Network Working Group                                      M. Kuehlewind
Internet-Draft                                               B. Trammell
Intended status: Informational                                ETH Zurich
Expires: January 4, 2018                                        D. Druta
                                                           July 03, 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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   This Internet-Draft will expire on January 4, 2018.

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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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . .   3
   2.  Features of the QUIC Wire Image . . . . . . . . . . . . . . .   3
     2.1.  QUIC Packet Header Structure  . . . . . . . . . . . . . .   3
     2.2.  Integrity Protection of the Wire Image  . . . . . . . . .   5
     2.3.  Connection ID and Rebinding . . . . . . . . . . . . . . .   5
     2.4.  Packet Numbers  . . . . . . . . . . . . . . . . . . . . .   5
     2.5.  Initial Handshake and PMTUD . . . . . . . . . . . . . . .   6
     2.6.  Version Negotiation and Greasing  . . . . . . . . . . . .   6
   3.  Specific Network Management Tasks . . . . . . . . . . . . . .   6
     3.1.  Stateful Treatment of QUIC Traffic  . . . . . . . . . . .   6
     3.2.  Measurement of QUIC Traffic . . . . . . . . . . . . . . .   7
     3.3.  DDoS Detection and Mitigation . . . . . . . . . . . . . .   8
     3.4.  QoS support and ECMP  . . . . . . . . . . . . . . . . . .   8
     3.5.  Load Balancing using the Connection ID  . . . . . . . . .   9
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

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
   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

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   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.

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 typically used during connection start or for other control
   processes while the short header will be used on most data packets to

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   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 7 header types, namely Version Negotiation, Client
      Initial, Server Stateless Retry, Server Cleartext, Client
      Cleartext, 0-RTT Protected, 1-RTT Protected (key phase 0), 1-RTT
      Protected (key phase 1), and Public Reset.

   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 3.5 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 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
      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 lit of versions that
      is supported by the sender.  However the version in the version
      field of the header is the reflected version of the clients

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      initial packet and is therefore explicitly not supported by the

   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.  Different key phases are indicated with the
      use of the long header by using to different header types for
      protected long header packets.

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
   validate 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 connection ID is proposed by the server during
   connection establishment, and 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].

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

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   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.  Specific Network Management Tasks

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

3.1.  Stateful Treatment of QUIC Traffic

   Stateful network devices such as firewalls use exposed header
   information to support state setup and tear-down.  [STATEFULNESS]
   provides a general model for in-network state management on these
   devices, independent of transport protocol.  Features already present
   in QUIC may be used for state maintenance in this model.  Here, there
   are two important goals: distinguishing valid QUIC connection
   establishment from other traffic, in order to establish state; and
   determining the end of a QUIC connection, in order to tear that state

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   Both, 1-RTT and O-RTT connection establishment, using a TLS handshake
   on stream 0, is detectable using heuristics similar to those used to
   detect TLS over TCP.  0-RTT connection may additional also send data
   packets, right after the client hello.  These data may be reorder in
   the network, therefore it may be possible that 0-RTT Protected data
   packet are seen before the Client Initial packet.

   Exposure of connection shutdown is currently under discussion; see and

3.2.  Measurement of QUIC Traffic

   Passive measurement of TCP performance parameters is commonly
   deployed in access and enterprise networks to aid troubleshooting and
   performance monitoring without requiring the generation of active
   measurement traffic.

   The presence of packet numbers on all QUIC packets allows the trivial
   one-sided estimation of packet loss and reordering between the sender
   and a given observation point.  However, since retransmissions are
   not identifiable as such, loss between an observation point and the
   receiver cannot be reliably estimated.

   The lack of any acknowledgement information or timestamping
   information in the QUIC packet header makes running passive
   estimation of latency via round trip time (RTT) impossible.  RTT can
   only be measured at connection establishment time, by observing the
   Client Initial packet and the Server's reply to this packet which
   maybe a Server Cleartext, Version Negotiation, or Server Stateless
   Retry packet.

   Note that adding a packet number echo (as in or to the public header
   would allow passive RTT measurement at on-path observation points.
   For efficiency purposes, this packet number echo need not be carried
   on every packet, and could be made optional, allowing endpoints to
   make a measurability/efficiency tradeoff; see section 4 of [IPIM].
   Note further that this facility would have significantly better
   measurability characteristics than sequence-acknowledgement-based RTT
   measurement currently available in TCP on typical asymmetric flows,
   as adequate samples will be available in both directions, and packet
   number echo would be decoupled from the underlying acknowledgment
   machinery; see e.g.  [Ding2015]

   Note in-network devices can inspect and correlate connection IDs for
   partial tracking of mobility events.

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3.3.  DDoS Detection and Mitigation

   For enterprises and network operators one of the biggest management
   challenges is dealing with Distributed Denial of Service (DDoS)
   attacks.  Some network operators offer Security as a Service (SaaS)
   solutions that detect attacks by monitoring, analyzing and filtering
   traffic.  These approaches generally utilize network flow data
   [RFC7011].  If any flows pose a threat, usually they are routed to a
   "scrubbing environment" where the traffic is filtered, allowing the
   remaining "good" traffic to continue to the customer environment.

   This type of DDoS mitigation is fundamentally based on tracking state
   for flows (see Section 3.1) that have receiver confirmation and a
   proof of return-routability, and classifying flows as legitimate or
   DoS traffic.  The QUIC packet header currently does not support an
   explicit mechanism to easily distinguish legitimate QUIC traffic from
   other UDP traffic.  However, the first packet in a QUIC connection
   will usually be a Client Initial packet.  This can be used to
   identify the first packet of the connection.

   If the QUIC handshake was not observed by the defense system, the
   connection ID can be used as a confirmation signal as per
   [STATEFULNESS] if present in both directions.

   Further, 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.  This problem is also related to these issues under discussion:

3.4.  QoS support and ECMP

   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 connection to the same server might be used,
   given that establishing a new connection using 0-RTT support is cheap
   and fast.

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   QoS mechanisms in the network MAY also use the connection ID for
   service differentiation as usually a change of connection ID is bind
   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.

3.5.  Load Balancing using the Connection ID

   The Connection ID is used in part to support load balancing in
   content distribution networks (CDNs), which operate complex,
   geographically distributed pools of back-end servers, fronted by load
   balancing systems.  These load balancers are responsible for
   identifying the most appropriate server for each connection and for
   routing all packets belonging to that connection to the chosen

   Load balancers are often deployed in pools for redundancy and load
   sharing.  For high availability, it is important that when packets
   belonging to a flow start to arrive at a different load balancer in
   the load balancer pool, the packets continue to be forwarded to the
   original server in the server pool.

   Support for seamless connection migration is an important design goal
   of QUIC - a necessity due to the proliferation of mobile connected
   devices.  This connection persistence provides an additional
   challenge for multi-homed anycast-based services often employed by
   large content owners and CDNs.  The challenge is that a migration to
   a different network in the middle of the connection greatly increases
   the chances of the packets routed to a different anycast point of
   presence (POP) due to the new network's different connectivity and
   Internet peering arrangements.  The load balancer in the new POP,
   potentially thousands of miles away, will not have information about
   the established flow and would not be able to route it back to the
   original POP.

   Load balancers may cooperate with servers or server pools behind them
   to use a server-generated Connection ID value, in order to support
   stateless load balancing, even across NAT rebinding or other address
   change events (see Section 2.3).  See section 5.7 of [QUIC].

   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

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   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.  IANA Considerations

   This document has no actions for IANA.

5.  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.

6.  Contributors

   Igor Lubashev contributed text to Section 3.5 on the use of the
   connection ID for load balancing.

7.  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.

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8.  References

8.1.  Normative References

   [QUIC]     Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
              and Secure Transport", draft-ietf-quic-transport-04 (work
              in progress), June 2017.

              Bishop, M., "Hypertext Transfer Protocol (HTTP) over
              QUIC", draft-ietf-quic-http-04 (work in progress), June

              Thomson, M. and S. Turner, "Using Transport Layer Security
              (TLS) to Secure QUIC", draft-ietf-quic-tls-04 (work in
              progress), June 2017.

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

8.2.  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, <>.

   [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,

              Kuehlewind, M., Trammell, B., and J. Hildebrand,
              "Transport-Independent Path Layer State Management",
              draft-trammell-plus-statefulness-03 (work in progress),
              March 2017.

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Authors' Addresses

   Mirja Kuehlewind
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


   Brian Trammell
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich


   Dan Druta


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