< draft-ietf-behave-turn-05.txt   draft-ietf-behave-turn-06.txt >
Behave J. Rosenberg Behave J. Rosenberg
Internet-Draft Cisco Internet-Draft Cisco
Intended status: Standards Track R. Mahy Intended status: Standards Track R. Mahy
Expires: May 18, 2008 Plantronics Expires: July 25, 2008 Plantronics
P. Matthews P. Matthews
Avaya Avaya
D. Wing January 22, 2008
Cisco
November 15, 2007
Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Using Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN) Traversal Utilities for NAT (STUN)
draft-ietf-behave-turn-05 draft-ietf-behave-turn-06
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
Abstract Abstract
This specification defines an extension of the Session Traversal If a host is located behind a NAT, then in certain situations it can
Utilities for NAT (STUN) Protocol for asking the STUN server to relay be impossible for that host to communicate directly with other hosts
packets towards a client. This extension, called Traversal Using (peers) located behind other NATs. In these situations, it is
Relays around NAT (TURN), is useful for hosts behind address necessary for the host to use the services of an intermediate node
dependent NATs. The extension purposefully restricts the ways in that acts as a communication relay. This specification defines a
which the relayed address can be used. In particular, it prevents protocol, called TURN (Traversal Using Relays around NAT), that
users from running general purpose servers on ports obtained from the allows the host to control the operation of the relay and to exchange
TURN server. packets with its peers using the relay.
The TURN protocol can be used in isolation, but is more properly used
as part of the ICE (Interactive Connectivity Establishment) approach
to NAT traversal.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Overview of Operation . . . . . . . . . . . . . . . . . . . . 5
3. Overview of Operation . . . . . . . . . . . . . . . . . . . . 5 2.1. Transports . . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Transports . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2. Allocations . . . . . . . . . . . . . . . . . . . . . . . 8
3.2. About Tuples . . . . . . . . . . . . . . . . . . . . . . . 9 2.3. Exchanging Data with Peers . . . . . . . . . . . . . . . . 9
3.3. Keepalives . . . . . . . . . . . . . . . . . . . . . . . . 10 2.4. Permissions . . . . . . . . . . . . . . . . . . . . . . . 10
4. TURN Framing Mechanism . . . . . . . . . . . . . . . . . . . . 11 2.5. Channels . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. General Behavior . . . . . . . . . . . . . . . . . . . . . . . 11 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 12
6. Managing Allocations . . . . . . . . . . . . . . . . . . . . . 13 4. General Behavior . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 13 5. Managing Allocations . . . . . . . . . . . . . . . . . . . . . 14
6.1.1. Initial Allocate Requests . . . . . . . . . . . . . . 13 5.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 14
6.1.2. Refresh Requests . . . . . . . . . . . . . . . . . . . 14 5.1.1. Initial Allocate Requests . . . . . . . . . . . . . . 14
6.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 15 5.1.2. Refresh Requests . . . . . . . . . . . . . . . . . . . 15
6.2.1. Initial Allocate Requests . . . . . . . . . . 15 5.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 16
6.2.2. Refresh Requests . . . . . . . . . . . . . . . . . . . 18 5.2.1. Receiving an Allocate Request . . . . . . . . . . . . 16
7. Sending and Receiving Data . . . . . . . . . . . . . . . . . . 19 5.2.2. Refresh Requests . . . . . . . . . . . . . . . . . . . 20
7.1. Client Behavior . . . . . . . . . . . . . . . . . . . . . 19 6. Send and Data Indications . . . . . . . . . . . . . . . . . . 21
7.1.1. Sending . . . . . . . . . . . . . . . . . . . . . . . 19 6.1. Forming and Sending an Indication . . . . . . . . . . . . 21
7.1.2. Receiving . . . . . . . . . . . . . . . . . . . . . . 20 6.2. Receiving an Indication . . . . . . . . . . . . . . . . . 22
7.2. Server Behavior . . . . . . . . . . . . . . . . . . . . . 20 6.3. Relaying . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.2.1. Receiving Data from the Client . . . . . . . . . . . . 20 7. Channel Mechanism . . . . . . . . . . . . . . . . . . . . . . 23
7.2.2. Receiving Data from Peers . . . . . . . . . . . . . . 22 7.1. Forming and Sending a ChannelBind Request . . . . . . . . 23
7.2.3. Allocation Activity Timer and Permission Timeout . . . 23 7.2. Receiving a ChannelBind Request and Sending a Response . . 24
8. New Attributes . . . . . . . . . . . . . . . . . . . . . . . . 23 7.3. Receiving a ChannelBind Response . . . . . . . . . . . . . 25
8.1. CHANNEL-NUMBER . . . . . . . . . . . . . . . . . . . . . . 23 7.4. The ChannelData Message . . . . . . . . . . . . . . . . . 25
8.2. LIFETIME . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.5. Forming and Sending a ChannelData Message . . . . . . . . 25
8.3. BANDWIDTH . . . . . . . . . . . . . . . . . . . . . . . . 24 7.6. Receiving a ChannelData Message . . . . . . . . . . . . . 26
8.4. PEER-ADDRESS . . . . . . . . . . . . . . . . . . . . . . . 24 7.7. Relaying . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.5. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 8. New STUN Methods . . . . . . . . . . . . . . . . . . . . . . . 27
8.6. RELAY-ADDRESS . . . . . . . . . . . . . . . . . . . . . . 24 9. New STUN Attributes . . . . . . . . . . . . . . . . . . . . . 27
8.7. REQUESTED-PORT-PROPS . . . . . . . . . . . . . . . . . . . 24 9.1. CHANNEL-NUMBER . . . . . . . . . . . . . . . . . . . . . . 28
8.8. REQUESTED-TRANSPORT . . . . . . . . . . . . . . . . . . . 25 9.2. LIFETIME . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.9. REQUESTED-IP . . . . . . . . . . . . . . . . . . . . . . . 26 9.3. BANDWIDTH . . . . . . . . . . . . . . . . . . . . . . . . 28
9. New Error Response Codes . . . . . . . . . . . . . . . . . . . 26 9.4. PEER-ADDRESS . . . . . . . . . . . . . . . . . . . . . . . 28
10. Client Discovery of TURN Servers . . . . . . . . . . . . . . . 27 9.5. DATA . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
11. Security Considerations . . . . . . . . . . . . . . . . . . . 27 9.6. RELAY-ADDRESS . . . . . . . . . . . . . . . . . . . . . . 28
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 9.7. REQUESTED-PORT-PROPS . . . . . . . . . . . . . . . . . . . 28
12.1. New STUN Methods . . . . . . . . . . . . . . . . . . . . . 29 9.8. REQUESTED-TRANSPORT . . . . . . . . . . . . . . . . . . . 30
12.2. New STUN Attributes . . . . . . . . . . . . . . . . . . . 30 9.9. REQUESTED-IP . . . . . . . . . . . . . . . . . . . . . . . 30
12.3. New STUN Response Codes . . . . . . . . . . . . . . . . . 30 10. New STUN Error Response Codes . . . . . . . . . . . . . . . . 30
13. IAB Considerations . . . . . . . . . . . . . . . . . . . . . . 30 11. Client Discovery of TURN Servers . . . . . . . . . . . . . . . 31
14. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 12. Security Considerations . . . . . . . . . . . . . . . . . . . 32
15. Changes since version -04 . . . . . . . . . . . . . . . . . . 35 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 36 14. IAB Considerations . . . . . . . . . . . . . . . . . . . . . . 34
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36 15. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
17.1. Normative References . . . . . . . . . . . . . . . . . . . 36 16. Changes from Previous Versions . . . . . . . . . . . . . . . . 35
17.2. Informative References . . . . . . . . . . . . . . . . . . 36 16.1. Changes from -05 to -06 . . . . . . . . . . . . . . . . . 35
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 16.2. Changes from -04 to -05 . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 39 17. Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
17.1. Open Issues . . . . . . . . . . . . . . . . . . . . . . . 37
17.2. Closed Issues . . . . . . . . . . . . . . . . . . . . . . 39
18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 40
19. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
19.1. Normative References . . . . . . . . . . . . . . . . . . . 40
19.2. Informative References . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
Intellectual Property and Copyright Statements . . . . . . . . . . 43
1. Introduction 1. Introduction
NOTE TO THE READER: This document is a work-in-progress. Please see
the list of open and closed issues in Section 17. With only a few
exceptions, if there is an open issue the text has NOT been updated
in this area pending resolution of this issue - keep this in mind
when reading the text. In addition, in the interest of getting the
document out quickly in order to make progress on open issues, the
authors have elected to release the document is a bit more "raw"
state than they would prefer, resulting in some rough spots in the
presentation.
Session Traversal Utilities for NAT (STUN) Session Traversal Utilities for NAT (STUN)
[I-D.ietf-behave-rfc3489bis] provides a suite of tools for [I-D.ietf-behave-rfc3489bis] provides a suite of tools for
facilitating the traversal of NAT. Specifically, it defines the facilitating the traversal of NAT. Specifically, it defines the
Binding method, which is used by a client to determine its reflexive Binding method, which is used by a client to determine its reflexive
transport address towards the STUN server. The reflexive transport transport address towards the STUN server. The reflexive transport
address can be used by the client for receiving packets from peers, address can be used by the client for receiving packets from peers,
but only when the client is behind "good" NATs. In particular, if a but only when the client is behind "good" NATs. In particular, if a
client is behind a NAT whose mapping behavior [RFC4787] is address or client is behind a NAT whose mapping behavior [RFC4787] is address or
address and port dependent (sometimes called "bad" NATs), the address and port dependent (sometimes called "bad" NATs), the
reflexive transport address will not be usable for communicating with reflexive transport address will not be usable for communicating with
skipping to change at page 5, line 5 skipping to change at page 5, line 14
should only be used as a last resort. Protocols using relayed should only be used as a last resort. Protocols using relayed
transport addresses should make use of mechanisms to dynamically transport addresses should make use of mechanisms to dynamically
determine whether such an address is actually needed. One such determine whether such an address is actually needed. One such
mechanism, defined for multimedia session establishment protocols mechanism, defined for multimedia session establishment protocols
based on the offer/answer protocol in RFC 3264 [RFC3264], is based on the offer/answer protocol in RFC 3264 [RFC3264], is
Interactive Connectivity Establishment (ICE) [I-D.ietf-mmusic-ice]. Interactive Connectivity Establishment (ICE) [I-D.ietf-mmusic-ice].
Though originally invented for Voice over IP applications, TURN is Though originally invented for Voice over IP applications, TURN is
designed to be a general-purpose relay mechanism for NAT traversal. designed to be a general-purpose relay mechanism for NAT traversal.
2. Terminology 2. Overview of Operation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", This section gives an overview of the operation of TURN. It is non-
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this normative.
document are to be interpreted as described in RFC 2119 [RFC2119].
Relayed Transport Address: A transport address that terminates on a In a typical configuration, a TURN client is connected to a private
server, and is forwarded towards the client. The TURN Allocate network [RFC1918] and through one or more NATs to the public
request can be used to obtain a relayed transport address, for Internet. On the public Internet is a TURN server. Elsewhere in the
example. Internet are one or more peers that the TURN client wishes to
communicate with. These peers may or may not be behind one or more
NATs.
TURN client: A STUN client that implements this specification. It +---------+
obtains a relayed transport address that it provides to a small | |
number of peers (usually one). | |
/ | Peer A |
Client's TURN // | |
Host Transport Server / | |
Address Address +-+ // +---------+
10.1.1.2:17240 192.0.2.15:3478 |N|/ 192.168.100.2:16400
| | |A|
| +-+ | /|T|
| | | | / +-+
v | | | / 192.0.2.210:18200
+---------+ | | |+---------+ / +---------+
| | |N| || | // | |
| TURN | | | v| TURN |/ | |
| Client |----|A|----------| Server |------------------| Peer B |
| | | |^ | |^ ^| |
| | |T|| | || || |
+---------+ | || +---------+| |+---------+
| || | |
| || | |
+-+| | |
| | |
| | |
Client's | Peer B
Server-Reflexive Relayed Transport
Transport Address Transport Address Address
192.0.2.1:7000 192.0.2.15:9000 192.0.2.210:18200
TURN server: A STUN server that implements this specification. It Figure 1
relays data between a TURN client and its peer(s).
Peer: A node with which the TURN client wishes to communicate. The Figure 1 shows a typical deployment. In this figure, the TURN client
TURN server relays traffic between the TURN client and its and the TURN server are separated by a NAT, with the client on the
peer(s). private side and the server on the public side of the NAT. This NAT
is assumed to be a "bad" NAT; for example, it might have a mapping
property of address-and-port-dependent mapping (see [RFC4787]) for a
description of what this means).
Allocation: The IP address and port granted to a client through an The client has allocated a local port on one of its addresses for use
Allocate request, along with related state, such as permissions in communicating with the server. The combination of an IP address
and expiration timers. and a port is called a TRANSPORT ADDRESS and since this (IP address,
port) combination is located on the client and not on the NAT, it is
called the client's HOST transport address.
5-tuple: A combination of the source IP address and port, The client sends TURN messages from its host transport address to a
destination IP address and port, and transport protocol (UDP, or transport address on the TURN server which is known as the TURN
TCP). It uniquely identifies a TCP connection or bi-directional SERVER ADDRESS. The client learns the server's address through some
flow of UDP datagrams. unspecified means (e.g., configuration), and this address is
typically used by many clients simultaneously. The TURN server
address is used by the client to send both commands and data to the
server; the commands are processed by the TURN server, while the data
is relayed on to the peers.
Permission: A record of an IP address and transport of a peer that Since the client is behind a NAT, the server sees these packets as
is permitted to send traffic to the TURN client. The TURN server coming from a transport address on the NAT itself. This address is
will only forward traffic to its client from remote peers that known as the client's SERVER-REFLEXIVE transport address; packets
match an existing permission. sent by the server to the client's server-reflexive transport address
will be forwarded by the NAT to the client's host transport address.
3. Overview of Operation The client uses TURN commands to allocate a RELAYED transport
address, which is an transport address located on the server. The
server ensures that there is a one-to-one relationship between the
client's server-reflexive transport address and the relayed transport
address; thus a packet received at the relayed transport address can
be unambiguously relayed by the server to the client.
In a typical configuration, a TURN client is connected to a private The client will typically communicate this relayed transport address
network and through one or more NATs to the public Internet. On the to one or more peers through some mechanism not specified here (e.g.,
public Internet is a TURN server. Elsewhere in the Internet are one an ICE offer or answer [I-D.ietf-mmusic-ice]). Once this is done,
or more peers that the TURN client wishes to communicate with. This peers can send data packets to the relayed transport address and the
specification defines a framing mechanism and several new STUN server will forward them to the client. In the reverse direction,
methods. Together, these add the ability for a STUN server to act as the client can send data packets to the server (at its TURN server
a packet relay. address) and these will be forwarded by the server to the appropriate
peer, and the peer will see them as coming from the relayed transport
address; in this direction, the client must specify the appropriate
peer.
The framing mechanism serves two purposes. First, it contains a 2.1. Transports
length field that allow TURN nodes to find the boundaries between
chunks of application data when the communication with the TURN
server is over a stream-based transport such as TCP. Second, it
carries a channel number. Channel zero is used for TURN control
messages, while the other channel numbers are used for application
data traveling to or from various peers. The channel number allows
the client to know which peer sent data to it, and to specify which
peer is to be the recipient of data. Application data flowing on any
non-zero channel is unencapsulated, meaning that the application data
starts immediately after the framing header. The framing header is
just four bytes. This allows TURN to operate with minimal overhead,
which is important for the real-time protocols it is designed to
support. Application data can also flow in encapsulated format,
meaning that it is carried in certain TURN messages on channel 0.
Channel numbers are independent in each direction: for example,
channel 5 might indicate one peer in the client to server direction,
but a different peer in the server to client direction.
When the client wants to obtain a relayed transport address, the TURN as defined in this specification only allows the use of UDP
client first sends an Allocate request to the server, which the between the server and the peer. However, this specification allows
server authenticates. The server generates an Allocate response with the use of any one of UDP, TCP, or TLS over TCP to carry the TURN
the allocated address, port, and target transport. All other STUN messages between the client and the server.
messages defined by this specification happen in the context of an
+----------------------------+---------------------+
| TURN client to TURN server | TURN server to peer |
+----------------------------+---------------------+
| UDP | UDP |
| TCP | UDP |
| TLS over TCP | UDP |
+----------------------------+---------------------+
For TURN clients, using TLS over TCP to communicate with the TURN
server provides two benefits. First, the client can be assured that
the addresses of its peers are not visible to any attackers between
it and the server. Second, the client may be able to communicate
with TURN servers using TLS when it would not be able to communicate
with the same server using TCP or UDP, due to the policy of a
firewall between the TURN client and its server. In this second
case, TLS between the client and TURN server facilitates traversal.
There is a planned extension to TURN to add support for TCP between
the server and the peers [I-D.ietf-behave-turn-tcp]. For this
reason, allocations that use UDP between the server and the peers are
known as UDP allocations, while allocations that use TCP between the
server and the peers are known as TCP allocations. This
specification describes only UDP allocations.
2.2. Allocations
To allocate a relayed transport address, the client uses an Allocate
transaction. The client sends a Allocate Request to the server, and
the server replies with an Allocate Response containing the allocated
relayed transport address. The client can include attributes in the
Allocate Request that describe the type of allocation it desires
(e.g., the lifetime of the allocation). And since relaying data can
require lots of bandwidth, the server may require that the client
authenticate itself using STUN's long-term credential mechanism, to
show that it is authorized to use the server.
Once a relayed transport address is allocated, a client must keep the
allocation alive. This is done by the client periodically doing a
Refresh transaction with the server, where the client includes the
allocated relayed transport address in the Refresh Request. TURN
deliberately uses a different method (Refresh rather than Allocate)
for refreshes to ensure that the client is informed if the allocation
vanishes for some reason.
The frequency of the Refresh transaction is determined by the
lifetime of the allocation. The client can request a lifetime in the
Allocate Request and may modify its request in a Refresh Request, and
the server always indicates the actual lifetime in the response. The
client must issue a new Refresh transaction within 'lifetime' seconds
of the previous Allocate or Refresh transaction. If a client no
longer wishes to use an Allocation, it should do a Refresh
transaction with a requested lifetime of 0.
Note that sending or receiving data from a peer DOES NOT refresh the
allocation. allocation.
A successful Allocate transaction just reserves a transport address The server remembers the 5-tuple used in the Allocate Request.
on the TURN server. Data does not flow through an allocated Subsequent transactions between the client and the server use this
transport address until the TURN client asks the TURN server to open same 5-tuple. In this way, the server knows which client owns the
a permission, which is done with a Send Indication. While the client allocated relayed transport address. If the client wishes to
can request more than one permission per allocation, it needs to allocate a second relayed transport address, it must use a different
request each permission explicitly and one at a time. This insures 5-tuple for this allocation (e.g., by using a different client host
that a client can't use a TURN server to run a traditional server, address).
and partially protects the client from DoS attacks.
Once a permission is open, the client can then receive data flowing While the terminology used in this document refers to 5-tuples,
back from its peer. Initially this data is encapsulated in a Data the TURN server can store whatever identifier it likes that yields
Indication. Since multiple permissions can be open simultaneously, identical results. Specifically, many implementations use a file-
the Data Indication contains the PEER-ADDRESS attribute so the TURN descriptor in place of a 5-tuple to represent a TCP connection.
client knows which peer sent the data, and a CHANNEL-NUMBER attribute
so the client knows how the server will refer to traffic from this
peer when sent unencapsulated. Likewise when the client initially
sends to a new peer, it uses a Send Indication with the peer address
in the PEER-ADDRESS attribute, along with a channel number so the
server knows how the client will refer to unencapsulated data to this
peer.
TURN TURN peer 2.3. Exchanging Data with Peers
client server
|--- Allocate Req -->| |
|<-- Allocate Resp ---| |
| | |
|--- Send (chan 2) -->| data |
| |============>|
|<-- ChannelConfirm --| |
| | data |
| |<============|
|<-- Data (chan 5) ---| |
|--- ChannelConfirm ->| |
| | |
|--- [2] + data ----->| data |
| |============>|
| | data |
| |<============|
|<-- [5] + data ------| |
Figure 1: Example Usage of Channels The client can use the relayed transport address to exchange data
with its peers by using Send and Data indications. A Send Indication
is sent from a client to the TURN server and contains, in attributes
inside the message, the transport address of the peer and the data to
be sent to that peer. When the TURN server receives the Send
Indication, it extracts the data from the Send Indication and sends
it in a UDP datagram to the peer, using the allocated relay address
as the source address. In the reverse direction, UDP datagrams
arriving at the relay address on the TURN server are converted into
Data Indications and sent to the client, with the transport address
of the peer included in an attribute in the Data Indication.
When the client and server communicate over UDP, data and control Note that a client can use a single relayed transport address to
messages can arrive out of order. For this reason, the client needs exchange data with multiple peers at the same time.
to verify the server knows the client channel mapping before the TURN TURN Peer Peer
client sends unencapsulated, and the server needs to verify the client server A B
client knows the server channel mapping before the server sends |--- Allocate Req -->| | |
unencapsulated. When the client and server communicate over UDP, a |<-- Allocate Resp ---| | |
Channel Confirmation indication is sent after the Send (or Data) | | | |
indication so the client (or server) knows that it can send |--- Send (Peer A)--->| | |
unencapsulated. | |=== data ===>| |
| | | |
| |<== data ====| |
|<-- Data (Peer A)----| | |
| | | |
|--- Send (Peer B)--->| | |
| |=== data =================>|
| | | |
| |<== data ==================|
|<-- Data (Peer B)----| | |
Figure 1 demonstrates how this works. The client performs an Figure 2
Allocate Request, and gets a response. It decides to send data to a
specific peer. Initially, it sends data to that peer using a TURN
Send indication on channel 0. That Send Indication tells the TURN
server that, once confirmed, the client will send data unencapsulated
to that peer on channel 2. Whenever the TURN server receives a Send
indication, it stores the mapping from channel number to peer, and
sends a ChannelConfirm indication (on channel 0). Once the
confirmation has been received by the client, the client can send
data to the peer on channel 2. Prior to receipt of the
ChannelConfirm, any other data the client wishes to send to the peer
is sent using Send indications, all of which indicate that channel 2
is to be used for unencapsulated data. The same procedure happens
from server to client; the TURN server initially sends data using a
Data indication on channel 0, and once confirmed with a
ChannelConfirm, it can send it unencapsulated on its selected channel
(channel 5 in the example).
Over a reliable transport, such as TCP, the confirmation step is not In the figure above, the client first allocates a relayed transport
needed so the Channel Confirmation indication is not used. Clients address. It then sends data to Peer A using a Send Indication; at
can immediately send the next piece of data to the peer on the the server, the data is extracted and forwarded in a UDP datagram to
requested channel. Peer A, using the relayed transport address as the source transport
address. When a UDP datagram from Peer A is received at the relayed
transport address, the contents are placed into a Data Indication and
forwarded to the client. A similar exchange happens with Peer B.
Allocations can also request specific attributes such as the desired 2.4. Permissions
Lifetime of the allocation and the maximum Bandwidth. Clients can
also request specific port assignment behavior, for example, a
specific port number, odd or even port numbers, or pairs of
sequential port numbers.
3.1. Transports To ease concerns amongst enterprise IT administrators that TURN could
be used to bypass corporate firewall security, TURN includes the
notion of permissions. TURN permissions mimic the address-restricted
filtering mechanism of NATs that comply with [RFC4787].
TURN clients can communicate with a TURN server using UDP, TCP, or A TURN server will drop a UDP datagram arriving at a relayed
TLS over TCP. A TURN server can then relay traffic between a transport address from a peer unless the client has recently sent
reliable transport used between the client and server (TCP or TLS data to a peer with the same IP address (the port numbers can
over TCP), and UDP used from server to peer. When relaying data sent differ). See the normative description for the precise definition of
from a stream-based protocol to a UDP peer, the TURN server emits "recently".
datagrams which are the same length as the length field in the TURN
framing or the length of the DATA attribute in a Send Indication.
Likewise, when a UDP datagram is received by the TURN server and
relayed to the client over a stream-based transport, the length of
the datagram is the length of the TURN framing or Data Indication's
DATA attribute.
The following table shows the possible combinations of transport A permission will timeout if not refreshed periodically. The client
protocols from client to server and from server to peer: refreshes a permission by sending data to the corresponding peer.
Data received from the peer DOES NOT refresh the permission.
+-----------------------+---------------------+ 2.5. Channels
| client to TURN server | TURN server to peer |
+-----------------------+---------------------+
| UDP | UDP |
| TCP | UDP |
| TLS | UDP |
+-----------------------+---------------------+
For TURN clients, using TLS over TCP provides two benefits. When In some applications, the overhead of using Send and Data indications
using TLS, the client can be assured that the address of the client's can be substantial. For example, for applications like VoIP which
peers are not visible to an attacker except by traffic analysis utilize small packets, Send and Data Indications, with 36 bytes of
downstream of the TURN server. Second, the client may be able to overhead, can have a substantial impact on overall bandwidth usage.
communicate with TURN servers using TLS when it would not be able to To remedy this, TURN clients can assign a CHANNEL to a peer. Data to
communicate with the same server using TCP or UDP, due to the and from such a peer can then be sent using an alternate packet
configuration of a firewall between the TURN client and its server. format that adds only 4 bytes per packet of overhead.
TLS between the client and TURN server in this case just facilitates
traversal.
In addition, an extension to TURN is planned to add support for TCP The alternate packet format is known as the ChannelData message. The
allocations [I-D.ietf-behave-turn-tcp]. ChannelData message does not use the STUN header used by other TURN
messages, but instead has a 4-byte header that includes a number
known as a channel number.
3.2. About Tuples To create a channel, the client sends a ChannelBind request to the
server, and includes an unallocated channel number and the transport
address of the peer. Once the client receives the response to the
ChannelBind request, it can send data to that peer using a
ChannelData message. Similarly, once the server has received the
request, it can relay data from that peer towards the client using a
ChannelData message. There is no way to modify channel bindings, so
once a channel is bound to a peer, it remains bound for the lifetime
of the allocation.
To relay data to and from the correct location, the TURN server When the server receives a ChannelData message from the client, it
maintains an association between the 5-tuple used to communicate with uses the channel number to determine the destination peer and then
the client and the 5-tuple used to communicate with each of the forwards the data inside a UDP datagram to the peer. In the reverse
client's peers. The 5-tuple on the client side will consist of the direction, when a UDP datagram arives at the relayed transport
client's reflexive address -- the apparent source address and port of address from that peer, the server inserts it into a ChannelData
the client (typically as rewritten by the last NAT)--and the message containing the channel number bound to that peer; in this way
destination address and port used by the TURN server. The figure the client can determine the peer that send the UDP datagram.
below (Figure 2) shows a typical topology. In this diagram, the TURN TURN Peer Peer
client 5-tuple is for a UDP flow between 192.0.2.1:7000 and client server A B
192.0.2.15:3490. The 5-tuple between the TURN server and Peer B is |--- Allocate Req -->| | |
for a UDP flow between 192.0.2.15:9000 (the TURN allocated address) |<-- Allocate Resp ---| | |
and 192.0.2.210:18200. | | | |
|--- Send (Peer A)--->| | |
| |=== data ===>| |
| | | |
| |<== data ====| |
|<-- Data (Peer A)----| | |
| | | |
|- ChannelBind Req -->| | |
| (Peer A to 0x4001) | | |
| | | |
|<- ChannelBind Resp -| | |
| | | |
|-- [0x4001] data --->| | |
| |=== data ===>| |
| | | |
| |<== data ====| |
|<- [0x4001] data --->| | |
| | | |
|--- Send (Peer B)--->| | |
| |=== data =================>|
| | | |
| |<== data ==================|
|<-- Data (Peer B)----| | |
While the terminology used in this document refers to 5-tuples, Figure 3
the TURN server can store whatever identifier it likes that yields
identical results. Specifically, many implementations may use a
file-descriptor in place of a 5-tuple to represent a TCP
connection.
+---------+ The figure above shows the channel mechanism in use. The client
| | begins by allocating a relayed transport address, and then uses that
| | address to exchange data with Peer A. After a bit, the client decides
/ | Peer A | to bind a channel to Peer A. To do this, it sends a ChannelBind
Client's TURN // | | Request to the server, specifying the transport address of Peer A and
Host Server / | | a channel number (0x4001). After that, the client can send
Address Address // +---------+ application data encapsulated inside ChannelData messages to Peer A:
10.1.1.2:17240 192.0.2.15:3490 / 192.0.2.180:16400 this is shown as "[0x4001] data" where 0x4001 is the channel number.
| | //
| +-+ | /
| | | | /
v | | | // 192.0.2.210:18200
+---------+ | | |+---------+ / +---------+
| | |N| || | // | |
| TURN | | | v| TURN |/ | |
| Client |----|A|----------| Server |------------------| Peer B |
| | | |^ | |^ ^| |
| | |T|| | || || |
+---------+ | || +---------+| |+---------+
| || | |
| || | |
+-+| | |
| | |
|
Client's TURN Peer B
Reflexive Allocated Transport
Address Address Address
192.0.2.1:7000 192.0.2.15:9000 192.0.2.210:18200
Figure 2 Note that ChannelData messages can only be used for peers to which
the client has bound a channel. In the example above, Peer A has
been bound to a channel, but Peer B has not, so application data to
and from Peer B uses Send and Data indications.
3.3. Keepalives Channel bindings are always initiated by the client.
Since the main purpose of STUN and TURN is to traverse NATs, it is 3. Terminology
natural to consider which elements are responsible for generating
sufficient periodic traffic to insure that NAT bindings stay alive.
TURN clients need to send data frequently enough to keep both NAT
bindings and the TURN server permissions fresh. Like NAT bindings,
the TURN server permissions are refreshed by ordinary data traffic
relayed from the client to the peer. Unlike permissions, allocations
on the TURN server have an explicit expiration time and need to be
refreshed explicitly by the client with a TURN Refresh request. When
an allocation expires, all permissions associated with that
allocation are automatically deleted.
4. TURN Framing Mechanism 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].
All TURN control messages and all application data sent between the Readers are expected to be familar with [I-D.ietf-behave-rfc3489bis]
client and the server MUST start with the TURN framing header. This and the terms defined there.
header is used for two purposes: indicating the channel number, and
for framing.
TURN uses a channel number to distinguish control traffic from data, The following terms are used in this document:
and to distinguish among multiple peers using the same allocation.
Channel number zero is reserved for TURN control messages. All TURN
requests, responses and indications between the client and server
MUST be sent on channel 0, and MUST NOT be sent on any other channel.
Channel 0xFFFF is reserved for future use and MUST NOT be used by
clients or servers compliant to this specification. Other channel
numbers are assigned and communicated as described in Section 7.
Because the framing is always used, TURN needs to run on a separate
port number from unframed STUN requests.
Over stream-based transports, the TURN client and server also need to TURN: A protocol spoken between a TURN client and a TURN server. It
include an explicit length so that the TURN server can perform is an extension to the STUN protocol [I-D.ietf-behave-rfc3489bis].
conversion from streams to datagrams and vice versa. TURN framing The protocol allows a client to allocate and use a relayed
has a 2 octet channel number and a 2 octet length field. Over transport address.
stream-based transports, the length field counts the number of octets
immediately after the length field itself. Over UDP the length is
always set to zero.
0 1 2 3 TURN client: A STUN client that implements this specification.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Channel Number | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Channel numbers are always defined within a particular allocation. TURN server: A STUN server that implements this specification. It
If a client has multiple allocations on a TURN server, there is no relays data between a TURN client and its peer(s).
relationship whatsoever between the channel numbers in each
allocation. Once created, a channel number persists for the lifetime
of the allocation. There is no way to explicitly remove a channel.
Consequently, a client which obtains an allocation with the intent of
holding it for extremely long periods, possibly for communication
with many different peers over time, may eventually exhaust the set
of channels. In that case, the client will need to obtain a new
allocation.
5. General Behavior Peer: A host with which the TURN client wishes to communicate. The
TURN server relays traffic between the TURN client and its
peer(s). The peer does not interact with the TURN server using
the protocol defined in this document; rather, the peer receives
data sent by the TURN server and the peer sends data towards the
TURN server.
Host Transport Address: A transport address allocated on a host.
Server-Reflexive Transport Address: A transport address on the
"public side" of a NAT. This address is allocated by the NAT to
correspond to a specific host transport address.
Relayed Transport Address: A transport address that exists on a TURN
server. If a permission exists, packets that arrive at this
address are relayed towards the TURN client.
Allocation: The transport address granted to a client through an
Allocate request, along with related state, such as permissions
and expiration timers. See also Relayed Transport Address.
5-tuple: A combination of the source IP address and port,
destination IP address and port, and transport protocol (UDP or
TCP). A 5-tuple uniquely identifies a TCP connection or the bi-
directional flow of UDP datagrams.
Permission: The IP address and transport protocol (but not the port)
of a peer that is permitted to send traffic to the TURN server and
have that traffic relayed to the TURN client. The TURN server
will only forward traffic to its client from peers that match an
existing permission.
4. General Behavior
After the initial Allocate transaction, all subsequent TURN After the initial Allocate transaction, all subsequent TURN
transactions need to be sent in the context of a valid allocation. transactions need to be sent in the context of a valid allocation.
The source and destination IP address and ports for these TURN The source and destination IP address and ports for these TURN
messages MUST match the internal 5-tuple of an existing allocation. messages MUST match the those used in the initial Allocate Request.
These are processed using the general server procedures in These are processed using the general server procedures in
[I-D.ietf-behave-rfc3489bis] with a few important additions. For [I-D.ietf-behave-rfc3489bis] with a few important additions. For
requests (in this specification, the only subsequent request possible requests, if there is no matching allocation, the server MUST
is a Refresh request), if there is no matching allocation, the server generate a 437 (Allocation Mismatch) error response. For
MUST generate a 437 (Allocation Mismatch) error response. For
indications, if there is no matching allocation, the indication is indications, if there is no matching allocation, the indication is
silently discarded. An Allocate request MUST NOT be sent by a client silently discarded. An Allocate request MUST NOT be sent by a client
within the context of an existing allocation. Such a request MUST be within the context of an existing allocation. Such a request MUST be
rejected by the server with a 437 (Allocation Mismatch) error rejected by the server with a 437 (Allocation Mismatch) error
response. response.
A subsequent request MUST be authenticated using the same username A subsequent request MUST be authenticated using the same username,
and realm as the one used in the Allocate request that created the password and realm as the one used in the Allocate request that
allocation. If the request was authenticated but not with the created the allocation. If the request was authenticated but not
matching credential, the server MUST reject the request with a 401 with the matching credential, the server MUST reject the request with
(Unauthorized) error response. a 401 (Unauthorized) error response.
When a server returns an error response, it MAY include an ALTERNATE- When a server returns an error response, it MAY include an ALTERNATE-
SERVER attribute if it has positive knowledge that the problem SERVER attribute if it has positive knowledge that the problem
reported in the error response will not be a problem on the alternate reported in the error response will not be a problem on the alternate
server. For example, a 443 response (Invalid IP Address) with an server. For example, a 443 response (Invalid IP Address) with an
ALTERNATE-SERVER means that the other server is responsible for that ALTERNATE-SERVER means that the other server is responsible for that
IP address. A 442 (Unsupported Transport Protocol) with this IP address. A 442 (Unsupported Transport Protocol) with this
attribute means that the other server is known to support that attribute means that the other server is known to support that
transport protocol. A 507 (Insufficient Capacity) means that the transport protocol. A 507 (Insufficient Capacity) means that the
other server is known to have sufficient capacity. Using the other server is known to have sufficient capacity. Using the
skipping to change at page 12, line 44 skipping to change at page 14, line 10
response can only be done if the rejecting server has definitive response can only be done if the rejecting server has definitive
knowledge of available capacity on the target. This will require knowledge of available capacity on the target. This will require
some kind of state sharing mechanism between TURN servers, which is some kind of state sharing mechanism between TURN servers, which is
beyond the scope of this specification. If a TURN server attempts to beyond the scope of this specification. If a TURN server attempts to
redirect to another server without knowledge of available capacity, redirect to another server without knowledge of available capacity,
it is possible that all servers are in a congested state, resulting it is possible that all servers are in a congested state, resulting
in series of rejections that only serve to further increase the load in series of rejections that only serve to further increase the load
on the system. This can cause congestion collapse. on the system. This can cause congestion collapse.
If a client sends a request to a server and gets a 500 class error If a client sends a request to a server and gets a 500 class error
response without an ALTERNATE-SERVER, or the transaction times out response without an ALTERNATE-SERVER, or the STUN transaction times
without a response, and the client was utilizing the SRV procedures out without a response, and the client was utilizing the SRV
of [I-D.ietf-behave-rfc3489bis] to contact the server, the client procedures of [I-D.ietf-behave-rfc3489bis] to contact the server, the
SHOULD try another server based on those procedures. However, the client SHOULD try another server based on those procedures. However,
client SHOULD cache the fact that the request to this server failed, the client SHOULD cache the fact that the request to this server
and not retry that server again for a configurable period of time. failed, and not retry that server again for a configurable period of
Five minutes is RECOMMENDED. time. Five minutes is RECOMMENDED.
TURN clients and servers MUST NOT include the FINGERPRINT attribute TURN clients and servers MUST NOT include the FINGERPRINT attribute
in any of the methods defined in this document. in any of the methods defined in this document.
6. Managing Allocations 5. Managing Allocations
Communications between a TURN client and a TURN server on a new flow Communications between a TURN client and a TURN server begin with an
begin with an Allocate transaction. All subsequent transactions Allocate transaction. All subsequent transactions happen in the
happen in the context of that allocation. The client refreshes context of that allocation, and happen on the same 5-tuple. The
allocations and deallocates them using a Refresh transaction. client refreshes allocations and deallocates them using a Refresh
transaction.
6.1. Client Behavior 5.1. Client Behavior
6.1.1. Initial Allocate Requests 5.1.1. Initial Allocate Requests
When a client wishes to obtain a transport address, it sends an When a client wishes to obtain a transport address, it sends an
Allocate request to the server. This request is constructed and sent Allocate request to the server. This request is constructed and sent
using the general procedures defined in [I-D.ietf-behave-rfc3489bis]. using the general procedures defined in [I-D.ietf-behave-rfc3489bis].
Clients MUST implement the long term credential mechanism defined in Clients MUST implement the long term credential mechanism defined in
[I-D.ietf-behave-rfc3489bis], and be prepared for the server to use [I-D.ietf-behave-rfc3489bis], and be prepared for the server to
it. demand credentials for requests.
The client SHOULD include a BANDWIDTH attribute, which indicates the The client SHOULD include a BANDWIDTH attribute, which indicates the
maximum bandwidth that will be used with this binding. If the maximum bandwidth that will be used with this binding. If the
maximum is unknown, the attribute is not included in the request. maximum is unknown, the attribute is not included in the request.
OPEN ISSUE: Bandwidth is very much underspecified. Is anyone
actually using it for capacity planning? If not we should remove.
The client MAY request a particular lifetime for the allocation by The client MAY request a particular lifetime for the allocation by
including it in the LIFETIME attribute in the request. including it in the LIFETIME attribute in the request.
The client MUST include a REQUESTED-TRANSPORT attribute. In this The client MUST include a REQUESTED-TRANSPORT attribute. In this
specification, the REQUESTED-TRANSPORT will always be UDP. This specification, the REQUESTED-TRANSPORT MUST always be UDP. This
attribute is included to allow for future extensions to TURN. attribute is included to allow for future extensions to TURN (e.g.,
[I-D.ietf-behave-turn-tcp])
The client MAY include a REQUESTED-PORT-PROPS or REQUESTED-IP The client MAY include a REQUESTED-PORT-PROPS or REQUESTED-IP
attribute in the request to obtain specific types of transport attribute in the request to obtain specific types of transport
addresses. Whether these are needed depends on the application using addresses, if desired.
the TURN server. As an example, the Real Time Transport Protocol
(RTP) [RFC3550] requires that RTP and RTCP ports be an adjacent pair,
even and odd respectively, for compatibility with a previous version
of that specification. The REQUESTED-PORT-PROPS attribute allows the
client to ask the relay for those properties.
Processing of the response follows the general procedures of Processing of the response follows the general procedures of
[I-D.ietf-behave-rfc3489bis]. A successful response will include [I-D.ietf-behave-rfc3489bis]. A successful response will include
both a RELAY-ADDRESS and an XOR-MAPPED-ADDRESS attribute, providing both a RELAY-ADDRESS and an XOR-MAPPED-ADDRESS attribute, providing
both a relayed transport address and a reflexive transport address, both a relayed transport address and a reflexive transport address,
respectively, to the client. The value of the LIFETIME attribute in respectively, to the client. The value of the LIFETIME attribute in
the response indicates the amount of time after which the server will the response indicates the amount of time after which the server will
expire the allocation, if not refreshed with a Refresh request. The expire the allocation, if not refreshed with a Refresh request. The
server will allow the user to send and receive at least the amount of server will allow the user to send and receive at least the amount of
data indicated in the BANDWIDTH attribute per allocation. (At its data indicated in the BANDWIDTH attribute per allocation. (At its
skipping to change at page 14, line 21 skipping to change at page 15, line 29
If the response is an error response and contains a 442, 443 or 444 If the response is an error response and contains a 442, 443 or 444
error code, the client knows that its requested properties could not error code, the client knows that its requested properties could not
be met. The client MAY retry with different properties, with the be met. The client MAY retry with different properties, with the
same properties (in a hope that something has changed on the server), same properties (in a hope that something has changed on the server),
or give up, depending on the needs of the application. However, if or give up, depending on the needs of the application. However, if
the client retries, it SHOULD wait 500ms, and if the request fails the client retries, it SHOULD wait 500ms, and if the request fails
again, wait 1 second, then 2 seconds, and so on, exponentially again, wait 1 second, then 2 seconds, and so on, exponentially
backing off. backing off.
6.1.2. Refresh Requests 5.1.2. Refresh Requests
TURN permissions are kept alive by traffic flowing through them, and
persist for the lifetime of the allocation. However, The allocations
themselves have to be kept alive through Refresh Requests.
Before 3/4 of the lifetime of the allocation has passed (the lifetime Before 3/4 of the lifetime of the allocation has passed (the lifetime
of the allocation is conveyed in the LIFETIME attribute of the of the allocation is conveyed in the LIFETIME attribute of the
Allocate Response), the client SHOULD refresh the allocation with a Allocate Response), the client SHOULD refresh the allocation with a
Refresh transaction if it wishes to keep the allocation. Refresh transaction if it wishes to keep the allocation.
To perform a refresh, the client generates a Refresh Request. The To perform a refresh, the client generates a Refresh Request. The
client MUST use the same username, realm and password for the Refresh client MUST use the same username, realm and password for the Refresh
request as it used in its initial Allocate Request. The Refresh request as it used in its initial Allocate Request. The Refresh
request MAY contain a proposed LIFETIME attribute. The client MAY request MAY contain a proposed LIFETIME attribute. The client MAY
include a BANDWIDTH attribute if it wishes to request more or less include a BANDWIDTH attribute if it wishes to request more or less
bandwidth than in the original request. If absent, it indicates no bandwidth than in the original request (this might also be the first
change in the requested bandwidth from the Allocate request. The time the TURN client indicates bandwidth to the TURN server). If the
client MUST NOT include a REQUESTED-IP, REQUESTED-TRANSPORT, or BANDWIDTH attribute is absent, it indicates no change in the
REQUESTED-PORT-PROPS attribute in the Refresh request. requested bandwidth from the Allocate request. The client MUST NOT
include a REQUESTED-IP, REQUESTED-TRANSPORT, or REQUESTED-PORT-PROPS
attribute in the Refresh request.
In a successful response, the LIFETIME attribute indicates the amount In a successful response, the LIFETIME attribute indicates the amount
of additional time (the number of seconds after the response is of additional time (the number of seconds after the response is
received) that the allocation will live without being refreshed. A received) that the allocation will live without being refreshed. A
successful response will also contain a BANDWIDTH attribute, successful response will also contain a BANDWIDTH attribute,
indicating the bandwidth the server is allowing for this allocation. indicating the bandwidth the server is allowing for this allocation.
Note that an error response does not imply that the allocation has Note that an error response does not imply that the allocation has
expired, just that the refresh has failed. expired, just that the refresh has failed.
If a client no longer needs an allocation, it SHOULD perform an If a client no longer needs an allocation, it SHOULD perform an
explicit deallocation. If the client wishes to explicitly remove the explicit deallocation. If the client wishes to explicitly remove the
allocation because it no longer needs it, it sends a Refresh request, allocation because it no longer needs it, it sends a Refresh request,
but sets the LIFETIME attribute to zero. This will cause the server but sets the LIFETIME attribute to zero. This will cause the server
to remove the allocation, and all associated permissions and channel to remove the allocation, and all associated permissions and channel
numbers. For connection-oriented transports such as TCP, the client numbers. For connection-oriented transports such as TCP, the client
can also remove the allocation (and all associated bindings) by can also remove the allocation (and all associated bindings) by
closing the relevant connection with the TURN server. closing the relevant connection with the TURN server.
6.2. Server Behavior 5.2. Server Behavior
The server first processes the request according to the base protocol
procedures in [I-D.ietf-behave-rfc3489bis], extended with the
procedures for the long-term credential mechanism.
6.2.1. Initial Allocate Requests 5.2.1. Receiving an Allocate Request
When the server receives an Allocate request, the server attempts to When the server receives an Allocate request, the server attempts to
allocate a relayed transport address. It first looks for the allocate a relayed transport address.
BANDWIDTH attribute in the request. If present, the server
determines whether or not it has sufficient capacity to handle a When the server receives the Allocate Request, it begins by
binding that will generate the requested bandwidth. processing it according to the base protocol procedures described in
[I-D.ietf-behave-rfc3489bis], plus the Long-Term Credential Mechanism
procedures if the server is using this mechanism.
It then checks if the 5-tuple used for the Allocate Request matches
the 5-tuple used for an existing allocation. If there is a match,
then:
o If the transport protocol is UDP, and the transaction id in the
request message matches the transaction id used for the original
allocation, then the server treats this as a retransmission of the
original request, and replies with the same response as it did to
the original request. The server may do this by either storing
its original response and resending it, or by rebuilding its
original response from other state data.
o If the transport protocol is not UDP, or if the transaction id in
the request message does not match the transaction id used for the
original allocation, then the server replies with an error
response containing the error code 437 Allocation Mismatch.
If the 5-tuple does not match an existing allocation, then processing
continues as described below.
5.2.1.1. BANDWIDTH
The server checks for the BANDWIDTH attribute in the request. If
present, the server determines whether or not it has sufficient
capacity to handle a binding that will generate the requested
bandwidth.
If it does, the server attempts to allocate a transport address for If it does, the server attempts to allocate a transport address for
the client. The Allocate Request can contain several additional the client. The Allocate Request can contain several additional
attributes that allow the client to request specific characteristics attributes that allow the client to request specific characteristics
of the transport address. of the transport address. If it doesn't, it sends an error response.
6.2.1.1. REQUESTED-TRANSPORT 5.2.1.2. REQUESTED-TRANSPORT
First, the server checks for the REQUESTED-TRANSPORT attribute. This The server checks for the REQUESTED-TRANSPORT attribute. This
indicates the transport protocol requested by the client. This indicates the transport protocol requested by the client. This
specification defines a value for UDP only, but support for TCP specification defines a value for UDP only, but support for TCP
allocations is planned in [I-D.ietf-behave-turn-tcp]. allocations is planned in [I-D.ietf-behave-turn-tcp].
As a consequence of the REQUESTED-TRANSPORT attribute, it is As a consequence of the REQUESTED-TRANSPORT attribute, it is
possible for a client to connect to the server over TCP or TLS possible for a client to connect to the server over TCP or TLS
over TCP and request a UDP transport address. In this case, the over TCP and request a UDP transport address. In this case, the
server will relay data between the transports. server will relay data between the transports.
If the requested transport is supported, the server allocates a port If the requested transport is supported, the server allocates a port
using the requested transport protocol. If the REQUESTED-TRANSPORT using the requested transport protocol. If the REQUESTED-TRANSPORT
attribute contains a value of the transport protocol unknown to the attribute contains a value of the transport protocol unknown to the
server, or known to the server but not supported by the server in the server, or known to the server but not supported by the server in the
context of this request, the server MUST reject the request and context of this request, the server MUST reject the request and
include a 442 (Unsupported Transport Protocol) in the response. If include a 442 (Unsupported Transport Protocol) in the response. If
the request did not contain a REQUESTED-TRANSPORT attribute, the the request did not contain a REQUESTED-TRANSPORT attribute, the
server MUST use the same transport protocol as the request arrived server MUST use the same transport protocol as the request arrived
on. on.
6.2.1.2. REQUESTED-IP 5.2.1.3. REQUESTED-IP
Next, the server checks for the REQUESTED-IP attribute. If present, The server checks for the REQUESTED-IP attribute. If present, it
it indicates a specific IP address from which the client would like indicates a specific IP address from which the client would like its
its transport address allocated. (The client could do this if it transport address allocated. (The client could do this if it
requesting the second address in a specific port pair). If this IP requesting the second address in a specific port pair). If this IP
address is not a valid one for allocations on the server, the server address is not a valid one for allocations on the server, the server
MUST reject the request and include a 443 (Invalid IP Address) error MUST reject the request and include a 443 (Invalid IP Address) error
code in the response, or else redirect the request to a server that code in the response, or else redirect the request to a server that
is known to support this IP address. If the IP address is one that is known to support this IP address. If the IP address is one that
is valid for allocations (presumably, the server is configured to is valid for allocations (presumably, the server is configured to
know the set of IP addresses from which it performs allocations), the know the set of IP addresses from which it performs allocations), the
server MUST provide an allocation from that IP address. If the server MUST provide an allocation from that IP address. If the
attribute is not present, the selection of an IP address is at the attribute is not present, the selection of an IP address is at the
discretion of the server. discretion of the server.
6.2.1.3. REQUESTED-PORT-PROPS 5.2.1.4. REQUESTED-PORT-PROPS
Finally, the server checks for the REQUESTED-PORT-PROPS attribute. The server checks for the REQUESTED-PORT-PROPS attribute. If
If present, it indicates specific port properties desired by the present, it indicates specific port properties desired by the client.
client. This attribute is split into two portions: one portion for This attribute is split into two portions: one portion for port
port behavior and the other for requested port alignment (whether the behavior and the other for requested port alignment (whether the
allocated port is odd, even, reserved as a pair, or at the discretion allocated port is odd, even, reserved as a pair, or at the discretion
of the server). of the server).
If the port behavior requested is for a Specific Port, the server If the port behavior requested is for a Specific Port, the server
MUST attempt to allocate that specific port for the client. If the MUST attempt to allocate that specific port for the client. If the
specific port is not available (in use or reserved), the server MUST specific port is not available (in use or reserved), the server MUST
reject the request with a 444 (Invalid Port) response. For example, reject the request with a 444 (Invalid Port) response. For example,
the STUN server could reject a request for a Specific Port because the STUN server could reject a request for a Specific Port because
the port is temporarily reserved as part of an adjacent pair of the port is temporarily reserved as part of an adjacent pair of
ports, or because the requested port is a well-known port (1-1023). ports, or because the requested port is a well-known port (1-1023).
skipping to change at page 16, line 51 skipping to change at page 18, line 41
of the next higher port" alignment is similar to requesting an even of the next higher port" alignment is similar to requesting an even
port. It is a request for an even port, and MUST be rejected by the port. It is a request for an even port, and MUST be rejected by the
server if an even port cannot be provided, or redirected to an server if an even port cannot be provided, or redirected to an
alternate server. However, it is also a hint from the client that alternate server. However, it is also a hint from the client that
the client will request the next higher port with a separate Allocate the client will request the next higher port with a separate Allocate
request. As such, it is a request for the server to allocate an even request. As such, it is a request for the server to allocate an even
port whose next higher port is also available, and furthermore, a port whose next higher port is also available, and furthermore, a
request for the server to not allocate that one higher port to any request for the server to not allocate that one higher port to any
other request except for one that asks for that port explicitly. The other request except for one that asks for that port explicitly. The
server can honor this request for adjacency at its discretion. The server can honor this request for adjacency at its discretion. The
only constraint is that the allocated port has to be even. only constraint is that the allocated port number MUST be even.
Port alignment requests exist for compatibility with Port alignment requests exist for compatibility with
implementations of RTP which predate RFC 3550. These implementations of RTP which predate [RFC3550]. These
implementations use the port numbering conventions in (now implementations use the port numbering conventions in (now
obsolete) RFC 1889. obsolete) [RFC1889].
6.2.1.4. Creating the Allocation 5.2.1.5. Lifetime
The server checks for a LIFETIME attribute. If present, it indicates
the lifetime the client would like the server to assign to the
allocation.
If the LIFETIME attribute is malformed, or if the requested lifetime
value is less than 32 seconds, the server replies with an error
response with an error code of XXX Lifetime Malformed or Invalid.
5.2.1.6. Creating the Allocation
If any of the requested or desired constraints cannot be met, whether If any of the requested or desired constraints cannot be met, whether
it be bandwidth, transport protocol, IP address or port, instead of it be bandwidth, transport protocol, IP address or port, the server
rejecting the request, the server can alternately redirect the client can redirect the client to a different server that may be able to
to a different server that may be able to fulfill the request. This fulfill the request. This is accomplished using the 300 error
is accomplished using the 300 error response and ALTERNATE-SERVER response and ALTERNATE-SERVER attribute. If the server does not
attribute. If the server does not redirect and cannot service the redirect and cannot service the request because the server has
request because the server has reached capacity, it sends a 507 reached capacity, it sends a 507 (Insufficient Capacity) response.
(Insufficient Capacity) response. The server can also reject the The server can also reject the request with a 486 (Allocation Quota
request with a 486 (Allocation Quota Reached) if the user or client Reached) if the user or client is not authorized to request
is not authorized to request additional allocations. additional allocations.
The server SHOULD only allocate ports in the range 1024-65535. This The server SHOULD only allocate ports from the range 49152 - 65535
is one of several ways to prohibit relayed transport addresses from (the Dynamic and/or Private Port range [Port-Numbers]), unless the
being used to attempt to run standard services. TURN server application knows, through some means not specified here,
that other applications running on the same host as the TURN server
application will not be impacted by allocating ports outside this
range. This condition can often be satisfied by running the TURN
server application on a dedicated machine and/or by arranging that
any other applications on the machine allocate ports before the TURN
server application starts. In any case, the TURN server SHOULD NOT
allocate ports in the range 0 - 1023 (the Well-Known Port range) to
discourage clients from using TURN to run standard services.
Once a port is allocated, the server associates the allocation with Once a port is allocated, the server associates the allocation with
the 5-tuple used to communicate between the client and the server. the 5-tuple used to communicate between the client and the server.
For TCP, this amounts to associating the TCP connection from the TURN For TCP, this amounts to associating the TCP connection from the TURN
client with the allocated transport address. client with the allocated transport address.
The new allocation MUST also be associated with the username, The new allocation MUST also be associated with the username,
password and realm used to authenticate the request. These password and realm used to authenticate the request. These
credentials are used in all subsequent requests to ensure that only credentials are used in all subsequent requests to ensure that only
the same client can use or modify the allocation it was given. the same client can use or modify the allocation it was given.
In addition, the allocation created by the server is associated with In addition, the allocation created by the server is associated with
a set of permissions. Each permission is a specific IP address a set of permissions and a set of channel bindings. Each set is
identifying an external client. Initially, this list is null. initially empty.
If the LIFETIME attribute was present in the request, and the value If the LIFETIME attribute was present in the request, and the value
is larger than the maximum duration the server is willing to use for is larger than the maximum duration the server is willing to use for
the lifetime of the allocation, the server MAY lower it to that the lifetime of the allocation, the server MAY lower it to that
maximum. However, the server MUST NOT increase the duration maximum. However, the server MUST NOT increase the duration
requested in the LIFETIME attribute. If there was no LIFETIME requested in the LIFETIME attribute. If there was no LIFETIME
attribute, the server may choose a duration at its discretion. Ten attribute, the server may choose a duration at its discretion. Ten
minutes is RECOMMENDED. In either case, the resulting duration is minutes is RECOMMENDED. In either case, the resulting duration is
added to the current time, and a timer, called the allocation added to the current time, and a timer, called the allocation
expiration timer, is set to fire at or after that time. expiration timer, is set to expire at or after that time. Note that
Section 7.2.3 discusses behavior when the timer fires. Note that the the LIFETIME attribute in an Allocate request can be zero, though
LIFETIME attribute an Allocate request can be zero, though this is this is effectively a no-op, since it will create and destroy the
effectively a no-op, since it will create and destroy the allocation allocation in one transaction.
in one transaction.
6.2.1.5. Sending the Allocate Response 5.2.1.7. Sending the Allocate Response
Once the port has been obtained and the allocation expiration timer Once the port has been obtained and the allocation expiration timer
has been started, the server generates an Allocate Response using the has been started, the server generates an Allocate Response using the
general procedures defined in [I-D.ietf-behave-rfc3489bis], including general procedures defined in [I-D.ietf-behave-rfc3489bis], including
the ones for long term authentication. The transport address the ones for long term authentication. The transport address
allocated to the client MUST be included in the RELAY-ADDRESS allocated to the client MUST be included in the RELAY-ADDRESS
attribute in the response. In addition, this response MUST contain attribute in the response. In addition, this response MUST contain
the XOR-MAPPED-ADDRESS attribute. This allows the client to the XOR-MAPPED-ADDRESS attribute. This allows the client to
determine its reflexive transport address in addition to a relayed determine its reflexive transport address in addition to a relayed
transport address, from the same Allocate request. transport address, from the same Allocate request.
The server MUST add a LIFETIME attribute to the Allocate Response. The server MUST add a LIFETIME attribute to the Allocate Response.
This attribute contains the duration, in seconds, of the allocation This attribute contains the duration, in seconds, of the allocation
expiration timer associated with this allocation. expiration timer associated with this allocation.
The server MUST add a BANDWIDTH attribute to the Allocate Response. The server MUST add a BANDWIDTH attribute to the Allocate Response.
This MUST be equal to the attribute from the request, if one was This MUST be equal to the attribute from the request, if one was
present. Otherwise, it indicates a per-allocation limit that the present. Otherwise, it indicates a per-allocation limit that the
server is placing on the bandwidth usage on each binding. Such server is placing on the bandwidth usage on each binding. Such
limits are needed to prevent against denial-of-service attacks (See limits are needed to prevent against denial-of-service attacks (see
Section 11). Section 12).
6.2.2. Refresh Requests 5.2.2. Refresh Requests
A Refresh request is processed using the general server and long term A Refresh request is processed using the general server and long term
authentication procedures in [I-D.ietf-behave-rfc3489bis]. It is authentication procedures in [I-D.ietf-behave-rfc3489bis]. It is
used to refresh and extend an allocation, or to cause an immediate used to refresh and extend an allocation, or to cause an immediate
deallocation. It is processed as follows. deallocation. It is processed as follows.
First, the request MUST be authenticated using the same shared secret First, the request MUST be authenticated using the same shared secret
as the one associated with the allocation. If the request was as the one associated with the allocation. If the request was
authenticated but not with such a matching credential, the server authenticated but not with such a matching credential, the server
MUST generate a Refresh Error Response with a 401 response. MUST generate a Refresh Error Response with a 401 response.
If the Refresh request contains a BANDWIDTH attribute, the server If the Refresh request contains a BANDWIDTH attribute, the server
checks that it can relay the requested volume of traffic. checks that it can relay the requested volume of traffic.
Finally, a Refresh Request will set a new allocation expiration timer Finally, a Refresh Request will set a new allocation expiration timer
for the allocation, effectively canceling the previous allocation for the allocation, effectively canceling the previous allocation
expiration timer. As with an Allocate request, the server can offer expiration timer. As with an Allocate request, the server MAY
a shorter allocation lifetime, but never a longer one. utilize a shorter allocation lifetime, but MUST NOT utilize a longer
lifetime.
A success Refresh response MUST contain a LIFETIME attribute and a A success Refresh response MUST contain a LIFETIME attribute. If its
BANDWIDTH attribute. associated Allocate request contained the BANDWIDTH attribute, or
this Refresh request contained a new BANDWIDTH attribute, the
response MUST also contain the BANDWIDTH attribute.
7. Sending and Receiving Data 6. Send and Data Indications
As described in Section 4, TURN allows a client to send and receive TURN supports two ways to send and receive data from peers. This
data without utilizing TURN Send and Data indications, by sending and section describes the use of Send and Data indications, while
receiving them on channels. Before sending client-to-peer or peer- Section 7 describes the use of the Channel Mechanism.
to-client data for a new peer, a TURN client or server needs to
assign a channel number that corresponds to that remote peer. Once a
channel number is assigned, it remains assigned through the duration
of the allocation. It cannot be unassigned or reassigned to a
different peer.
7.1. Client Behavior 6.1. Forming and Sending an Indication
7.1.1. Sending When the client has data to send to a peer, it uses a Send Indication
to pass the data to the server. When the server has data to send to
the client, it uses a Data Indication to pass the data to the client.
A client can also use a Send Indication without a DATA attribute to
install or refresh a permission for the specified IP address. Both
indications are formed following the general rules described in [ref
3489bis] with the extra considerations described below.
When the client wants to forward data to a peer, it checks if it has A Send Indication MUST contain a PEER-ADDRESS attribute and MAY
assigned a channel number for communications with this peer (as contain a DATA attribute, while a Data Indication MUST contain both
identified by its IP address and port) over this allocation: attributes. The PEER-ADDRESS attribute contains the transport
address of the peer to which the data is to be sent (in the case of a
Send Indication) or from which the data was received (in the case of
a Data Indication). This peer address is the transport address of
the peer as seen by the server, which may not be the same as the host
transport address of the peer. The DATA attribute contains the
actual application data. Note that the application data may need to
be padded to ensure the DATA attribute length is a multiple of 4.
o If one has not been assigned, the client assigns one of its own No other attributes are included. For example, neither the
choosing. This channel number MUST be one that is currently FINGERPRINT attribute nor any authentication attributes are included.
unassigned by the client for this allocation. It MUST be between The latter holds even if the server is using the Long-Term Credential
1 and 65534. It is RECOMMENDED that the client choose one of the Mechanism, since indications cannot be authenticated using this
unassigned numbers randomly, rather than sequentially. The state mechanism.
of the channel is set to unconfirmed.
o If one has been assigned, that channel MUST be selected. Both the Send and Data indications MUST be sent using the 5-tuple of
the original allocation. Thus, in the case of the Send Indication,
the source transport address is the client's host transport address,
the destination transport address is the TURN server address, and the
transport protocol is the same as was used for the Allocate request.
For the Data Indication, the source and destination transport
addresses are the reverse.
Next, the client checks if the channel number has been confirmed by 6.2. Receiving an Indication
the server. If the channel number has been confirmed, the client
simply sends the data to the TURN server with the appropriate channel
number in the TURN framing.
If the channel number has not been confirmed, the client creates a When a Send Indication is received at the server, or a Data
Send indication. It places the selected channel number in a CHANNEL- Indication is received at the client, the receiver first does the
NUMBER attribute, the peer IP address and port in a PEER-ADDRESS basic indication processing described in [3489bis]. Once this is
attribute, and puts the data to be sent in a DATA attribute. (If the done, it does the processing specific to the Send and Data methods
client just wishes to create a permission, it can omit the DATA described below.
attribute.) If the Send indication is sent over a reliable transport
(ex: TCP), the client marks that the channel number as confirmed.
When the client receives a ChannelConfirmation Indication, and the
channel number, IP address and port match the channel number assigned
to that peer, the client marks that the channel number is confirmed.
Since Send is an Indication, it generates no response. The client A Send Indication MUST contain a PEER-ADDRESS attribute and MAY
must rely on application layer mechanisms to determine if the data contain a DATA attribute, while a Data Indication MUST contain both
was received by the peer. A ChannelConfirmation Indication just attributes. Any other attributes appearing in the message are
means that some Send indication was received by the TURN server. It treated as unexpected.
does not mean that a specific Send indication was received by the
peer.
Note that Send Indications are not authenticated and do not TODO: Add check that Send or Data indication arrives with
contain a MESSAGE-INTEGRITY attribute. Just like non-relayed data appropriate 5-tuple. Since this check applies to all STUN
sent over UDP or TCP, the authenticity and integrity of this data messages, not just Send and Data indications, perhaps this goes
can only be assured using security mechanisms at higher layers. under the general processing section.
7.1.2. Receiving 6.3. Relaying
When the client receives a Data indication, it: When the server receives a valid Send Indication contains a DATA
attribute, it forms a UDP datagram as follows:
o records the channel number used by the server (from the CHANNEL- o the source transport address is the relayed transport address of
NUMBER attribute) and associates it with the IP address and port the allocation, where the allocation is determined by the 5-tuple
in the PEER-ADDRESS attribute, which identify the peer that sent on which the Send Indication arrived;
the data. The resulting mapping from channel number to transport
address MUST be stored by the client for the duration of the
allocation.
o delivers the contents of the DATA attribute to the client o the destination transport address is taken from the PEER-ADDRESS
application as if it was received from the peer's IP address and attribute;
port.
o If the Data indication was received over UDP, the client MUST o the data following the UDP header is the contents of the value
confirm the channel used by the server, by sending a field of the DATA attribute;
ChannelConfirmation Indication to the server. This indication
MUST contain the same PEER-ADDRESS and CHANNEL-NUMBER attributes
included in the Data indication. This indication is sent to the
server on channel 0 using the 5-tuple associated with this
allocation. Note that, due to round trip delays, a client may
receive several Data indications with the same channel number for
the same remote peer. It MUST process each as defined here,
resulting in several ChannelConfirmation indications.
When the client receives unencapsulated data, it checks the received o the Length field in the UDP header is set to the Length field of
channel number. If the client has a mapping associated with the the DATA attribute;
server channel number it delivers the data to the client application
as if it was received directly from that peer. Otherwise, it
silently discards the data.
7.2. Server Behavior o the Checksum field in the UDP header is computed as described in
[RFC 768].
7.2.1. Receiving Data from the Client The resulting UDP datagram is then sent to the peer.
When the server receives a Data indication from the client, it: When the server receives a valid Send Indication (with or without a
DATA attribute), it also updates the permission associated with the
IP address contained in the PEER-ADDRESS attribute. For a certain
interval after the permission is updated, UDP datagrams received from
peers with source IP address equal to the IP address contained in the
PEER-ADDRESS attribute can be forwarded to the client. Note that
only the IP addresses are considered and the port numbers are
irrelevent. This permission is specific to the allocation and has no
affect on any other allocation. The recommended length of time is 60
seconds from when the Send Indication is received.
o records the channel number used by the client (from the CHANNEL- When the server receives a UDP datagram with a destination transport
NUMBER attribute) and associates it with the IP address and port address corresponding to an active (i.e., still alive) allocation,
in the PEER-ADDRESS attribute, which identify the peer to which then it first checks to see if it is permitted to relay the datagram.
the data is to be sent. The resulting mapping from channel number If it is not permitted, the UDP datagram MUST be discarded.
to peer transport address MUST be stored by the server for the
duration of the allocation.
o sends the contents of the DATA attribute in a UDP datagram, If relaying is permitted, the server forms and send a Data Indication
sending it to the PEER-ADDRESS and sending from the allocated as described in Section 6.1, using the data following the UDP header
transport address. as the application data.
o if one doesn't exist, creates a permission for the IP address from 7. Channel Mechanism
the PEER-ADDRESS (the port is ignored), and attaches the
permission to the allocation
o checks if a timer has been set for this permission. If none has As described in the overview, channel mechanism provides a way for a
been started, the server starts one. It is RECOMMENDED that it client and server to send application data using ChannelData
have a value of sixty seconds. If the timer is already running, messages, which have less overhead than Send and Data indications.
it MUST be reset.
o If the Send indication was received over UDP, the server MUST Channel bindings are always initiated by the client. The client can
confirm the channel used by the client, by sending a bind a channel to a peer at any time during the lifetime of the
ChannelConfirmation Indication to the client. This indication allocation. The client may bind a channel to a peer before
MUST contain the same PEER-ADDRESS and CHANNEL-NUMBER attributes exchanging data with it, or after exchanging data with it (using Send
included in the Send indication. This indication is sent to the and Data indications) for some time, or may choose never to bind a
client on channel 0 using the 5-tuple associated with this channel it. The client can also bind channels to some peers while
allocation. Note that, due to round trip delays, a server may not binding channels to other peers.
receive several Send indications with the same channel number for
the same remote peer. It MUST process each as defined here,
resulting in several ChannelConfirmation indications.
When the server receives unencapsulated data, it checks the received Once a channel is bound to a peer, the channel binding cannot be
channel number: changed. There is no way to unbind a channel or bind it to a
different peer.
o If the server has a mapping associated with the client channel Channel bindings are specific to an allocation, so that a binding in
number it: one allocation has no relationship to a binding in any other
allocation. If an allocation expires, all its channel bindings
expire with it.
* sends a UDP datagram to the peer using the transport address 7.1. Forming and Sending a ChannelBind Request
from the mapping, and sends from the allocated transport
address.
* checks if a permission activity timer is running for the When a client wishes to bind a channel to a peer in an allocation, it
destination IP address of the peer. If one is not running, the forms a ChannelBind Request. The Request formed following the
server starts one. It is RECOMMENDED that it have a value of general rules described in [I-D.ietf-behave-rfc3489bis] with the
sixty seconds. If the timer is already running, it MUST be extra considerations described below.
reset.
o If the server has no mapping, it silently discards the data. A ChannelBind Request MUST contain both a CHANNEL-NUMBER attribute
and a PEER-ADDRESS attribute. The CHANNEL-NUMBER attribute specifies
the number of the channel that the client wishes to bind to the peer.
The channel number MUST be in the range 0x4000 to 0xFFFE (inclusive)
and the channel MUST NOT be already bound to a different peer. It is
acceptable to rebind a channel to the peer it is already bound to.
The PEER-ADDRESS attribute specifies the peer address to bind the
channel to.
7.2.2. Receiving Data from Peers Once formed, the ChannelBind Request is sent using the 5-tuple for
the allocation.
If a server receives a UDP packet on an allocated UDP transport The client SHOULD be prepared to receive ChannelData messages on the
address, it checks the permissions associated with that allocation. channel as soon as it has sent the ChannelBind Request. Over UDP, it
If the source IP address of the UDP packet matches one of the is possible for the client to receive these before it receives a
permissions (the source port is not used), the UDP packet is ChannelBind Success Response.
accepted. Otherwise, it is discarded. If the packet is accepted, it
is forwarded to the client as described below.
The server checks if it has assigned a channel number for Over UDP, the client SHOULD NOT send ChannelData messages on the
communications from this peer (as identified by its IP address and channel until it has received a ChannelBind Success Response for the
port) over this allocation: binding attempt. Sending them before the success response is
received risks having them dropped by the server if he ChannelBind
Request was lost.
o If one has not been assigned, the client assigns one of its own 7.2. Receiving a ChannelBind Request and Sending a Response
choosing. This channel number MUST be one that is currently
unassigned by the server for this allocation. It MUST be between
1 and 65534. It is RECOMMENDED that the server choose one of the
unassigned numbers randomly, rather than sequentially. The state
of the channel is set to unconfirmed.
o If one has been assigned, that channel MUST be selected. When the server receives a ChannelBind Request, it first does the
basic request processing described in [I-D.ietf-behave-rfc3489bis].
Once this is done, it does the processing specific to the ChannelBind
method described below.
Note that data from peers does not reset the permission activity The server checks that the ChannelBind Request contains both a
timer. CHANNEL-NUMBER attribute and a PEER-ADDRESS attribute. If the PEER-
ADDRESS attribute is missing or malformed, then the server rejects
the request with an Error Response containing the error code XXX
"Peer address missing or invalid". If the CHANNEL-NUMBER attribute
is missing or malformed, or the channel number is not in the range
0x4000 to 0xFFFE (inclusive), or the channel is already bound to
another peer (already bound to the same peer is OK) the server
rejects the request with an Error Response containing the error code
XXX "Channel number missing or invalid". Otherwise, if no errors are
detected, the server replies with a ChannelBind Success Response.
Next, the server checks if the channel number has been confirmed by 7.3. Receiving a ChannelBind Response
the client. If the channel number has been confirmed, the server
simply sends the data to the client with the appropriate channel
number in the TURN framing.
If the channel number has not been confirmed, the server creates a When the client receives a ChannelBind response (either success or
Data indication. It places the selected channel number in a CHANNEL- error), it processes it as specified in [3489bis]. Any additional
NUMBER attribute, the peer IP address and port in a PEER-ADDRESS processing is implementation specific.
attribute, and puts the data to be sent in a DATA attribute. If the
Data indication is sent over a reliable transport (ex: TCP), the
server marks that the channel number as confirmed. When the server
receives a ChannelConfirmation Indication, and the channel number, IP
address and port match the channel number assigned to that peer, the
server marks that the channel number is confirmed.
Since Data is an Indication, it generates no response. The server 7.4. The ChannelData Message
does not provide reliability for the data. When sending over a
reliable transport to the client, if the server is unable to send the
data received from the peer (for example, because the TCP connection
cannot accept any more messages right now), it can silently discards
UDP data received from the peer.
Note that Send Indications are not authenticated and do not The ChannelData message is used to carry application data between the
contain a MESSAGE-INTEGRITY attribute. Just like non-relayed data client and the server. It has the following format:
sent over UDP or TCP, the authenticity and integrity of this data
can only be assured using security mechanisms at higher layers.
7.2.3. Allocation Activity Timer and Permission Timeout 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Channel Number | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ Application Data /
/ /
| |
| +-------------------------------+
| |
+-------------------------------+
When the allocation activity timer expires, the server MUST destroy The Channel Number field specifies the number of the channel on which
the allocation. This involves freeing the allocated transport the data is traveling, and thus the address of the peer that is
address, deleting permissions and channel numbers, and removing other sending or is to receive the data. The channel number MUST be in the
state associated with the allocation. range 0x4000 - 0xFFFF, with channel number 0xFFFF being reserved for
possible future extensions.
When a permission times out, the TURN server MUST NOT forward a Channel numbers 0x0000 - 0x3FFF cannot be used because bits 0 and 1
packet from that TURN peer to the TURN client. are used to distinguish ChannelData messages from STUN-formatted
messages (i.e., Allocate, Send, Data, ChannelBind, etc). STUN-
formatted messages always have bits 0 and 1 as "00", while
ChannelData messages use combinations "01", "10", and "11".
8. New Attributes The Length field specifies the length in bytes of the application
data field (i.e., it does not include the size of the ChannelData
header). Note that 0 is a valid length.
The Application Data field carries the data the client is trying to
send to the peer, or that the peer is sending to the client.
7.5. Forming and Sending a ChannelData Message
Once a client has bound a channel to a peer, then when the client has
data to send to that peer it may use either a ChannelData message or
a Send Indication; that is, the client is not obligated to use the
channel when it exists and may freely intermix the two message types
when sending data to the peer. The server, on the other hand, SHOULD
use the ChannelData message if a channel has been bound to the peer.
The fields of the ChannelData message are filled in as described in
Section 7.4.
Over stream transports, the ChannelData message MUST be padded to a
multiple of four bytes in order to ensure the alignment of subsequent
messages. The padding is not reflected in the length field of the
ChannelData message, so the actual size of a ChannelData message
(including padding) is (4 + Length) rounded up to the nearest
multiple of 4. Over UDP, the padding is not required but MAY be
included.
The ChannelData message is then sent on the 5-tuple associated with
the allocation.
7.6. Receiving a ChannelData Message
The receiver of the ChannelData message uses bits 0 and 1 to
distinguish it from STUN-formatted messages, as described in
Section 7.4.
If the ChannelData message is received in a UDP datagram, and if the
UDP datagram is too short to contain the claimed length of the
ChannelData message (i.e., the UDP header length field value is less
than the ChannelData header length field value + 4 + 8), then the
message is silently discarded.
If the ChannelData message is received over TCP or over TLS over TCP,
then the actual length of the ChannelData message is as described in
Section 7.5.
If the ChannelData message is received on a channel which is not
bound to any peer, then the message is silently discarded.
7.7. Relaying
When the server receives a valid ChannelData message, it forms a UDP
datagram as follows: the source transport address is the relayed
transport address of the allocation, where the allocation is
determined by the 5-tuple on which the ChannelData message arrived;
the destination transport address is the peer address to which the
channel is bound; the data following the UDP header is the contents
of the data field of the ChannelData message; the Length field in the
UDP header is set to the Length field of the ChannelData message + 8;
and the Checksum field in the UDP header is computed as described in
[RFC 768]. The resulting UDP datagram is then sent to the peer.
The server also updates the permission associated with the IP address
part of the peer address to which the UDP datagram is sent.
When the server receives a UDP datagram with a destination transport
address corresponding to an active (i.e., still alive) allocation,
then it first checks to see if it is permitted to relay the datagram.
If the allocation contains an active permission for the source IP
address (from the IP header) of the received UDP datagram, then the
UDP datagram is permitted. Otherwise, the UDP datagram MUST be
discarded.
To relay the UDP datagram, the server forms and send a ChannelData
message as described in Section 7.5
8. New STUN Methods
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.
Request/Response Transactions
0x003 : Allocate
0x004 : Refresh
Indications
0x006 : Send
0x007 : Data
9. New STUN Attributes
This STUN extension defines the following new attributes: This STUN extension defines the following new attributes:
0x000C: CHANNEL-NUMBER 0x000C: CHANNEL-NUMBER
0x000D: LIFETIME 0x000D: LIFETIME
0x0010: BANDWIDTH 0x0010: BANDWIDTH
0x0012: PEER-ADDRESS 0x0012: PEER-ADDRESS
0x0013: DATA 0x0013: DATA
0x0016: RELAY-ADDRESS 0x0016: RELAY-ADDRESS
0x0018: REQUESTED-PORT-PROPS 0x0018: REQUESTED-PORT-PROPS
0x0019: REQUESTED-TRANSPORT 0x0019: REQUESTED-TRANSPORT
0x0022: REQUESTED-IP 0x0022: REQUESTED-IP
8.1. CHANNEL-NUMBER 9.1. CHANNEL-NUMBER
The channel number attribute represents the channel number assigned The CHANNEL-NUMBER attribute contains the number of the channel. It
by the sender, that corresponds with the peer specified in the PEER- is a 16-bit unsigned integer, followed by a two-octet RFFU field
ADDRESS attribute. It is a 16-bit unsigned integer, plus two octets which MUST be set to 0 on transmission and ignored on reception.
of padding which MUST be set to zero.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Channel Number | Reserved = 0 | | Channel Number | RFFU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8.2. LIFETIME 9.2. LIFETIME
The lifetime attribute represents the duration for which the server The lifetime attribute represents the duration for which the server
will maintain an allocation in the absence of a refresh. It is a 32 will maintain an allocation in the absence of a refresh. It is a 32
bit unsigned integral value representing the number of seconds bit unsigned integral value representing the number of seconds
remaining until expiration. remaining until expiration.
8.3. BANDWIDTH 9.3. BANDWIDTH
The bandwidth attribute represents the peak bandwidth, measured in The bandwidth attribute represents the peak bandwidth, measured in
kilobits per second, that the client expects to use on the allocation kilobits per second, that the client expects to use on the allocation
in each direction. in each direction.
8.4. PEER-ADDRESS 9.4. PEER-ADDRESS
The PEER-ADDRESS specifies the address and port of the peer as seen The PEER-ADDRESS specifies the address and port of the peer as seen
from the TURN server. It is encoded in the same way as XOR-MAPPED- from the TURN server. It is encoded in the same way as XOR-MAPPED-
ADDRESS. ADDRESS.
8.5. DATA 9.5. DATA
The DATA attribute is present in most Send Indications and Data The DATA attribute is present in most Send Indications and Data
Indications. It contains raw payload data that is to be sent (in the Indications. It contains raw payload data that is to be sent (in the
case of a Send Request) or was received (in the case of a Data case of a Send Request) or was received (in the case of a Data
Indication). Indication).
8.6. RELAY-ADDRESS 9.6. RELAY-ADDRESS
The RELAY-ADDRESS is present in Allocate responses. It specifies the The RELAY-ADDRESS is present in Allocate responses. It specifies the
address and port that the server allocated to the client. It is address and port that the server allocated to the client. It is
encoded in the same way as XOR-MAPPED-ADDRESS. encoded in the same way as XOR-MAPPED-ADDRESS.
8.7. REQUESTED-PORT-PROPS 9.7. REQUESTED-PORT-PROPS
This attribute allows the client to request certain properties for This attribute allows the client to request certain properties for
the port that is allocated by the server. The attribute can be used the port that is allocated by the server. The attribute can be used
with any transport protocol that has the notion of a 16 bit port with any transport protocol that has the notion of a 16 bit port
space (including TCP and UDP). The attribute is 32 bits long. Its space (including TCP and UDP). The attribute is 32 bits long. Its
format is: format is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved = 0 | A | Specific Port Number | | Reserved = 0 | A | Specific Port Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The two bits labeled A in the diagram above are for requested port The two bits labeled A in the diagram above are for requested port
alignment and have the following meaning: alignment and have the following meaning:
00 no specific port alignment 00 no specific port alignment
01 odd port number 01 odd port number
10 even port number 10 even port number
11 even port number; reserve next higher port 11 even port number; reserve next higher port
If the value of the A field is 00 (no specific port alignment), then If the value of the A field is 00 (no specific port alignment), then
the Specific Port Number field can either be 0 or some non-zero port the Specific Port Number field can either be 0 or some non-zero port
number. If the Specific Port Number field is 0, then the client is number. If the Specific Port Number field is 0, then the client is
not putting any restrictions on the port number it would like not putting any restrictions on the port number it would like
allocated. If the Specific Port Number is some non-zero port number, allocated. If the Specific Port Number is some non-zero port number,
then the client is requesting that the server allocate the specified then the client is requesting that the server allocate the specified
port. port and the server MUST provide that port.
If the value of the A field is 01 (odd port number), then the If the value of the A field is 01 (odd port number), then the
Specific Port Number field must be zero, and the client is requesting Specific Port Number field MUST be zero, and the client is requesting
the server allocate an odd-numbered port. the server allocate an odd-numbered port. The server MUST provide an
odd port number.
If the value of the A field is 10 (even port number), then the If the value of the A field is 10 (even port number), then the
Specific Port number field must be zero, and the client is requesting Specific Port number field MUST be zero, and the client is requesting
the server allocate an even-numbered port. the server allocate an even-numbered port. The server MUST provide
an even port number.
If the value of the A field is 11 (even port number; reserve next If the value of the A field is 11 (even port number; reserve next
higher port), then the Specific Port Number field must be zero, and higher port), then the Specific Port Number field MUST be zero, and
the client is requesting the server allocate an even-numbered port. the client is requesting the server allocate an even-numbered port.
In addition, the client is requesting the server reserve the next The server MUST return an even port number. In addition, the client
higher port (i.e., N+1 if the server allocates port N), and should is requesting the server reserve the next higher port (i.e., N+1 if
only allocate the N+1 port number if it is explicit requested (with a the server allocates port N). The server SHOULD only allocate the
subsequent request specifying that exact port number) N+1 port number if it is explicitly requested (with a subsequent
request specifying that exact port number by the same TURN client,
over a different alllocation).
In all cases, if a port with the requested properties cannot be In all cases, if a port with the requested properties cannot be
allocated, the server responds with a error response with an error allocated, the server MUST respond with a error response with an
code of 444 (Invalid Port). error code of 444 (Invalid Port).
8.8. REQUESTED-TRANSPORT 9.8. REQUESTED-TRANSPORT
This attribute is used by the client to request a specific transport This attribute is used by the client to request a specific transport
protocol for the allocated transport address. It is a 32 bit protocol for the allocated transport address. It has the following
unsigned integer. Its values are: format:
0 1 2 3
0x0000 0000: UDP 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
0x0000 0001: Reserved for TCP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol | RFFU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If an Allocate request is sent over TCP and requests a UDP The Protocol field specifies the desired protocol. The codepoints
allocation, or an Allocate request is sent over TLS over TCP and used in this field are taken from those allowed in the Protocol field
requests a UDP allocation, the server will relay data between the two in the IPv4 header and the NextHeader field in the IPv6 header
transports. [Protocol-Numbers]. This specification only allows the use of
codepoint 17 (User Datagram Protocol).
Extensions to TURN can define additional transport protocols in an The RFFU field is set to zero on transmission and ignored on
IETF-consensus RFC. receiption. It is reserved for future uses.
8.9. REQUESTED-IP 9.9. REQUESTED-IP
The REQUESTED-IP attribute is used by the client to request that a The REQUESTED-IP attribute is used by the client to request that a
specific IP address be allocated to it. This attribute is needed specific IP address be allocated by the TURN server. This attribute
since it is anticipated that TURN servers will be multi-homed so as is needed since it is anticipated that TURN servers will be multi-
to be able to allocate more than 64k transport addresses. As a homed so as to be able to allocate more than 64k transport addresses.
consequence, a client needing a second transport address on the same As a consequence, a client needing a second transport address on the
interface as a previous one can make that request. same interface as a previous one can use this attribute to request a
remote address from the same TURN server interface as the TURN
client's previous remote address.
The format of this attribute is identical to XOR-MAPPED-ADDRESS. The format of this attribute is identical to XOR-MAPPED-ADDRESS.
However, the port component of the attribute is ignored by the However, the port component of the attribute MUST be ignored by the
server. If a client wishes to request a specific IP address and server. If a client wishes to request a specific IP address and
port, it uses both the REQUESTED-IP and REQUESTED-PORT-PROPS port, it uses both the REQUESTED-IP and REQUESTED-PORT-PROPS
attributes. attributes.
9. New Error Response Codes 10. New STUN Error Response Codes
This document defines the following new Error response codes: This document defines the following new error response codes:
437 (Allocation Mismatch): A request was received by the server that 437 (Allocation Mismatch): A request was received by the server that
requires an allocation to be in place, but there is none, or a requires an allocation to be in place, but there is none, or a
request was received which requires no allocation, but there is request was received which requires no allocation, but there is
one. one.
442 (Unsupported Transport Protocol): The Allocate request asked for 442 (Unsupported Transport Protocol): The Allocate request asked for
a transport protocol to be allocated that is not supported by the a transport protocol to be allocated that is not supported by the
server. If the server is aware of another server that supports server. If the server is aware of another server that supports
the requested protocol, it SHOULD include the other server's the requested protocol, it SHOULD include the other server's
skipping to change at page 27, line 5 skipping to change at page 31, line 26
443 (Invalid IP Address): The Allocate request asked for a transport 443 (Invalid IP Address): The Allocate request asked for a transport
address to be allocated from a specific IP address that is not address to be allocated from a specific IP address that is not
valid on the server. valid on the server.
444 (Invalid Port): The Allocate request asked for a port to be 444 (Invalid Port): The Allocate request asked for a port to be
allocated that is not available on the server. allocated that is not available on the server.
486 (Allocation Quota Reached): The user or client is not authorized 486 (Allocation Quota Reached): The user or client is not authorized
to request additional allocations. to request additional allocations.
(tbd) (Channel Number Missing or Invalid): The request requires a
channel number, but the CHANNEL-NUMBER attribute is missing, or
the specified channel number is invalid in some way.
(tbd) (Peer Address Missing or Invalid): The request requires a peer
transport address, but the PEER-ADDRESS attribute is missing, or
the specified peer transport address is invalid in some way.
(tbd) (Lifetime Malformed or Invalid): The LIFETIME attribute is
malformed or the specified lifetime is invalid in some way.
507 (Insufficient Capacity): The server cannot allocate a new port 507 (Insufficient Capacity): The server cannot allocate a new port
for this client as it has exhausted its relay capacity. for this client as it has exhausted its relay capacity.
10. Client Discovery of TURN Servers 11. Client Discovery of TURN Servers
The STUN extensions introduced by TURN differ from the binding The STUN extensions introduced by TURN differ from the binding
requests defined in [I-D.ietf-behave-rfc3489bis] in that they are requests defined in [I-D.ietf-behave-rfc3489bis] in that they are
sent with additional framing and demand substantial resources from sent with additional framing and demand substantial resources from
the TURN server. In addition, it seems likely that administrators the TURN server. In addition, it seems likely that administrators
might want to block connections from clients to the TURN server for might want to block connections from clients to the TURN server for
relaying separately from connections for the purposes of binding relaying separately from connections for the purposes of binding
discovery. As a consequence, TURN runs on a separate port from STUN. discovery. As a consequence, TURN runs on a separate port from STUN.
The client discovers the address and port of the TURN server using The client discovers the address and port of the TURN server using
the same DNS procedures defined in [I-D.ietf-behave-rfc3489bis], but the same DNS procedures defined in [I-D.ietf-behave-rfc3489bis], but
using an SRV service name of "turn" (or "turns" for TURN over TLS) using an SRV service name of "turn" (or "turns" for TURN over TLS)
instead of just "stun". instead of just "stun".
For example, to find TURN servers in the example.com domain, the TURN For example, to find TURN servers in the example.com domain, the TURN
client performs a lookup for '_turn._udp.example.com', client performs a lookup for '_turn._udp.example.com',
'_turn._tcp.example.com', and '_turns._tcp.example.com' if the STUN '_turn._tcp.example.com', and '_turns._tcp.example.com' if the STUN
client wants to communicate with the TURN server using UDP, TCP, or client wants to communicate with the TURN server using UDP, TCP, or
TLS over TCP, respectively. TLS over TCP, respectively.
11. Security Considerations 12. Security Considerations
TURN servers allocate bandwidth and port resources to clients, in TURN servers allocate bandwidth and port resources to clients, in
contrast to the Binding method defined in contrast to the Binding method defined in
[I-D.ietf-behave-rfc3489bis]. Therefore, a TURN server requires [I-D.ietf-behave-rfc3489bis]. Therefore, a TURN server requires
authentication and authorization of STUN requests. This authentication and authorization of STUN requests. This
authentication is provided by mechanisms defined in the STUN authentication is provided by mechanisms defined in the STUN
specification itself, in particular digest authentication. specification itself, in particular digest authentication.
Because TURN servers allocate resources, they can be susceptible to Because TURN servers allocate resources, they can be susceptible to
denial-of-service attacks. All Allocate transactions are denial-of-service attacks. All Allocate transactions are
skipping to change at page 29, line 25 skipping to change at page 34, line 10
Relay servers are useful even for users not behind a NAT. They can Relay servers are useful even for users not behind a NAT. They can
provide a way for truly anonymous communications. A user can cause a provide a way for truly anonymous communications. A user can cause a
call to have its media routed through a TURN server, so that the call to have its media routed through a TURN server, so that the
user's IP addresses are never revealed. user's IP addresses are never revealed.
Any relay addresses learned through an Allocate request will not Any relay addresses learned through an Allocate request will not
operate properly with IPSec Authentication Header (AH) [RFC4302] in operate properly with IPSec Authentication Header (AH) [RFC4302] in
transport or tunnel mode. However, tunnel-mode IPSec ESP [RFC4303] transport or tunnel mode. However, tunnel-mode IPSec ESP [RFC4303]
should still operate. should still operate.
12. IANA Considerations 13. IANA Considerations
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.
12.1. New STUN Methods
Request/Response Transactions
0x003 : Allocate
0x004 : Refresh
Indications Since TURN is an extension to STUN [I-D.ietf-behave-rfc3489bis], the
0x006 : Send methods, attributes and error codes defined in this specification are
0x007 : Data new method, attributes, and error codes for STUN. This section
0x009 : Channel Confirmation directs IANA to add these new protocol elements to the IANA registry
of STUN protocol elements.
12.2. New STUN Attributes The codepoints for the new STUN methods defined in this specification
are listed in Section 8.
0x000C: CHANNEL-NUMBER The codepoints for the new STUN attributes defined in this
0x000D: LIFETIME specification are listed in Section 9.
0x0010: BANDWIDTH
0x0012: PEER-ADDRESS
0x0013: DATA
0x0016: RELAY-ADDRESS
0x0018: REQUESTED-PORT-PROPS
0x0019: REQUESTED-TRANSPORT
0x0022: REQUESTED-IP
12.3. New STUN Response Codes The codepoints for the new STUN error codes defined in this
specification are listed in Section 10.
437 Allocation Mismatch Extensions to TURN can be made through IETF consensus.
442 Unsupported Transport Protocol
443 Invalid IP Address
444 Invalid Port
486 Allocation Quota Reached
507 Insufficient Capacity
13. IAB Considerations 14. IAB Considerations
The IAB has studied the problem of "Unilateral Self Address Fixing", The IAB has studied the problem of "Unilateral Self Address Fixing",
which is the general process by which a client attempts to determine which is the general process by which a client attempts to determine
its address in another realm on the other side of a NAT through a its address in another realm on the other side of a NAT through a
collaborative protocol reflection mechanism RFC 3424 [RFC3424]. The collaborative protocol reflection mechanism [RFC3424]. The TURN
TURN extension is an example of a protocol that performs this type of extension is an example of a protocol that performs this type of
function. The IAB has mandated that any protocols developed for this function. The IAB has mandated that any protocols developed for this
purpose document a specific set of considerations. purpose document a specific set of considerations.
TURN is an extension of the STUN protocol. As such, the specific TURN is an extension of the STUN protocol. As such, the specific
usages of STUN that use the TURN extensions need to specifically usages of STUN that use the TURN extensions need to specifically
address these considerations. Currently the only STUN usage that address these considerations. Currently the only STUN usage that
uses TURN is ICE [I-D.ietf-mmusic-ice]. uses TURN is ICE [I-D.ietf-mmusic-ice].
14. Example 15. Example
In this example, a TURN client is behind a NAT. This TURN client is TBD
running SIP. The client has a private address of 10.0.1.1. The TURN
server is on the public side of the NAT, and is listening for TURN
requests on 192.0.2.3:8776. The public side of the NAT has an IP
address of 192.0.2.1. The client is attempting to send a SIP INVITE
to a peer, and wishes to allocate an IP address and port for
inclusion in the SDP of the INVITE. Normally, TURN would be used in
conjunction with ICE when applied to SIP. However, to keep the
example simple, TURN is shown without ICE.
The client communicates with a SIP user agent on the public network. 16. Changes from Previous Versions
This user agent uses a 192.0.2.17:12734 for receipt of its RTP
packets.
10.0.1.1 192.0.2.1 192.0.2.3 192.0.2.17 Note to RFC Editor: Please remove this section prior to publication
Client NAT TURN Server Peer of this document as an RFC.
| | | |
|(1) Allocate |(2) Allocate | |
|S=10.0.1.1:4334 |S=192.0.2.1:63346 | |
|D=192.0.2.3:8776 |D=192.0.2.3:8776 | |
|------------------>|------------------>| |
| | | |
|(4) Error |(3) Error | |
|S=192.0.2.3:8776 |S=192.0.2.3:8776 | |
|D=10.0.1.1:4334 |D=192.0.2.1:63346 | |
|<------------------|<------------------| |
| | | |
|(5) Allocate |(6) Allocate | |
|S=10.0.1.1:4334 |S=192.0.2.1:63346 | |
|D=192.0.2.3:8776 |D=192.0.2.3:8776 | |
|------------------>|------------------>| |
| | | |
| | (allocates port 32766) |
| | | |
| | | |
|(8) Response |(7) Response | |
|RA=192.0.2.3:32766 |RA=192.0.2.3:32766 | |
|MA=192.0.2.1:63346 |MA=192.0.2.1:63346 | |
|S=192.0.2.3:8776 |S=192.0.2.3:8776 | |
|D=10.0.1.1:4334 |D=192.0.2.1:63346 | |
|<------------------|<------------------| |
| | | |
|(9) SIP INVITE | | |
|SDP=192.0.2.3:32766| | |
|---------------------------------------------------------->|
| | | |
|(10) SIP 200 OK | | |
|SDP=192.0.2.17:12734 | |
|<----------------------------------------------------------|
| | | |
| | |(11) RTP |
| | |S=192.0.2.17:12734 |
| | |D=192.0.2.3:32766 |
| | |<------------------|
| | | |
| | (no permission; packet dropped) |
| | | |
|(12) SIP ACK | | |
|---------------------------------------------------------->|
| | | |
|(13) Send Indic. |(14) Send Indic. | |
|TURN Channel=0 |TURN Channel=0 | |
|STUN DATA=RTP |STUN DATA=RTP | |
|CHANNEL-NUMER=77 |CHANNEL-NUMBER=77 | |
|PA=192.0.2.17:12734|PA=192.0.2.17:12734| |
|S=10.0.1.1:4334 |S=192.0.2.1:63346 | |
|D=192.0.2.3:8776 |D=192.0.2.3:8776 | |
|------------------>|------------------>| |
| | | |
| | permission created |
| | | |
| | |(15) RTP |
| | |S=192.0.2.3:32766 |
| | |D=192.0.2.17:12734 |
| | |------------------>|
| | | |
|(17) ChannelConf |(16) ChannelConf | |
|TURN Channel=0 |TURN Channel=0 | |
|CHANNEL-NUMBER=77 |CHANNEL-NUMBER=77 | |
|PA=192.0.2.17:12734|PA=192.0.2.17:12734| |
|S=192.0.2.3:8776 |S=192.0.2.3:8776 | |
|D=10.0.1.1:4334 |D=192.0.2.1:63346 | |
|<------------------|<------------------| |
| | | |
|(18) TURN Framed |(19) TURN Framed | |
|TURN Channel=77 |TURN Channel=77 |(20) RTP |
|S=10.0.1.1:4334 |S=192.0.2.1:63346 |S=192.0.2.3:32766 |
|D=192.0.2.3:8776 |D=192.0.2.3:8776 |D=192.0.2.17:12734 |
|------------------>|------------------>|------------------>|
| | | |
|(23) Data Indic. |(22) Data Indic. | |
|TURN Channel=0 |TURN Channel=0 | |
|CHANNEL-NUMBER=33 |CHANNEL-NUMBER=33 |(21) RTP |
|S=192.0.2.3:8776 |S=192.0.2.3:8776 |S=192.0.2.17:12734 |
|D=10.0.1.1:4334 |D=192.0.2.1:63346 |D=192.0.2.3:32766 |
|<------------------|<------------------|<------------------|
| | | |
|(24) ChannelConf |(25) ChannelConf | |
|TURN Channel=0 |TURN Channel=0 | |
|CHANNEL-NUMBER=33 |CHANNEL-NUMBER=33 | |
|S=10.0.0.1:4334 |S=192.0.2.3:8776 | |
|D=192.0.2.3:8776 |D=192.0.2.3:8776 | |
|------------------>|------------------>| |
| | | |
|(28) TURN Framed |(27) TURN Framed | |
|TURN Channel=33 |TURN Channel=33 |(26) RTP |
|S=192.0.2.3:8776 |S=192.0.2.3:8776 |S=192.0.2.17:12734 |
|D=10.0.1.1:4334 |D=192.0.2.1:63346 |D=192.0.2.3:32766 |
|<------------------|<------------------|<------------------|
| | | |
Figure 12 This section lists the changes between the various versions of this
specification.
The message flow is shown in Figure 12. In step 1-2, the client 16.1. Changes from -05 to -06
allocates a UDP port from the local operating system on its private
interface, obtaining 4334. It then attempts to obtain a port for RTP
traffic. RTCP processing is not shown in the example.
In step 1, the client sends an Allocate Request (1) with a source o Changed the mechanism for allocating channels to the one proposed
address (denoted by S) of 10.0.1.1:4334 and a destination (denoted by by Eric Rescorla at the Dec 2007 IETF meeting.
D) of 192.0.2.3:8776. This passes through the NAT (2), which
allocates a new UDP port (63346) on the NAT's public interface
(192.0.2.1), and creates an internal mapping between the internal
address 10.0.1.1:4334 and that external address 192.0.2.1:63346. The
NAT sends this request to the TURN server (3). The TURN server
challenges the request, requesting credentials by sending a STUN
error and including the NONCE and REALM attributes. Message 3 is
relayed, by the NAT, to the TURN client (4). The client sends a new
request (from the same UDP port), including its credentials (5, 6).
The TURN server authenticates the request. The TURN server allocates
a new UDP port on one of its interfaces, 192.0.2.3:32766. The TURN
server puts 192.0.2.3:32766 into the RELAY-ADDRESS (denoted by RA)
attribute of the response, and puts the source IP address and UDP
port of the request (as seen by the TURN server) into the XOR-MAPPED-
ADDRESS attribute (denoted by MA). In step 7, this message is sent
back to the TURN client and relayed by the NAT in step 8.
The client now proceeds to perform a basic SIP call setup. In o Removed the framing mechanism (which was used to frame all
message 9, the TURN client includes the TURN server's address (which messages) and replaced it with the ChannelData message. As part
it learned in message 8) in the SDP of its INVITE (e.g., using syntax of this change, noted that the demux of ChannelData messages from
described in[I-D.ietf-mmusic-ice]). The called party responds with TURN messages can be done using the first two bits of the message.
its SDP in a provisional response (18x) or a final response (200 Ok).
The called party's SDP includes its IP address and UDP port,
192.0.2.17:12734. Immediately after sending its 200 Ok, the called
party sends an RTP packet to the TURN server's IP address (11). This
RTP packet is dropped by the TURN server, because the TURN server has
not been given permission to relay that data. Incoming packets are
dropped until a permission is created. The SIP exchange completes
with an SIP 200 Ok message (12).
Steps 13-20 show the client performing a channel allocation. The o Rewrote the sections on transmitted and receiving data as a result
TURN client needs to send an RTP packet. Since no channels and no of the above to changes, splitting it into a section on Send and
permissions have been created, the TURN client sends the RTP packet Data Indications and a separate section on channels.
inside of a Send Indication, using channel number 0, with the
CHANNEL-NUMBER attribute set to the channel number the TURN client
wants to use for subsequent communication with this TURN peer (77 is
shown in the example). The TURN peer's IP address and UDP port
(which were learned from the SDP answer received in step 10) are
placed in the PEER-ADDRESS attribute (denoted by PA). In message 13,
the TURN client sends this Send Indication, and it is relayed by the
NAT to the TURN server (14). Upon receipt of that message, the TURN
server creates a permission, which allows subsequent traffic from
that same peer address to be relayed to that TURN client's IP address
and UDP port. The TURN server sends the contents of the Send
Indication's DATA attribute towards the PEER-ADDRESS (15); this will
typically be an RTP packet. Note that the source address and port of
message 15 is the TURN server's address, 192.0.2.3:32766, which is
the allocated transport address communicated to the TURN client in
messages 7 and 8.
In step 16, the TURN server sends a channel confirmation message to o Clarified the handling of Allocate Request messages. In
the TURN client. Once the TURN client receives this message, it can particular, subsequent Allocate Request messages over UDP with the
forgo using the Send Indication for that channel. Instead, it can same transaction id are not an error but a retransmission.
utilize the channel number in the TURN framing header. Steps 18 and
19 show the TURN client sending a message to TURN server using the
TURN framing header, with channel=1. Step 20 shows the TURN server
removing the TURN framing and sending the RTP packet to the TURN
peer.
Steps 21-28 show an RTP packet from the TURN peer, which causes a o Restricted the range of ports available for allocation to the
channel allocation by the TURN server. In packet 21, an RTP packet Dynamic and/or Private Port range, and noted when ports outside
is sent by the TURN peer to the TURN server. There is an existing this range can be used.
permission (created in step 14), so the TURN server accepts this
incoming RTP packet. The TURN server knows the TURN client to send
this packet to, but does not yet have a channel assigned for traffic
in this direction. The TURN server chooses a channel number (33 in
the example), and sends a Data Indication to the TURN client (message
22). The NAT relays this to the TURN client (message 23). The TURN
client sends an Channel Confirmation message (24) which is relayed by
the NAT (25). When the TURN server receives the Channel
Confirmation, it no longer needs to use a Send Indication for traffic
from that remote peer; instead, it can use TURN framing with its
chosen channel number (33). The next RTP packet that arrives from
that peer (26) is sent by the TURN server using TURN framing
indicating the channel number (message 27) and relayed by the NAT to
the TURN client (28).
15. Changes since version -04 o Changed the format of the REQUESTED-TRANSPORT attribute. The
previous version used 00 for UDP and 01 for TCP; the new version
uses protocol numbers from the IANA protocol number registry. The
format of the attribute also changed.
This section lists the major changes between thiis document and o Made a large number of changes to the non-normative portion of the
draft-ietf-behave-turn-04: document to reflect technical changes and improve the
presentation.
o Added the Issues section.
16.2. Changes from -04 to -05
o Removed the ability to allocate addresses for TCP relaying. This o Removed the ability to allocate addresses for TCP relaying. This
is now covered in a separate document. However, communication is now covered in a separate document. However, communication
between the client and the server can still run over TCP or TLS/ between the client and the server can still run over TCP or TLS/
TCP. This resulted in the removal of the Connect method and the TCP. This resulted in the removal of the Connect method and the
TIMER-VAL and CONNECT-STAT attributes. TIMER-VAL and CONNECT-STAT attributes.
o Added the concept of channels. All communication between the o Added the concept of channels. All communication between the
client and the server flows on a channel. Channels are numbered client and the server flows on a channel. Channels are numbered
0..65535. Channel 0 is used for TURN messages, while the 0..65535. Channel 0 is used for TURN messages, while the
skipping to change at page 36, line 15 skipping to change at page 37, line 5
o Added a discussion of what happens if a client's public binding on o Added a discussion of what happens if a client's public binding on
its outermost NAT changes. its outermost NAT changes.
o The document now consistently uses the term "peer" as the name of o The document now consistently uses the term "peer" as the name of
a remote endpoint with which the client wishes to communicate. a remote endpoint with which the client wishes to communicate.
o Rewrote much of the document to describe the new concepts. At the o Rewrote much of the document to describe the new concepts. At the
same time, tried to make the presentation clearer and less same time, tried to make the presentation clearer and less
repetitive. repetitive.
16. Acknowledgements 17. Issues
The authors would like to thank Marc Petit-Huguenin for his comments NOTE to RFC Editor: Please remove this section prior to publication
and suggestions. of this document as an RFC.
17. References This section lists the open and now closed issues in this document.
The descriptions here are brief, and the reader should consult the
corresponding thread on the mailing list for a more in-depth
description of the issue and the resolutions being considered.
17.1. Normative References 17.1. Open Issues
1. Bandwidth: What should we do with the BANDWIDTH attribute, which
is currently ill-specified? Should we remove it? Or should we
try to come up with a good specification, perhaps using ideas
from RSVP?
2. Permission Policy: What should the permission policy be?
Address-restricted, as is currently specified in the document?
Or address-and-port-restricted, as many firewalls implement
today? Or should we leave this open to the implementor, under
the assumption that the IT administrator will only allow clients
to contact those servers that implement whatever permission
policy the IT administrator can accept?
3. Port Adjacency: The spec currently allows a client to request
that the server allocate a port and also reserve the next higher
port number for a possible future allocation (on a different
5-tuple). However, the exact behavior of the server in this
case is ill-specified. For example, must the next-higher-port
be available for the allocation of the lower port number to
succeed? How long is the next-higher-port reserved? 30 seconds?
For the lifetime of the lower-numbered-port's allocation? Or
should we just ditch this feature, since it is difficult to
implement, it is at odds with port randomization, and paired
port numbers applications don't work well with NATs anyway?
4. Demuxing ChannelData messages: How does a client or server demux
STUN-formatted messages from ChannelData messages? Does it use
the first two bits (as currently specified) or just one bit?
And how many channels do we need anyway? Some people are
questioning the need for any more than 200 channels. If we
don't need many channels, then the demux algorithm might become
simpler.
5. Deallocating Channels: Do we need a mechanism for deallocating
channels? Some have argued for this feature, because a TURN
server administrator will want a way to recover resources for
channels no longer in active use. If yes, then what is the
mechanism? For example, should a channel binding expire when
the corresponding permission expires?
6. Permissions and Channel Allocations: Should allocating a channel
for a peer automatically install a permission for that peer's IP
address?
7. Permission and Allocation Lifetimes: What should the default
permission lifetime be? Should there be a minumum value?
Should there be a way for the client to modify the permission
lifetime? Should there be a way for the client to learn the
current permission lifetime? And what is the relationship of
the permission lifetime to the allocation lifetime? Does it
make sense for the allocation lifetime to be less than the
permission lifetime?
8. Preserving bits in the IP header: What bits (if any) should be
preserved in the IP header when a packet is relayed by the
server? The bits under consideration are currently the Don't
Fragment (DF) bit, the Explicit Congestion Notification (ECN)
bits, and the DiffServ (DS) bits.
9. Exceeding the Path MTU Size: TURN adds an overhead of 4 bytes
(ChannelData msg) or 36 bytes (Send or Data Indication), thus
potentially exceeding the path MTU between the client and
server. This could either cause IP fragmentation, or cause the
packet to be dropped if the DF bit is set. Who handles this
problem? Does TURN need to handle this, or is this left up to
the application to handle?
10. Allowed PEER-ADDRESS values: Should there be any restrictions on
the IP address the client can specify in the PEER-ADDRESS
attribute? Are multicast addresses allowed? What about
0.0.0.0? Any other restrictions?
11. Discarding UDP datagrams: If the server discards a received UDP
datagram on the relayed transport address (because there is no
corresponding permission), then does the server send an ICMP
response? If so, what error code does it use? (What does RFC
4787 say about the corresponding situation in NATs? I believe
many NATs silently discard these packets by default, or have a
"stealth mode" that enables this behavior.)
12. Authentication: Is the use of STUN's Long-Term Authentication
Mechanism by a TURN server mandatory? The document currently
implicitly assumes "yes", but what about someone who wants to
operate a public TURN server?
13. Re-using the 5-tuple: If an allocation expires, is there any
reason a client should not be able to immediately create a new
allocation using the same 5-tuple?
14. Password change: Is it possible to change the password for the
Long-Term Authentication mechanism during the lifetime of an
allocation? If so, how is it done?
15. IPv6: TURN probably works fine in an all IPv6 environment, but
there are a number of mixed IPv4/IPv6 cases that are ill-
specified. As an example, the server needs to check that the
PEER-ADDRESS in a Send Indication is of the same address family
as the relayed transport address. Should we carefully work
through all these cases and make sure we have caught them all,
or should we just state that this document covers the IPv4 case
only, and punt the specification of IPv6 and mixed IPv4/IPv6
operation to draft-ietf-behave-turn-ipv6? Does the current
interest in resurecting IPv4-to-IPv6 NATs have any impact on
TURN?
17.2. Closed Issues
1. Channel Allocation: Should TURN use the mechanism proposed by EKR
to allocate channels? RESOLUTION: Yes. Document now reflects
this.
2. Stateful Allocations: Does a TURN server need to distinguish
between the case where the client retransmits the initial
Allocate Request because the Allocate Response was lost and the
case where the client sends an Allocate Request because it thinks
the allocation does not exist? RESOLUTION: Yes. Document now
reflects this.
3. Port Range: From what range of port numbers should a TURN server
allocate ports? RESOLUTION: The server SHOULD allocate from the
Dynamic and/or Private Port range unless it is sure it will not
interfere with other apps on the same machine. Document now
reflects this.
4. Framing Header for STUN-formatted messages: Should TURN use the
framing mechanism for STUN-formatted messages? RESOLUTION: NO.
Document now reflects this. However, see related issues.
5. Length field in ChannelData header: Over UDP, the length of the
application data field in the ChannelData message can be
determined from the length field in the UDP header. So should
the length field in the ChannelData header be set to zero in this
case? RESOLUTION: No, the ChannelData length field should have
the same semantics over both TCP and UDP. Document now reflects
this.
18. Acknowledgements
The authors would like to thank the various participants in the
BEHAVE working group for their many comments on this draft. Marc
Petit-Huguenin, Remi Denis-Courmont, Cullen Jennings, Lars Eggert,
Magnus Westerlund, and Eric Rescorla have been particularly helpful,
with Eric also suggesting the channel allocation mechanism.
Christian Huitema was an early contributor to this document and was a
co-author on the first few drafts. Finally, the authors would like
to thank Dan Wing for his huge help in restarting progress on this
draft after work had stalled.
19. References
19.1. Normative References
[I-D.ietf-behave-rfc3489bis] [I-D.ietf-behave-rfc3489bis]
Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for (NAT) (STUN)", "Session Traversal Utilities for (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-12 (work in progress), draft-ietf-behave-rfc3489bis-13 (work in progress),
November 2007. November 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
17.2. Informative References 19.2. Informative References
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC1889] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", RFC 1889, January 1996.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264, with Session Description Protocol (SDP)", RFC 3264,
June 2002. June 2002.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, [RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005. December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005. RFC 4303, December 2005.
skipping to change at page 37, line 22 skipping to change at page 41, line 31
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation [RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127, (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007. RFC 4787, January 2007.
[I-D.ietf-behave-turn-tcp] [I-D.ietf-behave-turn-tcp]
Rosenberg, J. and R. Mahy, "Traversal Using Relays around Rosenberg, J. and R. Mahy, "Traversal Using Relays around
NAT (TURN) Extensions for TCP Allocations", NAT (TURN) Extensions for TCP Allocations",
draft-ietf-behave-turn-tcp-00 (work in progress), draft-ietf-behave-turn-tcp-00 (work in progress),
November 2007. November 2007.
[Port-Numbers]
"IANA Port Numbers Registry",
<http://www.iana.org/assignments/port-numbers>.
[Protocol-Numbers]
"IANA Protocol Numbers Registry", 2005,
<http://www.iana.org/assignments/protocol-numbers>.
Authors' Addresses Authors' Addresses
Jonathan Rosenberg Jonathan Rosenberg
Cisco Systems, Inc. Cisco Systems, Inc.
Edison, NJ Edison, NJ
US USA
Email: jdrosen@cisco.com Email: jdrosen@cisco.com
URI: http://www.jdrosen.net URI: http://www.jdrosen.net
Rohan Mahy Rohan Mahy
Plantronics, Inc. Plantronics, Inc.
Email: rohan@ekabal.com Email: rohan@ekabal.com
Philip Matthews Philip Matthews
Avaya, Inc. Avaya, Inc.
1135 Innovation Drive 1135 Innovation Drive
Ottawa, Ontario K2K 3G7 Ottawa, Ontario K2K 3G7
Canada Canada
Phone: +1 613 592-4343 x223 Phone: +1 613 592-4343 x223
Fax: Fax:
Email: philip_matthews@magma.ca Email: philip_matthews@magma.ca
URI: URI:
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
Phone:
Fax:
Email: dwing@cisco.com
URI:
Full Copyright Statement Full Copyright Statement
Copyright (C) The IETF Trust (2007). Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors contained in BCP 78, and except as set forth therein, the authors
retain all their rights. retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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