Dynamic Host Configuration Working D. Hankins Group ISC Internet-Draft March 23, 2009 Intended status: Standards Track Expires: September 24, 2009 Dynamic Host Configuration Protocol Option for Dual-Stack Lite draft-dhankins-softwire-tunnel-option-03 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 September 24, 2009. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes how Dual-Stack Lite configuration (the Softwire Concentrator (SC)'s address) can be obtained by a Softwire Hankins Expires September 24, 2009 [Page 1] Internet-Draft DS Lite Option March 2009 Initiator (SI) via DHCPv6. Table of Contents 1. Requirements Language . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The Dual-Stack Lite DHCPv6 Option . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 6. Normative References . . . . . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 5 Hankins Expires September 24, 2009 [Page 2] Internet-Draft DS Lite Option March 2009 1. Requirements Language In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL", "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as described in BCP 14, RFC 2119 [RFC2119]. 2. Introduction Dual-Stack Lite [draft-ietf-softwire-dual-stack-lite-00] is a method to extend IPv4 access to an IPv6-only addressed host. One of its key components is an IPv4-over-IPv6 tunnel, commonly referred to as a Softwire, but a host will not know if the network it is attached to offers Dual-Stack Lite support, and if it did would not know the remote end of the tunnel to establish a connection. These are two separate pieces of information; 1) Should I shut down my dual-stack IPv4 side, and use the softwire exclusively for IPv4 access? 2) At what IPv6 address should I establish a softwire connection? These two questions can be answered with one DHCPv6 [RFC3315] option. DISCUSSION: It can be argued that if you inform a client it should perform Dual-Stack Lite, but fail to deliver an IPv6 tunnel endpoint, then its IPv4 access is certainly broken. If you give the client an IPv6 tunnel endpoint but fail to inform it that it must use Dual- Stack Lite for IPv4 access, then again its access is likely broken, or is operating in a degraded mode of service (if an operator offers a Dual-Stack Lite method of access, there either isn't any native IPv4 access, or the Dual-Stack Lite method works better than native access - if a network had better native IPv4 access than Dual-Stack Lite access, there would be no reason to extend the service). So the presence of a tunnel address also indicates the intent to use it. 3. The Dual-Stack Lite DHCPv6 Option The Dual-Stack Lite DHCPv6 Option is simply an IPv6 address. Hankins Expires September 24, 2009 [Page 3] Internet-Draft DS Lite Option March 2009 The Dual-Stack Lite Option Format follows: 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_DS_LITE (TBD) | length (16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | IPv6 Address | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The code for this option is TBD. The length is precisely 16. The IPv6 Address field is an IPv6 address. The DS Lite option MAY appear in the root scope of a DHCPv6 packet. It MUST NOT appear inside any IA_NA, IA_TA, IA_PD, IAADDR, or similar. If configured with a value, DHCPv6 servers will include the Softwires option if it appears on the client's Option Request Option (OPTION_ORO). RFC 3315 Section 17.2.2 [RFC3315] describes how a DHCPv6 client and server negotiate configuration values using the ORO. A client that supports DS Lite MUST include OPTION_DS_LITE on its OPTION_ORO. There is no reasonable expectation that a server will reply with the DS Lite option if it has not been requested. If the client receives a DS Lite Option, it MUST verify the option length is precisely 16 octets, and ignore the option otherwise. Provided it is of valid length, the client SHOULD terminate or withdraw any DHCPv4 [RFC2131] configuration on the same interface. If DHCPv4 configuration has concluded, the client SHOULD perform a DHCPRELEASE as it tears down its IPv4 configuration. The client SHOULD establish a softwire tunnel to the included IPv6 address. DISCUSSION: The author's best understanding of the current epistemology on IPv6 multihoming is that the client will have IPv6 addresses on multiple different IPv6 prefixes. If a host is multihomed, then, it is strange enough to wonder how DHCPv6 configuration will work as most DHCPv6 clients will attach to only one DHCPv6 server. It is even stranger to wonder how the client would react if all of its multiple homes wished to provide IPv4 access via DS Lite. Would a client establish more than one tunnel? Perhaps this option should permit multiple IPv6 addresses? Hankins Expires September 24, 2009 [Page 4] Internet-Draft DS Lite Option March 2009 4. Security Considerations This document does not present any new security issues, but as with all DHCPv6-derived configuration state, it is completely possible that the configuration is being delivered by a third party (Man In The Middle). As such, there is no basis to trust that the access the DS-Lite softwire connection represents can be trusted, and it should not therefore bypass any security mechanisms such as IP firewalls. RFC 3315 [RFC3315] discusses DHCPv6 related security issues. 5. IANA Considerations IANA is requested to allocate one DHCPv6 Option code, referencing this document. 6. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, July 2003. [draft-ietf-softwire-dual-stack-lite-00] Durand, A., Droms, R., Haberman, B., and J. Woodyatt, "Dual-stack lite broadband deployments post IPv4 exhaustion", March 2009. Author's Address David W. Hankins Internet Systems Consortium, Inc. 950 Charter Street Redwood City, CA 94063 US Phone: +1 650 423 1307 Email: David_Hankins@isc.org Hankins Expires September 24, 2009 [Page 5]