Dynamic Host Configuration Working D. Hankins Group ISC Internet-Draft October 26, 2009 Intended status: Standards Track Expires: April 29, 2010 Dynamic Host Configuration Protocol Option for Dual-Stack Lite draft-dhankins-softwire-tunnel-option-04 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 April 29, 2010. 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 April 29, 2010 [Page 1] Internet-Draft DS Lite Option October 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 . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Hankins Expires April 29, 2010 [Page 2] Internet-Draft DS Lite Option October 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-01] 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 operator's intent for the client to use the Softwire. 3. The Dual-Stack Lite DHCPv6 Option The Dual-Stack Lite DHCPv6 Option is simply a list of IPv6 addresses in binary representation. Hankins Expires April 29, 2010 [Page 3] Internet-Draft DS Lite Option October 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 (Nx16) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | IPv6 Address 0 | | | | | +---------------------------------------------------------------+ | | | IPv6 Address 1 | | | | | +---------------------------------------------------------------+ | ... | +---------------------------------------------------------------+ | | | IPv6 Address N | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The code for this option is TBD. The length MUST be a multiple of 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 DS Lite 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 a multiple of 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. Hankins Expires April 29, 2010 [Page 4] Internet-Draft DS Lite Option October 2009 The client SHOULD establish a Softwire tunnel to the first IPv6 address ("IPv6 Address 0"), and incrementally attempt the next address in series ("IPv6 Address 1" etc) if present until a Softwire can be established. The specifics of timeout intervals are not mentioned. If at any time the Softwire is forcibly disconnected, the client MUST restart connection at the start of the list. Note carefully that through normal DHCPv6 Renew processes, the option's contents may be updated, and fresh versions of the configuration should be obtained from the DHCPv6 client in a timely manner. DISCUSSION: The author believes that as Softwires are a "routing layer" solution, they are likely to be managed in networks using routing layer tools - the application of anycasting, or simply the use of "role addresses" that can be quickly re-routed from failed servers and applied to surviving servers. This argues a simplification for the client to be given only one IPv6 address, as the routing layer can ensure that address is terminated in the most useful place. However, upon further discussion it seems to the author that it is also necessary to provide routing protocol operators to employ more than one route; so that faults with one route in the table are not devastating. For this purpose, (N) addresses are made available. 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. draft-ietf-softwire-dual-stack-lite-01 [draft-ietf-softwire-dual-stack-lite-01] discusses DS Lite related security issues. 5. IANA Considerations IANA is requested to allocate one DHCPv6 Option code, referencing this document. Hankins Expires April 29, 2010 [Page 5] Internet-Draft DS Lite Option October 2009 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-01] Durand, A., "Dual-stack lite broadband deployments post IPv4 exhaustion", July 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 April 29, 2010 [Page 6]