6lowpan Working Group Z. Shelby, Ed. Internet-Draft Sensinode Intended status: Standards Track P. Thubert Expires: August 27, 2009 Cisco J. Hui Arch Rock S. Chakrabarti IP Infusion E. Nordmark Sun February 23, 2009 Neighbor Discovery for 6LoWPAN draft-ietf-6lowpan-nd-01 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 August 27, 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents Shelby, et al. Expires August 27, 2009 [Page 1] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 carefully, as they describe your rights and restrictions with respect to this document. Abstract This document specifies Neighbor Discovery optimized for 6LoWPAN. The 6LoWPAN format allows IPv6 to be used over very constrained wireless networks often making use of extended multihop topologies. However, the use of standard IPv6 Neighbor Discovery over 6LoWPAN networks has several problems. Standard Neighbor Discovery was not designed for wireless links, and the standard IPv6 link concept and heavy use of multicast makes it inefficient. This document spefies a new mechanism allowing efficient Duplicate Address Detection over entire 6LoWPAN networks. In addition it specifies context dissemination for use with router advertisements, claim and defend addressing, and the support of extended LoWPANs over backbone links. Shelby, et al. Expires August 27, 2009 [Page 2] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. Goals & Assumptions . . . . . . . . . . . . . . . . . . . 6 1.2. Why not standard IPv6 ND? . . . . . . . . . . . . . . . . 7 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Bootstrapping . . . . . . . . . . . . . . . . . . . . . . 13 3.2. Basic operation . . . . . . . . . . . . . . . . . . . . . 14 3.3. Optional features . . . . . . . . . . . . . . . . . . . . 15 4. 6LoWPAN ND Messages . . . . . . . . . . . . . . . . . . . . . 15 4.1. Router Registration/Confirmation Message . . . . . . . . . 16 4.2. Router Advertisement Message . . . . . . . . . . . . . . . 18 4.3. NS/NA Messages . . . . . . . . . . . . . . . . . . . . . . 19 4.4. 6LoWPAN ND Message Options . . . . . . . . . . . . . . . . 20 4.4.1. Address Option . . . . . . . . . . . . . . . . . . . . 20 4.4.2. 6LoWPAN Prefix Information Option . . . . . . . . . . 21 4.4.3. Multihop Information Option . . . . . . . . . . . . . 23 4.4.4. Owner Interface Identifier Option . . . . . . . . . . 23 5. LoWPAN Subnet . . . . . . . . . . . . . . . . . . . . . . . . 24 6. LoWPAN Node Specification . . . . . . . . . . . . . . . . . . 25 6.1. Forming addresses . . . . . . . . . . . . . . . . . . . . 25 6.2. Registration process . . . . . . . . . . . . . . . . . . . 26 6.3. Next-hop determination . . . . . . . . . . . . . . . . . . 28 6.4. Address lookup . . . . . . . . . . . . . . . . . . . . . . 28 7. LoWPAN Router Specification . . . . . . . . . . . . . . . . . 29 7.1. Router Configuration Variables . . . . . . . . . . . . . . 29 7.2. Becoming an Advertising Interface . . . . . . . . . . . . 29 7.3. Router Advertisement Message Content . . . . . . . . . . . 29 7.4. Sending Unsolicited Router Advertisements . . . . . . . . 31 7.5. Ceasing To Be an Advertising Interface . . . . . . . . . . 31 7.6. Processing Router Solicitations . . . . . . . . . . . . . 31 7.7. Router Advertisement Consistency . . . . . . . . . . . . . 31 7.8. Relaying a Router Registration Message . . . . . . . . . . 31 7.9. Relaying a Router Confirmation Message . . . . . . . . . . 31 8. LoWPAN Edge Router Specification . . . . . . . . . . . . . . . 31 8.1. Registration process . . . . . . . . . . . . . . . . . . . 32 8.2. Exposing the Edge Router . . . . . . . . . . . . . . . . . 34 8.3. Forwarding packets . . . . . . . . . . . . . . . . . . . . 35 8.4. Address collision detection and resolution . . . . . . . . 35 8.5. Duplicate OII detection . . . . . . . . . . . . . . . . . 37 8.6. Fault tolerance . . . . . . . . . . . . . . . . . . . . . 38 9. Ad-hoc LoWPAN Operation . . . . . . . . . . . . . . . . . . . 39 10. Message Examples . . . . . . . . . . . . . . . . . . . . . . . 39 10.1. Basic RR/RC message exchange . . . . . . . . . . . . . . . 39 10.2. Relayed RR/RCC message exchange . . . . . . . . . . . . . 40 10.3. Router advertisement . . . . . . . . . . . . . . . . . . . 41 11. Security Considerations . . . . . . . . . . . . . . . . . . . 42 Shelby, et al. Expires August 27, 2009 [Page 3] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 43 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43 14.1. Normative References . . . . . . . . . . . . . . . . . . . 43 14.2. Informative References . . . . . . . . . . . . . . . . . . 44 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 45 Shelby, et al. Expires August 27, 2009 [Page 4] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 1. Introduction The IPv6 over IEEE 802.15.4 [RFC4944] document has specified IPv6 headers carried over an IEEE 802.15.4 and similar network with the help of an adaptation header which comes before the IP header. A LoWPAN link is characterized as lossy, low-power, low bit-rate, short range, with long deep sleep periods. Multicast as used in IPv6 Neighbor Discovery [RFC4861] is not desirable in such a wireless low- power, lossy network. Moreover, LoWPAN links are transient in nature; they are not always considered to be in a fixed network nor they are bounded by our standard definition of a wired-link. The link is in reality defined by reachability and radio strength. The standard IPv6 Neighbor Discovery [RFC4861] control messages and their default frequency also attribute to unnecessary loss of power in 6LoWPAN networks. Neighbor discovery for 6LoWPAN provides for basic bootstrapping and network operation, along with advanced features such as claim and defend addressing and extended LoWPANs over backbone links, while avoiding the use of multicast and providing both mesh under and route over support. Unlike standard IPv6 ND [RFC4861], this document takes the characteristics of low-power, lossy wireless networks and links into account. A LoWPAN network is composed of a potentially large amount of radio links, eventually federated by a backbone or a backhaul link. Although a given link has broadcast capabilities, the aggregation of links is a complex Non-Broadcast MultiAccess (NBMA, [RFC2491]) structure with no multicast capabilities. This specification introduces a registration mechanism over the radio edge of the NBMA network and proxy operation over the federating backbone or backhaul. That registration mechanism provides a service somewhat similar to MARS ([RFC2022]) for the limited purpose of ND NS/NA, and in a lot simpler and less generic fashion. For those link scope multicast that could not be avoided, such as ND RAs, Trickle may be used to optimize the dissemination of the information in the Low Power network. The concept of a LoWPAN whiteboard located at Edge Routers is introduced, which allows for duplicate address detection and claim and defend addressing for the entire LoWPAN. Address resolution simplifications are included to make LoWPAN operation efficient and reduce LoWPAN Node complexity. A new registration/confirmation message sequence is specified, allowing nodes to register their IPv6 addresses with an Edge Router whiteboard. The ER whiteboard makes use of soft bindings, thus nodes send Shelby, et al. Expires August 27, 2009 [Page 5] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 periodic registration messages in order to maintain their bindings. Changes in network topology, and mobility between ERs and subnets are supported. The dissemination of RA information throughout multihop route over networks is also discussed. This document also specifies the seamless integration of an extended LoWPAN and multiple Edge Routers on a shared backbone link (e.g. Ethernet) to form a single IPv6 subnet. This allows nodes to keep the same IPv6 address throughout a large network, and allows for easy communications with backbone link IPv6 hosts. The document defines two new ICMPv6 messages: Router Registration and Router Confirmation. In addition a new 6LOWPAN_ER anycast address is introduced, allowing for nodes to send register without knowing the specific Edge Router's or Router's unicast address. 1.1. Goals & Assumptions This document has the following main goals and makes several assumptions. Goals: o Avoid the use of multicast for ND messages inside the LoWPANs. o Disseminate context information throughout the LoWPAN. o Minimize the complexity of LoWPAN nodes. o Interconnect LoWPANs with backbone links seamlessly. o Provide a mechanism for claim and defend addressing. Assumptions: o Either [RFC4944] or [I-D.ietf-6lowpan-hc] 6LoWPAN header compression used. o Link layer technology may be IEEE 802.15.4 as in [RFC4944], or any other suitable link-layer. o Link-local addresses are derived from an EUI-64 identifier. o The use of optimistic DAD. o Mesh-under nodes know the edge router link-layer addresses of their mesh network from some L2 mechanism. Shelby, et al. Expires August 27, 2009 [Page 6] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 o A subnet includes all the LoWPAN nodes and their backbone link. 1.2. Why not standard IPv6 ND? IPv6 Neighbor Discovery [RFC4861] provides several important functions such as Router Discovery, Address Resolution, Duplicate Address Detection, Redirect, Prefix and Parameter Discovery. Following power-on and initialisation of the network in IPv6 ethernet networks, a node joins the solicited-node multicast address on the interface and then it performs duplicate address detection (DAD) for the acquired link-local address by sending solicited-node multicast message to the link. After that it sends multicast messages to all- router address to solicit router advertisements. Once the host receives a valid router advertisement with the "A" flag, it autoconfigures the IPv6 address with the advertised prefix in the rotuer advertisement (RA). Besides this, the IPv6 routers usually send router advertisements periodically on the network. It sends the RA to all-node multicast address. Nodes send Neighbor Solicitation/ Neighbor Advertisement messages to resolve the IPv6 address of the destination on the link. These NS/NA messages are also often multicast messages and it assumes that the node is on the same link and relies on the fact that the destination node is always powered and generally reliable. A LoWPAN network typically uses two types of L2 addresses - 16-bit short addresses and 64-bit unique addresses as defined in [RFC4944]. Moreover, the link bandwidth is often on the order of less than 100 bytes where we often might need to use header compression and use a minimum payload. The network is lossy and low-powered, and it does not provide multicast capability at the link-layer, thus simulating multicast behavior by both using broadcast or sending a number of unicast messages, both expensive for the low-powered network and the low-processing capable nodes. Often these low-powered nodes conserve energy by using sleep schedules; waking them up to receive IPv6 signaling messages such as multicast messages for NS, and periodic RA is not practical. Nor they are capable of processing address- resolution for its neighbors effectively. Due to radio strength of its neighboring router or its own strength, a node may often move from one router to another without physically moving from one place to another. Considering the above characteristics in a LoWPAN, and IPv6 Neighbor Discovery [RFC4861] base protocol requirements, it was concluded that standard Neighbor Discovery is not suitable as it is and a 6lowpan-specific ND definition would be useful and efficient for the wide deployment of IPv6 over low-powered wireless networks of embedded devices. Shelby, et al. Expires August 27, 2009 [Page 7] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 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 [RFC2119]. Readers are expected to be familiar with all the terms and concepts that are discussed in "Neighbor Discovery for IP version 6" [RFC4861], "IPv6 Stateless Address Autoconfiguration" [RFC4862], "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals" [RFC4919] and "Transmission of IPv6 Packets over IEEE 802.15.4 Networks" [RFC4944]. Readers would benefit from reading "Mobility Support in IPv6" [RFC3775], "Neighbor Discovery Proxies (ND Proxy)" [RFC4389] and "Optimistic Duplicate Address Detection" [RFC4429] prior to this specification for a clear understanding of state of the art in ND proxy and binding. This document defines additional terms: LoWPAN Host A node that only sources or sinks IPv6 datagrams. Referred to as a host in this document. The term node is used when the the differentiation between host and router is not important. LoWPAN Edge Router An IPv6 router that interconnects the LoWPAN to another network. Referred to as an Edge Router in this document. LoWPAN Router A node that forwards datagrams between arbitrary source- destination pairs using a single 6LoWPAN/802.15.4 interface. A LoWPAN Router may also serve as a LoWPAN Host - both sourcing and sinking IPv6 datagrams. Refered to as a router in this document. All LoWPAN Routers perform ND message relay on behalf of other nodes. Mesh Under A LoWPAN configuration where the link-local scope is defined by the boundaries of the LoWPAN and includes all nodes within. Forwarding is achieved at L2 between mesh nodes. Shelby, et al. Expires August 27, 2009 [Page 8] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Route Over A LoWPAN configuration where the link-local scope is defined by those nodes reachable over a single radio transmission. Due to the time-varying characteristics of wireless communication, the neighbor set may change over time even when nodes maintain the same physical locations. Multihop is achieved using IP routing. Backbone Link This is an IPv6 link that interconnects two or more Edge Routers. It is expected to be deployed as a high speed backbone in order to federate a potentially large set of LoWPANS. Backhaul Link This is an IPv6 link that connects a single Edge Router to another network. Extended LoWPAN This is the aggregation of multiple LoWPANs as defined in [RFC4919] interconnected by a backbone link via Edge Routers and forming a single subnet. LoWPAN Link In a LoWPAN, a link can be a very instable set of nodes, for instance the set of nodes that can receive a packet that is broadcast over the air. Such a set may vary from one packet to the next as the node moves or as the radio propagation conditions change. LoWPAN Subnet A subnet including a LoWPAN or Extended LoWPAN, together with the backbone link with the same subnet prefix and prefix length. Binding The association of the LoWPAN node IPv6 address and Interface ID with associated whiteboard and ND states including the remaining lifetime of that association. Registration Shelby, et al. Expires August 27, 2009 [Page 9] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 The process during which a LoWPAN node sends a Router Registration ND message to an Edge Router causing a binding for the LoWPAN node to be registered. 3. Protocol Overview Neighbor discovery for 6LoWPAN provides additions and optimizations to IPv6 ND [RFC4861] specifically supporting 6LoWPAN networks. Basic bootstrapping and network maintenenace mechanisms are provided, and the use of multicast is avoided. Duplicate address detection and claim and defend addressing are supported as part of bootstrapping. This is achieved using a whiteboard located on the 6LoWPAN Edge Routers of the LoWPAN network. Extended LoWPANs over backbone links are optionally supported. Multihop route-over networks are supported by routers relaying ND messages. ND for 6LoWPAN is designed to work with many network topologies, including isolated ad-hoc networks, single ER networks, and networks with multiple ERs interconnected by a backbone link. The use of both IEEE 802.15.4 and other suitable 6LoWPAN link-layer technologies is considered. Both the use of mesh under forwarding and route over routing are supported. | | | +-----+ | | Edge | | router +-----+ m m m m m m m m m: Mesh node m m m m m m m LoWPAN Figure 1: A Mesh under LoWPAN. In a mesh under network, shown above, multihop forwarding is dealt with below layer 3. Thus the entire LoWPAN forms a link-layer mesh. This means that the IPv6 link-local scope includes all the nodes of the LoWPAN. Link-local scope stops however at the ER, and does not include any backbone link. The implication of this regarding ND for Shelby, et al. Expires August 27, 2009 [Page 10] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 6LoWPAN, is that it can always be assumed that the ER and hosts are on the same link. In these networks only LoWPAN Node and Edge Router functionalities are needed. Multicast with mesh under technologies most often induces flooding, and therefore it is avoided. | | | +-----+ | | Edge | | router +-----+ r h r r r h r h r h h: Host h r r h r: Router h h h LoWPAN Figure 2: A Route over LoWPAN. A route over network performs multihop using standard layer 3 IP routing. The link-local scope is defined by a LoWPAN link, which includes nodes reachable over a single radio transmission at each instant. The implication for ND for 6LoWPAN is that if the ER is out of radio range of a host, the ND messages require relaying by intermediate routers. In these networks also LoWPAN Router functionality needs to be implemented by all routers in the LoWPAN. Multicast may also involve flooding in such networks and often does not work, and thus is avoided. Shelby, et al. Expires August 27, 2009 [Page 11] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Infrastructure Cloud z z z Backhaul link z z +-----+ | | Edge | | router +-----+ o o o o o o o o o o o: Any node o o o o o o o LoWPAN Figure 3: A LoWPAN connected to a backhaul link. The simplest topology is a LoWPAN connected by a single Edge Router to another network, over a so-called backhaul link. The Edge Router maintains a whiteboard of all hosts in the network. The Edge Router terminates 6LoWPAN framing from the LoWPAN, and forwards packets. The LoWPAN subnet covers all the interfaces in the LoWPAN, which have the same prefix and prefix length. Shelby, et al. Expires August 27, 2009 [Page 12] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Infrastucture Cloud | | +-----+ +-----+ | | Gateway | | Host | | | | +-----+ +-----+ | | | Backbone link | +--------------------+------------------+ | | | +-----+ +-----+ +-----+ | | Edge | | Edge | | Edge | | router | | router | | router +-----+ +-----+ +-----+ o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o Extended LoWPAN OII Figure 4: Backbone link and edge routers with a 6LoWPAN subnet In the backbone link topology, a backbone link federates multiple LoWPANs into a single LoWPAN Subnet, the Extended LoWPAN. Each LoWPAN is anchored at one or more Edge Router. The Edge Routers interconnect the LoWPANs over the backbone link. A node can move freely from a LoWPAN anchored at an Edge Router to a LoWPAN anchored at another Edge Router on the same backbone link and conserve all IPv6 address it has formed. The following sections summarizes how ND for 6LoWPAN works, starting with bootrapping on the network, maintenance of the network, and finally optional features. 3.1. Bootstrapping A Host first performs stateless autoconfiguration of its link-local unicast address for each LoWPAN interface from its EUI-64 as in [RFC4944]. When a LoWPAN Host wants to join a LoWPAN network, it does so by listening for Route Advertisements from Edge Routers or routers, or by broadcasting a Router Solicitations. If a valid prefix is advertised in the RA, the host may form an optimistic global unique address with stateless autoconfiguration. Next the Host registers with an on-link Edge Router or router by Shelby, et al. Expires August 27, 2009 [Page 13] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 sending a Router Registration (RR) message to it, either unicast or using the 6LOWPAN_ER anycast address. These message exchanges are illustrated below. The RR contains the addresses the node wants to register. If the network is configured to support whiteboard claim and defend, e.g., generating short addresses for nodes, this is indicated in the RA message with the M flag. In such networks a node may request an address to be generated on its behalf by including an Address Option with the A flag and an address of length 0 in the RR. Note that registration must be performed separately for each interface of a Host. The Edge Router replies either directly with a Router Confirmation (RC), or through a router by relaying. Note that routers only exist in route over networks, and in mesh under networks nodes are on the same link with Edge Routers. This confirmation includes the set of addresses now bound to the whiteboard of the ER. The Host is now capable of using the LoWPAN, and the ER forwards on its behalf. Node Edge Router | | | ---------- Router Registration --------> | | | | <--------- Router Confirmation --------- | | | Figure 5: Basic ND registration exchange when the Node and Edge Router are on the same link. Node Router (relay) Edge Router | | | | ---- RR ---> | ---- RR ---> | | | | | <---- RC ---- | <---- RC ---- | | | | Figure 6: Relay ND registration exchange in route over networks. 3.2. Basic operation The whiteboard address bindings and assignments are soft, and thus must be renewed periodically as indicated by the lifetime of the binding. This is achieved by periodically sending a new RR to the ER. If a host moves, or the network topology changes, and the Shelby, et al. Expires August 27, 2009 [Page 14] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 current ER is no longer available, the host then starts the registration process with another ER. If the host is still in the same Extended LoWPAN (same prefix), its IPv6 addresses remain the same. Claim and defend addresses generated by the whiteboard must be remembered by the host and refreshed in order to keep the address. If the host moves to a different LoWPAN, with a different prefix, the bootstrapping process is initiated again. In route over networks, Routers that act as relays must disseminate RAs to their neighbors. The Edge Router initiates RAs, and this information is included in the RAs of each router. 3.3. Optional features This documents specifies a method for forming Extended LoWPAN networks with multiple ERs on a backbone link. This optional feature allows for DAD across the entire Extended LoWPAN and backbone links, seen as a single subnet. The method uniquely identifies the LoWPAN Host on the backbone, and overrides the claim on an address on behalf of a LoWPAN Host. Thus a Host can keep the same address, and appears the same to other hosts on the backbone link, regardless of moving its binding from one ER to another. 4. 6LoWPAN ND Messages This section introduces message formats for all messages used in this document. The new messages are all ICMPv6 messages and extend the capabilities of "The IPv6 Neighbor Discovery Protocol" [RFC4861]. In addition the ICMPv6 Router Advertisement is updated with new options. The following new ICMPv6 message types are defined: Router Registration Router Confirmation In addition, the following new ICMPv6 options are defined: Address Option 6LoWPAN Prefix Information Option Multihop Information Option Owner Interface Identifier Option Shelby, et al. Expires August 27, 2009 [Page 15] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 4.1. Router Registration/Confirmation Message The Router Registration (RR) and Router Confirmation (RC) messages are used by a Host to register with an ER, and for the ER to confirm the binding. Any option that is not recognized MUST be skipped silently. The Router Registration message is sent by the LoWPAN Node to an on-link ER or router, and may be sent unicast or to the 6LOWPAN_ER anycast address. This same message format is also used for relayed RR/RC messages, with an alternative code that is set when the message has been relayed. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TID | Status |P| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Owner Interface Identifier + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Binding option(s)... +-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7: Router Registration/Confirmation message format IP Fields: Source Address: The IPv6 address of the source. This address may be an optimistic address. Destination Address: The destination IPv6 address of an on-link Edge Router or Router. May be the 6LOWPAN_ER anycast address. Hop Limit: 255 ICMP Fields: Type: TBD1 for Router Registration, TBD2 for Router Confirmation. Code: 0 indicates a message sent directly from the orginating host. 1 indicates that the message has been relayed by a router. Shelby, et al. Expires August 27, 2009 [Page 16] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Checksum: The ICMP checksum. TID: A unique Transaction ID assigned by the host and used to match replies. A lollypop mechanism is used to increment the TID at each new message. TID is set to 0 upon booting, and is incremented with each RR message. After reaching 0xFFFF, the value loops to 16 (0xFF) and is incremented from there. Thus the values between 0-16 MUST only used after a boot or reboot. P: 1-bit Primary flag. Set to indicate that the router is primary and MAY represent the node if used in a backbone link setup. If the flag is not set then the router MUST not represent the node on the backbone. Flag is echoed in a confirmation. Status: 8-bit unsigned integer. Values TBD. 0 means unqualified success. Any value below 128 is a positive status that means that the binding was created or is being created optimistically. Lifetime: 32-bit unsigned integer. The amout of time in units of seconds remaining before the binding of this owner interface identifier, and all associated address options and configuration options, MUST be considered expired. A value of zero indicates that the Binding Cache entries for the registered owner interface identifier MUST be deleted. Reserved: This field is unused. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. Owner Interface Identifier: A globally unique identifier for the requesting host's interface. Typically the EUI-64 dervied IID. Possible Options: Address Option(s): An Address Option is included for each address the host wants to bind for this interface. Configuration options: Other configuration information requests and configuration settings may be carried in options of RR/RC messages. Such options are not defined in this document. Source link-layer address: Included in a Relay RR message in case the Owner Interface Identifier is not the same as the link- layer address of the host interface. Format as defined in [RFC4861] and [RFC4944]. If the RR was relayed, then this option MAY be added to the RC by the relaying router to indicate the identity of the ER for use by a host. Shelby, et al. Expires August 27, 2009 [Page 17] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Target link-layer address: Included in a relayed RC message in case the Owner Interface Identifier is not the same as the link-layer address of the host interface. Format as defined in [RFC4861] and [RFC4944]. MAY be included in an RR message from a host to a router to indicate the prefered Edge Router to relay the message to. Future versions of this protocol may define new option types. Receivers MUST silently ignore any options they do not recognized and continue processing the message. 4.2. Router Advertisement Message The RA message for 6LoWPAN is identical to the [RFC4861] RA message. The use of flags is defined in the 6LoWPAN context, and additional new options are identified. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cur Hop Limit |M|O|H|Prf|P|R|R| Router Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reachable Time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Retrans Timer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+ Figure 8: Router Advertisement Message Format IP Fields: Source Address: MUST be the link-local address assigned to the interface from which this message is sent. Destination Address: Typically the Source Address of an invoking Router Solicitation or the all-nodes multicast address. Hop Limit: 255 Shelby, et al. Expires August 27, 2009 [Page 18] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 ICMP Fields: Type: 134 Code: 0 Checksum: The ICMP checksum. Cur Hop Limit: As specified in [RFC4861]. M: As specified in [RFC4861] with the exception that managed mode here refers to the claim and defend address mechanism specified in this document, not DHCPv6 as in [RFC4861]. O: As specified in [RFC4861]. Prf: 2-bit signed integer. Default Router Preference as defined in [RFC4191]. Indicates whether to prefer this router over other default routers. LoWPAN Routers SHOULD set the preference to (00) for normal, and LoWPAN Edge Routers SHOULD set the preference to (01) for high. Router Lifetime: As specified in [RFC4861]. Reachable Time: As specified in [RFC4861]. Possible Options: 6LoWPAN Prefix Information Option: This option includes information about the prefixes of the LoWPAN along with other context information. Multihop Information Option: This option provides a sequence number associated with the current prefix options. It allows the prefix options themselves to be sent only periodically in unsolicited RAs. Future versions of this protocol may define new option types. Receivers MUST silently ignore any options they do not recognized and continue processing the message. 4.3. NS/NA Messages Neighbor Solicitation and Neighbor Advertisement messages are employed between ERs on the backbone link. A unique identifier is required in the message as an option to uniquely identify a host's interface. The standard NS/NA message is used in this document is as per [RFC4861] with the an additional Owner Interface Identifier Shelby, et al. Expires August 27, 2009 [Page 19] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Option defined in this document. The Owner Interface Identifier is the same as that carried in RR/RC messages and associated with bindings. 4.4. 6LoWPAN ND Message Options This section defines the new ND for 6LoWPAN message options. 4.4.1. Address Option The Address Option is used to indicate the address which a node wants to register with an ER in an RR, and to indicate the success or failure of that binding in an RC. Multiple Address Options can be included in a message. In order to be as compact as possible, fields are used to indicate the compression of the IPv6 address. The Address Option also allows for duplicate addresses (e.g. anycasts), the request of a generated address for claim and defend, or for an address to be removed. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Status | P | S | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |D|A|R| Reserved | IPv6 Address ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9: Address Option format Type: TBD3 Length: 8-bit unsigned integer. The length of the option (including the type and length fields) in units of 8 octets. Status: 8-bit unsigned integer. Values TBD. 0 means unqualified success. Any value below 128 is a positive status that means that the binding for this address was created or is being created optimistically. Only used in a confirmation. D: 1-bit Duplicate flag. When set, indicates that duplicates are allowed for this address (to support anycast) in a request. A: 1-bit Address Generation flag. Set to indicate that the host is requesting a generated address for claim and defend addressing. In a request when A is set the IPv6 address length is 0. Set to indicate that an address has been assigned in a confirmation. P and S are set to indicate the type of address requested and Shelby, et al. Expires August 27, 2009 [Page 20] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 assigned when A is set. Otherwise must be 0. R: 1-bit Removal flag. When set, indicates that this particular address binding MUST be removed from a whiteboard (in a request) or MUST not be used any longer (in a confirmation). P: 4-bit unsigned integer. Identifies prefix compression or type, if any. 0: Prefix is carried inline. 1: Prefix compressed and link-local (fe80:/10) is assumed. 2: Prefix compressed and the default prefix is assumed. 3-15: Reserved. S: 4-bit unsigned integer. Identifies suffix compression or type, if any. 0: Suffix carried inline. 1: Suffix compressed and assumes the same value as the Owner Interface Identifier field in the RR/RC message header. 2: Suffix compressed and is derived from the 6LoWPAN short address option as defined in RFC 4944. 3: Suffix is a 6LoWPAN 16-bit short address as defined in RFC 4944 or as appropriate for the link-layer of the LoWPAN. 4-15: Reserved. IPv6 Address: The IPv6 address to be registered with the ER, or confirmed by the ER. Parts of the address may be elided as per the P and S fields. 4.4.2. 6LoWPAN Prefix Information Option This option carries prefix information for LoWPANs, and is similar in use to the Prefix Information Option of [RFC4861]. However this option allows for the dissemination of multiple contexts identified by a Context Identifier (CID) for use in 6LoWPAN address compression. Shelby, et al. Expires August 27, 2009 [Page 21] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Prefix Length |L|A| CID | r | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Valid Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . Prefix . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: 6LoWPAN Prefix Information Option format Type: TBD4 Length: 8-bit unsigned integer. The length of the option (including the type and length fields) in units of 8 octets. Prefix Length: 8-bit unsigned integer. The number of leading bits in the Prefix that are valid. The value ranges from 0 to 128. The prefix length field provides necessary information for on-link determination (when combined with the L flag in the prefix information option). It also assists with address autoconfiguration as specified in [RFC4862], for which there may be more restrictions on the prefix length. L: 1-bit on-link flag. This flag MUST be unset for for route over LoWPANs and backbone link LoWPANs, and MAY be set for mesh-under LoWPANs without a backbone. A: 1-bit autonomous address-configuration flag. When set indicates that this prefix can be used for stateless address configuration as specified in [RFC4861]. CID: 4-bit Context Identifier for this prefix information. The use of this Context Identifier is not specified in this document. Valid Lifetime: 32-bit unsigned integer. The length of time in seconds (relative to the time the packet is sent) that the prefix is valid for the purpose of on-link determination. A value of all one bits (0xffffffff) represents infinity. Prefix: The IPv6 Prefix indicated for this context. This may be a partial prefix, or even an entire IPv6 address for use as a context for compression. Shelby, et al. Expires August 27, 2009 [Page 22] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 4.4.3. Multihop Information Option This option identifies the set of prefix information options by a sequence number. This allows for the full set of prefix information options to be sent only periodically in unsolicited RAs. If a host detects a difference in the sequence number of this option, then the prefix information has likely changed, and is then requested with an RS. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |V| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11: Multihop Information Option Type: TBD5 Length: 1 Sequence Number: 16-bit signed integer. Indicates the freshness of the information advertised by the RA. V: 1-bit flag. Indicates if the sequence number is valid and the router is advertising information obtained from another router. Reserved: This field is unused. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. 4.4.4. Owner Interface Identifier Option This option is for use with standard NS and NA messages between ERs over a backbone link. By using this option, the binding in question can be uniquely identified and matched with the whiteboard entries of each ER. Shelby, et al. Expires August 27, 2009 [Page 23] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | TID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Owner Interface Identifier + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 12: Owner Interface Identifier Option Type: TBD6 Length: 2 TID: A unique Transaction ID assigned by the host in the associated RR and used to match RC replies. Reserved: This field is unused. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. Owner Interface Identifier: A globally unique identifier for the host's interface associated with the binding for the NS/NA message in question. 5. LoWPAN Subnet In a LoWPAN, a link can be a very unstable set of nodes, for instance the set of nodes that can receive a packet that is broadcast over the air at that instant. Such a set may vary from one packet to the next as the node moves or as the radio propagation conditions change. In addition, a LoWPAN is an NBMA network. As a result, a link does not define the proper set of nodes to perform ND operations such as Duplicate Address Detection and Address Resolution, nor is it stable enough to be assigned a prefix usable for routing or address configuration. Therefore in ND for 6LoWPAN, those operations are performed over the entire LoWPAN or Extended LoWPAN. In LoWPANs it is critical that IP routing, homogeneous addressing across the LoWPAN, and the mobility of nodes are supported. In this document, a LoWPAN subnet is defined to be a collection of LoWPAN links interconnected by routers that have the same subnet prefix. In particular, DAD is performed over a LoWPAN subnet for all types of addresses, inclucing link-local. Thus a LoWPAN subnet Shelby, et al. Expires August 27, 2009 [Page 24] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 differs from the IPv6 subnet defined in [RFC4291] as the LoWPAN subnet is associated with a collection of links and is a multi-link subnet. In a LoWPAN, setting the hop-limit to 1 limits a packet to the link, but hop limit assumptions MUST NOT be made about the subnet. Multi-link subnet issues are discussed in [RFC4903]. The issues pointed out in [RFC4903] are not relevant in 6LoWPAN where existing applications do not exist, and the network is a variation of NBMA. In the backhaul model, the Edge Router's interface and all the LoWPAN Node interfaces registered to that Edge Router form a subnet. In that model, the Edge Router serves all the prefixes that are defined on the subnet and can be connected to an IP routed infrastructure. With the backhaul model, in a mesh under network the link and subnet are equivalent as the link spans the entire LoWPAN. In the backbone model, a Backbone Link federates multiple LoWPANs into a single subnet. Each LoWPAN is a collection of links anchored at an Edge Router. The Edge Routers interconnect the LoWPANs over the Backbone Link. A node can move freely from a LoWPAN anchored at an Edge Router to a LoWPAN anchored at another Edge Router in the same subnet and conserve its link-local and any other IPv6 address it has formed. 6. LoWPAN Node Specification Instead of relying on multicast ND messages for DAD and neighbor address resolution, LoWPAN Nodes make use of an Edge Router in the LoWPAN which keeps a whiteboard of all bound addresses from nodes attached to the same ER. In addition, ERs may support a backbone link, creating an extended LoWPAN sharing the same subnet prefix. This allows a node to change its point of attachment without changing its IPv6 addresses. This specification simplifies address resolution compared to standard IPv6 ND. Claim and defend addressing is also specified as part of the binding process. This section specifies LoWPAN node operations. 6.1. Forming addresses All nodes are required to autoconfigure at least one address, a link- local address, which is derived from the IEEE 64-bit extended MAC address that is globally unique to the interface as in [RFC4944]. As a result, knowledge of the 64-bit address of another LoWPAN Node is enough to derive its link-local address and reach it if on the same link. Another consequence is that the link-local address is presumably unique on the Extended LoWPAN, which enables the use of Optimistic Duplicate Address Detection (oDAD) [RFC4429] over the Shelby, et al. Expires August 27, 2009 [Page 25] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Transit Link and the LoWPAN. The address SHOULD be created as optimistic to enable its use in the binding process with the Edge Router. Nodes MAY learn the address of Edge Routers or Routers using traditional means such as L2 configuration or Router Advertisement messages. This specification also introduces a new anycast address 6LOWPAN_ER that the node can use to reach any Edge Router or router on the link. This specification tolerates movement within the LoWPAN so the node does not have to stick with a given router and MAY keep using the 6LOWPAN_ER anycast address for all its registrations. The node SHOULD also form a global unicast address, for routing inside the LoWPAN and reachability from outside of the Extended LoWPAN. If a valid prefix is available from an RA ('A' flag is set), then a global unicast address can be derived using SAA. This address is marked optimistic until confirmed by the ER. This specification includes a method for requesting a unique stateless address from the Edge Router by setting the 'A' flag in an Address Option during registration. This is useful for receiving a unique short address and, and works in a claim and defend fasion. The node can tell if address generation is available if the 'M' flag of the RA from that router is set. Address generation using the RR/RC mechanism is stateless. Although the address is generated by the ER and checked for uniqueness across the subnet using DAD, it is just like any other address binding in the whiteboard of the ER after assignment. Thus in order to keep using the assigned address the host must keep refreshing the address binding, including when moving to another ER in the same subnet. To simplify address resolution it is assumed that nodes within a LoWPAN use addresses in a homogeneous way and that the unicast IPv6 address IIDs resolve directly to a corresponding link-layer address. Thus avoiding address resolution whenever possible. 6.2. Registration process The binding process is very similar to that of a MIPv6 mobile node, though the messages used are new Neighbor Discovery ICMP messages. A LoWPAN Node address is tentative or optimistic as long as the binding is not confirmed by the Edge Router. The LoWPAN Node uses unicast Router Registrations to perform the binding. The destination address is that of an on-link Edge Router or router, or the 6LOWPAN_ER anycast address. Registration SHOULD be preferred with on-link ERs rather than Routers. The Preference Flag of the RA is used to differentiate between ERs and routers. The Shelby, et al. Expires August 27, 2009 [Page 26] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 source address is the link local address of the node. A unique Owner Interface Indentifier is included in the Router Registration so the binding can be identified throughout the subnet. This is usually the EUI-64 identifier of the interface. The RR message includes an Address Option for each address to be bound. Thus the message is structured as follows. ICMPv6 (Router Registration (Address Option[0], Address Option[1], Address Option[n])) A unique Transaction ID (TID) is included by the host in the RR message and used to match replies. A lollypop mechanism is used. TID is set to 0 upon booting, and is incremented with each RR message. After reaching 0xFFFF, the value loops to 16 (0xFF) and is incremented from there. Thus the values between 0-16 MUST only used after a boot or reboot. The acknowledgment to a Router Registration is a unicast Router Confirmation message that contains the status of the binding. The source of the packet is the link-local address of the Edge Router or Router. The destination address is the link-local address of the node. An Address Option for each confirmed or assigned address is included. Upon successful completion in the Router Confirmation message, the LoWPAN Node sets the address from optimistic or tentative to preferred. See Section 10 for detailed message examples. If no Router Confirmation is received within an implementation specific timeout and number of retries, then there may be no Edge Routers in the LoWPAN. In this case the hosts and routers SHOULD continue to operate using the optimistic address generated by SAA. See Section 9 for more information on ad-hoc network operation. This specification also introduces the concept of a secondary binding. For redundancy, a node might place a secondary binding with one or more other Edge Routers on the same or different LoWPANs. The 'P' flag in the Router Registration Indentity Request Option indicates whether the binding is primary. The use of this mechanism for fault tolerance is explained in Section 8.6. ER bindings have a timeout associated with them, therefore nodes must periodically send a new Router Registration message to renew the bindings. If a node no longer receives RCs from any router in the current subnet, the registration process begins from the beginning. Shelby, et al. Expires August 27, 2009 [Page 27] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 6.3. Next-hop determination Next-hop determination is performed as in Section 5.2 of [RFC4861] with the following exceptions. All prefixes are assumed to be off- link as the LoWPAN subnet with that prefix may be larger than the link in route over topologies, unless the destination address exists in the neighbor cache. Link-layer information should be used to maintain the neighbor cahce whenever possible rather than using ND traffic. The ERs and routers used for registration are kept in the default router List. Multicast addresses resolve to a broadcast as specified in [RFC4944]. 6.4. Address lookup A LoWPAN node does not use multicast for its Neighbor Solicitation as prescribed by the IPv6 ND [RFC4861] and oDAD [RFC4429]. When lookup is necessary, all NS messages are sent in unicast to the Edge Router, that answers in unicast as well. The message is a standard Neighbor Solicitation but for the destination is set to the Edge Router address or the well known 6LOWPAN_ER anycast address as opposed to the solicited-node multicast address for the destination address. A LoWPAN Node SHOULD retain a small queue for packets to neighbors awaiting to be delivered while address lookup is being performed. The size of the queue should be suitable to the available RAM of the node, and is not required to be a minimum of one buffer per neighbor as in [RFC4861]. The Target link-layer address in the response is either that of the destination if a short cut is possible over the LoWPAN, or that of the Edge Router if the destination is reachable over the Transit Link, in which case the Edge Router will terminate 6LoWPAN and relay the packet. A LoWPAN Node does not need to join the solicited-node multicast address for its own addresses and SHOULD NOT have to answer a multicast Neighbor Solicitation. It MAY be configured to answer a unicast NS but that is not required by this specification. Care must be used with the 6LOWPAN_ER and other anycast addresses, as anycast resolution is normally performed with a multicast NS/NA exchange. As nodes are not required to answer NS messages, the next hop determination process SHOULD map the anycast address to the link layer address of a neighbor using available L2 or other ND information. Shelby, et al. Expires August 27, 2009 [Page 28] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 7. LoWPAN Router Specification LoWPAN Routers are used in a route over configuration where the network is composed of overlapping link-local scopes. As a result, we extend ND as specified in [RFC4861] to operate over an entire LoWPAN subnet, rather than a single IP link. This section describes ND for 6LoWPAN router operations. Note that this section does not apply to mesh under LoWPANs. Network configuration parameters carried in Router Advertisements originate at Edge Routers and must disseminate to all routers and hosts within the LoWPAN. The Multihop Information Option is used to support information dissemination from one or more Edge Routers to all other nodes in the LoWPAN. The option includes a "V" flag which indicates that the information contained in the Router Advertisement is valid. The option also includes a sequence number to ensure that all nodes converge on the same settings. Because Router Registration/Confirmation exchanges only occur over link-local scope, such messages must be relayed between hosts and Edge Routers when separated by multiple IP hops. Every LoWPAN Router MUST also serve as a relay to ensure that any neighboring node can successfully participate in the LoWPAN. 7.1. Router Configuration Variables A router MUST allow conceptual variables as defined in Section 6.2.1 of [RFC4861]. 7.2. Becoming an Advertising Interface An interface may become an advertising interace as specified in Section 6.2.2 of [RFC4861]. A LoWPAN Router's interface MAY become an advertising interface before all of its router variables have been initializes. The router MUST learn these variables (e.g. AdvCurHopLimit, AdvReachableTime, prefix information, etc.) from neighboring routers. While the variables are not initialized, the router MAY send Router Advertisement with the "Solicit" flag set to solicit Router Advertisements from neighboring routers. However, the router MUST set the Router Lifetime field to zero while one or more of its variables are uninitialized. 7.3. Router Advertisement Message Content A router sends periodic as well as solicited Router Advertisements out its advertising interface. Outgoing Router Advertisements are Shelby, et al. Expires August 27, 2009 [Page 29] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 filled with the following values constistent with the message format given in this document. - In the Router Lifetime field: if the router has a default route, the interface's configured AdvDefaultLifetime. If the router does not have a default route, zero. - In the M and O flags: the current value of AdvManagedFlag and AdvOtherConfigFlag, respectively. - In the Preference flag: this flag is set to 00 to indicate that the sender is a LoWPAN Router. - In the Cur Hop Limit field: the current value of CurHopLimit. - In the Reachable Time field: the current value of AdvReachableTime. - In the Retrans Timer field: the current value of AdvRetransTimer. - In the options: - Multihop Information option: to indicate if the information contained in the Router Advertisement is valid and, if so, the freshness of the information contained in the Router Advertisement message. The option fields are set as follows: - In the "valid" flag: the current value of AdvInformationValid. - In the Sequence Number field: the current value of AdvInformationSequence. - 6LoWPAN Prefix Information options: one 6LoWPAN Prefix Information option for each prefix listed in AdvPrefixList with the option fields set from the information in the AdvPrefxList entry as follows: - In the "on-link" flag: the entry's AdvOnLinkFlag. - In the "Autonomous address configuration" flag: the entry's AdvAutonomousFlag. - In the Valid Lifetime field: the entry's AdvValidLifetime. Shelby, et al. Expires August 27, 2009 [Page 30] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 7.4. Sending Unsolicited Router Advertisements As specified in Section 6.2.4 of [RFC4861]. 7.5. Ceasing To Be an Advertising Interface As specified in Section 6.2.5 of [RFC4861]. 7.6. Processing Router Solicitations As specified in Section 6.2.6 of [RFC4861]. 7.7. Router Advertisement Consistency TBD 7.8. Relaying a Router Registration Message When a router receives a Router Registration message from a LoWPAN Node, it sets the Code field to 1 indicating that the message has been relayed. The IPv6 source address is set to that of the router. By default, the router relays Router Registration messages to the 6LOWPAN_ER anycast address. However, the router MAY be configured to use a list of destination addresses, which MAY include unicast addresses, the 6LOWPAN_ER anycast address, or other addresses selected by the network administrator. If the RR includes a Target link-layer address option, then that SHOULD be used to form the desination address as it indicates the ER which the LoWPAN node prefers. 7.9. Relaying a Router Confirmation Message When the router receives a Relay Router Confirmation message from an Edge Router, the Code field is set to 1. The Owner Interface Identifier is used to form the IPv6 Destination Address for the Router Confirmation message. If a Target link-layer address option is included in the message, then that is used to form the IPv6 destination address instead of the Owner Interface Identifier. The IPv6 source address is set to that of the Router. The Hop Limit of the Router Confirmation message is set to 255. 8. LoWPAN Edge Router Specification Edge Routers are introduced to scale the Neighbor Discovery Operations by reducing the amount of costly multicast ND messages over a LoWPAN subnet that may cover hundreds or thousands of nodes. Shelby, et al. Expires August 27, 2009 [Page 31] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Instead of multicasting ND messages, a LoWPAN Node performs unicast exchanges with an Edge Router to claim and lookup addresses using unicast and anycast addresses, and the Edge Router performs ND operations on its behalf over the Backbone Link when necessary, for example DAD. This specification documents the extensions to IPv6 Neighbor Discovery that enables a LoWPAN Node to claim and lookup addresses using an Edge Router as an intermediate proxy. The draft also documents the use of EUI-64 based link-local addresses and the way they are claimed by the Edge Routers over the Backbone link. This specification documents the LoWPAN whiteboard, a conceptual data structure that is similar to the MIPv6 binding cache. Another function of the Edge Router is to perform 6LoWPAN compression and uncompression between the LoWPAN and the Backbone Link and ensure MTU compatibility. Packets flow uncompressed over the Backbone Link and are routed normally towards a Gateway or an Application sitting on the Backbone link or on a different link that is reachable via IP. 8.1. Registration process Upon a new registration for a link-local or global unicast address based on an IEEE 64-bit extended MAC address, the Edge Router MAY use Optimistic DAD on the Transit Link. A positive acknowledgement can be sent to the 6LoWPAN node right away if oDAD is used on the Transit Link. A LoWPAN Node should be able to join a different Edge Router at any time without the complexities of terminating a current registration and renumbering. To enable this, the ND operation on the backbone link upon a Router Registration/Confirmation flow wins the address ownership over an ND operation that is done asynchronously, on behalf of the same LoWPAN Node, upon a prior registration. So an Edge Router that would happen to have a binding for that same address for the same LoWPAN Node identified by its EUI-64 address will yield and deprecate its binding. The new Owner Interface Identifier Option in NS/NA messages that carries the node EUI-64 address and the lollypop mechanism on the TID help differentiate an address collision over the backbone from a movement of a node from one Edge Router to the next. More details on collision detection and resolution are provided in Section 8.4. The override (O) bit is used to differentiate a registration flow from the asynchronous defense of an address by an edge router acting as a proxy. Upon a registration flow, an edge router doing DAD or Shelby, et al. Expires August 27, 2009 [Page 32] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 accepting a reregistration SHOULD set the override (O) bit in its NA messages. Asynchronously to the registration, the edge router SHOULD NOT set the override (O) bit in its NA messages and should yield to an NA message with the override (O) bit set. So the Edge Router operation on the transit link is similar to that of a Home Agent as specified in "Mobility Support for IPv6" [RFC3775] yet different. In particular, the Neighbor Advertisement message is used as specified in section "10.4.1. Intercepting Packets for a Mobile Node" with the exception that the override (O) bit is not set, indicating that this Edge Router acts as a proxy for the LoWPAN and will yield should another Edge Router claim that address on the Backbone Link. This specification also introduces the concept of a secondary binding. Upon a secondary binding, the Edge Router will not announce or defend the address on the backbone link, but will be able to forward packets to the node over its LoWPAN interface. This feature is used for fault tolerance, explained in Section 8.6. The Edge Router responds to a Router Registration with a Router Confirmation. The source address is a link-local address of the router and the destination is the optimistic address of the node from which the RR was received. The ER responds to relayed RR messages with an RC message, where the destination address is the address of the Router which sent the relayed RR message. If the Edge Router is primary for a registration as indicated by the 'P' flag and it is connected to a Backbone, then it SHOULD perform ND operations on the backbone. In particular the Egde Router SHOULD reject the registration if DAD fails on the backbone. When oDAD is used over the backbone the Edge Router MAY issue the Router Confirmation right away with a positive code, but if a collision is finally detected, it cancels the registration with an asynchronous Router Confirmation and a negative completion code on the same TID. If the RR message includes an Address Option with the 'A' flag set, this indicated the request of stateless address generation. If the ER supports managed address mode ('M' flag set in its RAs), then the ER aquires an appropriate, unique link-layer address for the network either by generating it and performing DAD, or with some other method. If successful, this address is returned in an Address Option of the RC with the 'A' flag set and the assigned IPv6 address formed from the generated link-layer address with the defualt prefix inline. Shelby, et al. Expires August 27, 2009 [Page 33] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 8.2. Exposing the Edge Router The Backbone link is used as reference for Neighbor Discovery operations. When an Edge Router does not have an entry in its registration table for a target node, it looks it up over the backbone using ND an operation in place for that medium. Edge Routers also represent the LoWPAN Nodes that are proactively registered to them. That way, a lookup over the backbone is not propagated over the LoWPANs, but answered by the Edge Router that has the registration for the target, if any. To enable proxying over the backbone Link, an Edge Router must join the solicited-node multicast address on that link for all the registered addresses of the nodes in its LoWPANs. The Edge Router answers the Neighbor Solicitation with a Neighbor Advertisement that indicates its own link-layer address in the Target link-layer address option. An Edge Router expects and answers unicast Neighbor Solicitations for all nodes in its LoWPANs. It answers as a proxy for the real target. The target link-layer address in the response is either that of the destination if a short cut is possible over the LoWPAN, or that of the Backbone Router if the destination is reachable over the Transit Link, in which case the Backbone Router will terminate 6LoWPAN and relay the packet. The Edge Router forms a link-local address in exactly the same way as any other node on the LoWPAN. The Edge Router configures the well known 6LOWPAN_ER anycast address on the LoWPAN interfaces where it serves as Edge Router. Note that the Edge Router will accept registration packets with a hop limit that is lower than 255 on that specific address. The Edge Router announces itself using Router Advertisement (RA) messages that are broadcasted periodically over the LOWPAN and the backbone link. The Edge Router MAY also announce any prefix that is configured on the transit link, and serve as the default gateway for any node on the Transit Link or on the attached LoWPANs. The transit link Maximum Transmission Unit serves as base for Path MTU discovery and Transport layer Maximum Segment Size negotiation (see section 8.3 of [RFC2460]) for all nodes in the LoWPANs. To achieve this, the Edge Router announces the MTU of the transit link over the LoWPAN using the MTU option in the RA message as prescribed in section "4.6.4. MTU" of IPv6 Neighbor Discovery [RFC4861]. LoWPAN Nodes SHOULD form IPv6 packets that are smaller than that MTU. Shelby, et al. Expires August 27, 2009 [Page 34] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 As a result, those packets should not require any fragmentation over the transit link though they might be intranet-fragmented over the LoWPAN itself as prescribed by [RFC4944]. More information on the MTU issue with regard to ND-proxying can be found in Neighbor Discovery Proxies [RFC4389] and [I-D.van-beijnum-multi-mtu]. 8.3. Forwarding packets Upon receiving packets on one of its LoWPAN interfaces, the Edge Router checks whether it has a binding for the source address. If it does, then the Edge Router can forward the packet to another LoWPAN Node or over the Backbone link. The hop limit is decremented upon forwarding. Otherwise, the Edge Router MUST discard the packet. If the packet is to be transmitted over the Transit link, then the 6LoWPAN sublayer is terminated and the full IPv6 packet is reassembled and expanded. When forwarding a packet from the Backbone Link towards a LoWPAN interface, the Edge Router performs the 6LoWPAN sublayer operations of compression and fragmentation and passes the packet to the lower layer for transmission. 8.4. Address collision detection and resolution The assumption in this section is that the OII that is carried in the registration messages and in the NS/NA messages is globally unique. When this assumption fails, and additional collision resolution mechanism takes place, as detailed in Section 8.5. The address collision can be detected within the edge router if the edge router already has a registration for a given address, or over the transit link using Duplicate Address Detection. The edge router in charge of the resolution is the edge router that handles the registration. The general principles are as follows: Mobility is included and welcome. A node may migrate its registration to a new edge router transparently and at any time. The protocol is designed to recognize the mobility and silently cleanup the registration states. A synchronous operation wins against a delayed proxy operation. An edge router that processes a router registration normally takes over an existing registration maintained by a defendant edge router. Shelby, et al. Expires August 27, 2009 [Page 35] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 The decision to migrate the registration from an edge router to another is made by the edge router that processes a Router Registration message based on its own states for that registration and ND exchanges over the transit link. A registration is identified by the (OII, IPv6 address) pair. A conflict occurs when a Router Registration is received for an IPv6 address that is already registered with a different OII at the same or another edge router. The resolution of such conflict is explained below. A conflict may also occur with a node that is already present on the transit link when the registration occurs, or with a node appears on the transit link while a registration already exists for its claimed address. The resolution of such conflict is done using standard Duplicate Address Detection as prescribed by [RFC4862]. Upon a Router Registration message, an edge router looks up an existing registration for that IPv6 address in its LoWPAN whiteboard. If the entry does not exist then the edge router looks up the address over the transit link using the NS (DAD) mechanism. The edge router SHOULD include an Owner Interface Identifier Option in the NS message. An edge router that defends that address for an existing registration MUST include an Owner Interface Identifier Option in the NA message and SHOULD NOT set set the Override (O) bit. If no entry is found for that address and DAD times out, the edge router accepts the registration: it creates an entry on the whiteboard, sends a positive Router Confirmation Message to the node, and advertises the address on the transit link. Since this happens asynchronously to the Router Registration, the edge router SHOULD NOT set set Override (O) bit in the NA message. If an entry is found in the whiteboard for the same (OII, IPv6 address) pair, additional checking is performed for duplicate OII detection as detailed in Section 8.5. If no duplication is detected, then the edge router accepts the update of the reservation: it updates a entry on the whiteboard, sends a positive Router Confirmation Message to the node, and advertises the address on the transit link. Since this happens synchronously to the Router Registration, the edge router SHOULD set set Override (O) bit in the NA message. If the address is already present on the transit link and defended by a remote edge router, then that edge router defends the address with the Override (O) bit reset and the Owner Interface Identifier Option in the NA message. Shelby, et al. Expires August 27, 2009 [Page 36] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 If the edge router receives an NA message during the DAD period, it checks for an Owner Interface Identifier Option in the NA message. If there is no OII or the (O) bit is set then this is a duplicate address, DAD fails and the registration is rejected. If there is an Owner Interface Identifier Option in the NA message and the OII is different, then DAD fails and the registration is rejected. If the OII is the same, additional checking is performed for duplicate OII detection as detailed in Section 8.5. If there is no duplication then the NA is ignored and the DAD timer keeps going. If the edge router receives an NS (DAD) message from another node during the DAD period, it checks for a Owner Interface Identifier Option in the NS message. If there is no OII then DAD fails and the registration is rejected. If there is an Owner Interface Identifier Option in the NA message and the OII is different, then DAD fails and the registration is rejected. If the OII is the same, then the greatest TID wins. In other words, if the TID in the registration is smaller than or equal to the TID in the OII Option then DAD fails and the registration is rejected. Otherwise the NS is ignored and the DAD timer keeps going. Other edge routers are informed of a take over decision by an NA with the Override (O) bit set and silently set their own state to non- operational. An edge router that looses ownership should attempt to keep the registration entry in the whiteboard till the end of the registration lifetime for the purpose of duplicate OII detection if memory capacity allows. The TID in the whiteboard entry is updated with that in the OII option in the NA. 8.5. Duplicate OII detection The TID is a sequential number that is used to control the normal operation of a registration and detect a duplicate Owner Interface Identifier during the Neighbor Discovery operations. The TID is set by a node in its Router Registration message and echoed by the edge router in the Router Confirmation message. At least the 4 most recent values for a TID are also kept by the edge router in the whiteboard entry for validation purpose. The TID is maintained using the lollypop mechanism. When a node starts or restarts, the TID is reset to zero. After that, it is incremented with each Router Registration. When the TID reaches its maximum value (0xFFFF) it wraps directly to its looping value at the base of the lollypop that is 16. So a value in the straight part of the lollypop (between 0 and 0xFF) is only used after a reboot and before the circular part of the lollypop is entered. Upon a positive Registration Confirmation, if the current TID is less Shelby, et al. Expires August 27, 2009 [Page 37] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 than 16, then the node sets it to 16. So a TID in the straight part denotes a node that just started/restarted and did not get registered yet. To compare TID1 and TID2, the following rules apply: If at least one of TID1 and TID2 is in the straight part of the lollipop (smaller than 16) then they compare directly. If both TID1 and TID2 are in the circular part then TID2 is greater than TID1 if (TID2 - TID1) is smaller than (TID1 - TID2). A TID value is consistent with the preceeding one if it is a small increment or decrement (more or less 16) from it. During normal operations, the TIDs saved in the white board entry should be consistent. As long as a TID is consistent with the previous one, it appears that the new message is coming from the same source as the previous one and there is no OII collision. If the TID is a small decrement then the registration messages crossed and that message should be ignored, but still there's no collision. If the TID jumps to a low value in the lollypop this can be interpreted as either a new node competing for the OII and a reboot by the node owning the registration. With this specification, this situation is optimistically interpreted as a reboot and not reported as a collision, but an actual collision will be detected and filtered out next. Otherwise, if an inconsistent TID value is detected between the new TID and the most recently accepted value, then the edge router compares with the older TID values that are saved in the whiteboard entry for that registration. This might occur for instance with an entry that was rendered non-operational when the address was taken over by another edge router. If the new value is consistent with a recent value then it appears that 2 sources are competing for the same OII and an OII collision should be logged. In that case the greater TID wins, that is if the new TID is greater than the previous one it is accepted, otherwise it is reported as a collision. If the new value is not consistent with a recent value saved in the whiteboard entry then it is rejected as a collision. 8.6. Fault tolerance This specification allows for a secondary registration. The secondary registration enables the node to prepare states within the Shelby, et al. Expires August 27, 2009 [Page 38] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 network and make the move quicker between primary and secondary. If an external keep alive mechanism is in place between the primary and the secondary edge routers, then the secondary registration enables the secondary edge router to start intercepting packets on the backbone and forwarding them to the node before the node even knows that the primary is no longer operational. The secondary registration also enables the node to bicast a packet for extra reliability, that is send a copy of a packet to both edge routers without being subject to ingress filtering. The mechanism that enables this filtering is not specified here. 9. Ad-hoc LoWPAN Operation LoWPAN networks by nature may often work in an ad-hoc fasion. Neighbor Discovery for 6LoWPAN may still be applied in such ad-hoc networks. If a router in the LoWPAN implements the Edge Router whiteboard functionality, then ND for 6LoWPAN can be applied in routers and nodes as specified in this document. The election of such an edge router in an ad-hoc network is not specified here. The Edge Router does not implement forwarding or backbone features, and must generate a prefix to advertise. If no Edge Router is available in the LoWPAN, then the whiteboard features specified in this draft are unavailable. The nodes in the LoWPAN SHOULD however continue to operate using SAA optimistic addresses after timing out on Router Registrations. 10. Message Examples This section provides basic examples of messages and options from this document. 10.1. Basic RR/RC message exchange In the basic case, when a host wanting to register to the whiteboard is on the same link with an Edge Router, a simple RR/RC message exchange occurs. In this example a host wants to register its address generated with SAA, and in addition requests a generated short address. First the Host sends an RR message to the Edge Router or to the 6LOWPAN_ER Anycast address. In this example the host wants to use the Edge Router as primary, uses a 600s lifetime, and its EUI-64 as the Owner Interface Indentifier. The message has two Address Shelby, et al. Expires August 27, 2009 [Page 39] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Options. The host has just booted, therefore the TID starts with 0. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = TBD | Code = 0 | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TID = 0 | Status = 0 |1| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime = 600 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Owner Interface Identifier = + | EUI-64 of the interface | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 13: Basic RR message. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = TBD | Length = 1 | Status = 0 | P=2 | S=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|0|0| Reserved | Padding = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 14: Address Option 1, for the SAA address. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = TBD | Length = 1 | Status = 0 | P=2 | S=3 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|1|0| Reserved | Padding = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 15: Address Option 2, for the requested address. 10.2. Relayed RR/RCC message exchange In case an Edge Router is not on-link, then the RR message from the previous example is sent to any on-link Router in exactly the same format. This Router in turn relays the message to an Edge Router. Shelby, et al. Expires August 27, 2009 [Page 40] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 As the OII of the Host is the same as its IID, the Router simply sets Code = 1 to indicate that the message was relayed. The destination IPv6 address is that of an Edge Router or the 6LOWPAN_ER Anycast address and the source IPv6 address that of the relaying router. The Address Options are not modified. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = TBD | Code = 1 | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TID = 0 | Status = 0 |1| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime = 600 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Owner Interface Identifier = + | EUI-64 of the interface | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 16: Relayed RR message. 10.3. Router advertisement Routers and Edge Routers in LoWPAN networks periodically send RA messages. In the following example is of an RA message sent by a Router. The only difference if an Edge Router would send the message is that the Preference flag would be 01 for high. In the example the M flag is set to indicate that generated addresses are available, the Preference flag is 00 for normal, and a 1200s Route Lifetime is advertised. A 6LoWPAN Prefix Information Option is included. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = 134 | Code = 0 | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Cur Hop Limit |1|0|0|00 |Rsrvd| Router Lifetime = 1200 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reachable Time = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Retrans Timer = 0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Shelby, et al. Expires August 27, 2009 [Page 41] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Figure 17: RA message example. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = TBD | Length = 2 | PL = 60 |0|1| CID=0 | r | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Valid Lifetime = 3000 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . Prefix = 2001:DB8::/60 . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 18: 6LoWPAN Prefix Information Option example. 11. Security Considerations This specification expects that the link layer is sufficiently protected, either by means of physical or IP security for the backbone link or MAC sublayer cryptography. In particular, it is expected that the LoWPAN MAC provides secure unicast to/from Routers and secure broadcast from the Routers in a way that prevents tempering with or replaying the RA messages. However, any future 6LoWPAN security protocol that applies to Neighbor Discovery for 6LoWPAN protocol, is out of scope of this document. The use of EUI-64 for forming the Interface ID in the link local address prevents the usage of Secure ND ([RFC3971] and [RFC3972]) and address privacy techniques. Considering the envisioned deployments and the MAC layer security applied, this is not considered an issue at this time. 12. IANA Considerations This document requires two new ICMPv6 message types: Router Registration (TBD1) Router Confirmation (TBD2) The document also requires four new ND option types under the subregistry "IPv6 Neighbor Discovery Option Formats": Shelby, et al. Expires August 27, 2009 [Page 42] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Address Option (TBD3) 6LoWPAN Prefix Information Option (TBD4) Multihop Information Option (TBD5) Owner Interface Identifier Option (TBD6) [TO BE REMOVED: This registration should take place at the following location: http://www.iana.org/assignments/icmpv6-parameters] There is also the need for a new link local anycast address, 6LOWPAN_ER for 6LoWPAN Edge Routers and Routers; used as a functional address. [TO BE REMOVED: This registration should take place at the following location: http://www.iana.org/assignments/ipv6-anycast-addresses] 13. Acknowledgments The authors thank Carsten Bormann, Geoff Mulligan and Julien Abeille for useful discussions and comments that have helped shaped and improve this document. 14. References 14.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2491] Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6 over Non-Broadcast Multiple Access (NBMA) networks", RFC 2491, January 1999. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, November 2005. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. Shelby, et al. Expires August 27, 2009 [Page 43] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) for IPv6", RFC 4429, April 2006. [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. [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, September 2007. 14.2. Informative References [I-D.ietf-6lowpan-hc] Hui, J. and P. Thubert, "Compression Format for IPv6 Datagrams in 6LoWPAN Networks", draft-ietf-6lowpan-hc-04 (work in progress), December 2008. [I-D.van-beijnum-multi-mtu] Beijnum, I., "Extensions for Multi-MTU Subnets", draft-van-beijnum-multi-mtu-02 (work in progress), February 2008. [RFC2022] Armitage, G., "Support for Multicast over UNI 3.0/3.1 based ATM Networks", RFC 2022, November 1996. [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 (ND Proxy)", RFC 4389, April 2006. [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, June 2007. [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals", RFC 4919, August 2007. Shelby, et al. Expires August 27, 2009 [Page 44] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Authors' Addresses Zach Shelby (editor) Sensinode Kidekuja 2 Vuokatti 88600 FINLAND Phone: +358407796297 Email: zach@sensinode.com Pascal Thubert Cisco Systems Village d'Entreprises Green Side 400, Avenue de Roumanille Batiment T3 Biot - Sophia Antipolis 06410 FRANCE Phone: +33 4 97 23 26 34 Email: pthubert@cisco.com Jonathan W. Hui Arch Rock Corporation 501 2nd St. Ste. 410 San Francisco, California 94107 USA Phone: +415 692 0828 Email: jhui@archrock.com Samita Chakrabarti IP Infusion 1188 Arquest Street Sunnyvale, California USA Phone: Email: samitac@ipinfusion.com Shelby, et al. Expires August 27, 2009 [Page 45] Internet-Draft Neighbor Discovery for 6LoWPAN February 2009 Erik Nordmark Sun Microsystems, Inc. 17 Network Circle Menlo Park, California 94025 USA Phone: Email: Erik.Nordmark@Sun.COM Shelby, et al. Expires August 27, 2009 [Page 46]