BEHAVE G. Camarillo Internet-Draft O. Novo Intended status: Standards Track Ericsson Expires: June 20, 2010 S. Perreault, Ed. Viagenie December 17, 2009 Traversal Using Relays around NAT (TURN) Extension for IPv6 draft-ietf-behave-turn-ipv6-08 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- 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). Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 20, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. Camarillo, et al. Expires June 20, 2010 [Page 1] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the BSD License. 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 . . . . . . . . . . . . . . . 12 10.2. New STUN Response Code Registry . . . . . . . . . . . . . 12 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 12. Normative References . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Camarillo, et al. Expires June 20, 2010 [Page 2] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 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 new error response codes. 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, 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., an IPv4 and an IPv6 address) needs to perform several allocation Camarillo, et al. Expires June 20, 2010 [Page 3] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 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 it 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 Type: the type of the REQUESTED-ADDRESS-FAMILY attribute is 0x0017. Camarillo, et al. Expires June 20, 2010 [Page 4] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 As specified in [RFC5389], 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 [RFC5389]: 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. If it contains both a RESERVATION-TOKEN and a REQUESTED-ADDRESS-FAMILY, the server replies with a 400 (Bad Request) Allocate Error Response. Following the rules in [RFC5389], 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 [RFC5389]. If the REQUESTED-ADDRESS-FAMILY attribute is absent, the server MUST allocate an IPv4 transport address to the TURN client. If allocation of IPv4 addresses is disabled by local policy, the server returns a a 440 (Address Family not Supported) Allocate Error Response. Camarillo, et al. Expires June 20, 2010 [Page 5] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 If the server does not support the address family requested by the client, it MUST generate an Allocate Error Response, and it MUST 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, and the attribute's value doesn't match the address family of the allocation, the server MUST reply with a 443 (Peer Address Family Mismatch) Refresh Error Response. 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 Camarillo, et al. Expires June 20, 2010 [Page 6] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 for the allocation. 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 a XOR-PEER-ADDRESS attribute with an address of the same address family as the relayed transport address for the allocation. 7.2. Receiving a ChannelBind Request If the 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. Camarillo, et al. Expires June 20, 2010 [Page 7] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 TURN relays performing any translation MUST translate the IP 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 2 of [I-D.ietf-behave-v6v4-xlate]. Alternative behavior: the relay sets the Hop Limit to the default value for outgoing packets. Fragmentation Camarillo, et al. Expires June 20, 2010 [Page 8] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 Preferred behavior: as specified in Section 2 of [I-D.ietf-behave-v6v4-xlate]. Alternative behavior: the relay assembles incoming fragments. The relay follows its default behavior to send outgoing packets. For both preferred and alternative behavior, the DONT-FRAGMENT attribute MUST be ignored by the server. 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. 8.2. 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 Camarillo, et al. Expires June 20, 2010 [Page 9] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 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 relay 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 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. For both preferred and alternative behavior, the DONT-FRAGMENT attribute MUST be ignored by the server. 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 Camarillo, et al. Expires June 20, 2010 [Page 10] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 Preferred behavior: as specified in Section 3 of [I-D.ietf-behave-v6v4-xlate]. 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 3 of [I-D.ietf-behave-v6v4-xlate]. Alternative behavior: the relay sets the Time to Live to the default value for outgoing packets. Fragmentation Preferred behavior: as specified in Section 3 of [I-D.ietf-behave-v6v4-xlate]. 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. Alternative behavior: the relay assembles incoming fragments. The relay follows its default behavior to send outgoing packets. For both preferred and alternative behavior, the DONT-FRAGMENT attribute MUST be ignored by the server. 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 [RFC5389] 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. Camarillo, et al. Expires June 20, 2010 [Page 11] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 10.1. New STUN Attribute Registry 0x0017: REQUESTED-ADDRESS-FAMILY 10.2. New STUN Response Code Registry 440 Address Family not Supported 443 Peer Address Family Mismatch 11. Acknowledgements The authors would like to thank Alfred E. Heggestad, Dan Wing, Marc Petit-Huguenin, Philip Matthews, and Remi Denis-Courmont for their feedback on this document. 12. Normative References [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-16 (work in progress), July 2009. [I-D.ietf-behave-v6v4-xlate] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation Algorithm", draft-ietf-behave-v6v4-xlate-05 (work in progress), December 2009. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3697] Rajahalme, J., Conta, A., Carpenter, B., and S. Deering, "IPv6 Flow Label Specification", RFC 3697, March 2004. [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, "Session Traversal Utilities for NAT (STUN)", RFC 5389, October 2008. Camarillo, et al. Expires June 20, 2010 [Page 12] Internet-Draft TURN Extension for IPv4/IPv6 transition December 2009 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 Simon Perreault (editor) Viagenie 2600 boul. Laurier, suite 625 Quebec, QC G1V 4W1 Canada Phone: +1 418 656 9254 Email: simon.perreault@viagenie.ca URI: http://www.viagenie.ca Camarillo, et al. 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