6man Working Group F. Costa Internet-Draft J-M. Combes Intended status: Standards Track X. Pougnard Expires: January 3, 2011 France Telecom Orange H. Li Huawei Technologies July 2, 2010 Duplicate Address Detection Proxy draft-costa-6man-dad-proxy-00 Abstract The document describes a mechanism allowing the use of Duplicate Address Detection (DAD) by IPv6 nodes in a VLAN N:1 with "split- horizon" model DSL architecture. Based on the DAD signalling, the first hop router stores all used addresses on the VLAN in a Binding Table. When a node performs DAD for an address already used by another node, the first hop router replies instead of this last one. 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 January 3, 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 Costa, et al. Expires January 3, 2011 [Page 1] Internet-Draft DAD-Proxy July 2010 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Why IETF solutions don't work? . . . . . . . . . . . . . . . . 4 3.1. Duplicate Address Detection . . . . . . . . . . . . . . . 4 3.2. Neighbor Discovery Proxy . . . . . . . . . . . . . . . . . 5 3.3. 6LoWPAN Neighbor Discovery . . . . . . . . . . . . . . . . 5 3.4. IPv6 Mobility Manager . . . . . . . . . . . . . . . . . . 5 4. Duplicate Address Detection Proxy (DAD-Proxy) specifications . . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. DAD-Proxy Data structure . . . . . . . . . . . . . . . . . 6 4.2. DAD-Proxy mechanism . . . . . . . . . . . . . . . . . . . 6 4.2.1. No entry exists for the tentative address . . . . . . 6 4.2.2. An entry already exists for the tentative address . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6.1. Interoperability with SEND . . . . . . . . . . . . . . . . 8 6.2. IP source address spoofing protection . . . . . . . . . . 9 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.1. Normative References . . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . . 9 Appendix A. Open issues . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Costa, et al. Expires January 3, 2011 [Page 2] Internet-Draft DAD-Proxy July 2010 1. Introduction This document explains why Duplicate Address Detection (DAD) mechanism [RFC4862] cannot be used in a VLAN N:1 with "split-horizon" model DSL architecture. One of the main reasons is IPv6 nodes on the same VLAN cannot have direct communication: all the messages between them must go through the first hop router. This document specifies a mechanism allowing the use of DAD by the hosts on the same VLAN. It only impacts the first hop router and it doesn't need modifications on the other IPv6 nodes. It is assumed in this document that Link-layer addresses on a VLAN are unique from the first hop router's point of view (e.g. in an untrusted Ethernet architecture this assumption can be guaranteed thanks to the use of "MAC Address Translation" mechanism performed upstream by a device between IPv6 nodes and the first hop router). 1.1. Requirements Language 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 RFC 2119 [RFC2119]. 2. Background Terminology in this document follows that in Neighbor Discovery for IP version 6 (IPv6) document [RFC4861] and IPv6 Stateless Address Autoconfiguration document [RFC4862]. In addition, this section defines additional terms related to the DSL architecture: Customer Premises Equipment (CPE) The first IPv6 node in a customer's network. Access Node (AN) The first aggregation point in the DSL access network. It is considered as a L2 bridge in this document. Broadband Network Gateway (BNG) The first hop router from the CPE's point of view. VLAN N:1 architecture A many-to-one forwarding scheme where many CPEs are connected to the same VLAN. The CPEs may be connected on the same or different Access Nodes. Costa, et al. Expires January 3, 2011 [Page 3] Internet-Draft DAD-Proxy July 2010 split-horizon model A model where CPEs cannot have direct layer 2 nor layer 3 communications between them (i.e. IP flows must be forwarded through the BNG via routing). The following figure shows where are the different entities defined above. +------+ +----+ | CPE3 |---------| AN | +------+ +----+ | | +------+ +----+ | CPE2 |---------| AN |---+ +------+ +----+ | +------+ | | | CPE1 |------------+ | +------+ +-----+ | BNG |--- Internet +-----+ Figure 1: DSL Architecture 3. Why IETF solutions don't work? In a DSL architecture depicted in Figure 1, CPE1,2,3 and BNG are IPv6 nodes, while AN is a special bridge providing links between CPEs and the BNG. AN enforces in a split-horizon mode so that all CPEs can only talk to BNG but not to each other. That said, each CPE is on a same link with BNG, but one CPE is not on a same link with any other CPE. 3.1. Duplicate Address Detection Duplicate Address Dectection (DAD) [RFC4862] is performed when an IPv6 node verifies the uniqueness of a tentative address. This node sends a Neighbour Solicitation (NS) message with the IP destination set to solicited-node multicast address of the tentative address. This NS message is multicasted to other nodes on a same link. When the tentative address is already used on the link by another node, this last one replies with a Neighbor Advertisement (NA) message to inform the first node. So when performing DAD, a node expects the NS messages are received by other nodes. However, in a DSL network depicted in Figure 1, split-horizon is implemented on AN to prevent CPEs from talking to each other Costa, et al. Expires January 3, 2011 [Page 4] Internet-Draft DAD-Proxy July 2010 directly. All packets sent out from a CPE would be forward by AN only to BNG but none of other CPE nodes. That said, NS messages sent by a certain CPE will be received only by BNG, which will never forward these NS messages to other CPEs. So, other CPEs have no idea that a certain address is used by another CPE. That means, in a network with split-horizon, DAD per RFC4862 can't work properly. 3.2. Neighbor Discovery Proxy Neighbor Discovery (ND) Proxy [RFC4389] is designed for forwarding ND messages between different IP links where the subnet prefix is the same. A ND Proxy function on a bridge forwards received ND messages to other segments with correct-link layer type address. When the ND proxy receives a multicast ND message, it forwards it to all other interfaces on a same link. In the DSL network depicted in Figure 1, when AN, acting as a ND Proxy, receives a ND message from a CPE, it will forward it to BNG but none of other CPEs, as only BNG is on the same link with the CPE. Hence, implementing ND Proxy on AN doesn't help a CPE acknowledge link-local addresses used by other CPEs. As the BNG MUST NOT forward link-local scoped messages sent from a CPE to other CPEs, ND Proxy cannot be implemented in the BNG. 3.3. 6LoWPAN Neighbor Discovery [I-D.ietf-6lowpan-nd] defines an optional modification of DAD for a 6LowPAN. When a 6LoWPAN node wants to configure an IPv6 address, it registers this one to one or more of its default router using the Address Registration option (ARO). If this address is already owned by another node, the router informs the 6LoWPAN node this address cannot be configured. A problem for this mechanism is that it requires modifications in hosts in order to support the Address Registration option. 3.4. IPv6 Mobility Manager According to [RFC3775], a home agent acts as a proxy for mobile nodes when these last ones are away from the home network: the home agent defends an mobile node's home address by replying to NS messages with NA messages. There is a problem for this mechanism if it is applied in the DSL network depicted in Figure 1. Operators of DSL networks require a NA message is only received by the sender of the corresponding NS message for security reason. However, the home agent per [RFC3775] Costa, et al. Expires January 3, 2011 [Page 5] Internet-Draft DAD-Proxy July 2010 multicasts NA messages on the home link and all nodes on this link will receive these NA messages. This shortcoming prevents this mechanism being deployed in a DSL network directly. 4. Duplicate Address Detection Proxy (DAD-Proxy) specifications 4.1. DAD-Proxy Data structure A BNG needs to store, in a Binding Table, information related to the IPv6 addresses generated by any CPE on a VLAN. Each entry in this Binding Table MUST contain the following fields: o IPv6 Address o Link-layer Address o Creation Time 4.2. DAD-Proxy mechanism When a CPE performs DAD, as specified in [RFC4862], it sends a Neighbor Solicitation (NS) message, with the unspecified address as source address, in order to check if a tentative address is already in use on the link. The BNG receives this message and MUST perform actions depending on the information in the Binding Table. 4.2.1. No entry exists for the tentative address When there is no entry for the tentative address, the BNG MUST create one with following information: o IPv6 Address Field set to the tentative address in the NS message. o Link-layer Address Field set to the Link-layer source address in the Link-layer Header of the NS message. o Creation Time set to the value of the BNG clock when the entry is created. 4.2.2. An entry already exists for the tentative address When there is an entry for the tentative address, the BNG MUST check the following conditions: o The address in the Target Address Field in the NS message is equal to the address in the IPv6 Address Field in the entry. Costa, et al. Expires January 3, 2011 [Page 6] Internet-Draft DAD-Proxy July 2010 o The source address of the IPv6 Header in the NS message is equal to the unspecified address. When these conditions are met and the source address of the Link- Layer Header in the NS message is equal to the address in the Link- Layer Address Field in the entry, that means the CPE is still performing DAD for this address. The BNG MUST NOT reply to the CPE. When these conditions are met and the source address of the Link- Layer Header in the NS message is not equal to the address in the Link-Layer Address Field in the entry, that means another CPE performs DAD for an already owned address. As shown in Figure 2, the BNG MUST reply to the CPE that has sent the NS message with a NA message which has the following format: Layer 2 Header Fields: Source Address The Link-layer address of the interface on which the BNG received the NS message. Destination Address The source address in the Layer 2 Header of the NS message received by the BNG. IPv6 Header Fields: Source Address An address assigned to the interface from which the advertisement is sent. Destination Address The all-nodes multicast address. ICMPv6 Fields: Target Address The tentative address already used. Target Link-layer address The Link-layer address of the interface on which the BNG received the NS message. Costa, et al. Expires January 3, 2011 [Page 7] Internet-Draft DAD-Proxy July 2010 CPE1 CPE2 BNG | | | (a)| | | | | | (b)|===================>| | | |(c) | | | | (d)| | | | | | (e)|=========>| | | | | |<=========|(f) | | | (a) CPE1 generated a tentative address (b) CPE1 performs DAD for this one (c) BNG updates its Binding Table (d) CPE2 generates a same tentative address (e) CPE2 performs DAD for this one (f) BNG informs CPE2 that DAD fails Figure 2 The BNG and the CPE MUST support the Unicast Transmission of IPv6 Multicast Messages on Link-layer [I-D.gundavelli-v6ops-l2-unicast], to be able, respectively, to generate and to process such a packet format. 5. IANA Considerations No new options or messages are defined in this document. 6. Security Considerations 6.1. Interoperability with SEND If SEcure Neighbor Discovery (SEND) [RFC3971] is used, the mechanism specified in this document may break the security. Indeed, if an entry already exists and the BNG has to send a reply (cf. Section 4.2.2), the BNG doesn't own the private key(s) associated with to the Cryptographically Generated Addresses (CGA) [RFC3972] to correctly sign the proxied ND messages [I-D.ietf-csi-sndp-prob]. To keep the same level of security, Secure Proxy ND Support for SEND [I-D.ietf-csi-proxy-send] SHOULD be used and implemented on the BNG and the CPEs. Costa, et al. Expires January 3, 2011 [Page 8] Internet-Draft DAD-Proxy July 2010 6.2. IP source address spoofing protection To ensure a protection against IP source address spoofing in data packets, this proposal may be used in combinaison with Source Address Validation Improvement (SAVI) mechanisms [I-D.ietf-savi-fcfs] [I-D.ietf-savi-send]. 7. Acknowledgments TbD 8. References 8.1. Normative References [I-D.gundavelli-v6ops-l2-unicast] Gundavelli, S., Townsley, M., Troan, O., and W. Dec, "Unicast Transmission of IPv6 Multicast Messages on Link- layer", draft-gundavelli-v6ops-l2-unicast-00 (work in progress), February 2010. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. 8.2. Informative References [I-D.ietf-6lowpan-nd] Shelby, Z., Chakrabarti, S., and E. Nordmark, "Neighbor Discovery Optimization for Low-power and Lossy Networks", draft-ietf-6lowpan-nd-10 (work in progress), June 2010. [I-D.ietf-csi-proxy-send] Krishnan, S., Laganier, J., Bonola, M., and A. Garcia- Martinez, "Secure Proxy ND Support for SEND", draft-ietf-csi-proxy-send-04 (work in progress), May 2010. [I-D.ietf-csi-sndp-prob] Combes, J., Krishnan, S., and G. Daley, "Securing Neighbor Discovery Proxy: Problem Statement", Costa, et al. Expires January 3, 2011 [Page 9] Internet-Draft DAD-Proxy July 2010 draft-ietf-csi-sndp-prob-04 (work in progress), January 2010. [I-D.ietf-savi-fcfs] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS- SAVI: First-Come First-Serve Source-Address Validation for Locally Assigned Addresses", draft-ietf-savi-fcfs-03 (work in progress), May 2010. [I-D.ietf-savi-send] Bagnulo, M. and A. Garcia-Martinez, "SEND-based Source- Address Validation Implementation", draft-ietf-savi-send-03 (work in progress), May 2010. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", June 2004. [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, March 2005. [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery Proxies", RFC 4389, April 2006. Appendix A. Open issues o A same VLAN on n different interfaces (n > 1) of a BNG? o What happens when the BNG receives a NA message with O-bit set to 1 (e.g. the Link-Layer address of the CPE has changed)? o When to remove a entry from the Binding Table? Authors' Addresses Fabio Costa France Telecom Orange 38 rue du General Leclerc 92794 Issy-les-Moulineaux Cedex 9 France Email: fabio.costa@orange-ftgroup.com Costa, et al. Expires January 3, 2011 [Page 10] Internet-Draft DAD-Proxy July 2010 Jean-Michel Combes France Telecom Orange 38 rue du General Leclerc 92794 Issy-les-Moulineaux Cedex 9 France Email: jeanmichel.combes@orange-ftgroup.com Xavier Pougnard France Telecom Orange 2 avenue Pierre Marzin 22300 Lannion France Email: xavier.pougnard@orange-ftgroup.com Hongyu Li Huawei Technologies Huawei Industrial Base Shenzhen China Email: lihy@huawei.com Costa, et al. Expires January 3, 2011 [Page 11]