[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03

Internet Engineering Task Force                            T. Stach, Ed.
Internet-Draft                                                 A. Hutton
Intended status: Informational         Siemens Enterprise Communications
Expires: December 29, 2013                                     J. Uberti
                                                                  Google
                                                           June 27, 2013


       RTCWEB Considerations for NATs, Firewalls and HTTP proxies
           draft-hutton-rtcweb-nat-firewall-considerations-01

Abstract

   This document describes mechanism to enable media stream
   establishment for Real-Time Communication in WEB-browsers (RTCWEB) in
   the presence of network address translators, firewalls and HTTP
   proxies.  HTTP proxy and firewall policies applied in many private
   network domains introduce obstacles to the successful establishment
   of media stream via RTCWEB.  This document examines some of these
   policies and develops requirements on the web browsers designed to
   provide the best possible chance of media connectivity between RTCWEB
   peers.

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 http://datatracker.ietf.org/drafts/current/.

   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 December 29, 2013.

Copyright Notice

   Copyright (c) 2013 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
   (http://trustee.ietf.org/license-info) in effect on the date of



Stach, et al.           Expires December 29, 2013               [Page 1]


Internet-Draft                RTCWEB NAT-FW                    June 2013


   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Considerations for NATs/Firewalls independent of HTTP proxies   3
     2.1.  NAT/Firewall open for outgoing UDP and TCP traffic  . . .   3
     2.2.  NAT/Firewall open only for TCP traffic  . . . . . . . . .   4
     2.3.  NAT/Firewall open only for TCP-based HTTP(s) traffic  . .   4
   3.  Considerations for NATs/Firewalls in presence of HTTP proxies   5
     3.1.  HTTP proxy with NAT/Firewall open for
           outgoing UDP and TCP traffic  . . . . . . . . . . . . . .   5
     3.2.  HTTP proxy with NAT/Firewall open only for TCP traffic  .   5
     3.3.  HTTP proxy assisted TURN server connection  . . . . . . .   5
       3.3.1.  TURN server connection via TCP  . . . . . . . . . . .   5
       3.3.2.  TURN server connection via UDP  . . . . . . . . . . .   7
   4.  Other Approaches  . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  TURN server connection via WebSocket  . . . . . . . . . .   7
     4.2.  Port Control Protocol . . . . . . . . . . . . . . . . . .   7
     4.3.  HTTP Fallback for RTP Media Streams . . . . . . . . . . .   7
   5.  Requirements for RTCWEB-enabled browsers  . . . . . . . . . .   8
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Many organizations, e.g. an enterprise, a public service agency or a
   university, deploy Network Address Translators (NAT) and firewalls
   (FW) at the border to the public internet.  RTCWEB relies on ICE
   [RFC5245] in order to establish a media path between two RTCWEB peers
   in the presence of such NATs/FWs.  As last resort in order to cater
   for NAT/FWs with address and port dependent filtering characteristics
   [RFC4787], the peers will introduce a TURN server [RFC5766] in the
   public internet as a media relay.  Some use cases and requirements
   relating to RTCWEB NAT/FW traversal can be found in
   [draft-ietf-rtcweb-use-cases-and-requirements].




Stach, et al.           Expires December 29, 2013               [Page 2]


Internet-Draft                RTCWEB NAT-FW                    June 2013


   If an organization wants to support RTCWEB such a TURN server may be
   located in the DMZ of the private network of that organization where
   it is still under administrative control.

   In certain environments with very restrictive FW policies a TURN
   server in the public internet may not be sufficient to establish
   connectivity towards the RTCWEB peer for RTP-based media [RFC3550].
   Such policies can include blocking of all UDP based traffic and
   allowing only HTTP(S) traffic to the TCP ports 80/443.  In addition
   access to the World Wide Web from inside an organization is often
   only possible via a HTTP proxy.

   This document examines impact of NAT/FW policies in Section 2.
   Additional impacts due to the presence of a HTTP proxy are examined
   in Section 3.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Considerations for NATs/Firewalls independent of HTTP proxies

   This section covers aspects of how NAT/FW characteristic influence
   the establishment of a media stream.  Additional aspects introduced
   by the presence of a HTTP proxy are covered in Section 3.

   If the NATs serving caller and callee both show port and address
   dependent filtering behavior the need for a TURN server arises in
   order to establish connectivity for media streams.  The TURN server
   will relay the RTP packet to the RTCWEB peer using UDP.  How the RTP
   packets can be transported from the RTCWEB client within the private
   network to the TURN server depends on what the firewall will let pass
   through.

   Other types of NATs do not require using the TURN relay.
   Nevertheless, the FW rules and policies still affect how media
   streams can be established.

2.1.  NAT/Firewall open for outgoing UDP and TCP traffic

   This scenario assumes that the NAT/FW is transparent for all outgoing
   traffic independent of using UDP or TCP as transport protocol.  This
   case is used as starting point for introduction of more restrictive
   firewall policies.  It presents the least critical example with
   respect to the establishment of the media streams.




Stach, et al.           Expires December 29, 2013               [Page 3]


Internet-Draft                RTCWEB NAT-FW                    June 2013


   The TURN server can be reached directly from within the private
   network via the NAT/FW and the ICE procedures will reveal that media
   can be sent via the TURN server.  The TURN client will send its media
   to the allocated resources at the TURN server via UDP.

   Dependent on the port range that is used for RTCWEB media streams,
   the same statement would be true if the NAT/Firewall would allow UDP
   traffic for a restricted UDP port range only.

2.2.  NAT/Firewall open only for TCP traffic

   This scenario assumes that the NAT/FW is transparent for outgoing
   traffic only using TCP as transport protocol.  This gives two options
   for media stream establishment dependent on the NAT's filtering
   characteristics.  Either transport RTP over TCP or contacting the
   TURN server via TCP.

   In the first case the browser needs to use ICE-TCP [RFC6544] and
   provide active, passive and/or simultaneous-open TCP candidates.
   Assuming the peer also provides TCP candidates, a connectivity check
   for a TCP connection between the two peers should be successful.

   In the second case the browser needs to contact the TURN server via
   TCP for allocation of an UDP-based relay address at the TURN server.
   The ICE procedures will reveal that RTP media can be sent via the
   TURN relay using the TCP connection between TURN client and TURN
   server.  The TURN server would then relay the RTP packets using UDP,
   as well as other UDP-based protocols.  ICE-TCP is not needed in this
   context.

   Note that the second case is not to be mixed up with TURN/TCP
   [RFC6062], which deals with how to establish a TCP connection to the
   peer.  For this document we assume that the TURN server can reach the
   peer always via UDP, possibly via a second TURN server.

2.3.  NAT/Firewall open only for TCP-based HTTP(s) traffic

   In this case the firewall blocks all outgoing traffic except for TCP
   traffic to port 80 for HTTP or 443 for HTTPS.  A TURN server
   listening to its default ports (3478 for TCP/UDP, 5349 for TLS) would
   not be reachable in this case.

   However, the TURN server can still be reached when it is configured
   to listen to the HTTP(S) ports as well.  In addition the RTCWEB
   clients need to be configured to contact the TURN server over the
   HTTP(S) ports and/or needs to be able to tell the browser
   accordingly.




Stach, et al.           Expires December 29, 2013               [Page 4]


Internet-Draft                RTCWEB NAT-FW                    June 2013


3.  Considerations for NATs/Firewalls in presence of HTTP proxies

   This section considers a scenario where all HTTP(S) traffic is routed
   via an HTTP proxy.  Note: If both RTCWEB clients are located behind
   the same HTTP proxies, we, of course, assume that ICE would give us a
   direct media connection within the private network.  We consider this
   case as out of the scope of this document.

3.1.  HTTP proxy with NAT/Firewall open for outgoing UDP and TCP traffic

   As in Section 2.1 we assume that the NAT/FW is transparent for all
   outgoing traffic independent of using UDP or TCP as transport
   protocol.  The HTTP proxy has no impact on the transport of media
   streams in this case.  Consequently, the same considerations as in
   Section 2.1 apply with respect to the traversal of the NAT/FW.

3.2.  HTTP proxy with NAT/Firewall open only for TCP traffic

   As in Section 2.2 we assume that the NAT/FW is transparent only for
   outgoing TCP traffic.  The HTTP proxy has no impact on the transport
   of media streams in this case.  Consequently, the same considerations
   as in Section 2.2 apply with respect to the traversal of the NAT/FW.

3.3.  HTTP proxy assisted TURN server connection

3.3.1.  TURN server connection via TCP

   Different from the previous scenarios, we assume that the NAT/FW
   accepts outgoing traffic only via a TCP connection that is initiated
   from the HTTP proxy.  Consequently, a RTCWEB client would have to use
   the HTTP CONNECT method [RFC2616] in order to get access to the TURN
   server via the HTTP proxy.  The HTTP CONNECT request needs to convey
   the TURN Server URI or transport address.  As a result the HTTP Proxy
   will establish a TCP connection to the TURN server, i.e. the TURN
   server only has to handle a standard TCP connection and an update to
   the TURN protocol or the TURN software is not needed.

   Afterwards, the RTCWEB client could upgrade the connection to use
   TLS, forward STUN/TURN traffic via the HTTP proxy and use the TURN
   server as media relay.  Note that upgrading in this case is not to be
   misunderstood as usage of the HTTP UPGRADE method as specified in
   [RFC2817] as this would require the TURN server to support HTTP.  We
   rather envisage the following sequence:

   o  the browser opens a TCP connection to the HTTP proxy,

   o  the browser issues a HTTP CONNECT request to the HTTP proxy with
      the TURN server address in the Request URI,



Stach, et al.           Expires December 29, 2013               [Page 5]


Internet-Draft                RTCWEB NAT-FW                    June 2013


   o  the HTTP proxy opens a TCP connection to the TURN server and
      "bridges" the incoming and outgoing TCP connections together,
      forming a virtual end-to-end TCP connection,

   o  the browser can do a TLS handshake over the virtual end-to-end TCP
      connection with the TURN server.

   If it is not possible to use HTTP CONNECT in this way it will not be
   possible to establish connectivity between the RTCWEB peers and the
   ICE connectivity checks will fail.

   Strictly speaking the TLS upgrade is not necessary, but using TLS
   would also prevent the HTTP proxy from sniffing into the data stream
   and provides the same flow as HTTPS and might improve
   interoperability with proxy servers.  Some tests (done a while ago)
   indicated that there are proxies performing Deep Packet inspection
   (DPI) that expect to see at least a SSL handshake and, possibly,
   valid SSL records.  The application has the ability to control
   whether SSL is used by the parameters it supplies to the TURN URI
   (e.g. turns: vs. turn:), so the decision to do TURN/TCP to port 443
   versus TURN/TLS to port 443 could be left up to the application or
   possibly the browser configuration script.

   In contrast to using UDP or TCP for transporting the STUN messages,
   the browser would now need to first establish a HTTP over TCP
   connection to the HTTP proxy, upgrade to using TLS and then switch to
   using this TLS connection for transport of STUN messages.  It is also
   desirable that the browser detects the need to connect to the TURN
   server through a HTTP proxy automatically in order to achieve
   seamless deployment and interoperability.  The browser should use the
   same proxy selection procedure for TURN as currently done for HTTP.
   The user or network administrator should not be required to change
   browser or proxy script configuration.

   Further considerations apply to the default connection timeout of the
   HTTP proxy connection to the TURN server and the timeout of the TURN
   server allocation.  Whereas [RFC5766] specifies a 10 minutes default
   lifetime of the TURN allocation, typical proxy connection lifetimes
   are in the range of 60 seconds if no activity is detected.  Thus, if
   the RTCWEB client wants to pre-allocate TURN ressources it needs to
   refresh TURN allocations more frequently in order to keep the TCP
   connection to its TURN server alive.









Stach, et al.           Expires December 29, 2013               [Page 6]


Internet-Draft                RTCWEB NAT-FW                    June 2013


3.3.2.  TURN server connection via UDP

   If a local TURN server under administrative control of the
   organization is deployed it is desirable to reach this TURN server
   via UDP.  The TURN server could be specified in the proxy
   configuration script, giving the browser the possibility to learn how
   to access it.  Then, when gathering candidates, this TURN server
   would always be used such that the RTCWEB client application could
   get UDP traffic out to the internet.

4.  Other Approaches

4.1.  TURN server connection via WebSocket

   The RTCWEB client could connect to a TURN server via WebSocket
   [RFC6455] as described in [draft-chenxin-behave-turn-WebSocket].
   This might have benefits in very restrictive environments where HTTPS
   is not permitted through the proxy.  However, such environments are
   also likely to deploy DPI boxes which would eventually complain
   against usage of WebSocket or block RTCWEB traffic based on other
   heuristic means.  It is also to be expected that an environment that
   does not allow HTTPS will also forbid usage of WebSocket over TLS.

   In addition, usage of TURN over WebSocket puts an additional burden
   on existing TURN server implementation to support HTTP and WebSocket.
   The resulting benefit seems rather small, thus TURN over WebSocket is
   left for further study.

4.2.  Port Control Protocol

   As a further alternative, the Port Control Protocol (PCP) [RFC6887]
   allows to configure how incoming IPv6 or IPv4 packets are translated
   and forwarded by a NAT/FW.  However, this document does not examine
   benefits of PCP for the management of the local NAT/FW, but leaves
   this for further study until PCP is deployed more widely.

4.3.  HTTP Fallback for RTP Media Streams

   As an alternative to using a TURN server it was proposed to send RTP
   directly over HTTP [draft-miniero-rtcweb-http-fallback].  This
   approach bears some similarities with TURN as it also uses a RTP
   relay.  However, it uses HTTP GET and POST requests to receive and
   send RTP packets.

   Despite a number of open issues, the proposal addreses some corner
   cases.  However, the expected benefit in form of an increased success
   rate for establishment of a media stream seems rather small, thus
   HTTP fallback is left for further study.



Stach, et al.           Expires December 29, 2013               [Page 7]


Internet-Draft                RTCWEB NAT-FW                    June 2013


5.  Requirements for RTCWEB-enabled browsers

   For the purpose of relaying RTCWEB media streams or data channels a
   browser needs to be able to

   o  connect to a TURN server via UDP, TCP and TLS,

   o  connect to a TURN server via a HTTP proxy using the HTTP connect
      method,

   o  connect to a TURN server via the HTTP(s) ports 80/443 instead of
      the default STUN ports 3478/5349,

   o  upgrade the HTTP proxy-relayed connection to the TURN server to
      use TLS,

   o  use the same proxy selection procedure for TURN as currently done
      for HTTP,

   o  switch the usage of the HTTP proxy-relayed connection with the
      TURN server from HTTP to STUN/TURN,

   o  use a preconfigured or standardized port range for UDP-based media
      streams or data channels,

   o  learn from the proxy configuration script about the presence of a
      local TURN server and use it for sending UDP traffic to the
      internet,

   o  support ICE-TCP for TCP-based direct media connection to the
      RTCWEB peer.

6.  Acknowledgements

   The authors want to thank Heinrich Haager for all his input during
   many valuable discussions.

   Furthermore, the authors want to thank for comments and suggestions
   received from ...

7.  IANA Considerations

   This memo includes no request to IANA.

8.  Security Considerations

   TBD




Stach, et al.           Expires December 29, 2013               [Page 8]


Internet-Draft                RTCWEB NAT-FW                    June 2013


9.  References

9.1.  Normative References

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

9.2.  Informative References

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC2817]  Khare, R. and S. Lawrence, "Upgrading to TLS Within HTTP/
              1.1", RFC 2817, May 2000.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC4787]  Audet, F. and C. Jennings, "Network Address Translation
              (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
              RFC 4787, January 2007.

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

   [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, April 2010.

   [RFC6062]  Perreault, S. and J. Rosenberg, "Traversal Using Relays
              around NAT (TURN) Extensions for TCP Allocations", RFC
              6062, November 2010.

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol", RFC
              6455, December 2011.

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

   [RFC6887]  Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)", RFC 6887, April
              2013.




Stach, et al.           Expires December 29, 2013               [Page 9]


Internet-Draft                RTCWEB NAT-FW                    June 2013


   [draft-chenxin-behave-turn-WebSocket]
              Xin. Chen , "Traversal Using Relays around NAT (TURN)
              Extensions for WebSocket Allocations ", 2013, <http://
              tools.ietf.org/html/draft-chenxin-behave-turn-WebSocket>.

   [draft-ietf-rtcweb-use-cases-and-requirements]
              C. Holmberg, S. Hakansson, G. Eriksson , "Web Real-Time
              Communication Use-cases and Requirements ", 2012, <http://
              tools.ietf.org/html/draft-ietf-rtcweb-use-cases-and-
              requirements>.

   [draft-miniero-rtcweb-http-fallback]
              L. Miniero , "HTTP Fallback for RTP Media Streams ", 2012,
              <http://tools.ietf.org/html/draft-miniero-rtcweb-http-
              fallback>.

Authors' Addresses

   Thomas Stach (editor)
   Siemens Enterprise Communications
   Dietrichgasse 27-29
   Vienna  1030
   AT

   Email: thomas.stach@siemens-enterprise.com


   Andrew Hutton
   Siemens Enterprise Communications
   Technology Drive
   Nottingham  NG9 1LA
   UK

   Email: andrew.hutton@siemens-enterprise.com


   Justin Uberti
   Google
   747 6th Ave S
   Kirkland, WA  98033
   US

   Email: justin@uberti.name








Stach, et al.           Expires December 29, 2013              [Page 10]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/