Network Working Group                                      M. Kuehlewind
Internet-Draft                                                 Z. Sarker
Intended status: Informational                                  Ericsson
Expires: 10 September 2020                                    T. Fossati
                                                               L. Pardue
                                                            9 March 2020

           Use Cases and Requirements for QUIC as a Substrate


   In situations where direct connectivity is not available or desired,
   proxies in the network are used to forward and potentially translate
   traffic.  TCP is often used as a proxying or tunneling protocol.
   QUIC is a new, emerging transport protocol and there is a similar
   expectation that it too will be used as a substrate once it is widely
   deployed.  Using QUIC instead of TCP in existing scenarios will allow
   proxying and tunneling services to maintain the benefits of QUIC
   natively, without degrading the performance and security
   characteristics.  QUIC also opens up new opportunities for these
   services to have lower latency and better multistreaming support.
   This document summarizes current and future usage scenarios to derive
   requirements for QUIC as a substrate and to provide additional
   considerations for proxy signaling and control protocol as proposed
   by MASQUE.

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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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 10 September 2020.

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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Usage Scenarios . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Obfuscation via Tunneling . . . . . . . . . . . . . . . .   3
     2.2.  Advanced Support of User Agents . . . . . . . . . . . . .   5
       2.2.1.  Security and Access Policy Enforcement  . . . . . . .   6
     2.3.  Frontend Support for Load Balancing and Migration/
           Mobility  . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.4.  IoT Gateways  . . . . . . . . . . . . . . . . . . . . . .   7
     2.5.  Multi-hop Chaining Usage  . . . . . . . . . . . . . . . .   8
       2.5.1.  Considerations for Multiple Encryption  . . . . . . .   9
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   9
   4.  Review of Existing Approaches . . . . . . . . . . . . . . . .  10
   5.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  11
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   QUIC is a new transport protocol that was developed with a focus on
   optimizing HTTP traffic by supporting multiplexing without head-of-
   line-blocking and integrating security directly into the transport.
   This tight integration of security allows the transport and security
   handshakes to be combined into a single round-trip exchange, after
   which both the transport connection and authenticated encryption keys
   are ready.

   Based on the expectation that QUIC will be widely used for HTTP, it
   follows that there will also be a need to enable the use of QUIC for
   HTTP proxy services.

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   Beyond HTTP, however, QUIC provides a general-purpose transport
   protocol that can be used for many other kinds of traffic, whenever
   the features provided by QUIC (compared to existing options, like
   TCP) are beneficial to the high-layer service.  Specifically, QUIC's
   ability to multiplex, encrypt data, and migrate between network paths
   makes it ideal for solutions that needs to tunnel or proxy traffic.

   Existing proxies that are not based on QUIC are often transparent.
   That is, they do not require the cooperation of the ultimate
   connection endpoints, and are often not visible to one or both of the
   endpoints.  If QUIC provides the basis for future tunneling and
   proxying solutions, it is expected that this relationship will
   change.  At least one of the endpoints will be aware of the proxy and
   explicitly coordinate with it.  This allows client hosts to make
   explicit decisions about the services they request from proxies (for
   example, simple forwarding or more advance, e.g. performance-
   optimizing, services), and to do so using a secure communication
   channel between themselves and the proxy.

   MASQUE [I-D.schinazi-masque] is a proposed framework that allows
   running multiple network or application services inside one QUIC
   connection to be forwarded to one or more target servers.  The end-
   to-end traffic between the client and the target server will be
   tunnelled in a (outer) QUIC connection between the client and the
   MASQUE server.  This outer connection can also be used to securely
   exchange additional signal or control information between the MASQUE
   server and the client.

   This document describes some of the use cases for using QUIC for
   proxying and tunneling, as proposed by MASQUE, and explains the
   protocol impacts and tradeoffs of such deployments.

2.  Usage Scenarios

2.1.  Obfuscation via Tunneling

   Tunnels are used in many scenarios within the core of the network
   from a client endpoint to a proxy middlepoint on the way towards the
   server.  In many cases, when the client explicitly decides to use the
   support of a proxy in order to connect to a server, it does so
   because a direct connection may be blocked or impaired.  This can
   either be the case in e.g. enterprise network where traffic is
   firewalled and web traffic needs to be routed over an explicitly
   provided HTTP proxy, or other reasons for blocking of certain
   services e.g. due to censorship, data exfiltration protection, etc.

   Tunneling through a proxy server can provide various benefits,

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   particularly when using a proxy that has a secure multiplexed channel
   like QUIC:

   *  Obfuscating the traffic patterns of the traffic from the
      perspective of observers between the client and the proxy.  If the
      content of connections to many end servers can be coalesced as one
      flow, it becomes increasingly difficult for observers to detect
      how many inner connections are being used, or what the content of
      those connections are.

   *  Obfuscating the client's IP address from the perspective of
      observers after the proxy, to the end server itself.  This allows
      the client to reduce information leaked about its actual location,
      improving privacy.

   *  Obfuscating the end server's IP address from the observers between
      the client and the proxy, which protects the identity of a private
      server's address or circumvents local firewall rules.

   In any of these tunneling scenarios, including those deployed today,
   the client explicitly decides to make use of a proxy service while it
   is usually fully transparent for the server, or even with the
   intention to hide the client's identity from the server.  This is
   explicitly part of the design as these services are targeting an
   impaired or otherwise constrained network setup.

   Therefore, in this usage scenario the client knows the proxy's
   address and explicitly selects to connect to the proxy in order to
   instruct the proxy to forward its traffic to a specific target
   server.  Often the proxy is also preconfigured to "know" the client
   and therefore the client needs to authenticate itself (e.g. using
   HTTP Transport Authentication [I-D.schinazi-httpbis-transport-auth]).
   But even without authentication, at a minimum, the client needs to
   communicate directly with the proxy to provide the address of the
   target server it wants to connect to, e.g. using HTTP CONNECT, and
   potentially other information needed to inform the behaviour of the

   Usually the server is not aware of the proxy in the middle, so the
   proxy needs to re-write the IP address of any traffic inside the
   tunnel to ensure that the return traffic is also routed back to the
   proxy.  This is also often used to conceal the address/location of
   the client to the server, e.g. to access local content that would not
   be accessible by the client at its current location otherwise.

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2.2.  Advanced Support of User Agents

   Depending on the traffic that is sent "over" the proxy, it is also
   possible that the proxy can perform additional support services if
   requested by the client.  Today, Performance Enhancing Proxies (PEPs)
   usually work transparently by either fully or partially terminating
   the transport connection.  For many of these support services the
   termination is actually not needed and may even be problematic.
   However, it is often the only, or at least easiest, solution if no
   direct communication with the client is available.  Enabling these
   services based on an explicit tunnel setup between the client and the
   proxy provides such a communication channel and makes it possible to
   exchange information in a private and authenticated way.

   It is expected that in-network functions are usually provided close
   to the client e.g. hosted by the access network provider.  Having
   this direct relation between the endpoint and the network service is
   also necessary in order to discover the service, as the assumption is
   that a client knows how to address the proxy service and which
   service is offered (besides forwarding).  Such a setup is especially
   valuable in access networks with challenging link environments such
   as satellite or cellular networks.  While end-to-end functions need
   to be designed to handle all kind of network conditions, direct
   support from the network can help to optimize for the specific
   characteristics of the access network such as use of link-specific
   congestion control or local repair mechanisms.

   Further, if not provided by the server directly, a network support
   function can also assist the client to adapt or prioritize the
   traffic based on user preferences or device characteristics and
   capabilities.  Again, especially if the access network is
   constrained, this can benefit both the network provider to save
   resources and the client to receive the desired service quicker or
   less impaired.  Such a service could even be extended to include
   caching or pre-fetching if the necessary trust relationship between
   the client and the proxy exists.

   Depending on the function requested, the proxy would need to access
   or alter the traffic or context which is limiting due to the
   necessary trust.  Therefore alternative models should be pursued in
   most cases.  One such model is explicit exchange of information about
   the current network state from the proxy to the client.  This enables
   some services to function by having the end-to-end peers act on or
   inject the learned information from the proxy into the end-to-end
   connection(s).  Thus achieving the benefits without the need to
   access the content or some of the traffic metadata directly.
   Especially transport layer optimizations do not need access to the
   actual user content.  Network functions should generally minimize

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   dependencies to higher layer characteristics as those may change

   Similar to previous usage scenario, in this setup the client
   explicitly selects the proxy and specifies the requested support
   function.  Often the server may not need to be aware of it but
   depending on the optimization function, server cooperation could be
   beneficial as well.  Usually though, it is expected that even if the
   server is aware, no direct information exchange is needed between the
   proxy and the server.  Instead, any needed information will be
   provided "over" the client and thus, the client and the proxy need a
   direct and secured communication channel in order to request and
   configure a service and exchange or expose the needed information and

2.2.1.  Security and Access Policy Enforcement

   Some deployment models may wish to enforce security or access
   policies on traffic flowing between domains (physical, logical,
   administrative, security etc.).  To support this, endpoints
   coordinate through a gateway that can require information about the
   transport layer, application layer and application content.  Policy
   is generally configured out-of-band, either statically or through
   some independent control plane.

   In one use case, the enforcement function controls egress traffic; a
   client connects to a proxy, typically inside the same domain, in
   order to cross the domain boundary.  In another use case, the
   enforcement function controls ingress traffic; a client connects to a
   proxy that controls access to the ultimate destination.  This may be
   deployed inside the target domain, near it, or further away as a part
   of a third-party security service.  Clients are usually remote and
   diverse, and use connections that have crossed several other domains
   (with or without tunnels).

   Enforcement functions typically require some form of client
   authentication such as username, password, or certificate.
   Authentication is enforced at the earliest stage of communication.

   Enforcement rules might require access to transport characteristics
   of the ultimate endpoints (such as client source IP address).  This
   might change as traffic moves between domains, whether tunneling is
   used or not.  Therefore, it can be desirable to encapsulate original
   information in form accessible to the enforcement function.

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2.3.  Frontend Support for Load Balancing and Migration/Mobility

   Application service providers aiming to improve access flexibility
   might use proxies in front of their services.

   In one usage scenario the client communicates with a reverse proxy
   that assists with access to and selection of the content requested.
   This proxy that may or may not be under the authority of the service
   provider.  Today such reverse proxies terminate the connection,
   including the security association, and as such appear as the
   communication endpoint to the client.  Terminating both transport and
   security may be problematic if the proxy provider is not under the
   direct authority of the actual service provider (e.g. a contracted
   third party).

   In another usage scenario the client communicates with a frontend
   proxy that manages traffic steering to assist with load balancing or
   migration for mobility support of server or client.  This proxy is
   more likely to be located close to the server and under the same
   administrative domain, or at least has some trust relationship with
   the application service provider.  The server may have its own
   communication channel with the proxy or tunnel endpoint in order to
   provide data that is used for decision making.  Meanwhile, the client
   is usually not aware of any specifics of the setup behind the
   substrate endpoint.  However, improving visibility may benefit future
   explicit tunneling or proxying approaches.

2.4.  IoT Gateways

   A number of IoT devices are connected via a low-power wireless
   network (e.g., a Bluetooth LE piconet) and need to talk to their
   parent cloud service to provide sensor readings or receive firmware

   When end-to-end IP connectivity is not possible or desirable for at
   least some of the devices, one or more IP capable nodes in the
   piconet can be designated as ad-hoc gateways to forward sensor
   traffic to the cloud and vice-versa.  In other scenarios, a less
   constrained node - sometimes called a "smart gateway" - can provide
   the forwarding role permanently.  In both cases, the gateway node
   routes messages based on client's session identifiers, which need to
   be unique among all the active participants so that the gateway can
   route unambiguously.  The access network attachment is expected to
   change over time but the end-to-end communication (especially the
   security association) needs to persist for as long as possible.

   A strong requirement for these deployments is privacy: data on the
   public Internet (i.e., from the gateway to the cloud service) needs

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   to be made as opaque as possible to passive observers, possibly
   hiding the natural traffic patterns associated with the sensor
   network.  A mechanism to provide discovery of the proxy node to the
   rest of the piconet is also typically necessary.

   Today, the above requirements can be met by composing an end-to-end
   secure channel (e.g., based on DTLS sessions with client-chosen
   connection IDs [I-D.ietf-tls-dtls-connection-id] or application layer
   TLS [I-D.friel-tls-atls] from the sensors to the cloud together with
   a multiplexed secure tunnel (e.g., using HTTP/2 WebSockets [RFC8441],
   or a proprietary shim) from the gateway to the cloud.  In the future,
   a more homogeneous solution could be provided by QUIC for both the
   end-to-end and tunneling services, thus simplifying code dependencies
   on the gateway nodes.

2.5.  Multi-hop Chaining Usage

   Providing a generic approach to use QUIC as a substrate also enables
   the combination of multiple of the above use cases.  For example,
   employing multiple obfuscating proxies in sequence, where the
   communication with each proxy is individually secured, can enable
   onion-like layered security.  Each proxy will only know the address
   of the prior hop and after itself, similar as provided by onion
   routing in Tor project [TOR].

   Further, it would also be possible to chain proxies for different
   reasons.  A client may select proxying support from its access
   network, while a web service provider may utilize a front-end load
   balancing proxy to provide end-to-end secure communication with the
   applications components servers.  Here the proxy and the load
   balancer have different tasks.  The access network proxy optimizes
   the aggregated data transport.  The load balancer needs to route
   different set of end-to-end protected data that it aggregates.  A
   third example would be multiple proxies to cooperate and maybe
   exchange measurement information in order to optimize the QUIC
   connection over a specific segment.

   The above examples indicates that a solution likely have to consider
   how to establish a security model so that endpoints can selectively
   choose what connection related information to share with the
   different proxy entities.  The possible efficiency should also be
   consider and multiple layers of encapsulation should be avoided when
   the security model allows for it.

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2.5.1.  Considerations for Multiple Encryption

   Using QUIC in a multi-hop fashion will generally cause all user data
   to be encrypted multiple times, once for each hop.  There are two
   main reasons to encrypt data multiple times in a multi-hop network:

   1.  To ensure that no hop can see both the connection metadata of the
       client and the server (thus obfuscating IP addresses and other
       related data that is visible in cleartext in the transport
       protocol headers).

   2.  To prevent an attacker from being able to correlate data between
       different hops to identify a particular flow of data as it passes
       through multiple hops.

   However, multiple layers of encryption can have a noticeable impact
   on the end-to-end latency of data.  When a Tor-like approach is used,
   each piece of user data will be encrypted N times, where N is the
   number of hops.  Devices such as IoT devices that may not have
   support for cryptographic optimizations, or are constrained in terms
   of processing or power usage, could be significantly slowed down due
   to the extra overhead or not be able to process such traffic at all.

   Since QUIC is an encrypted transport, the content of all packets
   after the handshake is opaque to any attacker.  Short-header packets,
   particularly those that have zero-length Connection IDs, only send
   encrypted fields.  Thus, for all packets beyond the QUIC handshake,
   encrypting packets multiple times through a multi-hop proxy primarily
   achieves benefit 2) described above, since benefit 1) is already
   achieved by QUIC being forwarded without re-encryption.  If a
   deployment is more concerned with benefit 1) than benefit 2), it
   might be preferable to use a solution that forwards QUIC packets
   without re-encrypting once QUIC handshakes are complete.

3.  Requirements

   To use QUIC as a substrate, it could be beneficial if unreliable
   transmission is supported as well as having a way to potentially
   influence or disable congestion control if the inner tunnel traffic
   is known to be congestion controlled.

   Communication between the client and proxy is more likely to be
   realized as a separate protocol on top of QUIC or HTTP as e.g.
   proposed by MASQUE.  However, a QUIC extensibility mechanism could be
   used to indicate to the receiver that QUIC is used as a substrate and
   potentially additional information about which protocol is used for
   communication between these entities.  A similar mechanism could be
   realized in HTTP instead.  In both cases it is important that the

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   QUIC connection cannot be identified as a substrate by an observer on
   the path.

   With QUIC, the use of proxying functions cannot be done
   transparently.  Instead, proxies needs to be explicitly discoverable.
   The simplest form of such discovery could include pre-configuration
   or via out-of-band signaling.  The proxy could also be discovered
   through advertisement when a client is connected to a network (for
   example, the Dynamic Host Configuration Protocol).  Alternatively,
   the client could obtain a white-listed proxy address when making
   first contact with the server (CNAME/IPaddress).  In both cases the
   proxy needs to have a routable address and name.

4.  Review of Existing Approaches

   As already mentioned, HTTP proxies are usually realized by use of the
   HTTP CONNECT method (see Section 4.3.6 of [RFC7231]).  This is
   commonly used to establish a tunnelled TLS session over a TCP
   connection to an origin server identified by a request-target.  In
   HTTP/1.1, the entire client-to-proxy HTTP connection is converted
   into a tunnel.  In HTTP/2 (see Section 8.3 of [RFC7540]) and HTTP/3
   (see Section 4.2 of [I-D.ietf-quic-http]), a single stream gets
   dedicated to a tunnel.  Conventional HTTP CONNECT is only specified
   to open a TCP connection between proxy and server, even in HTTP/3, so
   it enables forwarding based on a split TCP-TCP or QUIC-TCP connection
   but unaltered payload traffic.  There is no currently-specified HTTP
   mechanism to instruct a proxy to create a UDP or IP association to
   the server.  [HINT] contains a deeper analysis of the problem space
   and potential solutions.  Of those explored, a good candidate for
   MASQUE is the Extended CONNECT method [RFC8441], accepts a
   ":protocol" pseudo-header that could be used to express an
   alternative protocol between proxy and server.

   An explicit proxy control protocol is the SOCKS protocol [RFC1928].
   Version 6 is currently under standardization
   [I-D.olteanu-intarea-socks-6] which provides fast connection
   establishment.  Use of QUIC could even further improve that.
   However, SOCKS provides support to establish forwarding sockets using
   a new connection (with a different port).  This behavior is visible
   to the path and not necessary if the underlying transport is
   multiplexing capable, as QUIC is.  A SOCKS-like protocol could still
   be used for negotiation and authentication between the client and the
   proxy.  An example proposal for this approach is

   In that sense the TCP PROXY protocol could also be seen as a light-
   weight version of SOCKS (see  This

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   protocol was never standardized and only provides a limited set of

5.  Contributors

   Magnus Westerlund has contributed two paragraphs on combining

   Tommy Pauly has contributed text on multiple layers of encryption,
   and other edits to the use cases.

6.  References

6.1.  Normative References

              Schinazi, D., "The MASQUE Protocol", Work in Progress,
              Internet-Draft, draft-schinazi-masque-02, 8 January 2020,

6.2.  Informative References

   [HINT]     Pardue, L., "HTTP-initiated Network Tunnelling (HiNT)",
              Work in Progress, Internet-Draft, draft-pardue-httpbis-
              http-network-tunnelling-01, 18 October 2018,

              Friel, O., Barnes, R., Pritikin, M., Tschofenig, H., and
              M. Baugher, "Application-Layer TLS", Work in Progress,
              Internet-Draft, draft-friel-tls-atls-04, 4 November 2019,

              Bishop, M., "Hypertext Transfer Protocol Version 3
              (HTTP/3)", Work in Progress, Internet-Draft, draft-ietf-
              quic-http-27, 21 February 2020, <

              Rescorla, E., Tschofenig, H., and T. Fossati, "Connection
              Identifiers for DTLS 1.2", Work in Progress, Internet-
              Draft, draft-ietf-tls-dtls-connection-id-07, 21 October
              2019, <

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              Olteanu, V. and D. Niculescu, "SOCKS Protocol Version 6",
              Work in Progress, Internet-Draft, draft-olteanu-intarea-
              socks-6-08, 4 November 2019, <

              Piraux, M. and O. Bonaventure, "Tunneling Internet
              protocols inside QUIC", Work in Progress, Internet-Draft,
              draft-piraux-quic-tunnel-00, 4 November 2019,

              Schinazi, D., "HTTP Transport Authentication", Work in
              Progress, Internet-Draft, draft-schinazi-httpbis-
              transport-auth-01, 8 January 2020, <

   [RFC1928]  Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D., and
              L. Jones, "SOCKS Protocol Version 5", RFC 1928,
              DOI 10.17487/RFC1928, March 1996,

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,

   [RFC8441]  McManus, P., "Bootstrapping WebSockets with HTTP/2",
              RFC 8441, DOI 10.17487/RFC8441, September 2018,

   [TOR]      "TOR Project", 5 June 2019, <>.

Authors' Addresses

   Mirja Kuehlewind


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   Zaheduzzaman Sarker


   Thomas Fossati


   Lucas Pardue


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