Network Working Group F. Xia Internet-Draft B. Sarikaya Intended status: Standards Track Huawei USA Expires: May 20, 2008 November 17, 2007 Using DHCPv6 for Prefix Delegation in IEEE 802.16 Networks 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 May 20, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Xia & Sarikaya Expires May 20, 2008 [Page 1] Internet-Draft Prefix Delegation November 2007 Abstract In the 802.16 Per-MS interface prefix model, one prefix can only be assigned to one interface of a mobile station by an access router and different mobile stations can't share a prefix. Managing Per-MS interface prefixes is likely to increase the processing load at the access router. Based on the idea that DHCPv6 servers can manage prefixes as well as addresses, we propose a new technique in which the access router offloads delegation and release tasks of the prefixes to an DHCPv6 server. The access router first requests a prefix for an incoming mobile station to the DHCPv6 server. The access router next advertises the prefix information to the mobile station with a Router Advertisement message. When the mobile station hands off, the prefix is returned to the DHCPv6 server. We also describe how AAA servers can help in prefix delegation. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Prefix Delegation Using DHCPv6 . . . . . . . . . . . . . . . . 4 3.1. Prefix Request Procedure for Stateless Address Configuration . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Prefix Request Procedure for Stateful Address Configuration . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Prefix Release Procedure . . . . . . . . . . . . . . . . . 6 3.4. Renumbering . . . . . . . . . . . . . . . . . . . . . . . 7 3.4.1. Renumbering Through Renew Message . . . . . . . . . . 7 3.4.2. Server Initiated Reconfiguration . . . . . . . . . . . 7 3.5. Miscellaneous Considerations . . . . . . . . . . . . . . . 7 3.5.1. Triggers for an AR to initiate prefix request procedure . . . . . . . . . . . . . . . . . . . . . . 7 3.5.2. How to generate IAID . . . . . . . . . . . . . . . . . 7 3.5.3. Policy to delegate prefixes . . . . . . . . . . . . . 8 4. Prefix Delegation Using RADIUS and Diameter . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. Protocol Variables . . . . . . . . . . . . . . . . . . . . . . 9 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Intellectual Property and Copyright Statements . . . . . . . . . . 12 Xia & Sarikaya Expires May 20, 2008 [Page 2] Internet-Draft Prefix Delegation November 2007 1. Introduction Figure 1 illustrates the key elements of a typical IEEE 802.16d/e access network. Customer | Access Provider | Service Provider Premise | | (Backend Network) +------+ |DHCP | +-----+ +-----+ +------+ +--------+ |Server| | MS |--(802.16)--| BS |-----+Access+---+ Edge |--+------+ +-----+ +-----+ |Router| | Router +==>ISP Network +--+---+ +--------+ +-----+ +-----+ | | +------+ | MS |--(802.16)--| BS |--------+ +--|AAA | +-----+ +-----+ |Server| +------+ Figure 1: Key elements of a typical IEEE 802.16d/e access network Mobile stations (MS) attach to a base station (BS) through 802.16d/e air interface. A BS manages connectivity of MSs and extend connections to an Access Router (AR). The Access router is the first IP hop router of MSs. As to IPv6 addressing, there are two models, shared prefix and Per-MS interface prefix. In the shared prefix model, an IPv6 prefix is shared by multiple MSs. While in the Per-MS interface prefix model, a prefix is only assigned to one interface of the MS. Different MSs can't share a prefix, and an interface can have multiple prefixes. [RFC4968] briefly compares the two models. Per-MS interface prefix model has some advantages, such as, no complicated duplicate address detection (DAD), fit naturally to the point-to-point links and so on. In Per-MS interface prefix model, prefix management is an issue. When an MS attaches an AR, the AR requests one or more prefixes for the MS. When the MS detaches the AR, the prefixes should be released. When the MS becomes idle, the AR should hold the prefixes allocated. When an operator wants to renumber its network, prefixes with different lifetime are advertised to the MS. DHCPv6 is a preferable way to manage the prefixes. At the same time, AAA protocols, RADIUS and Diameter, can be used in prefix delegation. Xia & Sarikaya Expires May 20, 2008 [Page 3] Internet-Draft Prefix Delegation November 2007 2. 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 BCP 14 [RFC2119]. This document uses the terminology defined in [RFC3315], [RFC3633] and [I-D.ietf-16ng-ps-goals]. 3. Prefix Delegation Using DHCPv6 3.1. Prefix Request Procedure for Stateless Address Configuration +-------+ +-------+ +-----------+ | MS | | AR | |DHCP Server| +-------+ +-------+ +-----------+ | | | | 1 N/W Entry & Auth | | |<--------------------->| | | |2 Relay-forward/Solicit| | |---------------------> | | | | | |3 Relay-reply/Advertise| | |<--------------------- | | | | | |4 Relay-forward/Request| | |---------------------> | | | | | |5 Relay-reply/Reply | | |<--------------------- | |6 Initial Service Flow | | | Established | | |<--------------------->| | | | | | 7 Router Advertisement| | |<----------------------| | | | | | 8 MLD Join | | |---------------------->| | | | | | 9 DAD Procedure | | |<--------------------->| | | | | Figure 2: Prefix request There are two function modules in the AR, DHCP Client and DHCP Relay. Xia & Sarikaya Expires May 20, 2008 [Page 4] Internet-Draft Prefix Delegation November 2007 DHCP messages should be relayed if the AR and a DHCP server are not connected directly, otherwise DHCP relay function in the AR is not necessary. Figure 2 illustrates the scenario that the AR and the DHCP Server aren't connected directly: 1. An MS performs initial network entry and authentication procedures. 2. On successful completion of Step 1, the AR initiates DHCP Solicit procedure to request prefixes for the MS. The AR creates and transmits a Solicit message as described in sections 17.1.1, "Creation of Solicit Messages" and 17.1.2, "Transmission of Solicit Messages" of RFC 3315. The AR creates an IA_PD and assigns it an IAID. The AR MUST include the IA_PD option in the Solicit message. 3. The DHCP server sends an Advertise message to the AR in the same way as described in section 17.2.2, "Creation and transmission of Advertise messages" of RFC 3315. 4. The AR uses the same message exchanges as described in section 18, "DHCP Client-Initiated Configuration Exchange" of RFC 3315 to obtain or update prefixes from a DHCP server. The AR and the DHCP server use the IA_PD Prefix option to exchange information about prefixes in much the same way as IA Address options are used for assigned addresses. 5. AR stores the prefix information it received in the Reply message. 6. A virtual link called initial service flow is created for exchanging control traffic between MS and AR and becomes active. The initial service flow is defined in [I-D.ietf-16ng-ipv6-over-ipv6cs]. 7. The AR advertises prefixes to MS with RA once the virtual link is active. 8. The MS constructs a solicited node multicast address for the corresponding Link Local Address and sends MLD Join request for the solicited node multicast address. 9. The MS starts verifying address uniqueness by sending a DAD NS on the virtual link. AR can check the address uniqueness within the virtual link scope. 4-way exchange between AR as requesting router (RR) and DHCP server as delegating router (DR) in Figure 2 MAY be reduced into a two message exchange using the Rapid Commit option [RFC3315]. AR includes a Rapid Commit option in the Solicit message. DR then sends a Reply message containing one or more prefixes. 3.2. Prefix Request Procedure for Stateful Address Configuration After the initial network entry and authentication, a transport connection is established for the MS. DHCPv6 client at the MS sends Xia & Sarikaya Expires May 20, 2008 [Page 5] Internet-Draft Prefix Delegation November 2007 DHCP Request to DHCP Relay function at AR. DHCP Relay sends DHCP Request with DHCP Forward message to DHCP Server. AR MUST set the link-address field of DHCP Forward to the aggregate prefix. DHCP Server assigns an address and a unique prefix for MS's interface and replies with DHCP Reply message which is relayed to DHCP Relay in Relay-reply message and AR sends DHCP Reply message with the new prefix to MS. MS configures its interface with the address assigned by DHCP server in DHCP Reply message. 3.3. Prefix Release Procedure +-------+ +-------+ +-----------+ | MS | | AR | |DHCP Server| +-------+ +-------+ +-----------+ | | | | 1 De-registration | | | Handover, or others | | |<--------------------->| | | |2 Relay-forward/Release| | |---------------------->| | | | | |3 Relay-reply/Reply | | |<--------------------- | | | | | | | Figure 3: Prefix Release Prefixes can be released in two ways, prefix aging or DHCP release procedure. In the former way, a prefix SHOULD not be used by an MS when the prefix ages, and the DHCP Server can delegate it to another MS. A prefix lifetime is delivered from the DHCPv6 server to the MS through DHCP IA_PD Prefix option [RFC3633] and RA Prefix Information option [RFC4861]. Figure 3 illustrates how the AR releases prefixes to an DHCP Server which isn't connected directly: 1. An MS detachment signaling, such as switch-off or handover, triggers prefix release procedure. 2. The AR initiates a Release message to give back the prefixes to the DHCP server. 3. The server responds with a Reply message, and then the prefixes can be reused by other MSs. Xia & Sarikaya Expires May 20, 2008 [Page 6] Internet-Draft Prefix Delegation November 2007 3.4. Renumbering 3.4.1. Renumbering Through Renew Message To extend the valid and preferred lifetimes for the prefixes associated with an MS, the AR sends a Renew message to the DHCP server. The server determines new lifetimes for the prefixes and returns the prefix to AR in a Reply message. The DHCP server MAY add new prefixes to the MS for renumbering in its Reply message. For a more detailed description of these message, refer to [RFC3633] and of renumbering, refer to [RFC4192]. 3.4.2. Server Initiated Reconfiguration DHCP server initiates a configuration message exchange with the AR by sending a Reconfigure message. The reconfigure message triggers the AR to send Renew message as described in Section 3.4.1. 3.5. Miscellaneous Considerations 3.5.1. Triggers for an AR to initiate prefix request procedure There are some other triggers for an AR to initiate prefix request procedure besides network entry and authentication, such as, when an AR receives handover initiate (HI) message in FMIPv6 [RFC4068], or other handover signaling. After getting an incoming MS' necessary information (such as MAC address), the AR SHOULD initiate prefix request procedure as soon as possible. 3.5.2. How to generate IAID IAID is 4 bytes in length and should be unique in an AR scope. Prefix table SHOULD be maintained. Prefix table contains IAID, MAC address and the prefix(es) assigned to MS. MAC address of the interface SHOULD be stored in the prefix table and this field is used as the key for searching the table. IAID SHOULD be set to Start_IAID, an integer of 4 octets. The following IAID generation algorithm is used: 1. Set this IAID value in IA_PD Prefix Option. Request prefix for this MS as in Section 3.1 or Section 3.2. 2. Store IAID, MAC address and the prefix(es) received in the next entry of the prefix table. 3. Increment IAID. Prefix table entry for an MS that handsover to another AR MUST be removed. IAID value is released to be reused. Xia & Sarikaya Expires May 20, 2008 [Page 7] Internet-Draft Prefix Delegation November 2007 3.5.3. Policy to delegate prefixes AR should broadcast the prefix(es) dynamically upstream as the route information of all the MSs connected to this AR. In point-to-point links, this causes high routing protocol traffic (IGMP, OSPF, etc.) due to Per-MS interface prefixes. To solve the problem, route aggregation SHOULD be used. For example, each AR can be assigned a /48 or /32 prefix (aggregate prefix) while each interface of MS can be assigned a /64 prefix. The /64 prefix is an extension of /48 one, for example, an AR's /48 prefix is 3FFE:FFFF:0::/48, an interface of MS is assigned 3FFE:FFFF:0:2::/64 prefix. The AR only broadcasts it's /48 or /32 prefix information to Internet. This policy can be enforced as follows: DHCP Relay MUST set the link- address field in the Relay Forward message to the aggregate prefix (/48, /32, or /16 prefix assigned to the AR). 4. Prefix Delegation Using RADIUS and Diameter In the bootstrapping procedure, an AR as RADIUS client sends Access- Request message with an MS' information to RADIUS server. If the MS passes the authentication, the RADIUS server MAY send Access-Accept message with prefix information to the AR using Framed-IPv6-Prefix attribute. There is no prefix delegation involved in this process. Using such a process AR can handle initial prefix assignments to MSs but managing lifetime of the prefixes is totally left to the AR. Also AR can not use Framed-IPv6-Prefix attribute based assignment for MSs that handover but no full authentication is executed. [RFC4818] defines a RADIUS attribute Delegated-IPv6-Prefix that carries an IPv6 prefix to be delegated. This attribute is usable within either RADIUS or Diameter. [RFC4818] recommends the delegating router to use AAA server to receive the prefixes to be delegated using Delegated-IPv6-Prefix attribute/AVP. DHCP server as the delegating router in Figure 2 MAY send an Access- Request packet containing Delegated-IPv6-Prefix attribute to the RADIUS server to request prefixes. In the Access-Request message, the delegating router MAY provide a hint by the AR that it would prefer a prefix, for example, a /48 prefix. The RADIUS server MAY delegate a /64 prefix which is an extension of the /48 prefix in an Access-Accept message containing Delegated-IPv6-Prefix attribute. The attribute can appear multiple times when RADIUS server assigns multiple prefixes. When Diameter is used, DHCP server as the delegating router in Figure 2 sends AA-Request message. AA-Request message MAY contain Xia & Sarikaya Expires May 20, 2008 [Page 8] Internet-Draft Prefix Delegation November 2007 Delegated-IPv6-Prefix AVP. Diameter server replies with AA-Answer message. AA-Answer message MAY contain Delegated-IPv6-Prefix AVP. The AVP can appear multiple times when Diameter server assigns multiple prefixes to MS. The Delegated-IPv6-Prefix AVP MAY appear in an AA-Request packet as a hint by the AR to the Diameter server that it would prefer a prefix, for example, a /48 prefix. Diameter server MAY delegate in an AA-Answer message with a /64 prefix which is an extension of the /48 prefix. AR MUST advertize the prefix(es) to MS in RtrAdv message. Prefix release and site renumbering are open issues for RADIUS/ Diameter protocols to manage prefixes. 5. Security Considerations This draft introduces no additional messages. Comparing to [RFC3633], [RFC2865] and [RFC3588] there is no additional threats to be introduced. DHCPv6, RADIUS and Diameter security procedures apply. 6. Protocol Variables Start_IAID 4 octet integer value. It can be initialized to ZERO. 7. IANA Considerations None. 8. Acknowledgements The authors are grateful to Bernie Volz and other members of DHC WG for their comments on the draft. 9. References 9.1. Normative References [I-D.ietf-16ng-ipv6-over-ipv6cs] Patil, B., Xia, F., Sarikaya, B., Choi, J., and S. Madanapalli, "Transmission of IPv6 via the IPv6 CS over Xia & Sarikaya Expires May 20, 2008 [Page 9] Internet-Draft Prefix Delegation November 2007 IEEE 802.16 Networks", draft-ietf-16ng-ipv6-over-ipv6cs-11 (work in progress), November 2007. [I-D.ietf-16ng-ps-goals] Jee, J., "IP over 802.16 Problem Statement and Goals", draft-ietf-16ng-ps-goals-02 (work in progress), August 2007. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote Authentication Dial In User Service (RADIUS)", RFC 2865, June 2000. [RFC2866] Rigney, C., "RADIUS Accounting", RFC 2866, June 2000. [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. [RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko, "Diameter Base Protocol", RFC 3588, September 2003. [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003. [RFC4068] Koodli, R., "Fast Handovers for Mobile IPv6", RFC 4068, July 2005. [RFC4818] Salowey, J. and R. Droms, "RADIUS Delegated-IPv6-Prefix Attribute", RFC 4818, April 2007. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. 9.2. Informative References [RFC4192] Baker, F., Lear, E., and R. Droms, "Procedures for Renumbering an IPv6 Network without a Flag Day", RFC 4192, September 2005. [RFC4968] Madanapalli, S., "Analysis of IPv6 Link Models for 802.16 Xia & Sarikaya Expires May 20, 2008 [Page 10] Internet-Draft Prefix Delegation November 2007 Based Networks", RFC 4968, August 2007. Authors' Addresses Frank Xia Huawei USA 1700 Alma Dr. Suite 500 Plano, TX 75075 Phone: +1 972-509-5599 Email: xiayangsong@huawei.com Behcet Sarikaya Huawei USA 1700 Alma Dr. Suite 500 Plano, TX 75075 Email: sarikaya@ieee.org Xia & Sarikaya Expires May 20, 2008 [Page 11] Internet-Draft Prefix Delegation November 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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 Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Xia & Sarikaya Expires May 20, 2008 [Page 12]