Network Working Group                                      M. Kuehlewind
Internet-Draft                                               B. Trammell
Intended status: Informational                                ETH Zurich
Expires: April 28, 2018                                 October 25, 2017

              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 April 28, 2018.

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   Copyright (c) 2017 IETF Trust and the persons identified as the
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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.  Integrity Protection of the Wire Image  . . . . . . . . .   5
     2.3.  Connection ID and Rebinding . . . . . . . . . . . . . . .   5
     2.4.  Packet Numbers  . . . . . . . . . . . . . . . . . . . . .   6
     2.5.  Initial Handshake and PMTUD . . . . . . . . . . . . . . .   6
     2.6.  Version Negotiation and Greasing  . . . . . . . . . . . .   6
   3.  Network-visible information about QUIC flows  . . . . . . . .   6
     3.1.  Identifying QUIC traffic  . . . . . . . . . . . . . . . .   7
       3.1.1.  Identifying Negotiated Version  . . . . . . . . . . .   7
       3.1.2.  Rejection of Garbage Traffic  . . . . . . . . . . . .   7
     3.2.  Connection confirmation . . . . . . . . . . . . . . . . .   7
     3.3.  Flow association  . . . . . . . . . . . . . . . . . . . .   8
     3.4.  Flow teardown . . . . . . . . . . . . . . . . . . . . . .   8
     3.5.  Round-trip time measurement . . . . . . . . . . . . . . .   8
     3.6.  Packet loss measurement . . . . . . . . . . . . . . . . .   9
     3.7.  Flow symmetry measurement . . . . . . . . . . . . . . . .   9
   4.  Specific Network Management Tasks . . . . . . . . . . . . . .   9
     4.1.  Stateful treatment of QUIC traffic  . . . . . . . . . . .   9
     4.2.  Passive network performance measurement and
           troubleshooting . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  Server cooperation with load balancers  . . . . . . . . .  10
     4.4.  DDoS Detection and Mitigation . . . . . . . . . . . . . .  10
     4.5.  QoS support and ECMP  . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  12
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   QUIC [QUIC] 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 mutable by the

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   network, and will therefore be integrity-protected to the extent

   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, 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, also the
   wire image of the header format can change.  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 need to be fixed.

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

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2.1.  QUIC Packet Header Structure

   The QUIC packet header is under active development; see section 5 of
   [QUIC] for the present header structure.

   The first bit of the QUIC header indicates the present of a long
   header that exposes more information than the short header.  The long
   header is used during connection start including version negotiation,
   server retry, and 0-RTT data while the short header is used after the
   handshake and therefore on most data packets to limited unnecessary
   header overhead.  The fields and location of these fields as defined
   by the current version of QUIC for the long header are fixed for all
   future version as well.  However, note that future versions of QUIC
   may provide additional fields.  In the current version of quic the
   long header for all header types has a fixed length, containing,
   besides the Header Form bit, a 7-bit header Type, a 64-bit Connection
   ID, a 32-bit Packet Number, and a 32-bit Version.  The short header
   is variable length where bits after the Header Form bit indicate the
   present on the Connection ID, and the length of the packet number.

   The following information may be exposed in the packet header:

   o  header type: the long header has a 7-bit header type field
      following the Header Form bit.  The current version of QUIC
      defines 6 header types, namely Version Negotiation, Client
      Initial, Server Stateless Retry, Server Cleartext, Client
      Cleartext, 0-RTT Protected.

   o  connection ID: The connection ID is always present on the long and
      optionally present on the short header indicated by the Connection
      ID Flag.  If present at the short header it at the same position
      then for the long header.  The position and length pf the
      congestion ID itself as well as the Connection ID flag in the
      short header is fixed for all versions of QUIC.  The connection ID
      identifies the connection associated with a QUIC packet, for load-
      balancing and NAT rebinding purposes; see Section 4.3 and
      Section 2.3.  Therefore it is also expected that the Connection ID
      will either be present on all packets of a flow or none of the
      short header packets.  However, this field is under endpoint
      control and there is no protocol mechanism that hinders the
      sending endpoint to revise its decision about exposing the
      Connection ID at any time during the connection.

   o  packet number: Every packet has an associated packet number.  The
      packet number increases with each packet, and the least-
      significant bits of the packet number are present on each packet.
      In the short header the length of the exposed packet number field

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      is defined by the (short) header type and can either be 8, 16, or
      32 bits.  See Section 2.4.

   o  version number: The version number is present on the long headers
      and identifies the version used for that packet, expect for the
      Version negotiation packet.  The version negotiation packet is
      fixed for all version of QUIC and contains a list of versions that
      is supported by the sender.  The version in the version field of
      the Version Negotiation packet is the reflected version of the
      Client Initial packet and is therefore explicitly n ot supported
      by the sender.

   o  key phase: The short header further has a Key Phase flag that is
      used by the endpoint identify the right key that was used to
      encrypt the packet.

2.2.  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, such as the
   version number.  Therefore, devices on path MUST NOT change any
   information or bits in QUIC packet headers.  As alteration of header
   information would cause packet drop due to a failed integrity check
   at the receiver, or can even lead to connection termination.

2.3.  Connection ID and Rebinding

   The connection ID in the QUIC packer header is used to allow 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.  The client set a Connection ID in the Initial
   Client packet that will be used during the handshake.  A new
   connection ID is then provided by the server during connection
   establishment, that will be used in the short header after the
   handshake.  Further a server might provide additional connection IDs
   that can the used by the client at any time during the connection.
   Therefore if a flow changes one of its IP addresses it may keep the
   same connection ID, or the connection ID may also change together
   with the IP address migration, avoiding linkability; see Section 7.6
   of [QUIC].

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2.4.  Packet Numbers

   The packet number field is always present in the QUIC packet header.
   The packet number exposes the least significant 32, 16, or 8 bits of
   an internal packet counter per flow direction that increments with
   each packet sent.  This packet counter is initialized with a random
   31-bit initial value at the start of a connection.

   Unlike TCP sequence numbers, this packet number increases with every
   packet, including those containing only acknowledgment or other
   control information.  Indeed, whether a packet contains user data or
   only control information is intentionally left unexposed to the
   network.  The packet number increases with every packet but they
   sender may skip packet numbers.

   While loss detection in QUIC is based on packet numbers, congestion
   control by default provides richer information than vanilla TCP does.
   Especially, QUIC does not rely on duplicated ACKs, making it more
   tolerant of packet re-ordering.

2.5.  Initial Handshake and PMTUD

   [Editor's note: text needed.]

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

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   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.

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: a Client Initial with a given version followed by Server
   Cleartext packet with the same version implies acceptance of that

   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 3.3.

   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 requires cleartext packets and is using a
   TLS handshake on stream 0.  Therefore it is detectable using
   heuristics similar to those used to detect TLS over TCP. 0-RTT

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   connection may additional also send data packets, right after the
   Client Initial with the TLS client hello.  These data may be
   reordered in the network, therefore it may be possible that 0-RTT
   Protected data packets are seen before the Client Initial packet.

3.3.  Flow association

   The QUIC Connection ID (see Section 2.3) 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] 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.

3.4.  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 are currently under discussion: see

3.5.  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.  The delay
   between the Client Initial packet and the Server Cleartext packet
   sent back to the client represents the RTT component on the path
   between the observer and the server, and the delay between this
   packet and the Client Cleartext packet in reply represents the RTT
   component on the path between the observer and the client.  This
   measurement necessarily includes any application delay at both sides.
   Note that the Server's reply mayalso be a Version Negotiation or
   Server Stateless Retry packet.  In this case the Client will send
   another Client Initial or the connection will fail.

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   The lack of any acknowledgement information or timestamping
   information in the QUIC wire image makes running passive RTT
   estimation impossible.

   Changes to this behavior are currently under discussion: see

3.6.  Packet loss measurement

   All QUIC packets carry packet numbers in cleartext, and while the
   protocol allows packet numbers to be skipped, skipping is not
   recommended in the general case.  This allows the trivial one-sided
   estimation of packet loss and reordering between the sender and a
   given observation point ("upstream loss").  However, since
   retransmissions are not identifiable as such, loss between an
   observation point and the receiver ("downstream loss") cannot be
   reliably estimated.

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 3.4) 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

   Extremely limited loss and RTT measurement are possible by passive
   observation of QUIC traffic; see Section 3.5 and Section 3.6.

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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.

   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.  For traffic where the classification
   step did not observe a QUIC handshake, the presence of packets
   carrying the same Connection ID in both directions is a further
   indication of legitimate traffic.  Note that these classification
   techniques help only against floods of garbage traffic, not against
   DDoS attacks using legitimate QUIC clients.

   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.  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.  See also

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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
   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 2.4), 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.

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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

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, <>.

   [QUIC]     Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-07 (work
              in progress), October 2017.

              Bishop, M., "Hypertext Transfer Protocol (HTTP) over
              QUIC", draft-ietf-quic-http-07 (work in progress), October

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              Thomson, M. and S. Turner, "Using Transport Layer Security
              (TLS) to Secure QUIC", draft-ietf-quic-tls-07 (work in
              progress), October 2017.

   [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,

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

Authors' Addresses

   Mirja Kuehlewind
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


   Brian Trammell
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


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