One document matched: draft-ietf-behave-turn-tcp-03.xml
<?xml version="1.0"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc compact='yes'?>
<?rfc subcompact='no'?>
<?rfc symrefs='yes'?>
<rfc category="std" ipr="trust200902" docName="draft-ietf-behave-turn-tcp-03.txt">
<front>
<title abbrev="TURN TCP">
Traversal Using Relays around NAT (TURN) Extensions for TCP Allocations </title>
<author initials="S." surname="Perreault" fullname="Simon Perreault" role="editor">
<organization>Viagénie</organization>
<address>
<postal>
<street>2600 boul. Laurier, suite 625</street>
<city>Québec</city>
<region>QC</region>
<code>G1V 4W1</code>
<country>Canada</country>
</postal>
<phone>+1 418 656 9254</phone>
<email>simon.perreault@viagenie.ca</email>
<uri>http://www.viagenie.ca</uri>
</address>
</author>
<author initials="J.R." surname="Rosenberg"
fullname="Jonathan Rosenberg">
<organization>Cisco Systems</organization>
<address>
<postal>
<street>600 Lanidex Plaza</street>
<city>Parsippany</city> <region>NJ</region>
<code>07054</code>
<country>US</country>
</postal>
<phone>+1 973 952-5000</phone>
<email>jdrosen@cisco.com</email>
<uri>http://www.jdrosen.net</uri>
</address>
</author>
<date year="2009" />
<area>Transport</area>
<workgroup>Behave</workgroup>
<keyword>NAT</keyword>
<keyword>TURN</keyword>
<keyword>STUN</keyword>
<abstract>
<t>This specification defines an extension of Traversal
Using Relays around NAT (TURN), a relay protocol for NAT traversal, to
allows a TURN client to request TCP allocations, and defines new
requests and indications for the TURN server to open and accept TCP
connections with the client's peers. TURN and this extension both
purposefully restrict the ways in which the relayed address can be
used. In particular, it prevents users from running general purpose
servers from ports obtained from the STUN server.
</t> </abstract> </front>
<middle>
<section title="Introduction">
<t>
Traversal Using Relays around NAT (TURN)
<xref target="I-D.ietf-behave-turn"/> is an extension to the Session
Traversal Utilities for NAT <xref target="RFC5389"/> protocol. TURN
allows for clients to communicate with a TURN server, and ask it to
allocate ports on one of its host interfaces, and then relay traffic
between that port and the client itself. TURN, when used in concert
with STUN and Interactive Connectivity Establishment (ICE)
<xref target="I-D.ietf-mmusic-ice"/> form a solution for NAT traversal
for UDP-based media sessions.
</t>
<t>
However, TURN itself does not provide a way for a client to allocate a
TCP-based port on a TURN server. Such an allocation is needed for
cases where a TCP-based session is desired with a peer, and NATs
prevent a direct TCP connection. Examples include application sharing
between desktop softphones, or transmission of pictures during a voice
communications session.
</t>
<t>
This document defines an extension to TURN which allows a client to
obtain a TCP allocation. It also allows the client to initiate
connections from that allocation to peers, and accept connection
requests from peers made towards that allocation.
</t>
</section>
<section title="Conventions">
<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"/>.</t>
</section>
<section title="Overview of Operation">
<figure anchor="fig-turn-tcp-mod" title="TURN TCP Model"><artwork><![CDATA[
+--------+
| |
| Peer1 |
/ | |
/ | |
/ +--------+
/
/
/ Peer Data 1
/
+--------+ Control +--------+ /
| | -------------- | | /
| Client | Client Data 1 | TURN |
| | -------------- | Server | \
| | -------------- | | \
+--------+ Client Data 2 +--------+ \
\
\
\ +--------+
\ | |
Peer Data 2 \ | Peer2 |
\ | |
| |
+--------+
]]></artwork></figure>
<t>
The overall model for TURN-TCP is shown in
<xref target="fig-turn-tcp-mod"/>. The client will have two different
types of connections to its TURN server. For each allocated port, it
will have a single control connection. Control connections are used to
obtain allocations and open up new connections. Furthermore, for each
connection to a peer, the client will have a single connection to its
TURN server. These connections are called data
connections. Consequently, there is a data connection from the client
to its TURN server (the client data connection) and one from the TURN
server to a peer (the peer data connection). Actual application data
is sent on these connections. Indeed, after an initial TURN message
which binds the client data connection to a peer data connection, only
application data can be sent - no TURN messaging. This is in contrast
to the control connection, which only allows TURN messages and not
application data.
</t>
<t>
To obtain a TCP-based allocation, a client must have a TCP or TLS
connection to its TURN server. Using that connection, it sends an
Allocate request. That request contains a REQUESTED-TRANSPORT
attribute, which indicates a TCP-based allocation is desired. A server
which supports this extension will allocate a TCP port and begin
listening for connection requests on that port. It then returns the
allocated port to the client in the resposne to the Allocate
request. The connection on which the Allocate request was sent is
the control connection.
</t>
<t>
If a client wishes to establish a TCP connection to a peer from that
allocated address, it issues a Connect request to the TURN server over
the control connection. That request contains a XOR-PEER-ADDRESS
attribute identifying the peer IP address and port to which a
connection is to be made. The TURN server attempts to open the TCP
connection, and assuming it succeeds, then responds to the Connect
request with a success response. The server also creates a connection
identifier associated with this connection, and passes that connection
identifier back to the client in the success response.
</t>
<t>
In order to actually send data on the new connection or otherwise
utilize it in any way, the client establishes a new TCP connection to
its TURN server. Once established, it issues a ConnectionBind request
to the server. That request echoes back the connection identifier to
the TURN server. The TURN server uses it to correlate the two
connections. As a consequence, the TCP connection to the peer is
associated with a TCP connection to the client 1-to-1. The two
connections are now data connections. At this point, if the server
receives data from the peer, it forwards that data towards the client,
without any kind of encapsulation. Any data received by the TURN
server from the client over the client data connection are forwarded
to the peer, again without encapsulation or framing of any kind. Once
a connection has been bound using the ConnectionBind request, TURN
processing is no longer permitted on the connection.
</t>
<t>
In a similar way, when a peer opens a TCP connection towards the allocated port,
the server checks if there is a permission in place for that peer. If there is
none, the connection is closed. Permissions are created with the
CreatePermission request sent over the control connection, just as for
UDP TURN. If there is a permission in place, the TURN server sends, to
the client, a ConnectionAttempt Indication over the control
connection. That indication contains a connection identifier. Once
again, the client initiates a separate TCP connection to its TURN
server, and over that connection, issues a ConnectionBind
request. Once received, the TURN server will begin relaying data back and forth.
The server closes the peer data connection if no ConnectionBind request is
received after a timeout.
</t>
<t>
If the client closes a client data connection, the corresponding peer
data connection is closed. If the peer closes a peer data connection, the
corresponding client data connection is closed. In this way, the status of
the connection is directly known to the client.
</t>
<t>
The TURN server will relay the data between the client and peer data
connections, utilizing an internal buffer. However, back pressure is
used in order to achieve end-to-end flow control. If the buffer from
client to peer fills up, the TURN server ceases to read off the client
data connection, which causes TCP backpressure through the OS towards
the client.
</t>
</section>
<section title="Client Processing">
<section title="Creating an Allocation">
<t>
To create a TCP allocation, a client MUST initiate a new TCP or TLS
connection to its TURN server, identical to the TCP or TLS procedures
defined in <xref target="I-D.ietf-behave-turn"/>. TCP allocations
cannot be obtained using a UDP association between client and server.
</t>
<t>
Once set up, a client MUST send a TURN Allocate request. That request
MUST contain a REQUESTED-TRANSPORT attribute whose value is 6,
corresponding to TCP.
</t>
<t>
The request MUST NOT include a DONT-FRAGMENT, RESERVATION-TOKEN or
EVEN-PORT attribute. The corresponding features are specific to UDP
based capabilities and are not utilized by TURN-TCP. However, a
LIFETIME attribute MAY be included, with semantics identical to the
UDP case.
</t>
<t>
The procedures for authentication of the Allocate request and
processing of success and failure responses are identical to those for
TCP.
</t>
<t>
Once a success response is received, the TCP connection to the TURN
server is called the control connection for that allocation.
</t>
</section>
<section title="Refreshing an Allocation">
<t>
The procedures for refreshing an allocation are identical to those for
UDP. Note that the Refresh MUST be sent on the control connection.
</t>
</section>
<section title="Initiating a Connection">
<t>
To initiate a TCP connection to a peer, a client MUST send a Connect
request over the control channel for the desired allocation.
The Connect request MUST include a
XOR-PEER-ADDRESS attribute containing the IP address and port of the
peer to which a connection is desired.
</t>
<t>
If the connection is successfully established, the client will receive
a success response. That response will contain a CONNECTION-ID
attribute. The client MUST initiate a new TCP connection to the
server, utilizing the same destination IP address and port to which the control
connection was established. This connection MUST be made using a
different local IP address and/or port. Once established, the client MUST
send a ConnectionBind request. That request MUST include the
CONNECTION-ID attribute, mirrored from the Connect Success
response. When a response to the ConnectionBind request is recevied,
if it is a success, the TCP connection on which it was sent is called
the client data connection corresponding to the peer.
</t>
<t>
If the result of the Connect request was a Error Response, and the
response code was XXX, it means that the TURN server was unable to
connect to the peer. The client MAY retry, but MUST wait at least 10
seconds.
</t>
</section>
<section title="Receiving a Connection">
<t>After an Allocate request is successfully processed by the server, the
client will start receiving a
ConnectionAttempt indication each time a peer attemps a new connection to
the allocated address. This indication will contain a CONNECTION-ID and a
XOR-PEER-ADDRESS attributes. If the client wishes to accept this connection,
it MUST initiate a new TCP connection to the server, utilizing the same
destination IP address and port to which the control connection was
established. This connection MUST be made using a different local IP
address and/or port. Once established, the client MUST send a ConnectionBind
request. That request MUST include the CONNECTION-ID attribute, mirrorred
from the ConnectionAttempt indication. When a response to the ConnectionBind
request is received, if it is a success, the TCP connection on which it was
sent is called the client data connection corresponding to the peer.</t>
</section>
<section title="Sending and Receiving Data">
<t>Once a client data connection is established, data sent on it by the client
will be relayed as-is to the peer by the server. Similarly, data sent by the
peer to the server will be relayed as-is to the client over the data
connection. Data on a data connection MUST NOT be interpreted as STUN
messages.</t>
</section>
<section title="Data Connection Maintenance">
<t>The client MUST refresh the allocation corresponding to a data connection,
using the Refresh request as defined in <xref
target="I-D.ietf-behave-turn"/>, for as long as it wants to keep the data
connection alive.</t>
<t>When the client wishes to terminate its relayed connection to the peer, it
closes the data connection to the server.</t>
<t>
<list style="empty">
<t>Note: No mechanism for keeping alive the NAT bindings (potentially on
the client data connection as well as on the peer data connection) is
included. This service is not provided by TURN-TCP. If such a feature is
deemed necessary, it can be implemented higher up the stack, in the
application protocol being tunneled inside TURN-TCP.</t>
</list>
</t>
</section>
</section>
<section title="TURN Server Behavior">
<section title="Receiving a TCP Allocate Request">
<t>The process is similar to that defined in <xref
target="I-D.ietf-behave-turn"/>, Section 6.2, with the following
exceptions:</t>
<t>
<list style="numbers">
<t>If the REQUESTED-TRANSPORT attribute is included and specifies a
protocol other than UDP or TCP, the server MUST reject the request with
a 442 (Unsupported Transport Protocol) error. (If the value is UDP, the
server MUST continue with the procedures of <xref
target="I-D.ietf-behave-turn"/> instead of this document.)</t>
<t>If the client connection transport is not TCP or TLS, the server MUST
reject the request with a 400 (Bad Request) error.</t>
<t>If the request contains the DONT-FRAGMENT, EVEN-PORT, or
RESERVATION-TOKEN attribute, the server MUST reject the request with a
400 (Bad Request) error.</t>
<t>A TCP relayed transport address MUST be allocated instead of a UDP
one.</t>
<t>The RESERVATION-TOKEN attribute MUST NOT be present in the success
response.</t>
</list>
</t>
<t>If all checks pass, the server MUST start accepting incoming TCP
connections on the relayed transport address. Refer to <xref
target="accept"/> for details.</t>
</section>
<section title="Receiving a Connect Request">
<t>When the server receives a Connect request, it processes as follows.</t>
<t>If the request is received on a control connection for which no allocation
exists, the server MUST return a 437 (Allocation Mismatch) error.</t>
<t>If the server has already successfully processed a Connect request for this
allocation with the same XOR-PEER-ADDRESS, and the resulting client and peer
data connections are either pending or active, it MUST return a 446
(Connection Already Exists) error.</t>
<t>If the request does not contain a XOR-PEER-ADDRESS attribute, or if such
attribute is invalid, the server MUST return a 400 (Bad Request) error.</t>
<t>Otherwise, the server MUST initiate an outgoing TCP connection. The local
endpoint is the relayed transport address associated with the allocation.
The remote endpoint is the one indicated by the XOR-PEER-ADDRESS
attribute. If the connection attempt fails or times out, the server MUST
return a XXX (Connection Timeout or Failure) error.</t>
<t>If the connection is successful, it is now called a peer data connection.
The server MUST buffer any data received from the peer. Data MUST NOT be
lost. It is up to the server to adjust its advertised TCP receive window
should the buffer size become a limiting factor.</t>
<t>The server MUST include the CONNECTION-ID attribute in the Connect success
response. The attribute's value MUST uniquely identify the peer data
connection.</t>
</section>
<section title="Receiving a TCP Connection on an Allocated Port" anchor="accept">
<t>When a server receives an incoming TCP connection on a relayed transport,
it processes as follows.</t>
<t>The server MUST accept the connection. If it is not successful,
nothing is sent to the client over the control connection.</t>
<t>If the connection is successfully accepted, it is now called a peer data
connection. The server MUST buffer any data received from the peer. Data
MUST NOT be lost. It is up to the server to adjust its advertised TCP
receive window should the buffer size become a limiting factor.</t>
<t>The server then sends a ConnectionAttempt indication to the client over the
control connection. The indication MUST include a XOR-PEER-ADDRESS attribute
containing the peer's address, as well as a CONNECTION-ID attribute uniquely
identifying the peer data connection.</t>
<t>If no ConnectionBind request associated with this peer data connection is
received after 30 seconds, the peer data connection MUST be closed.</t>
</section>
<section title="Receiving a ConnectionBind Request">
<t>When a server receives a ConnectionBind request, it processes as
follows.</t>
<t>If the client connection transport is not TCP or TLS, the server MUST
return a 400 (Bad Request) error.</t>
<t>If the request does not contain the CONNECTION-ID attribute, or if this
attribute does not refer to an existing pending connection, the server
MUST return a 400 (Bad Request) error.</t>
<t>Otherwise, the client connection is now called a client data connection.
Data received on it MUST be sent as-is to the associated peer data
connection.</t>
<t>Data received on the associated peer data connection MUST be sent as-is on
this client data connection. This includes data that was received after the
associated Connect or Listen request was successfully processed and before
this ConnectionBind request was received.</t>
<t>Data received on a client or peer data connection MUST NOT be interpreted
as a STUN message.</t>
</section>
<section title="Data Connection Maintenance">
<t>If the allocation associated with a data connection expires, the data
connection MUST be closed.</t>
<t>When a client data connection is closed or times out, the
server MUST close the corresponding peer data connection.</t>
<t>When a peer data connection is closed or times out, the
server MUST close the corresponding client data connection.</t>
</section>
</section>
<section title="IANA Considerations">
<t>
This specification defines several new STUN methods, STUN attributes,
and STUN response codes. This section directs IANA to add these new
protocol elements to the IANA registry of STUN protocol elements.
</t>
<section title="New STUN Methods">
<figure>
<preamble>This section lists the codepoints for the new STUN methods defined
in this specification. See elsewhere in this document for the semantics of
these new methods.</preamble>
<artwork>
0x0007 : Connect (only request/response semantics defined)
0x0008 : ConnectionBind (only request/response semantics defined)
0x0009 : ConnectionAttempt (only indication semantics defined)
</artwork></figure></section>
<section title="New STUN Attributes">
<figure>
<preamble>This STUN extension defines the following new attributes:</preamble>
<artwork>
0x002A : CONNECTION-ID
</artwork></figure>
<section title="CONNECTION-ID">
<t>The CONNECTION-ID attributes uniquely identifies a peer data connection. It
is a 32-bit unsigned integral value.</t>
</section>
<section title="New STUN response codes">
<figure><artwork>
446 Connection Already Exists
447 Connection Timeout or Failure
</artwork></figure>
</section>
</section>
<section title="Security Considerations">
<t>The methods, attribute, and error response codes defined in this document
do not have any special security considerations beyond those for other
attributes and Error response codes. All the security considerations
applicable to STUN <xref target="RFC5389"/> and TURN <xref
target="I-D.ietf-behave-turn"/> are applicable to this document as
well.</t>
</section>
<section title="Acknowledgements">
<t>Thanks to Rohan Mahy and Philip Matthews for their initial work on
getting this document started.</t>
<t>The authors would also like to thank Marc Petit-Huguenin for his
comments and suggestions.</t>
</section>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.5389"?>
<?rfc include="reference.I-D.draft-ietf-behave-turn-14"?>
<?rfc include="reference.RFC.2119"?>
</references>
<references title="Informative References">
<?rfc include="reference.I-D.draft-ietf-mmusic-ice-19"?>
</references>
</back>
</rfc>
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