Behave WG J. Korhonen Internet-Draft Nokia Siemens Networks Intended status: Standards Track T. Savolainen, Ed. Expires: January 2, 2011 Nokia July 1, 2010 EDNS0 Flags Indicating AAAA Record Synthesis and Format draft-korhonen-edns0-synthesis-flag-00.txt Abstract Advanced hosts and applications benefit of the knowledge of an IPv6 address, AAAA record, and a possible synthesis taking place in the network. This specification defines ENDS0 flag bits for communicating whether the synthesis is taking place, what is the used IPv6 address format, and the IPv6 prefix and suffix used by the DNS64. The communicated information enables hosts to perform a local IPv6 address synthesis and to extract the IPv4 address out of the synthesized 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 January 2, 2011. Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. Korhonen & Savolainen Expires January 2, 2011 [Page 1] Internet-Draft EDNS0 synthesis flags July 2010 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. Requirements and Terminology . . . . . . . . . . . . . . . . . 3 3. EDNS0 flags for indicating address synthesis . . . . . . . . . 3 4. Host behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. Normative References . . . . . . . . . . . . . . . . . . . . . 5 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Korhonen & Savolainen Expires January 2, 2011 [Page 2] Internet-Draft EDNS0 synthesis flags July 2010 1. Introduction As the networks transition to IPv6, connectivity to IPv4-only domains has to be provided. NAT64 [I-D.ietf-behave-v6v4-xlate-stateful] and DNS64 [I-D.ietf-behave-dns64] technologies can be utilized to make IPv4-only peers look like being reachable over IPv6. The DNS64 utilizes IPv6 address synthesis to create local IPv6 presentations of peers having only IPv4 addresses. Applications utilizing DNS for resolving peers' IPv6 addresses can work seamlessly through protocol translation taking place at NAT64. The DNS64 cannot serve applications that are not using DNS, such as those receiving and using IPv4 address referrals. Such applications could nevertheless be able to work through NAT64, provided they are able to create locally valid IPv6 presentations of peers' IPv4 addresses. This specification describes a method for advanced applications to learn the information required for a local IPv6 address synthesis. The knowledge of IPv6 address synthesizing taking place may also be useful if DNS64 is present in a dual-stack network access. In such cases hosts may choose to use IPv4 addresses instead of synthesized IPv6 addresses, and hence avoid traversal through NAT64. 2. Requirements and 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. EDNS0 flags for indicating address synthesis The mechanism for informing AAAA record synthesis taking place and the used addressing format is using three bits of the ENDS0 OPT header in the DNS response. The bits are structured as follows: Korhonen & Savolainen Expires January 2, 2011 [Page 3] Internet-Draft EDNS0 synthesis flags July 2010 +0 (MSB) +1 (LSB) +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 0: | EXTENDED-RCODE | VERSION | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ 2: |DO| SY | Z | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ Possible values for SY-bits are: 000 reserved 001 prefix length /32 010 prefix length /40 011 prefix length /48 100 prefix length /56 101 prefix length /64 110 prefix length /96 111 address is not synthesized Figure 1 The prefix length corresponds to the address formats documented in "IPv6 Addressing of IPv4/IPv6 Translators document" [I-D.ietf-behave-address-format] section 2.2. The absence of the EDNS0 option means that either no synthesis took place or the DNS64 does not support this specification. Either way, when the EDNS0 option is missing, the host cannot conclude for certain whether the AAAA response was synthesized or not. However, if the host knows the name it asked for cannot have a real AAAA record, it MAY search for the IPv4 address inside the received IPv6 address, and if found then make an educated guess of the address format used by the DNS64. The host MAY learn the IPv4 address via an A query, or have the address preconfigured. [Editor's note: currently using extended flags has the least on-wire overhead. However, it also allocates multiple scarce flag bits. Therefore, the use of extended OPTION-CODE could be an alternative approach.] 4. Host behavior A host requiring information for a local IPv6 address synthesis or NAT64 avoidance SHALL send a DNS query for an AAAA record of a well- known IPv4-only fully qualified domain name (e.g. ip4.example.com) [editor's note: whether this domain name must be reserved by IANA is to be decided]. This may happen, for example, at the moment the host is configured an IPv6 address of a DNS server. This may also happen Korhonen & Savolainen Expires January 2, 2011 [Page 4] Internet-Draft EDNS0 synthesis flags July 2010 at the time first DNS query for AAAA record is initiated. If a host receives a negative reply, it learns there is no NAT64 in the network. If the host receives AAAA reply, it knows the network is utilizing IPv6 address synthesis. If the received IPv6 address has a well-known prefix, the host can use that information for a local IPv6 address synthesis. If the prefix is not well-known, the host reads the ENDS0 flag values to learn the used address format. Using the learned prefix length information, the host extracts from the received IPv6 address the information used by the network for IPv6 address synthesis (prefix, suffix, u-bit). The information required for a local IPv6 address synthesis SHOULD be made available for applications to utilize. 5. Security Considerations No security considerations have been identified. 6. IANA Considerations EDNS0 RFC 2671 [RFC2671] defines 16 bit extended flag field in the OPT RR. These bits are encoded into the TTL field of the OPT record (see Section 4.6 of RFC 2671). This specification reserves three of extended flag bits as the SY- bits. It is requested that the next available consequent leftmost bits are allocated. 7. Acknowledgements The authors would like to acknowledge Andrew Sullivan for presenting general idea of ENDS0 option and SY-bit in Behave WG mailing list. 8. Normative References [I-D.ietf-behave-address-format] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. Li, "IPv6 Addressing of IPv4/IPv6 Translators", draft-ietf-behave-address-format-08 (work in progress), May 2010. [I-D.ietf-behave-dns64] Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum, Korhonen & Savolainen Expires January 2, 2011 [Page 5] Internet-Draft EDNS0 synthesis flags July 2010 "DNS64: DNS extensions for Network Address Translation from IPv6 Clients to IPv4 Servers", draft-ietf-behave-dns64-09 (work in progress), March 2010. [I-D.ietf-behave-v6v4-xlate-stateful] Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", draft-ietf-behave-v6v4-xlate-stateful-11 (work in progress), March 2010. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671, August 1999. Authors' Addresses Jouni Korhonen Nokia Siemens Networks Linnoitustie 6 FI-02600 Espoo Finland Email: jouni.nospam@gmail.com Teemu Savolainen (editor) Nokia Hermiankatu 12 D FI-33720 Tampere Finland Email: teemu.savolainen@nokia.com Korhonen & Savolainen Expires January 2, 2011 [Page 6]