BEHAVE Working Group D. Wing Internet-Draft Cisco Intended status: Informational October 23, 2008 Expires: April 26, 2009 Learning the Address Family Translator's IPv6 Prefix draft-wing-behave-learn-prefix-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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 April 26, 2009. Abstract In some IPv6/IPv4 translation scenarios it is necessary for an IPv6 host to know the IPv6 prefix used by its address family translator. In some of the IPv6/IPv4 translation proposals, the prefix is not fixed; that is, the prefix is chosen by the network operator. This specification provides several methods to learn the prefix and its length. Wing Expires April 26, 2009 [Page 1] Internet-Draft Learning the AFT's Prefix October 2008 Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Learning IPv6 Prefix and Length . . . . . . . . . . . . . . . . 3 3.1. Using DNS to Learn IPv6 Prefix and Length . . . . . . . . . 3 3.2. Using DHCP to Learn IPv6 Prefix and Length . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Wing Expires April 26, 2009 [Page 2] Internet-Draft Learning the AFT's Prefix October 2008 1. 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]. AFT: Address Family Translator. A device that translates between IP address families. DNS64: The function of synthesizing an AAAA response from an A record. 2. Introduction Several variations of Address Family Translators (AFT) have been proposed for IPv6/IPv6 coexistence. All of these operate by synthesizing DNS AAAA responses for hosts that do not have AAAA records -- this is generally called "DNS64" (also "DNS rewriting" or "DNS-ALG"). The DNS64 function, when used in conjunction with an AFT, allows a IPv6-only host to access IPv4-only hosts. This access, for the most part, is transparent to the IPv6 host -- to much the same degree that today's widely-deployed NATs are transparent to IPv4 hosts. But, like with today's NATs, there are applications which do not work with AFT or do not work with DNS64, and require IPv6 hosts to implement additional functionality. So far, one application has been identified which requires an IPv6 host to know the IPv6 prefix used by its address family translator (AFT): A DNSSEC security-aware stub resolver needs to securly obtain the IPv6 prefix. It uses this prefix to generate its own synthesized AAAA response from the un-translated A record [Sullivan-email], or to validate a synthesized AAAA response by removing the IPv6 prefix [Wing-email]. 3. Learning IPv6 Prefix and Length Both the IPv6 prefix and the prefix length need to be learned This can be done using DNS or DHCP, as described in the following sections. 3.1. Using DNS to Learn IPv6 Prefix and Length In order for an IPv6 host to determine if a NAT64 is present on its network, it sends a DNS query. Because a host doesn't always know its network's default domain name, the procedure described below provides a way for the host to learn it in order to authorize that Wing Expires April 26, 2009 [Page 3] Internet-Draft Learning the AFT's Prefix October 2008 network's address family translator: 1. Send a DNS AAAA query for "_aft_prefix", without a domain name. If this does not return an IPv6 address it means a address family translator is not present and processing MUST stop. 2. If validation of the returned IPv6 prefix is necessary, then: a. Send a DNS PTR query for that IPv6 address. This returns a fully-qualified hostname. b. Verify the full-qualified hostname is on the host's configured list of authorized translators. c. Send a DNS AAAA query for that hostname. d. Verify the AAAA response matches the IPv6 address obtained in step 1. e. Perform DNSSEC validation of the AAAA response. f. Send a DNS TXT query for the fully-qualfied name to learn the number of bits of the prefix (e.g., a 48 bit prefix would return the string "48"). g. Perform DNSSEC validation of the TXT response. 3. If validation of this information is not necessary, then: a. Send a DNS TXT query for "_aft_prefix", without the domain name, to learn the number of bits of the prefix. Note: The DNS server being queried is the DNS64. The DNS64 performs the AAAA synthesis function, which means the DNS64 is already aware of the prefix of the address family translator and the prefix length. Thus, is it already capable of returning information about the network's AFT. Discussion: without a domain name, it is unavoidable that root nameservers will see this query. Need to think about ways to reduce the effect of those queries (e.g., make them authoritative and return all 0's which will get cached). 3.2. Using DHCP to Learn IPv6 Prefix and Length A new DHCP option, OPTION_AFT_PREFIX, is defined. It contains the IPv6 prefix and its length. Wing Expires April 26, 2009 [Page 4] Internet-Draft Learning the AFT's Prefix October 2008 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_AFT_PREFIX | option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | prefix-length | | +-+-+-+-+-+-+-+-+ IPv6 prefix | | (up to 16 octets) | | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+ option-code: OPTION_AFT_PREFIX (TBD) option-length: 17 prefix-length: Length for this prefix in bits IPv6-prefix: An IPv6 prefix Figure 1: OPTION_AFT_PREFIX In order to conserve space, it is RECOMMENDED that only the significant bits of the IPv6 prefix be sent in the DHCP option. If the host implements a security-aware DNSSEC validator, it must validate and authorize that translator. To do this, it issues a ipv6.arpa PTR query on the IPv6 address learned via DHCPv6. This returns a name. The host then issues a AAAA query using that name, and DNSSEC validates the response. If the query validates, and the AAAA response contains an IPv6 address that matches the AFT-PREFIX learned from DHCPv6, and the host's administrator has authorized use of that AFT translator name, DNSSEC can use that prefix. Details of DNSSEC operation in conjunction with AFT are in [draft to be written providing DNSSEC details]. 4. Security Considerations After learning the IPv6 prefix of its translator by following the procedures in this specification, the IPv6 host will utilize this information for subsequent actions (e.g., sending a packet to it, or using that information to synthesize DNS records or to perform DNSSEC validation). If an attacker provides a fraudulent IPv6 to the IPv6 host, the attacker can become on-path for traffic to/from that IPv6 Wing Expires April 26, 2009 [Page 5] Internet-Draft Learning the AFT's Prefix October 2008 host and preform passive or active eavesdropping or traffic analysis. To protect against this attack, it is RECOMMENDED that IPv6 hosts be configured with the names of authorized translators and RECOMMENDED that IPv6 hosts uses DNSSEC to validate that name matches the IPv6 prefix learned via DNS or DHCPv6. 5. IANA Considerations A new DHCPv6 option, OPTION_AFT_PREFIX, needs to be assigned by IANA. The name "_aft_translator" should be reserved by IANA for this purpose. 6. Acknowledgements This draft was fostered by discussion on the 46translation mailing list and at the v4v6 Interim in Montreal. Special thanks to Iljitsch van Beijnum, Andrew Sullivan, Marcelo Bagnulo Braun, Fred Baker, and Xing Li for their comments and dialog. Thanks to Ralph Droms for his help with DHCPv6. Thanks to John Schnizlein for improving the DNS learning algorithm. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 7.2. Informative References [Sullivan-email] Sullivan, A., "DNSSEC Current Thinking", October 2008, . [Wing-email] Wing, D., "DNSSEC, approach 2", October 2008, . Wing Expires April 26, 2009 [Page 6] Internet-Draft Learning the AFT's Prefix October 2008 Author's Address Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA Email: dwing@cisco.com Wing Expires April 26, 2009 [Page 7] Internet-Draft Learning the AFT's Prefix October 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment This document was produced using xml2rfc v1.33 (of http://xml.resource.org/) from a source in RFC-2629 XML format. Wing Expires April 26, 2009 [Page 8]