Network Working Group                                          J. Uberti
Internet-Draft                                                  G. Shieh
Intended status: Standards Track                                  Google
Expires: July 18, 2017                                  January 14, 2017

                WebRTC IP Address Handling Requirements


   This document provides information and requirements for how IP
   addresses should be handled by WebRTC applications.

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
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   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 July 18, 2017.

Copyright Notice

   Copyright (c) 2017 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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Uberti & Shieh            Expires July 18, 2017                 [Page 1]

Internet-Draft             WebRTC IP Handling               January 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Detailed Design . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Application Guidance  . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  Informative References  . . . . . . . . . . . . . . . . . . .   6
   Appendix A.  Change log . . . . . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   As a technology that supports peer-to-peer connections, WebRTC may
   send data over different network paths than the path used for HTTP
   traffic.  This may allow a web application to learn additional
   information about the user, which may be problematic in certain
   cases.  This document summarizes the concerns, and makes
   recommendations on how best to handle the tradeoff between privacy
   and media performance.

2.  Problem Statement

   WebRTC enables real-time peer-to-peer communications by enumerating
   network interfaces and discovering the best route through the ICE
   [RFC5245]protocol.  During the ICE process, the peers involved in a
   session gather and exchange all the IP addresses they can discover,
   so that the connectivity of each IP pair can be checked, and the best
   path chosen.  The addresses that are gathered usually consist of an
   endpoint's private physical/virtual addresses, and its public
   Internet addresses.

   These addresses are exposed upwards to the web application, so that
   they can be communicated to the remote endpoint.  This allows the
   application to learn more about the local network configuration than
   it would from a typical HTTP scenario, in which the web server would
   only see a single public Internet address, i.e. the address from
   which the HTTP request was sent.

   The information revealed falls into three categories:

   1.  If the client is behind a NAT, the client's private IP addresses,
       typically [RFC1918]addresses, can be learned.

Uberti & Shieh            Expires July 18, 2017                 [Page 2]

Internet-Draft             WebRTC IP Handling               January 2017

   2.  If the client tries to hide its physical location through a VPN,
       and the VPN and local OS support routing over multiple interfaces
       (i.e., a "split-tunnel" VPN), WebRTC will discover the public
       address for the VPN as well as the ISP public address that the
       VPN runs over.

   3.  If the client is behind a proxy (a client-configured "classical
       application proxy", as defined in [RFC1919], Section 3), but
       direct access to the Internet is also supported, WebRTC's STUN
       [RFC5389]checks will bypass the proxy and reveal the public
       address of the client.

   Of these three concerns, #2 is the most significant concern, since
   for some users, the purpose of using a VPN is for anonymity.
   However, different VPN users will have different needs, and some VPN
   users (e.g.  corporate VPN users) may in fact prefer WebRTC to send
   media traffic directly, i.e., not through the VPN.

   #3 is a less common concern, as proxy administrators can control this
   behavior through organization firewall policy if desired, coupled
   with the fact that forcing WebRTC traffic through a proxy will have
   negative effects on both the proxy and on media quality.  For
   situations where this is an important consideration, use of a RETURN
   proxy, as described below, can be an effective solution.

   #1 is considered to be the least significant concern, given that the
   local address values often contain minimal information (e.g., or have built-in privacy protection (e.g.
   [RFC4941]IPv6 addresses).

   Note also that these concerns predate WebRTC; Adobe Flash Player has
   provided similar functionality since the introduction of RTMFP
   [RFC7016]in 2008.

3.  Goals

   Being peer-to-peer, WebRTC represents a privacy-enabling technology,
   and therefore we want to avoid solutions that disable WebRTC or make
   it harder to use.  This means that WebRTC should be configured by
   default to only reveal the minimum amount of information needed to
   establish a performant WebRTC session, while providing options to
   reveal additional information upon user consent, or further limit
   this information if the user has specifically requested this.
   Specifically, WebRTC should:

   o  Provide a privacy-friendly default behavior which strikes the
      right balance between privacy and media performance for most users
      and use cases.

Uberti & Shieh            Expires July 18, 2017                 [Page 3]

Internet-Draft             WebRTC IP Handling               January 2017

   o  For users who care more about one versus the other, provide a
      means to customize the experience.

4.  Detailed Design

   The key principles for the design are listed below:

   1.  By default, WebRTC should follow normal IP routing rules, to the
       extent that this is easy to determine (i.e., not considering
       proxies).  This can be accomplished by binding local sockets to
       the wildcard addresses ( for IPv4, :: for IPv6), which
       allows the OS to route WebRTC traffic the same way as it would
       HTTP traffic, and allows only the 'typical' public addresses to
       be discovered.

   2.  By default, support for direct connections between hosts (i.e.,
       without traversing a NAT or relay server) should be maintained.
       To accomplish this, the local IPv4 and IPv6 addresses of the
       interface used for outgoing STUN traffic should still be surfaced
       as candidates, even when binding to the wildcard addresses as
       mentioned above.  The appropriate addresses here can be
       discovered by the common trick of binding sockets to the wildcard
       addresses, connect()ing those sockets to some well-known public
       IP address (one particular example being ""), and then
       reading the bound local addresses via getsockname().  This
       approach requires no data exchange; it simply provides a
       mechanism for applications to retrieve the desired information
       from the kernel routing table.

   3.  Determining whether a web proxy is in use is a complex process,
       as the answer can depend on the exact site or address being
       contacted.  Furthermore, web proxies that support UDP are not
       widely deployed today.  As a result, when WebRTC is made to go
       through a proxy, it typically needs to use TCP, either ICE-TCP
       [RFC6544]or TURN-over-TCP [RFC5766].  Naturally, this has
       attendant costs on media quality as well as proxy performance,
       and should be avoided where possible.

   4.  RETURN [I-D.ietf-rtcweb-return]is a proposal for explicit
       proxying of WebRTC media traffic.  When RETURN proxies are
       deployed, media and STUN checks will go through the proxy, but
       without the performance issues associated with sending through a
       typical web proxy.

   Based on these ideas, we define four specific modes of WebRTC
   behavior, reflecting different media quality/privacy tradeoffs:

Uberti & Shieh            Expires July 18, 2017                 [Page 4]

Internet-Draft             WebRTC IP Handling               January 2017

   Mode 1:  Enumerate all addresses: WebRTC MUST bind to all interfaces
            individually and use them all to attempt communication with
            STUN servers, TURN servers, or peers.  This will converge on
            the best media path, and is ideal when media performance is
            the highest priority, but it discloses the most information.

   Mode 2:  Default route + associated local addresses: WebRTC MUST
            follow the kernel routing table rules (e.g., by binding
            solely to the wildcard address), which will typically cause
            media packets to take the same route as the application's
            HTTP traffic.  In addition, any private IPv4 and IPv6
            addresses associated with the kernel-chosen interface MUST
            be discovered through getsockname, as mentioned above, and
            provided to the application.  This ensures that direct
            connections can still be established in this mode.

   Mode 3:  Default route only: This is the the same as Mode 2, except
            that the associated private address MUST NOT be provided.
            This may cause traffic to hairpin through a NAT, fall back
            to the application TURN server, or fail altogether, with
            resulting quality implications.

   Mode 4:  Force proxy: This forces all WebRTC media traffic through a
            proxy, if one is configured.  If the proxy does not support
            UDP (as is the case for all HTTP and most SOCKS
            [RFC1928]proxies), or the WebRTC implementation does not
            support UDP proxying, the use of UDP will be disabled, and
            TCP will be used to send and receive media through the
            proxy.  Use of TCP will result in reduced quality, in
            addition to any performance considerations associated with
            sending all WebRTC media through the proxy server.

   Mode 1 MUST only be used when user consent has been provided; this
   thwarts the typical drive-by enumeration attacks.  The details of
   this consent are left to the implementation; one potential mechanism
   is to tie this consent to getUserMedia consent.

   In cases where user consent has not been obtained, Mode 2 SHOULD be
   used.  This allows applications to still achieve direct connections
   in many cases, even without consent (e.g., data channel
   applications).  However, user agents MAY choose a stricter default
   policy in certain circumstances.

   Note that when a RETURN proxy is configured for the interface
   associated with the default route, Mode 2 and 3 will cause any
   external media traffic to go through the RETURN proxy.  While the
   RETURN approach gives the best performance, a similar result can be
   achieved for non-RETURN proxies via an organization firewall policy

Uberti & Shieh            Expires July 18, 2017                 [Page 5]

Internet-Draft             WebRTC IP Handling               January 2017

   that only allows external WebRTC traffic to leave through the proxy
   (typically, over TCP).  This provides a way to ensure the proxy is
   used for any external traffic, but avoids the performance issues of
   Mode 4, where all media is forced through said proxy, for intra-
   organization traffic.

5.  Application Guidance

   The recommendations mentioned in this document may cause certain
   WebRTC applications to malfunction.  In order to be robust in all
   scenarios, the following guidelines are provided for applications:

   o  Applications SHOULD deploy a TURN server with support for both UDP
      and TCP connections to the server.  This ensures that connectivity
      can still be established, even when Mode 3 or 4 are in use,
      assuming the TURN server can be reached.

   o  Applications SHOULD detect when they don't have access to the full
      set of ICE candidates by checking for the presence of host
      candidates.  If no host candidates are present, Mode 3 or 4 above
      is in use; this knowledge can be useful for diagnostic purposes.

   o  Future versions of browsers may present an indicator to signify
      that the page is using WebRTC to set up a peer-to-peer connection.
      Applications MUST only use WebRTC in a fashion that is consistent
      with user expectations.

6.  Security Considerations

   This document is entirely devoted to security considerations.

7.  IANA Considerations

   This document requires no actions from IANA.

8.  Acknowledgements

   Several people provided input into this document, including Harald
   Alvestrand, Ted Hardie, Matthew Kaufmann, Eric Rescorla, Adam Roach,
   and Martin Thomson.

9.  Informative References

              Schwartz, B. and J. Uberti, "Recursively Encapsulated TURN
              (RETURN) for Connectivity and Privacy in WebRTC", draft-
              ietf-rtcweb-return-01 (work in progress), January 2016.

Uberti & Shieh            Expires July 18, 2017                 [Page 6]

Internet-Draft             WebRTC IP Handling               January 2017

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,

   [RFC1919]  Chatel, M., "Classical versus Transparent IP Proxies",
              RFC 1919, DOI 10.17487/RFC1919, March 1996,

   [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,

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              DOI 10.17487/RFC5245, April 2010,

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              DOI 10.17487/RFC5389, October 2008,

   [RFC5766]  Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
              Relays around NAT (TURN): Relay Extensions to Session
              Traversal Utilities for NAT (STUN)", RFC 5766,
              DOI 10.17487/RFC5766, April 2010,

   [RFC6544]  Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach,
              "TCP Candidates with Interactive Connectivity
              Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544,
              March 2012, <>.

   [RFC7016]  Thornburgh, M., "Adobe's Secure Real-Time Media Flow
              Protocol", RFC 7016, DOI 10.17487/RFC7016, November 2013,

Uberti & Shieh            Expires July 18, 2017                 [Page 7]

Internet-Draft             WebRTC IP Handling               January 2017

Appendix A.  Change log

   Changes in draft -03:

   o  Clarified when to use which modes.

   o  Use 2119 qualifiers to make normative statements.

   o  Defined 'proxy'.

   o  Mentioned split tunnels in problem statement.

   Changes in draft -02:

   o  Recommendations -> Requirements

   o  Updated text regarding consent.

   Changes in draft -01:

   o  Incorporated feedback from Adam Roach; changes to discussion of
      cam/mic permission, as well as use of proxies, and various
      editorial changes.

   o  Added several more references.

   Changes in draft -00:

   o  Published as WG draft.

Authors' Addresses

   Justin Uberti
   747 6th St S
   Kirkland, WA  98033


   Guo-wei Shieh
   747 6th St S
   Kirkland, WA  98033


Uberti & Shieh            Expires July 18, 2017                 [Page 8]