One document matched: draft-hutton-rtcweb-nat-firewall-considerations-01.xml
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<rfc category="info" docName="draft-hutton-rtcweb-nat-firewall-considerations-01" ipr="trust200902">
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you can add the attributes updates="NNNN" and obsoletes="NNNN"
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<!-- ***** FRONT MATTER ***** -->
<front>
<title abbrev="RTCWEB NAT-FW">RTCWEB Considerations for NATs, Firewalls and HTTP proxies </title>
<author fullname="Thomas Stach" initials="T." role="editor"
surname="Stach">
<organization>Siemens Enterprise Communications</organization>
<address>
<postal>
<street>Dietrichgasse 27-29</street>
<city>Vienna</city>
<region></region>
<code>1030</code>
<country>AT</country>
</postal>
<email>thomas.stach@siemens-enterprise.com</email>
</address>
</author>
<author fullname="Andrew Hutton" initials="A."
surname="Hutton">
<organization>Siemens Enterprise Communications</organization>
<address>
<postal>
<street>Technology Drive</street>
<city>Nottingham</city>
<region></region>
<code>NG9 1LA</code>
<country>UK</country>
</postal>
<email>andrew.hutton@siemens-enterprise.com</email>
</address>
</author>
<author fullname="Justin Uberti" initials="J."
surname="Uberti">
<organization>Google</organization>
<address>
<postal>
<street>747 6th Ave S</street>
<city>Kirkland</city>
<region>WA</region>
<code>98033</code>
<country>US</country>
</postal>
<email>justin@uberti.name</email>
</address>
</author>
<date year="2013" />
<!-- Meta-data Declarations -->
<area>General</area>
<workgroup>Internet Engineering Task Force</workgroup>
<keyword>RTCWEB, NAT, Firewall, HTTP proxy</keyword>
<abstract>
<t>
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.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
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 <xref target="RFC5245"></xref> 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
<xref target="RFC4787"></xref>,
the peers will introduce a TURN server
<xref target="RFC5766"></xref>
in the public internet as a media relay.
Some use cases and requirements relating to RTCWEB NAT/FW traversal can be found in
<xref target="draft-ietf-rtcweb-use-cases-and-requirements"></xref>.
</t>
<t>
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.
</t>
<t>
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
<xref target="RFC3550"></xref>.
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.
</t>
<t>
This document examines impact of NAT/FW policies in
<xref target="pure_FW"></xref>.
Additional impacts due to the presence of a HTTP proxy are examined in
<xref target="proxy_FW"></xref>.
</t>
<section title="Requirements Language">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
</section>
</section>
<section anchor="pure_FW" title="Considerations for NATs/Firewalls independent of HTTP proxies">
<t>
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 <xref target="proxy_FW"/>.
</t>
<t>
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.
</t>
<t>
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.
</t>
<section anchor="pure_FW_tcp_udp" title="NAT/Firewall open for outgoing UDP and TCP traffic">
<t>
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.
</t>
<t>
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.
</t>
<t>
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.
</t>
</section>
<section anchor="pure_FW_tcp" title="NAT/Firewall open only for TCP traffic">
<t>
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.
</t>
<t>
In the first case the browser needs to use ICE-TCP <xref target="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.
</t>
<t>
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.
</t>
<t>
Note that the second case is not to be mixed up with TURN/TCP <xref target="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.
</t>
</section>
<section anchor="pure_FW_http" title="NAT/Firewall open only for TCP-based HTTP(s) traffic">
<t>
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.
</t>
<t>
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.
</t>
</section>
</section>
<section anchor="proxy_FW" title="Considerations for NATs/Firewalls in presence of HTTP proxies">
<t>
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.
</t>
<section anchor="proxy_FW_tcp_udp" title="HTTP proxy with NAT/Firewall open for
outgoing UDP and TCP traffic">
<t>
As in
<xref target="pure_FW_tcp_udp"/>
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
<xref target="pure_FW_tcp_udp"/>
apply with respect to the traversal of the NAT/FW.
</t>
</section>
<section anchor="proxy_FW_tcp" title="HTTP proxy with NAT/Firewall open only for TCP traffic">
<t>
As in
<xref target="pure_FW_tcp"/>
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
<xref target="pure_FW_tcp"/>
apply with respect to the traversal of the NAT/FW.
</t>
</section>
<section anchor="proxy_relay" title="HTTP proxy assisted TURN server connection">
<section anchor="proxy_relay_turn" title="TURN server connection via TCP">
<t>
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
<xref target="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.
</t>
<t>
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 <xref target="RFC2817"/>
as this would require the TURN server to support HTTP.
We rather envisage the following sequence:
</t>
<t><list style="symbols">
<t>the browser opens a TCP connection to the HTTP proxy,
</t>
<t>the browser issues a HTTP CONNECT request to the HTTP proxy with
the TURN server address in the Request URI,
</t>
<t>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,
</t>
<t>the browser can do a TLS handshake over the virtual end-to-end TCP connection
with the TURN server.
</t>
</list> </t>
<t>
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.
</t>
<t>
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.
</t>
<t>
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.
</t>
<t>
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
<xref target="RFC5766"></xref> 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.
</t>
</section>
<section anchor="proxy_relay_tcp" title="TURN server connection via UDP">
<t>
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.
</t>
</section>
</section>
</section>
<section anchor="Alternatives" title="Other Approaches">
<section anchor="proxy_relay_ws" title="TURN server connection via WebSocket">
<t>
The RTCWEB client could connect to a TURN server via WebSocket
<xref target="RFC6455"></xref>
as described in
<xref target="draft-chenxin-behave-turn-WebSocket"></xref>.
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.
</t>
<t>
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.
</t>
</section>
<section anchor="PCP" title="Port Control Protocol">
<t>
As a further alternative,
the Port Control Protocol (PCP)
<xref target="RFC6887"></xref>
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.
</t>
</section>
<section anchor="RTPoverHTTP" title="HTTP Fallback for RTP Media Streams">
<t>
As an alternative to using a TURN server it was proposed to send RTP directly over HTTP
<xref target="draft-miniero-rtcweb-http-fallback"></xref>.
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.
</t>
<t>
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.
</t>
</section>
</section>
<section anchor="Requirements" title="Requirements for RTCWEB-enabled browsers">
<t>
For the purpose of relaying RTCWEB media streams or data channels a browser needs to be able to
</t>
<t><list style="symbols">
<t>
connect to a TURN server via UDP, TCP and TLS,
</t>
<t>
connect to a TURN server via a HTTP proxy using the HTTP connect method,
</t>
<t>
connect to a TURN server via the HTTP(s) ports 80/443 instead of the default STUN ports 3478/5349,
</t>
<t>
upgrade the HTTP proxy-relayed connection to the TURN server to use TLS,
</t>
<t>
use the same proxy selection procedure for TURN as currently done for HTTP,
</t>
<t>
switch the usage of the HTTP proxy-relayed connection with the TURN server from
HTTP to STUN/TURN,
</t>
<t>
use a preconfigured or standardized port range for UDP-based media streams or data channels,
</t>
<t>
learn from the proxy configuration script about the presence of a local TURN server and
use it for sending UDP traffic to the internet,
</t>
<t>
support ICE-TCP for TCP-based direct media connection to the RTCWEB peer.
</t>
</list></t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>
The authors want to thank Heinrich Haager for all his input during many valuable discussions.
</t>
<t>
Furthermore, the authors want to thank for comments and suggestions received from
...
<!-- Harald Alvestrand,
Cameron Byrne,
Gustavo Garcia,
Markus Isomaki,
Hadriel Kaplan,
Reinaldo Penno,
Roy Radhika,
Uwe Rauschenbach and Tirumaleswar Reddy.-->
</t>
</section>
<!-- Possibly a 'Contributors' section ... -->
<section anchor="IANA" title="IANA Considerations">
<t>This memo includes no request to IANA.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>
TBD
</t>
</section>
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<!-- References split into informative and normative -->
<references title="Normative References">
<!--?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?-->
&RFC2119;
</references>
<references title="Informative References">
<!-- Here we use entities that we defined at the beginning. -->
&RFC2616;
&RFC2817;
&RFC3550;
&RFC4787;
&RFC5245;
&RFC5766;
&RFC6062;
&RFC6455;
&RFC6544;
&RFC6887;
<!-- A reference written by an organization not a person. -->
<reference anchor="draft-ietf-rtcweb-use-cases-and-requirements"
target="http://tools.ietf.org/html/draft-ietf-rtcweb-use-cases-and-requirements">
<front>
<title>
Web Real-Time Communication Use-cases and Requirements
</title>
<author>
<organization>
C. Holmberg, S. Hakansson, G. Eriksson
</organization>
</author>
<date year="2012" />
</front>
</reference>
<reference anchor="draft-chenxin-behave-turn-WebSocket"
target="http://tools.ietf.org/html/draft-chenxin-behave-turn-WebSocket">
<front>
<title>
Traversal Using Relays around NAT (TURN) Extensions for WebSocket Allocations
</title>
<author>
<organization>
Xin. Chen
</organization>
</author>
<date year="2013" />
</front>
</reference>
<reference anchor="draft-miniero-rtcweb-http-fallback"
target="http://tools.ietf.org/html/draft-miniero-rtcweb-http-fallback">
<front>
<title>
HTTP Fallback for RTP Media Streams
</title>
<author>
<organization>
L. Miniero
</organization>
</author>
<date year="2012" />
</front>
</reference>
</references>
<!--
<section anchor="app-additional" title="Additional Stuff">
<t>This becomes an Appendix.</t>
</section>
Change Log
-->
</back>
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