Dynamic Host Configuration (DHC) J. Korhonen Internet-Draft Nokia Siemens Networks Updates: 3633 (if approved) T. Savolainen Intended status: Standards Track Nokia Expires: March 6, 2011 September 2, 2010 Prefix Exclude Option for DHCPv6-based Prefix Delegation draft-korhonen-dhc-pd-exclude-01.txt Abstract This specification defines an optional mechanism to allow exclusion of one specific prefix from a delegated prefix set when using DHCPv6- based prefix delegation. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on March 6, 2011. Copyright Notice Copyright (c) 2010 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 (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 Simplified BSD License. Korhonen & Savolainen Expires March 6, 2011 [Page 1] Internet-Draft PD Exclude Option September 2010 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements and Terminology . . . . . . . . . . . . . . . . . 3 3. Prefix Delegation with Excluded Prefixes . . . . . . . . . . . 3 3.1. Problem Background . . . . . . . . . . . . . . . . . . . . 3 3.2. Available Workarounds . . . . . . . . . . . . . . . . . . . 4 3.3. Proposed Solution . . . . . . . . . . . . . . . . . . . . . 5 4. Prefix Exclude Option . . . . . . . . . . . . . . . . . . . . . 5 5. Delegating Router Solicitation . . . . . . . . . . . . . . . . 6 5.1. Requesting Router . . . . . . . . . . . . . . . . . . . . . 6 5.2. Delegating Router . . . . . . . . . . . . . . . . . . . . . 7 6. Requesting Router Initiated Prefix Delegation . . . . . . . . . 8 6.1. Requesting Router . . . . . . . . . . . . . . . . . . . . . 8 6.2. Delegating Router . . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 Korhonen & Savolainen Expires March 6, 2011 [Page 2] Internet-Draft PD Exclude Option September 2010 1. Introduction This specification defines an optional mechanism and the related DHCPv6 option to allow exclusion of one specific prefix from a delegated prefix set when using DHCPv6-based prefix delegation. The prefix exclusion mechanism is targeted to deployments where DHCPv6-based prefix delegation is used but a single aggregatable route/refix has to represents one customer, instead of using one prefix for the link and another prefix for the customer network. The mechanism defined in this specification allows requesting router to use a prefix out of delegated prefix set on its link through which it exchanges DHCPv6 messages with the delegating router. 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. Prefix Delegation with Excluded Prefixes 3.1. Problem Background DHCPv6 Prefix Delegation (DHCPv6-PD) [RFC3633] has an explicit limitation described in Section 12.1 of [RFC3633] that a prefix delegated to a requesting router cannot be used by the delegating router. This restriction implies that the delegating router will have two (non aggregatable) routes towards a customer, one for the link between the requesting router and the delegating router and one for the customer site behind the requesting router. This approach works well with the unnumbered router model (i.e. routers on the link have no globally scoped prefixes). Also the same approach applies to the case where the prefix assigned to the requesting router link through which it received DHCP messages does not in any way need to be associated to the delegated prefixes. There are architectures and link models, where a host (e.g. a mobile router, also acting as a requesting router) always has a single (/64) prefix configured on its uplink interface and the delegating router is also requesting router's first hop router. Furthermore, it may be required that the prefix configured on the uplink interface has to be aggregatable with the delegated prefixes. This introduces a problem how to use DHCPv6-PD together with stateless [RFC4862] or stateful [RFC3315] address autoconfiguration on a link, where the /64 advertised on the link is also part of the prefix delegated (e.g /56) Korhonen & Savolainen Expires March 6, 2011 [Page 3] Internet-Draft PD Exclude Option September 2010 to the requesting router. 3.2. Available Workarounds The problem described in Section 3.1 can be solved in a multiple of ways. We list a number of possible solutions below that all allow a natural aggregation of the /64 prefix used on the link and the delegated prefix. Some of them are possible without modifications to [RFC3633] protocol but require new functionality in the delegating router or have other constraints. 1. Delegating and requesting router agree that a specific prefix from a delegated prefix set can be configured and used on the link where both delegating and requesting router are attached to. Both delegating and requesting router have to understand new enhanced DHCPv6-PD functionality and/or DHCPv6 options to achieve the desired outcome. This solution is described in Section 3.3. 2. A delegating router delegates only half of the prefix that was reserved for the requesting router. A /64 of the other half is used for (point-to-point) link where the delegating and requesting router are attached to. The other half of the reserved prefix get delegated to the requesting router. This solution has an obvious issue of "wasting" prefixes. One can argue that IPv6 has no issue of address shortage but solutions promoting greedy use of IPv6 prefixes should not advocated. This solution is one possible fallback mechanism when the solution described in Section 3.3 is not available in the requesting router. 3. A delegating router delegates a prefix that was reserved for the requesting router in a sets of longer prefixes. For example, if the reserved prefix is a /56 then it can be delegated as a set of /57, /58, /59, /60, /61, /62, /63 and one /64. The last remaining /64 is the prefix assigned to the uplink of the requesting router. The size of the DHCPv6 message may quickly become an issue when the delegating any reasonable sized prefix. This solution is one possible fallback mechanism when the solution described in Section 3.3 is not available in the requesting router. However, it is possible that legacy requesting router implementations cannot handle multiple delegated prefixes and therefore the solution 2) is probably a safer choice for a fallback mechanism. 4. A requesting router requests a single /64 for each of its downstream interfaces and a delegating router aggregates these /64 prefixes into a larger allocation. The size of the DHCPv6 message may quickly become an issue when the delegating any Korhonen & Savolainen Expires March 6, 2011 [Page 4] Internet-Draft PD Exclude Option September 2010 reasonable sized prefix. This solution is one possible fallback mechanism when the solution described in Section 3.3 is not available in the delegating router. However, it is not granted that legacy requesting router implementations can handle multiple delegated prefixes and therefore the solution 2) is probably a safer choice for a fallback mechanism. 3.3. Proposed Solution This specification defines a new DHCPv6 option, OPTION_PD_EXCLUDE (TBD1), that is used to exclude exactly one prefix from a delegated prefix defined in the OPTION_IAPREFIX. The OPTION_PD_EXCLUDE MUST only be included in the OPTION_IAPREFIX IAprefix-options field. There can be zero or one OPTION_PD_EXCLUDE option in one OPTION_IAPREFIX option. The OPTION_PD_EXCLUDE option allows prefix delegation where a requesting router is delegated a prefix (e.g. /56) and the delegating router uses one prefix (e.g. /64) on the link through which it exchanges DHCPv6 messages with the requesting router with a prefix out of the same delegated prefix set. A requesting router SHOULD include an OPTION_ORO option with the OPTION_PD_EXCLUDE option code in a Solicit, Request, Renew, Rebind, Confirm or Information-request message to inform the delegating router about the support for the prefix delegation functionality defined in this specification. A delegating router MAY include an OPTION_ORO option in a Reconfigure option to indicate which options the requesting router should request from the delegating router. The delegating router MAY include the unspecified address '::' in the OPTION_PD_EXCLUDE as an indication that the option was understood but there is no reason to exclude any prefix from the delegated prefix set. Otherwise, the delegating router includes the prefix in the OPTION_PD_EXCLUDE option that is excluded from the delegated prefix set. The requesting router MUST NOT assign the excluded prefix to any of its downstream interfaces. 4. Prefix Exclude Option 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_PD_EXCLUDE | option-len | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | prefix-len | IPv6-prefix (0 to 16 octets) ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Korhonen & Savolainen Expires March 6, 2011 [Page 5] Internet-Draft PD Exclude Option September 2010 Prefix Exclude Option o option-code: OPTION_PD_EXCLUDE (TBD1). o option-len: 1 + length of prefix in octets. Valid option-lens are between 1 and 17. o prefix-len: The length of the excluded prefix in bits. Valid prefix-lens are between 0 and 128. Prefix length of 0 means the unspecified address '::'. o IPv6-prefix: A variable length IPv6 prefix up to 128 bits. The prefix MUST be zero padded to the next full octet boundary. Trailing zero octets of the prefix SHOULD NOT be encoded into the prefix field. The unspecified address MUST NOT be encoded at all. The OPTION_PD_EXCLUDE option MUST only be included in the OPTION_IAPREFIX IAprefix-options [RFC3633] field. The OPTION_PD_EXCLUDE option MUST be located before the possible Status Code option in the IAprefix-options field. Any prefix excluded from the delegated prefix MUST be contained in OPTION_PD_EXCLUDE options within the corresponding OPTION_IAPREFIX. The prefix included in the OPTION_PD_EXCLUDE option share the same preferred-lifetime and valid-lifetime as the delegated prefix in the 'parent' OPTION_IAPREFIX option. The prefix in the OPTION_PD_EXCLUDE option MUST be part of the delegated prefix in the OPTION_IAPREFIX. For example, if the requesting router has earlier been assigned a 2001:db8:dead:beef::/64 prefix by the delegating router, and the delegated prefix in the OPTION_IAPREFIX is 2001:db8:dead:be00::/56, then the prefix in the OPTION_PD_EXCLUDE option MUST be 2001:db8:dead:beef::/64. 5. Delegating Router Solicitation The requesting router locates and selects a delegating router in the same way as described in Section 11 [RFC3633]. This specification only describes the additional steps required by the use of OPTION_PD_EXCLUDE option. 5.1. Requesting Router The requesting router may have an address configured on its uplink interface of other scope than link-local and in this case the problem described in Section 3.1 applies. If the requesting router implement Korhonen & Savolainen Expires March 6, 2011 [Page 6] Internet-Draft PD Exclude Option September 2010 the solution described in Section 3.3 then the requesting router MUST include the OPTION_PD_EXCLUDE option code in the OPTION_ORO option in the Solicit message. If the requesting router does not implement the solution described in this specification (see Section 3.3, it might still be possible for the requesting router to utilize the workaround 4) described in Section 3.2 through configuration. In this case the delegating router may still be able to delegate aggregated prefixes to the requesting router. Once receiving Advertisement message, the requesting router uses the prefix(es) received in OPTION_PD_EXCLUDE in addition to the advertised prefixes to choose the delegating router to respond to. If Advertisement message did not include OPTION_PD_EXCLUDE option or the prefix in the OPTION_PD_EXCLUDE option contains an unspecified address '::', then the requesting router MUST fall back to normal [RFC3633] behavior. Editor's Note: is there actually deployment case when multiple delegating routers would respond? 5.2. Delegating Router If the OPTION_ORO option in the Solicit message includes the OPTION_PD_EXCLUDE option code, then the delegating router knows that the requesting router supports the solution defined in this specification. If the Solicit message also contains an IA_PD option, the delegating router can delegate to the requesting router a prefix which includes the prefix already assigned to the requesting router's uplink interface. The delegating router includes the prefix originally or to be assigned to the requesting router in the OPTION_PD_EXCLUDE option within the OPTION_IAPREFIX IAprefix-option in the Advertise message. If the OPTION_ORO option in the Solicit message does not include the OPTION_PD_EXCLUDE option code, then the delegating router MUST fall back to normal [RFC3633] behavior. However, the delegating router could still delegate prefixes to the requesting router using workarounds 2), 3) or 4) described in Section 3.2. If the OPTION_ORO option in the Solicit message includes the OPTION_PD_EXCLUDE option code but the delegating router does not support the solution described in this specification, them the delegating router acts as specified in [RFC3633]. The requesting router MUST in this case also fall back to normal [RFC3633] behavior. Korhonen & Savolainen Expires March 6, 2011 [Page 7] Internet-Draft PD Exclude Option September 2010 6. Requesting Router Initiated Prefix Delegation The procedures described in the following sections are aligned with Section 12 of [RFC3633]. In this specification we only describe the additional steps required by the use of OPTION_PD_EXCLUDE option. 6.1. Requesting Router The requesting router behavior regarding the use of the OPTION_PD_EXCLUDE option is more or less identical to step described in Section 5.1. The only difference really is different used DHCPv6 messages. The requesting router uses a Release message to return the delegated prefix(es) to a delegating router. The prefix(es) to be released MUST be included in the IA_PDs along with the excluded prefix included in the OPTION_PD_EXCLUDE option. The requesting router MUST NOT use the OPTION_PD_EXCLUDE option to introduce additional excluded prefix in the Release message that it originally got a valid binding for. The requesting router must create sink routes for the delegated prefixes minus the excluded prefixes. This may be done by creating sink routes for delegated prefixes and more specific routes for the excluded prefixes. 6.2. Delegating Router The delegating router behavior regarding the use of the OPTION_PD_EXCLUDE option is more or less identical to step described in Section 5.2. The only difference really is DHCPv6 messages used to carry the OPTION_PD_EXCLUDE option. The delegating router may mark any prefix(es) in IA_PD Prefix options in a Release message from a requesting router as 'available' excluding the prefix included in the OPTION_PD_EXCLUDE options. If the Release message contains 'new' excluded prefix in any OPTION_PD_EXCLUDE option, the delegating router MUST send a Reply message with Status Code set to NoBinding for that IA_PD option. 7. Security Considerations Security considerations in DHCPv6 are described in Section 23 of [RFC3315], and for DHCPv6 Prefix Delegation in Section 12 of [RFC3633]. A malicious requesting router may unnecessarily fragment the Korhonen & Savolainen Expires March 6, 2011 [Page 8] Internet-Draft PD Exclude Option September 2010 delegating router prefix pools and cause additional load on the delegating router by defining excluded prefix(es). The excluded prefix(es) may cause the delegating router to react to neighbor discovery messages other than just ignoring them. 8. IANA Considerations A new DHCPv6 Option Code is reserved from DHCPv6 registry for DHCP Option Codes. OPTION_PD_EXCLUDE is set to TBD1 9. Acknowledgements Authors would like to thank Ralph Droms, Frank Brockners, Ted Lemon, Julien Laganier, Suresh Krishnan, Fredrik Garneij, Sri Gundavelli, Mikael Abrahamsson and Deng Hui for their valuable comments and discussions. Authors thank Ole Troan for his detailed review and suggestions to improve the text. 10. References 10.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, 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. [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003. 10.2. Informative References [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. Korhonen & Savolainen Expires March 6, 2011 [Page 9] Internet-Draft PD Exclude Option September 2010 Authors' Addresses Jouni Korhonen Nokia Siemens Networks Linnoitustie 6 FI-02600 Espoo Finland Email: jouni.nospam@gmail.com Teemu Savolainen Nokia Hermiankatu 12 D FI-33720 Tampere Finland Email: teemu.savolainen@nokia.com Korhonen & Savolainen Expires March 6, 2011 [Page 10]