BEHAVE G. Camarillo
Internet-Draft O. Novo
Intended status: Standards Track Ericsson
Expires: September 10, 2009 March 9, 2009
Traversal Using Relays around NAT (TURN) Extension for IPv6
draft-ietf-behave-turn-ipv6-06.txt
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Abstract
This document adds IPv6 support to Traversal Using Relays around NAT
(TURN). IPv6 support in TURN includes IPv4-to-IPv6, IPv6-to-IPv6,
and IPv6-to-IPv4 relaying. This document defines the REQUESTED-
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ADDRESS-FAMILY attribute for TURN. The REQUESTED-ADDRESS-FAMILY
attribute allows a client to explicitly request the address type the
TURN server will allocate (e.g., an IPv4-only node may request the
TURN server to allocate an IPv6 address).
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of Operation . . . . . . . . . . . . . . . . . . . . 3
4. Creating an Allocation . . . . . . . . . . . . . . . . . . . . 4
4.1. Sending an Allocate Request . . . . . . . . . . . . . . . 4
4.1.1. The REQUESTED-ADDRESS-FAMILY Attribute . . . . . . . . 4
4.2. Receiving an Allocate Request . . . . . . . . . . . . . . 5
4.2.1. Unsupported Address Family . . . . . . . . . . . . . . 6
4.3. Receiving an Allocate Error Response . . . . . . . . . . . 6
5. Refreshing an Allocation . . . . . . . . . . . . . . . . . . . 6
5.1. Sending a Refresh Request . . . . . . . . . . . . . . . . 6
5.2. Receiving a Refresh Request . . . . . . . . . . . . . . . 6
6. CreatePermission . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Sending a CreatePermission Request . . . . . . . . . . . . 6
6.2. Receiving a CreatePermission request . . . . . . . . . . . 7
6.2.1. Peer Address Family Mismatch . . . . . . . . . . . . . 7
7. Channels . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Sending a ChannelBind Request . . . . . . . . . . . . . . 7
7.2. Receiving a ChannelBind Request . . . . . . . . . . . . . 7
8. Packet Translations . . . . . . . . . . . . . . . . . . . . . 7
8.1. IPv4-to-IPv6 Translations . . . . . . . . . . . . . . . . 8
8.2. IPv6-to-IPv6 Translations . . . . . . . . . . . . . . . . 9
8.3. IPv6-to-IPv4 Translations . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10.1. New STUN Attribute Registry . . . . . . . . . . . . . . . 11
10.2. New STUN Response Code Registry . . . . . . . . . . . . . 11
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
12. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
Traversal Using Relays around NAT (TURN) [I-D.ietf-behave-turn] is a
protocol that allows for an element behind a NAT to receive incoming
data over UDP or TCP. It is most useful for elements behind
symmetric NATs that wish to be on the receiving end of a connection
to a single peer.
The base specification of TURN [I-D.ietf-behave-turn] only defines
IPv4-to-IPv4 relaying. This document adds IPv6 support to TURN,
which includes IPv4-to-IPv6, IPv6-to-IPv6, and IPv6-to-IPv4 relaying.
This document defines the REQUESTED-ADDRESS-FAMILY attribute, which
is an extension to TURN that allows a client to explicitly request
the address type the TURN server will allocate (e.g., an IPv4-only
node may request the TURN server to allocate an IPv6 address). This
document also defines and registers a new error response code with
the value 440 (Address Family not Supported).
2. Terminology
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 [RFC2119].
3. Overview of Operation
When a user wishes a TURN server to allocate an address of a specific
type, it sends an Allocate Request to the TURN server with a
REQUESTED-ADDRESS-FAMILY attribute. TURN can run over UDP and TCP,
as it allows for a client to request address/port pairs for receiving
both UDP and TCP.
Assuming the request is authenticated and has not been tampered with,
the TURN server allocates a transport address of the type indicated
in the REQUESTED-ADDRESS-FAMILY attribute. This address is called
the allocated transport address.
The TURN server returns the allocated address in the response to the
Allocate Request. This response contains a XOR-RELAYED-ADDRESS
attribute indicating the IP address and port that the server
allocated for the client.
TURN servers allocate a single relayed-transport-address per
allocation request. Therefore, Allocate Requests cannot carry more
than one REQUESTED-ADDRESS-FAMILY attribute. Consequently, a client
that wishes to allocate more than one address at a TURN server (e.g.,
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an IPv4 and an IPv6 address) needs to perform several allocation
requests (one allocation request per address).
A TURN server that supports a set of address families is assumed to
be able to relay packets between them. If a server does not support
the address family requested by a client, the server returns a 440
(Address Family not Supported) error response.
4. Creating an Allocation
The behavior specified here affects the processing defined in Section
6 of [I-D.ietf-behave-turn].
4.1. Sending an Allocate Request
A client that wishes to obtain a transport address of a specific
address type includes a REQUESTED-ADDRESS-FAMILY attribute, which is
defined in Section 4.1.1, in the Allocate Request that sends to the
TURN server. Clients MUST NOT include more than one REQUESTED-
ADDRESS-FAMILY attribute in an Allocate Request. The mechanisms to
formulate an Allocate Request are described in Section 6.1 of
[I-D.ietf-behave-turn].
Clients MUST NOT include a REQUESTED-ADDRESS-FAMILY attribute in an
Allocate request that contains a RESERVATION-TOKEN attribute.
4.1.1. The REQUESTED-ADDRESS-FAMILY Attribute
The REQUESTED-ADDRESS-FAMILY attribute is used by clients to request
the allocation of a specific address type from a server. The
following is the format of the REQUESTED-ADDRESS-FAMILY attribute.
Note that TURN attributes are TLV (Type-Length-Value) encoded, with a
16 bit type, a 16 bit length, and a variable-length value.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Family | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of REQUESTED-ADDRESS-FAMILY Attribute
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Type: the type of the REQUESTED-ADDRESS-FAMILY attribute is 0x0017.
As specified in [I-D.ietf-behave-rfc3489bis], attributes with values
between 0x0000 and 0x7FFF are comprehension-required, which means
that the client or server cannot successfully process the message
unless it understands the attribute.
Length: this 16-bit field contains the length of the attribute in
bytes. The length of this attribute is 4 bytes.
Family: there are two values defined for this field and specified in
[I-D.ietf-behave-rfc3489bis]: 0x01 for IPv4 addresses and 0x02 for
IPv6 addresses.
Reserved: at this point, the 24 bits in the reserved field MUST be
set to zero by the client and MUST be ignored by the server.
The REQUEST-ADDRESS-TYPE attribute MAY only be present in Allocate
Requests.
4.2. Receiving an Allocate Request
Assuming the request is authenticated and has not been tampered with,
the TURN server processes the Allocate request. Following the rules
in [I-D.ietf-behave-rfc3489bis], if the server does not understand
the REQUESTED-ADDRESS-FAMILY attribute, it generates an Allocate
Error Response, which includes an ERROR-CODE attribute with response
code 420 (Unknown Attribute). This response will contain an UNKNOWN-
ATTRIBUTE attribute listing the unknown REQUESTED-ADDRESS-FAMILY
attribute.
If the server can successfully process the request, it allocates a
transport address to the TURN client, called the allocated transport
address, and returns it in the response to the Allocate Request.
As specified in [I-D.ietf-behave-turn], the Allocate Response
contains the same transaction ID contained in the Allocate Request
and the XOR-RELAYED-ADDRESS attribute that sets it to the allocated
transport address.
The XOR-RELAYED-ADDRESS attribute indicates the allocated IP address
and port. It is encoded in the same way as the XOR-MAPPED-ADDRESS
[I-D.ietf-behave-rfc3489bis].
If the REQUESTED-ADDRESS-FAMILY attribute is absent, the server MUST
allocate an IPv4 transport address to the TURN client.
If the server does not support the address family requested by the
client, it MUST generate an Allocate Error Response, and it MUST
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include an ERROR-CODE attribute with the 440 (Address Family not
Supported) response code, which is defined in Section 4.2.1.
4.2.1. Unsupported Address Family
This document defines the following new error response code:
440 (Address Family not Supported): The server did not support the
address family requested by the client.
4.3. Receiving an Allocate Error Response
If the client receives an Allocate error response with the 440
(Unsupported Address Family) error code, the client SHOULD NOT retry
its request.
5. Refreshing an Allocation
The behavior specified here affects the processing defined in Section
7 of [I-D.ietf-behave-turn].
5.1. Sending a Refresh Request
To perform a binding refresh, the client generates a Refresh Request
as described in Section 7.1 of [I-D.ietf-behave-turn]. The client
MUST NOT include any REQUESTED-ADDRESS-FAMILY attribute in its
Refresh Request.
5.2. Receiving a Refresh Request
If a server receives a Refresh Request with a REQUESTED-ADDRESS-
FAMILY attribute, it MUST ignore the attribute and process the
request as if the attribute was not there.
6. CreatePermission
The behavior specified here affects the processing defined in Section
9 of [I-D.ietf-behave-turn].
6.1. Sending a CreatePermission Request
The client MUST only include XOR-PEER-ADDRESS attributes with
addresses of the same address family as the relayed transport address
for the allocation.
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6.2. Receiving a CreatePermission request
If an XOR-PEER-ADDRESS attribute contains an address of an address
family different than the relayed transport address for the
allocation, the server MUST generate an error response with the 443
(Peer Address Family Mismatch) response code, which is defined in
Section 6.2.1.
6.2.1. Peer Address Family Mismatch
This document defines the following new error response code:
443 (Peer Address Family Mismatch): A peer address was of a
different address family than the relayed transport address of the
allocation.
7. Channels
The behavior specified here affects the processing defined in Section
11 of [I-D.ietf-behave-turn].
7.1. Sending a ChannelBind Request
The client MUST only include XOR-PEER-ADDRESS attributes with
addresses of the same address family as the relayed transport address
for the allocation.
7.2. Receiving a ChannelBind Request
If an XOR-PEER-ADDRESS attribute contains an address of an address
family different than the relayed transport address for the
allocation, the server MUST generate an error response with the 443
(Peer Address Family Mismatch) response code, which is defined in
Section 6.2.1.
8. Packet Translations
The TURN specification [I-D.ietf-behave-turn] describes how TURN
relays should relay traffic consisting of IPv4 packets (i.e., IPv4-
to-IPv4 translations). The relay translates the IP addresses and
port numbers of the packets based on the allocation's state data.
How to translate other header fields is also specified in
[I-D.ietf-behave-turn]. This document addresses IPv4-to-IPv6, IPv6-
to-IPv4, and IPv6-to-IPv6 translations.
TURN relays performing any translation MUST translate the IP
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addresses and port numbers of the packets based on the allocation's
state information as specified in [I-D.ietf-behave-turn]. The
following sections specify how to translate other header fields.
As discussed in Section 2.6 of [I-D.ietf-behave-turn], translations
in TURN are designed so that a TURN server can be implemented as an
application that runs in userland under commonly available operating
systems and that does not require special privileges. The
translations specified in the following sections follow this
principle.
The descriptions below have two parts: a preferred behavior and an
alternate behavior. The server SHOULD implement the preferred
behavior. However, if that is not possible for a particular field,
then the server SHOULD implement the alternative behavior.
Note that the use of the behaviors specified in the following
sections is at the "should" level. Having its use at the "should"
level instead of at the "must" level makes it possible to use
different translation algorithms that may be developed in the
future.
8.1. IPv4-to-IPv6 Translations
Flow Label
Preferred behavior: The relay sets the Flow label to 0. The relay
can choose to set the Flow label to a different value if it
supports [RFC3697].
Alternative behavior: the relay sets the Flow label to the default
value for outgoing packets.
Hop Limit
Preferred behavior: as specified in Section 3.1 of [RFC2765].
Alternative behavior: the relay sets the Hop Limit to the default
value for outgoing packets.
Fragmentation
Preferred behavior: as specified in Section 3.1 of [RFC2765].
Alternative behavior: the relay assembles incoming fragments. The
relay follows its default behavior to send outgoing packets.
Extension Headers
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Preferred behavior: the relay sends outgoing packet without any
IPv6 extension headers, with the exception of the Fragmentation
header as described above.
Alternative behavior: same as preferred.
8.2. IPv6-to-IPv6 Translations
Flow Label
The relay should consider that it is handling two different IPv6
flows. Therefore, the Flow label [RFC3697] SHOULD NOT be copied as
part of the translation.
Preferred behavior: The relay sets the Flow label to 0. The relay
can choose to set the Flow label to a different value if it
supports [RFC3697].
Alternative behavior: the relay sets the Flow label to the default
value for outgoing packets.
Hop Limit
Preferred behavior: the relay acts as a regular router with
respect to decrementing the Hop Limit and generating an ICMPv6
error if it reaches zero.
Alternative behavior: the relay sets the Hop Limit to the default
value for outgoing packets.
Fragmentation
Preferred behavior: If the incoming packet did not include a
Fragment header and the outgoing packet size does not exceed the
outgoing link's MTU, the relay sends the outgoing packet without a
Fragment header.
If the incoming packet did not include a Fragment header and the
outgoing packet size exceeds the outgoing link's MTU, the delay
drops the outgoing packet and send an ICMP message of type 2 code
0 ("Packet too big") to the sender of the incoming packet. If the
packet is being sent to the peer, the relay reduces the MTU
reported in the ICMP message by 48 bytes to allow room for the
overhead of a Data indication.
If the incoming packet included a Fragment header and the outgoing
packet size (with a Fragment header included) does not exceed the
outgoing link's MTU, the relay sends the outgoing packet with a
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Fragment header. The relay sets the fields of the Fragment header
as appropriate for a packet originating from the server.
If the incoming packet included a Fragment header and the outgoing
packet size exceeds the outgoing link's MTU, the relay MUST
fragment the outgoing packet into fragments of no more than 1280
bytes. The relay sets the fields of the Fragment header as
appropriate for a packet originating from the server.
Alternative behavior: the relay assembles incoming fragments. The
relay follows its default behavior to send outgoing packets.
Extension Headers
Preferred behavior: the relay sends outgoing packet without any
IPv6 extension headers, with the exception of the Fragmentation
header as described above.
Alternative behavior: same as preferred.
8.3. IPv6-to-IPv4 Translations
Type of Service and Precedence
Preferred behavior: as specified in Section 4 of [RFC2765].
Alternative behavior: the relay sets the Type of Service and
Precedence to the default value for outgoing packets.
Time to Live
Preferred behavior: as specified in Section 4.1 of [RFC2765].
Alternative behavior: the relay sets the Time to Live to the
default value for outgoing packets.
Fragmentation
Preferred behavior: as specified in Section 4 of [RFC2765].
Additionally, when the outgoing packet's size exceeds the outgoing
link's MTU, the relay needs to generate an ICMP error (ICMPv6
Packet Too Big) reporting the MTU size. If the packet is being
sent to the peer, the relay SHOULD reduce the MTU reported in the
ICMP message by 48 bytes to allow room for the overhead of a Data
indication.
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Alternative behavior: the relay assembles incoming fragments. The
relay follows its default behavior to send outgoing packets.
9. Security Considerations
The attribute and error response code defined in this document do not
have any special security considerations beyond those for other
attributes and Error response codes. All the security considerations
applicable to STUN [I-D.ietf-behave-rfc3489bis] and TURN are
applicable to this document as well.
10. IANA Considerations
The IANA is requested to register the following values under the STUN
Attributes registry and under the STUN Response Code Registry.
10.1. New STUN Attribute Registry
0x0017: REQUESTED-ADDRESS-FAMILY
10.2. New STUN Response Code Registry
440 Address Family not Supported
11. Acknowledgements
The authors would like to thank Alfred E. Heggestad, Remi Denis-
Courmont, and Philip Matthews for their feedback on this document.
12. Normative References
[I-D.ietf-behave-rfc3489bis]
Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for (NAT) (STUN)",
draft-ietf-behave-rfc3489bis-18 (work in progress),
July 2008.
[I-D.ietf-behave-turn]
Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)",
draft-ietf-behave-turn-13 (work in progress),
February 2009.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm
(SIIT)", RFC 2765, February 2000.
[RFC3697] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering,
"IPv6 Flow Label Specification", RFC 3697, March 2004.
Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
Oscar Novo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Oscar.Novo@ericsson.com
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