6lowpan Working Group Z. Shelby, Ed. Internet-Draft Sensinode Intended status: Standards Track P. Thubert Expires: May 22, 2009 Cisco J. Hui Arch Rock S. Chakrabarti IP Infusion E. Nordmark Sun November 18, 2008 Neighbor Discovery for 6LoWPAN draft-ietf-6lowpan-nd-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 22, 2009. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document specifies Neighbor Discovery optimized for 6LoWPAN. Shelby, et al. Expires May 22, 2009 [Page 1] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 The 6LoWPAN format allows IPv6 to be used over very low-power, low- bandwidth 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, 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 prefix and context dissemination for use with router advertisements, allows for stateless address assignment, and the use of Neighbor Discovery Proxy. This document is an identical replacement of draft-shelby-6lowpan-nd-01. This document was now submitted as a 6lowpan working group document. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Goals & Assumptions . . . . . . . . . . . . . . . . . . . 5 1.2. Why not standard IPv6 ND? . . . . . . . . . . . . . . . . 6 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 8 3.1. Bootstrapping . . . . . . . . . . . . . . . . . . . . . . 12 3.2. Basic operation . . . . . . . . . . . . . . . . . . . . . 13 3.3. Optional features . . . . . . . . . . . . . . . . . . . . 13 4. 6LoWPAN ND Messages . . . . . . . . . . . . . . . . . . . . . 13 4.1. Router Registration/Confirmation Message . . . . . . . . . 14 4.2. Router Advertisement Message . . . . . . . . . . . . . . . 16 4.3. Neighbor Solicitation Message . . . . . . . . . . . . . . 18 4.4. 6LoWPAN ND Message Options . . . . . . . . . . . . . . . . 18 4.4.1. Address Option . . . . . . . . . . . . . . . . . . . . 18 4.4.2. 6LoWPAN Prefix Information Option . . . . . . . . . . 20 4.4.3. Multihop Information Option . . . . . . . . . . . . . 21 4.4.4. Host Interface Identifier Option . . . . . . . . . . . 21 5. LoWPAN Subnet . . . . . . . . . . . . . . . . . . . . . . . . 22 6. LoWPAN Node Specification . . . . . . . . . . . . . . . . . . 23 6.1. Forming addresses . . . . . . . . . . . . . . . . . . . . 23 6.2. Registration process . . . . . . . . . . . . . . . . . . . 24 6.3. Next-hop determination . . . . . . . . . . . . . . . . . . 25 6.4. Address lookup . . . . . . . . . . . . . . . . . . . . . . 25 7. LoWPAN Router Specification . . . . . . . . . . . . . . . . . 26 7.1. Router Configuration Variables . . . . . . . . . . . . . . 26 7.2. Becoming an Advertising Interface . . . . . . . . . . . . 27 7.3. Router Advertisement Message Content . . . . . . . . . . . 27 7.4. Sending Unsolicited Router Advertisements . . . . . . . . 29 7.5. Ceasing To Be an Advertising Interface . . . . . . . . . . 29 Shelby, et al. Expires May 22, 2009 [Page 2] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 7.6. Processing Router Solicitations . . . . . . . . . . . . . 29 7.7. Router Advertisement Consistency . . . . . . . . . . . . . 29 7.8. Relaying a Router Registration Message . . . . . . . . . . 29 7.9. Relaying a Router Confirmation Message . . . . . . . . . . 29 8. LoWPAN Edge Router Specification . . . . . . . . . . . . . . . 29 8.1. Registration process . . . . . . . . . . . . . . . . . . . 30 8.2. Exposing the Edge Router . . . . . . . . . . . . . . . . . 31 8.3. Forwarding packets . . . . . . . . . . . . . . . . . . . . 33 8.4. Fault tolerance . . . . . . . . . . . . . . . . . . . . . 33 9. Ad-hoc LoWPAN Operation . . . . . . . . . . . . . . . . . . . 33 10. Message Examples . . . . . . . . . . . . . . . . . . . . . . . 33 11. Security Considerations . . . . . . . . . . . . . . . . . . . 33 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 34 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34 14.1. Normative References . . . . . . . . . . . . . . . . . . . 34 14.2. Informative References . . . . . . . . . . . . . . . . . . 35 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 Intellectual Property and Copyright Statements . . . . . . . . . . 37 Shelby, et al. Expires May 22, 2009 [Page 3] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 1. Introduction The IPv6 over IEEE 802.15.4 [RFC4944] document has specified IPv6 headers carried over an IEEE 802.15.4 network with the help of an adaptation header which comes before the IP header. A LoWPAN network is characterized as a low-power, low bit-rate, short range, low cost network. Thus, all-node multicast defined in IPv6 Neighbor Discovery [RFC4861] is not often desirable in a wireless low-power, lossy network. In addition IEEE 802.15.4 and similar wireless technologies do not have multicast support, but supports broadcast. Broadcast messages could be used in some cases to represent all-node multicast messages, but periodic broadcast messages should be minimized in LoWPANs in order to conserve energy. Moreover, LoWPAN nodes 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 the 6lowpan network. The goal of this document is to minimize/remove periodic multicast signals used by IPv6 Neighbor Discovery [RFC4861] while enabling the LoWPAN to work as efficiently and optimally as possible and reducing the complexity of LoWPAN node implementations. Neighbor discovery for 6LoWPAN provides for basic bootstrapping, and network operation, along with advanced features such as stateless address assignment and ND-Proxy, while avoiding the use of multicast and providing both mesh under and route over support. Unlike standard IPv6 ND [RFC4861], this document takes the lossy characteristics of wireless networks into account. The concept of a LoWPAN whiteboard located at Edge Routers is introduced, which allows for duplicate address detection and stateless address assignment for the entire LoWPAN. Address resolution simplifications are included to make LoWPAN operation efficient and reduce LoWPAN Nodes complexity. A new registration/ confirmation message sequence is specified, allowing nodes to register their IPv6 addresses with an Edge Router, and to request global unique address assignment. The ER whiteboard makes use of soft bindings, thus nodes send periodic registration messages in order to maintain their binding and address assignments. 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. Shelby, et al. Expires May 22, 2009 [Page 4] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 This paper also specifies the use of ND Proxy by Edge Routers, allowing for 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 hosts to keep the same IPv6 address throughout a large network, and allows for easy communications with backbone link IPv6 hosts. This paper 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 prefix and context information throughout the LoWPAN. o Minimize the complexity of LoWPAN nodes. o Interconnect LoWPANs with backbone links seamlessly. o Provide a mechanism for stateles address assignment. Assumptions: o Either [RFC4944] or [draft-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. o A subnet covers all the LoWPANs and their backbone link with the same IPv6 global or local prefix. Shelby, et al. Expires May 22, 2009 [Page 5] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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. Besides 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. Besides due to radio strength of its neighboring router or its own strength, a node may often move between one subnet 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 protocol would be useful and efficient for wide deployment of IPv6 over low- powered wireless networks of embedded devices. Shelby, et al. Expires May 22, 2009 [Page 6] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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. Multihop forwarding is achieved at L2 between mesh nodes. Shelby, et al. Expires May 22, 2009 [Page 7] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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 2 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 Subnet A subnet including a LoWPAN or Extended LoWPAN, together with the backbone link sharing the same prefix. Binding The association of the LoWPAN node IPv6 address and Interface ID with associated whiteboard and proxy states including the remaining lifetime of that association. Registration 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] supporting 6LoWPAN low-power wireless stub networks. Basic bootstrapping and network maintenenace mechanisms Shelby, et al. Expires May 22, 2009 [Page 8] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 are provided, and the use of multicast for ND messages is avoided. Duplicate address detection and stateless address assignment are supported as part of bootstrapping. This is achieved using a whiteboard located on the 6LoWPAN Edge Routers of the LoWPAN network. Multihop route-over networks are supported by relaying ND messages. Finally, advanced features include the use of ND Proxy, and secondary Edge Router registrations. 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 on ND for 6LoWPAN, is that it can always be assumed that the ER and hosts are on the same link. Multicast with mesh under technologies most often induces flooding, and therefore it is avoided. Shelby, et al. Expires May 22, 2009 [Page 9] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 | | | +-----+ | | 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 those nodes reachable over a single radio transmission. 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. Multicast may also involve flooding in such networks, and is avoided. 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. Shelby, et al. Expires May 22, 2009 [Page 10] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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, and assigns addresses. The Edge Router terminates 6LoWPAN framing from the LoWPAN, and forwards packets. Multiple such networks may also overlap to form an Extended LoWPAN. 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 Figure 4: Backbone link and edge routers with a 6LoWPAN subnet In the backbone link topology, a backbone link federates multiple LoWPANs as a single IP link, 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 its link local and any other IPv6 address it has formed. If ND Proxy is used, a standard IPv6 Host on the backbone link can communicate with any host in the Extended LoWPAN and vice versa. The following sections explain the basics of how ND for 6LoWPAN works, starting with bootrapping on the network, maintenance of the network, and finally optional features such as ND Proxy. Shelby, et al. Expires May 22, 2009 [Page 11] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 3.1. Bootstrapping A Host first performs stateless autoconfiguration of its link-local address for each 6LoWPAN 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 local or global prefix is included 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 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 assign, e.g., short addresses to nodes, this is incidated in the RA message with the M flag. In such networks a node may request a stateless link-layer address to be assigned to it 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. This Confirmation includes the set of addresses now bound to the whiteboard of the ER, including a possible assigned addresses. 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. Node Router (relay) Edge Router | | | | ---- RR ---> | ---- RR ---> | | | | | <---- RC ---- | <---- RC ---- | | | | Shelby, et al. Expires May 22, 2009 [Page 12] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 Figure 6: Relay ND registration exchange. 3.2. Basic operation The whiteboard address binding and assignment 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 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, its IPv6 addresses remain the same. As assigned addresses are stateless, they 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 default 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 disseminates RAs, and this information is included in the RAs of each Router. 3.3. Optional features ND Proxy is specified in [RFC4389], and allows for two segments to be merged into a single IPv6 link. This documents explains the application of ND Proxy for use with Extended LoWPAN networks with multiple ERs on a backbone link. This optional feature allows for DAD across the entire Extended LoWPAN and backbone links, and for the subnet to appear as a single IPv6 link. This document extends ND Proxy to include an option to uniquely identify the LoWPAN Host on the backbone, and override 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. Forwarding can be performed automatically regardless of which ER the host is proxied by. 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 a new flag and options. The following new ICMPv6 message types are defined: Router Registration Router Confirmation Shelby, et al. Expires May 22, 2009 [Page 13] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 In addition, the following new ICMPv6 options are defined: Address Option 6LoWPAN Prefix Information Option Multihop Information Option Host Interface Identifier Option 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 Relay 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|X| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Host 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. Shelby, et al. Expires May 22, 2009 [Page 14] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 Destination Address: The destination IPv6 address of an Edge Router or Edge Router Relay. 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. Checksum: The ICMP checksum. TID: A unique Transaction ID assigned by the host and used to match replies. P: 1-bit Primary flag. Set to indicate that the router is primary and MAY proxy for the node if Proxy ND is used on the backbone link in a request. If the flag is not set then the router MUST not proxy for the node. Flag is echoed in a confirmation. X: 1-bit Proxy Flag. Only used in a confirmation, indicates that the router actually proxies for all of the addresses in the option fields that are being assigned to the node. This can only happen if the P flag is set as well. Set to 0 in a request. 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. Only used in a confirmation. Lifetime: 32-bit unsigned integer. The amout of time in units of seconds remaining before the binding of this node 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 host 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. Shelby, et al. Expires May 22, 2009 [Page 15] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 Host 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 Host Interface Identifier is not the same as the link-layer address of the host interface. Used as defined in [RFC4861] and [RFC4944]. If the RR was relayed, then this option is included in the RC to indicate the identity of the ER. Target link-layer address: Included in a Relay RC message in case the Host Interface Identifier is not the same as the link-layer address of the host interface. Used as defined in [RFC4861] and [RFC4944]. 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 based on the [RFC4861] RA message with the addition of a new flag "E". In addition 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|x|x|x|x|E|x| Router Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reachable Time | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Retrans Timer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options ... +-+-+-+-+-+-+-+-+-+-+-+ Shelby, et al. Expires May 22, 2009 [Page 16] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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 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 stateless address assignment mechanism specified in this document, not DHCPv6 as in [RFC4861]. O: As specified in [RFC4861]. x: Bits currently reserved for existing RA flags as per [RFC5175]. E: 1-bit "Edge Router" flag. When set, it indicates that the router is an Edge Router. Router Lifetime: As specified in [RFC4861]. Reachable Time: As specified in [RFC4861]. Possible Options: 6LoWPAN Prefix Information Option: This option includes information about the default subnet prefix for the LoWPAN along with other shared contexts for the subnet. 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. Shelby, et al. Expires May 22, 2009 [Page 17] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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. Neighbor Solicitation Message Neighbor Solicitation messages employed between ERs on the backbone link when ND proxy is used. A unique identifier is required in the message as an option to uniquely identify a host's interface. The standard NS message is used in this document is as per [RFC4861] with the an addition Host Interface Identifier Option defined in this document. The Host Interface Identifier is the same as that carried in RR/RC messages and associated with the 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 stateless address assignment, 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. Shelby, et al. Expires May 22, 2009 [Page 18] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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 Assignment flag. Set to indicate that the host is requesting stateless address assignment. 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 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 in use, 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 in use, if any. 0: Suffix carried inline. 1: Suffix compressed and assumes the same value as the Host 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. 3-15: 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. Shelby, et al. Expires May 22, 2009 [Page 19] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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. 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. When set, indicates that this prefix can be used for on-link determination. When not set the advertisement makes no statement about on-link or off-link properties of the prefix. In other words, if the L flag is not set a host MUST NOT conclude that an address derived from the prefix is off-link. That is, it MUST NOT update a previous indication that the address is on-link. A: 1-bit autonomous address-configuration flag. When set indicates that this prefix can be used for stateless address configuration as specified in [RFC4861]. Shelby, et al. Expires May 22, 2009 [Page 20] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 CID: 4-bit Context Identifier for this prefix information. The use of this Context Identifier is not specified in this document. 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. 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. Host Interface Identifier Option This option is for use with standard NS and NA messages between ERs over a backbone link together with ND-Proxy. 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 May 22, 2009 [Page 21] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Host Interface Identifier + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 12: Host Interface Identifier Option Type: TBD6 Length: 2 Reserved: This field is unused. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. Host 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 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. As a result, a link does not define the proper set of nodes to perform ND operations such as Duplicate Address Detection and Neighbor lookup. So in ND for 6LoWPAN, those operations are performed over a subnet. A subnet is a collection of LoWPAN links interconnected by routers that may share one or more local or global prefixes. In particular, DAD is performed over a subnet for all types of addresses, inclucing link local. In the backhaul model, an Edge Router and all the LoWPAN Nodes registered to that Edge Router form a subnet. In that model, the Edge Router serves all the prefixes that are defined on its subnet and can be connected to an IP routed infrastructure. In the backbone model, a Backbone Link federates multiple LoWPANs into a single IP subnet. Each LoWPAN is a collection of links anchored at an Edge Router. The Edge Routers interconnect the Shelby, et al. Expires May 22, 2009 [Page 22] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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 perform ND proxy on a backbone link, creating an extended LoWPAN sharing the same subnet prefix. ND proxy allows nodes to change their point of attachment without changing its IPv6 addresses. This specification simplifies address resolution compared to standard IPv6 ND. Stateless address assignment is also specified as part of the binding process. 6.1. Forming addresses All nodes are required to autoconfigure at least one address, a link- local address that is derived from the IEEE 64-bit extended MAC address that is globally unique to the device as in [RFC4944]. As a result, knowledge of the 64-bit address of another node on the same extended LoWPAN is enough to derive its link-local address and reach it over IP. 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 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 ER and MAY keep using the 6LOWPAN_ER anycast address for all its registrations. The node might also form Unique Local and Global Unicast addresses, for instance if it needs to be reachable from outside of the Extended LoWPAN. If a Global 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 Shelby, et al. Expires May 22, 2009 [Page 23] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 Address Option during registration. This is useful in the case of e.g. short addresses and avoids the need for a separate mechanism such as DHCPv6 or manual assignment. The node can tell if address assignment is available if the 'M' flag of the RA from that router is set. Address assignment 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 LoWPAN nodes are assigned addresses in a homogeneous so that the unicast IPv6 addresses IID resolve directly to a corresponding link-layer address. Thus avoiding address resolution when 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 source address is the link local address of the node. A unique Host 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 sending node. The RR message includes an Address Option for each address to be bound or requested. Thus the message is structured as follows. ICMPv6 (Router Registration (Address Options)) 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. The 'X' flag in the Router Confirmation Indentity Reply Option indicates that the Edge Router has completed DAD and now owns the Shelby, et al. Expires May 22, 2009 [Page 24] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 Binding Address over the Transit Link. 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 over a same or different LoWPANs. The 'P' flag in the Router Registration Indentity Request Option indicates whether the binding is primary. 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 (with the same network prefix), the registration process begins from the beginning. 6.3. Next-hop determination Next-hop determination is performed as in Section 5.2 of [RFC4861] with the following exceptions. Global and Local prefix are assumed to be off-link as the LoWPAN subnet with that prefix may be much 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 ND protocol [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 Shelby, et al. Expires May 22, 2009 [Page 25] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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. 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 must extend ND as specified in [RFC4861] to operate over an entire subnet, specifically the subnet controlled by Edge Routers, rather than a single IP link. 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 that 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 the following conceptual variables to be configured by system management. The specific variable names are used for demonstration purposes only, and an implementation is not required to have them, so long as its external behavior is consistent with that described in this document. The meaning of these variables are as defined in Section 6.2.1 of [RFC4861]. Default values are specified to simplify configuration in common cases. - IsRouter Shelby, et al. Expires May 22, 2009 [Page 26] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 - MaxRtrAdvInterval - MinRtrAdvInterval - AdvDefaultLifetime A router MUST allow the following conceptual variables to be configured by information received in Router Advertisement messages. The specific variable names are used for demonstration purposes only, and an implementation is not required to have them, so long as its external behavior is consistent with that described in this document. The meaning of these variables are as defined in Section 6.2.1 of [RFC4861]. However, default values are not relevant as a router should not be advertising such values until they have been received from other neighboring routers. - AdvManagedFlag - AdvOtherConfigFlag - AdvReachableTime - AdvRetransTimer - AdvCurHopLimit - AdvPrefixList 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 filled with the following values constistent with the message format Shelby, et al. Expires May 22, 2009 [Page 27] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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. - The E flag is not set. - 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 May 22, 2009 [Page 28] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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 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 wants to prefer. 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 Host 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 Host 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 subnet that may cover hundreds or thousands of nodes. Shelby, et al. Expires May 22, 2009 [Page 29] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 Instead of multicasting ND messages, a LoWPAN Node performs unicast exchanges to its Edge Router to claim and lookup addresses using unicast and anycast addresses, and the Edge Router proxies the ND requests over the Backbone Link when necessary. This specification documents the extensions to IPv6 Neighbor Discovery that enables a LoWPAN Node to claim and lookup addresses using a 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. For the purpose of Neighbor Discovery proxying, this specification documents the LoWPAN registration table, 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 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 renumber. To enable this, the ND proxy operation upon a Router Registration/Confirmation flow wins the address ownership over a ND proxy 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 Host Interface Identifier Option in NS/NA messages that carries the node EUI-64 address enables to differentiate an address collision from a movement of a node from one Edge Router to the next. Upon a registration flow, a node doing DAD SHOULD ignore NA without the the override (O) bit, and set the override (O) bit in its own NA messages. Asynchronously to the registration, a node 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 Shelby, et al. Expires May 22, 2009 [Page 30] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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 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. 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 in the Identity Request Option and it is connected to a Backbone, then it SHOULD perform proxy ND operations on the backbone and indicate so in the Router Confirmation message using the 'X' flag of the Identity Reply Option. 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 a stateless address assignment. 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 assigned link-layer address and the defualt prefix inline. 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 operation in place for that medium. Edge Routers also perform ND proxying for the LoWPAN Nodes that are proactively registered to them. That way, a lookup over the backbone is not Shelby, et al. Expires May 22, 2009 [Page 31] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 propagated over the LoWPANs, but answered by the proxy 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. It uses the same link local address for the Backbone Link and for all the associated LoWPAN(s) connected to that Edge Router. 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. A new (E) bit in the RA indicates the Edge Router capability. 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. 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]). Shelby, et al. Expires May 22, 2009 [Page 32] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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. 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. Fault tolerance To be completed in the next revision. 9. Ad-hoc LoWPAN Operation To be completed in the next revision. 10. Message Examples This section provides examples of creating and processing messages and options from this document along with example messages. To be completed in the next revision. 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. Shelby, et al. Expires May 22, 2009 [Page 33] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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": Address Option (TBD3) 6LoWPAN Prefix Information Option (TBD4) Multihop Information Option (TBD5) Host Interface Identifier Option (TBD6) A new flag is required for the IPv6 ND Router Advertisement called the "E - Edge Router Flag". 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/icmpv6-parameters] 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. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. Shelby, et al. Expires May 22, 2009 [Page 34] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 [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. [RFC5175] Haberman, B. and R. Hinden, "IPv6 Router Advertisement Flags Option", RFC 5175, March 2008. 14.2. Informative References [I-D.van-beijnum-multi-mtu] Beijnum, I., "Extensions for Multi-MTU Subnets", draft-van-beijnum-multi-mtu-02 (work in progress), February 2008. [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery Proxies (ND Proxy)", RFC 4389, April 2006. [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. Authors' Addresses Zach Shelby (editor) Sensinode Kidekuja 2 Vuokatti 88600 FINLAND Phone: +358407796297 Email: zach@sensinode.com Shelby, et al. Expires May 22, 2009 [Page 35] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 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 Erik Nordmark Sun Microsystems, Inc. 17 Network Circle Menlo Park, California 94025 USA Phone: Email: Erik.Nordmark@Sun.COM Shelby, et al. Expires May 22, 2009 [Page 36] Internet-Draft Neighbor Discovery for 6LoWPAN November 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Shelby, et al. Expires May 22, 2009 [Page 37]