit for RTT measurement by
   devices on path is only possible when both endpoints enable it.  Some
   endpoints may disable use of the spin bit by default, others only in
   specific deployment scenarios, e.g. for servers and clients where the
   RTT would reveal the presence of a VPN or proxy.  To avoid making
   these connections identifiable based on the usage of the spin bit, it
   is recommended that all endpoints randomly disable "spinning" for at
   least one eighth of connections, even if otherwise enabled by
   default.  An endpoint not participating in spin bit signaling for a
   given connection can use a fixed spin value for the duration of the
   connection, or can set the bit randomly on each packet sent.

   When in use and a QUIC flow sends data continuously, the latency spin
   bit in each direction changes value once per round-trip time (RTT).
   An on-path observer can observe the time difference between edges
   (changes from 1 to 0 or 0 to 1) 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

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   acknowledgements) and/or application layer delay (e.g., waiting for a
   response to be generated).  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

   However, application-limited and flow-control-limited senders can
   have application and transport layer delay, respectively, that are
   much greater than network RTT.  When the sender is application-
   limited and e.g. only sends small amount of periodic application
   traffic, where that period is longer than the RTT, measuring the spin
   bit provides information about the application period, not the
   network RTT.

   Since the spin bit logic at each endpoint considers only samples from
   packets that advance the largest packet number, signal generation
   itself is resistant to reordering.  However, reordering can cause
   problems at an observer by causing spurious edge detection and
   therefore inaccurate (i.e., lower) RTT estimates, if reordering
   occurs across a spin-bit flip in the stream.

   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 lost
   or reordered edges in the spin signal, as well as application or flow
   control limitation; for example, QoF [TMA-QOF] rejects component RTTs
   significantly higher than RTTs over the history of the flow.  These
   heuristics may use the handshake RTT as an initial RTT estimate for a
   given flow.  Usually such heuristics would also detect if the spin is
   either constant or randomly set for a connection.

   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.

4.  Specific Network Management Tasks

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

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4.1.  Stateful treatment of QUIC traffic

   Stateful treatment of QUIC traffic (e.g., at a firewall or NAT
   middlebox) 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.

   The QUIC header optionally contains a Connection ID which can be used
   as additional entropy beyond the 5-tuple, if needed.  The QUIC
   handshake needs to be observed in order to understand whether the
   Connection ID is present and what length it has.

4.2.  Passive network performance measurement and troubleshooting

   Limited RTT measurement is possible by passive observation of QUIC
   traffic; see Section 3.7.  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.  Guidance on assigning connection IDs is given in

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

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   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.  Distinguishing acknowledgment traffic

   Some deployed in-network functions distinguish pure-acknowledgment
   (ACK) packets from packets carrying upper-layer data in order to
   attempt to enhance performance, for example by queueing ACKs
   differently or manipulating ACK signaling.  Distinguishing ACK
   packets is trivial in TCP, but not supported by QUIC, since
   acknowledgment signaling is carried inside QUIC's encrypted payload,
   and ACK manipulation is impossible.  Specifically, heuristics
   attempting to distinguish ACK-only packets from payload-carrying
   packets based on packet size are likely to fail, and are emphatically

4.6.  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
   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 2.7), 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.

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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.

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 3.7 on the use
   of the spin bit.

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,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <>.

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, <

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

              Kuehlewind, M. and B. Trammell, "Applicability of the QUIC
              Transport Protocol", draft-ietf-quic-applicability-04
              (work in progress), April 2019.

              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", draft-ietf-quic-http-20 (work in progress),
              April 2019.

              Thomson, M., "Version-Independent Properties of QUIC",
              draft-ietf-quic-invariants-04 (work in progress), April

              Thomson, M. and S. Turner, "Using TLS to Secure QUIC",
              draft-ietf-quic-tls-20 (work in progress), April 2019.

              Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-20 (work
              in progress), April 2019.

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

   [RFC6928]  Chu, J., Dukkipati, N., Cheng, Y., and M. Mathis,
              "Increasing TCP's Initial Window", RFC 6928,
              DOI 10.17487/RFC6928, April 2013,

   [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, <>.

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

              Rescorla, E., Oku, K., Sullivan, N., and C. Wood,
              "Encrypted Server Name Indication for TLS 1.3", draft-
              ietf-tls-esni-03 (work in progress), March 2019.

   [TMA-QOF]  Trammell, B., Gugelmann, D., and N. Brownlee, "Inline Data
              Integrity Signals for Passive Measurement (in Proc. TMA
              2014)", April 2014.

              Trammell, B. and M. Kuehlewind, "The Wire Image of a
              Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April
              2019, <>.

Authors' Addresses

   Mirja Kuehlewind


   Brian Trammell
   Gustav-Gull-Platz 1
   8004 Zurich


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