Request for Comments: 7668
Category: Standards Track
ISSN: 2070-1721
TeliaSonera
T. Savolainen
M. Isomaki
Nokia
B. Patil
AT&T
Z. Shelby
ARM
C. Gomez
Universitat Politecnica de Catalunya/i2CAT
October 2015
IPv6 over BLUETOOTH(R) Low Energy
Abstract
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Bluetooth Smart is the brand name for the Bluetooth low energy feature in the Bluetooth specification defined by the Bluetooth Special Interest Group. The standard Bluetooth radio has been widely implemented and available in mobile phones, notebook computers, audio headsets, and many other devices. The low-power version of Bluetooth is a specification that enables the use of this air interface with devices such as sensors, smart meters, appliances, etc. The low- power variant of Bluetooth has been standardized since revision 4.0 of the Bluetooth specifications, although version 4.1 or newer is required for IPv6. This document describes how IPv6 is transported over Bluetooth low energy using IPv6 over Low-power Wireless Personal Area Network (6LoWPAN) techniques.
Status of This Memo
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This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7668.
Copyright Notice
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Copyright © 2015 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Table of Contents
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1. Introduction ...................................................3 1.1. Terminology and Requirements Language .......................3 2. Bluetooth Low Energy ...........................................4 2.1. Bluetooth LE Stack .........................................4 2.2. Roles and Topology for Link Layer ...........................5 2.3. Bluetooth LE Device Addressing .............................6 2.4. Bluetooth LE Packet Sizes and MTU ...........................6 3. Specification of IPv6 over Bluetooth Low Energy .................7 3.1. Protocol Stack .............................................8 3.2. Link Model .................................................8 3.2.1. IPv6 Subnet Model and Internet Connectivity .........9 3.2.2. Stateless Address Autoconfiguration ................10 3.2.3. Neighbor Discovery .................................12 3.2.4. Header Compression .................................13 3.2.4.1. Remote Destination Example ................14 3.2.4.2. Example of Registration of Multiple Addresses ........................15 3.2.5. Unicast and Multicast Address Mapping ..............16 4. Security Considerations ........................................16 5. References .....................................................17 5.1. Normative References ......................................17 5.2. Informative References ....................................18 Acknowledgements ..................................................20 Contributors ......................................................20 Authors' Addresses ................................................20
1. Introduction
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Bluetooth Smart is the brand name for the Bluetooth low energy feature (hereinafter, "Bluetooth LE") in the Bluetooth specification defined by the Bluetooth Special Interest Group [BTCorev4.1]. Bluetooth LE is a radio technology targeted for devices that operate with very low-capacity (e.g., coin cell) batteries or minimalistic power sources, which means that low power consumption is essential. Bluetooth LE is an especially attractive technology for Internet of Things applications, such as health monitors, environmental sensing, proximity applications, and many others.
Considering the potential for the exponential growth in the number of sensors and Internet connected devices, IPv6 is an ideal protocol for communication with such devices due to the large address space it provides. In addition, IPv6 provides tools for stateless address autoconfiguration, which is particularly suitable for sensor network applications and nodes that have very limited processing power or lack a full-fledged operating system or a user interface.
This document describes how IPv6 is transported over Bluetooth LE connections using IPv6 over Low-power Wireless Personal Area Network (6LoWPAN) techniques. RFCs 4944 [RFC4944], 6282 [RFC6282], and 6775 [RFC6775] were developed for 6LoWPAN and specify the transmission of IPv6 over IEEE 802.15.4 [IEEE802.15.4]. The Bluetooth LE link, in many respects, has similar characteristics to that of IEEE 802.15.4, and many of the mechanisms defined for IPv6 over IEEE 802.15.4 can be applied to the transmission of IPv6 on Bluetooth LE links. This document specifies the details of IPv6 transmission over Bluetooth LE links.
1.1. Terminology and Requirements Language
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].
The terms "6LoWPAN Node (6LN)", "6LoWPAN Router (6LR)", and "6LoWPAN Border Router (6LBR)" are defined as in [RFC6775], with an addition that Bluetooth LE central and Bluetooth LE peripheral (see Section 2.2) can both be either 6LN or 6LBR.
The acronyms "DAC", "DAM", "SAC", "SAM", and "CID" are used in this document as defined in [RFC6282]. They are expanded as follows:
- Destination Address Compression (DAC)
- Destination Address Mode (DAM)
- Source Address Compression (SAC)
- Source Address Mode (SAM)
- Context Identifier (CID)
2. Bluetooth Low Energy
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Bluetooth LE is designed for transferring small amounts of data infrequently at modest data rates with a very small energy expenditure per bit. The Bluetooth Special Interest Group (Bluetooth SIG) has introduced two trademarks: Bluetooth Smart for single-mode devices (a device that only supports Bluetooth LE) and Bluetooth Smart Ready for dual-mode devices (devices that support both Bluetooth and Bluetooth LE; note that Bluetooth and Bluetooth LE are different, non-interoperable radio technologies). In the rest of this document, the term "Bluetooth LE" is used regardless of whether this technology is supported by a single-mode or dual-mode device.
Bluetooth LE was introduced in Bluetooth 4.0, enhanced in Bluetooth 4.1 [BTCorev4.1], and developed even further in successive versions. Bluetooth SIG has also published the Internet Protocol Support Profile (IPSP) [IPSP], which includes the Internet Protocol Support Service (IPSS). The IPSP enables discovery of IP-enabled devices and establishment of a link-layer connection for transporting IPv6 packets. IPv6 over Bluetooth LE is dependent on both Bluetooth 4.1 and IPSP 1.0 or more recent versions of either specification to provide necessary capabilities.
Devices such as mobile phones, notebooks, tablets, smartwatches, and other handheld computing devices that incorporate chipsets implementing Bluetooth 4.1 or later will also have the low energy functionality of Bluetooth. Bluetooth LE is also expected to be included in many different types of accessories that collaborate with mobile devices such as phones, tablets, and notebook computers. An example of a use case for a Bluetooth LE accessory is a heart rate monitor that sends data via a mobile phone or smartwatch to a server on the Internet or sends data directly to the device.
2.1. Bluetooth LE Stack
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The lower layer of the Bluetooth LE stack consists of the Physical Layer (PHY), the Link Layer (LL), and a test interface called the Direct Test Mode (DTM). The Physical Layer transmits and receives the actual packets. The Link Layer is responsible for providing medium access, connection establishment, error control, and flow control. The Direct Test Mode is only used for testing purposes. The upper layer consists of the Logical Link Control and Adaptation
Protocol (L2CAP), Attribute Protocol (ATT), Security Manager (SM), Generic Attribute Profile (GATT), and Generic Access Profile (GAP) as shown in Figure 1. The Host Controller Interface (HCI) separates the lower layers, often implemented in the Bluetooth controller, from higher layers, often implemented in the host stack. GATT and Bluetooth LE profiles together enable the creation of applications in a standardized way without using IP. L2CAP provides multiplexing capability by multiplexing the data channels from the above layers. L2CAP also provides fragmentation and reassembly for large data packets. The Security Manager defines a protocol and mechanisms for pairing, key distribution, and a security toolbox for the Bluetooth LE device.
+-------------------------------------------------+ | Applications | +---------------------------------------+---------+ | Generic Attribute Profile | Generic | +--------------------+------------------+ Access | | Attribute Protocol | Security Manager | Profile | +--------------------+------------------+---------+ | Logical Link Control and Adaptation Protocol | - - -+-----------------------+-------------------------+- - - HCI | Link Layer | Direct Test Mode | +-------------------------------------------------+ | Physical Layer | +-------------------------------------------------+
Figure 1: Bluetooth LE Protocol Stack
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As shown in Section 3.1, IPv6 over Bluetooth LE requires an adapted 6LoWPAN layer that runs on top of Bluetooth LE L2CAP.
2.2. Roles and Topology for Link Layer
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Bluetooth LE defines two GAP roles of relevance herein: the Bluetooth LE central role and the Bluetooth LE peripheral role. A device in the central role (called "central" from now on) has traditionally been able to manage multiple simultaneous connections with a number of devices in the peripheral role (called "peripherals" from now on). A peripheral is commonly connected to a single central, but with versions of Bluetooth from 4.1 onwards, it can also connect to multiple centrals at the same time. In this document, for IPv6 networking purposes, the Bluetooth LE network (i.e., a Bluetooth LE piconet) follows a star topology shown in the Figure 2, where a router typically implements the Bluetooth LE central role and the rest of nodes implement the Bluetooth LE peripheral role. In the future, mesh networking and/or parallel connectivity to multiple centrals at a time may be defined for IPv6 over Bluetooth LE.
Peripheral --. .-- Peripheral \ / Peripheral ---- Central ---- Peripheral / \ Peripheral --' '-- Peripheral
Figure 2: Bluetooth LE Star Topology
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In Bluetooth LE, direct wireless communication only takes place between a central and a peripheral. This means that inherently the Bluetooth LE star represents a hub-and-spokes link model. Nevertheless, two peripherals may communicate through the central by using IP routing functionality per this specification.
2.3. Bluetooth LE Device Addressing
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Every Bluetooth LE device is identified by a 48-bit device address. The Bluetooth specification [BTCorev4.1] describes the device address of a Bluetooth LE device as follows: "Devices are identified using a device address. Device addresses may be either a public device address or a random device address". The public device addresses are based on the IEEE 802 standard [IEEE802]. Random device addresses and the Bluetooth LE privacy feature are described in the Bluetooth Generic Access Profile, Sections 10.8 and 10.7 of [BTCorev4.1], respectively. There are two types of random device addresses: static and private addresses. The private addresses are further divided into two sub-types: resolvable or non-resolvable addresses, which are explained in depth in the referenced Bluetooth specification. Once a static address is initialized, it does not change until the device is power cycled. The static address can be initialized to a new value after each power cycle, but that is not mandatory. The recommended time interval before randomizing new private address is 15 minutes, as determined by timer T_GAP(private_addr_int) in Table 17.1 of the Bluetooth Generic Access Profile [BTCorev4.1]. The selection of which device address types are used is implementation and deployment specific. In random addresses, the first 46 bits are randomized, and the last 2 bits indicate the random address type. Bluetooth LE does not support avoidance or detection of device address collisions. However, these 48-bit random device addresses have a very small probability of being in conflict within a typical deployment.
2.4. Bluetooth LE Packet Sizes and MTU
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The optimal MTU defined for L2CAP fixed channels over Bluetooth LE is 27 octets, including the L2CAP header of 4 octets. The default MTU for Bluetooth LE is hence defined to be 27 octets. Therefore, excluding the L2CAP header of 4 octets, a protocol data unit (PDU) size of 23 octets is available for upper layers. In order to be able to transmit IPv6 packets of 1280 octets or larger, a link-layer fragmentation and reassembly solution is provided by the L2CAP layer. The IPSP defines means for negotiating up a link-layer connection that provides an MTU of 1280 octets or higher for the IPv6 layer [IPSP]. The link-layer MTU is negotiated separately for each direction. Implementations that require an equal link-layer MTU for the two directions SHALL use the smallest of the possibly different MTU values.
3. Specification of IPv6 over Bluetooth Low Energy
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Bluetooth LE technology sets strict requirements for low power consumption and thus limits the allowed protocol overhead. 6LoWPAN standards [RFC6775] [RFC6282] provide useful functionality for reducing overhead, which is applied to Bluetooth LE. This functionality is comprised of link-local IPv6 addresses and stateless IPv6 address autoconfiguration (see Section 3.2.2), Neighbor Discovery (see Section 3.2.3), and header compression (see Section 3.2.4). Fragmentation features from 6LoWPAN standards are not used due to Bluetooth LE's link-layer fragmentation support (see Section 2.4).
A significant difference between IEEE 802.15.4 and Bluetooth LE is that the former supports both star and mesh topologies (and requires a routing protocol), whereas Bluetooth LE does not currently support the formation of multihop networks at the link layer. However, inter-peripheral communication through the central is enabled by using IP routing functionality per this specification.
In Bluetooth LE, a central node is assumed to be less resource constrained than a peripheral node. Hence, in the primary deployment scenario, central and peripheral will act as 6LoWPAN Border Router (6LBR) and a 6LoWPAN Node (6LN), respectively.
Before any IP-layer communications can take place over Bluetooth LE, nodes enabled by Bluetooth LE such as 6LNs and 6LBRs have to find each other and establish a suitable link-layer connection. The discovery and Bluetooth LE connection setup procedures are documented by the Bluetooth SIG in the IPSP specification [IPSP].
In the rare case of Bluetooth LE random device address conflict, a 6LBR can detect multiple 6LNs with the same Bluetooth LE device address, as well as a 6LN with the same Bluetooth LE address as the 6LBR. The 6LBR MUST ignore 6LNs with the same device address the 6LBR has, and the 6LBR MUST have at most one connection for a given Bluetooth LE device address at any given moment. This will avoid addressing conflicts within a Bluetooth LE network.
3.1. Protocol Stack
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Figure 3 illustrates how the IPv6 stack works in parallel to the GATT stack on top of the Bluetooth LE L2CAP layer. The GATT stack is needed herein for discovering nodes supporting the Internet Protocol Support Service. UDP and TCP are provided as examples of transport protocols, but the stack can be used by any other upper-layer protocol capable of running atop of IPv6.
+---------+ +----------------------------+ | IPSS | | UDP/TCP/other | +---------+ +----------------------------+ | GATT | | IPv6 | +---------+ +----------------------------+ | ATT | | 6LoWPAN for Bluetooth LE | +---------+--+----------------------------+ | Bluetooth LE L2CAP | - - +-----------------------------------------+- - - HCI | Bluetooth LE Link Layer | +-----------------------------------------+ | Bluetooth LE Physical | +-----------------------------------------+
Figure 3: IPv6 and IPSS on the Bluetooth LE Stack
3.2. Link Model
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The distinct concepts of the IPv6 link (layer 3) and the physical link (combination of PHY and Media Access Control (MAC)) need to be clear, and their relationship has to be well understood in order to specify the addressing scheme for transmitting IPv6 packets over the Bluetooth LE link. RFC 4861 [RFC4861] defines a link as "a communication facility or medium over which nodes can communicate at the link layer, i.e., the layer immediately below IP".
In the case of Bluetooth LE, the 6LoWPAN layer is adapted to support transmission of IPv6 packets over Bluetooth LE. The IPSP defines all steps required for setting up the Bluetooth LE connection over which 6LoWPAN can function [IPSP], including handling the link-layer fragmentation required on Bluetooth LE, as described in Section 2.4. Even though MTUs larger than 1280 octets can be supported, use of a 1280-octet MTU is RECOMMENDED in order to avoid need for Path MTU discovery procedures.
While Bluetooth LE protocols, such as L2CAP, utilize little-endian byte ordering, IPv6 packets MUST be transmitted in big-endian order (network byte order).
Per this specification, the IPv6 header compression format specified in RFC 6282 [RFC6282] MUST be used. The IPv6 payload length can be derived from the L2CAP header length and the possibly elided IPv6 address can be reconstructed from the link-layer address, used at the time of Bluetooth LE connection establishment, from the HCI Connection Handle during connection, compression context if any, and address registration information (see Section 3.2.3).
Bluetooth LE connections used to build a star topology are point-to- point in nature, as Bluetooth broadcast features are not used for IPv6 over Bluetooth LE (except for discovery of nodes supporting IPSS). After the peripheral and central have connected at the Bluetooth LE level, the link can be considered up, and IPv6 address configuration and transmission can begin.
3.2.1. IPv6 Subnet Model and Internet Connectivity
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In the Bluetooth LE piconet model (see Section 2.2), peripherals each have a separate link to the central and the central acts as an IPv6 router rather than a link-layer switch. As discussed in [RFC4903], conventional usage of IPv6 anticipates IPv6 subnets spanning a single link at the link layer. As IPv6 over Bluetooth LE is intended for constrained nodes, and for Internet of Things use cases and environments, the complexity of implementing a separate subnet on each peripheral-central link and routing between the subnets appears to be excessive. In the Bluetooth LE case, the benefits of treating the collection of point-to-point links between a central and its connected peripherals as a single multilink subnet rather than a multiplicity of separate subnets are considered to outweigh the multilink model's drawbacks as described in [RFC4903].
Hence, a multilink model has been chosen, as further illustrated in Figure 4. Because of this, link-local multicast communications can happen only within a single Bluetooth LE connection; thus, 6LN-to-6LN communications using link-local addresses are not possible. 6LNs connected to the same 6LBR have to communicate with each other by using the shared prefix used on the subnet. The 6LBR ensures address collisions do not occur (see Section 3.2.3) and forwards packets sent by one 6LN to another.
In a typical scenario, the Bluetooth LE network is connected to the Internet as shown in the Figure 4. In this scenario, the Bluetooth LE star is deployed as one subnet, using one /64 IPv6 prefix, with each spoke representing an individual link. The 6LBR is acting as router and forwarding packets between 6LNs and to and from Internet.
/ .---------------. / / 6LN \ / / \ \ / | \ | / | 6LN ----------- 6LBR ----- | Internet | <--Link--> / | \ \ / / \ \ 6LN / \ '---------------' \ \ <------ Subnet -----><-- IPv6 connection --> to Internet
Figure 4: Bluetooth LE Network Connected to the Internet
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In some scenarios, the Bluetooth LE network may transiently or permanently be an isolated network as shown in the Figure 5. In this case, the whole star consists of a single subnet with multiple links, where 6LBR is at central, routing packets between 6LNs. In the simplest case, the isolated network has one 6LBR and one 6LN.
.-------------------. / \ / 6LN 6LN \ / \ / \ | \ / | | 6LN --- 6LBR --- 6LN | | / \ | \ / \ / \ 6LN 6LN / \ / '-------------------' <--------- Subnet ---------->
Figure 5: Isolated Bluetooth LE Network
3.2.2. Stateless Address Autoconfiguration
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At network interface initialization, both 6LN and 6LBR SHALL generate and assign to the Bluetooth LE network interface IPv6 link-local addresses [RFC4862] based on the 48-bit Bluetooth device addresses (see Section 2.3) that were used for establishing the underlying Bluetooth LE connection. A 6LN and a 6LBR are RECOMMENDED to use private Bluetooth device addresses. A 6LN SHOULD pick a different Bluetooth device address for every Bluetooth LE connection with a 6LBR, and a 6LBR SHOULD periodically change its random Bluetooth device address. Following the guidance of [RFC7136], a 64-bit Interface Identifier (IID) is formed from the 48-bit Bluetooth device address by inserting two octets, with hexadecimal values of 0xFF and 0xFE in the middle of the 48-bit Bluetooth device address as shown in Figure 6. In the figure, letter 'b' represents a bit from the Bluetooth device address, copied as is without any changes on any bit. This means that no bit in the IID indicates whether the underlying Bluetooth device address is public or random.
|0 1|1 3|3 4|4 6| |0 5|6 1|2 7|8 3| +----------------+----------------+----------------+----------------+ |bbbbbbbbbbbbbbbb|bbbbbbbb11111111|11111110bbbbbbbb|bbbbbbbbbbbbbbbb| +----------------+----------------+----------------+----------------+
Figure 6: Formation of IID from Bluetooth Device Address
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The IID is then prepended with the prefix fe80::/64, as described in RFC 4291 [RFC4291] and as depicted in Figure 7. The same link-local address SHALL be used for the lifetime of the Bluetooth LE L2CAP channel. (After a Bluetooth LE logical link has been established, it is referenced with a Connection Handle in HCI. Thus, possibly changing device addresses do not impact data flows within existing L2CAP channels. Hence, there is no need to change IPv6 link-local addresses even if devices change their random device addresses during L2CAP channel lifetime).
10 bits 54 bits 64 bits +----------+-----------------+----------------------+ |1111111010| zeros | Interface Identifier | +----------+-----------------+----------------------+
Figure 7: IPv6 Link-Local Address in Bluetooth LE
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A 6LN MUST join the all-nodes multicast address. There is no need for 6LN to join the solicited-node multicast address, since 6LBR will know device addresses and hence link-local addresses of all connected 6LNs. The 6LBR will ensure no two devices with the same Bluetooth LE device address are connected at the same time. Detection of duplicate link-local addresses is performed by the process on the 6LBR responsible for the discovery of IP-enabled Bluetooth LE nodes and for starting Bluetooth LE connection establishment procedures. This approach increases the complexity of 6LBR, but reduces power consumption on both 6LN and 6LBR in the link establishment phase by reducing the number of mandatory packet transmissions.
After link-local address configuration, the 6LN sends Router Solicitation messages as described in [RFC4861], Section 6.3.7.
For non-link-local addresses, 6LNs SHOULD NOT be configured to embed the Bluetooth device address in the IID by default. Alternative schemes such as Cryptographically Generated Addresses (CGAs) [RFC3972], privacy extensions [RFC4941], Hash-Based Addresses (HBAs) [RFC5535], DHCPv6 [RFC3315], or static, semantically opaque addresses [RFC7217] SHOULD be used by default. In situations where the Bluetooth device address is known to be a private device address and/ or the header compression benefits of embedding the device address in the IID are required to support deployment constraints, 6LNs MAY form a 64-bit IID by utilizing the 48-bit Bluetooth device address. The non-link-local addresses that a 6LN generates MUST be registered with the 6LBR as described in Section 3.2.3.
The tool for a 6LBR to obtain an IPv6 prefix for numbering the Bluetooth LE network is out of scope of this document, but can be, for example, accomplished via DHCPv6 Prefix Delegation [RFC3633] or by using Unique Local IPv6 Unicast Addresses (ULAs) [RFC4193]. Due to the link model of the Bluetooth LE (see Section 3.2.1) the 6LBR MUST set the "on-link" flag (L) to zero in the Prefix Information Option in Neighbor Discovery messages [RFC4861] (see Section 3.2.3). This will cause 6LNs to always send packets to the 6LBR, including the case when the destination is another 6LN using the same prefix.
3.2.3. Neighbor Discovery
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'Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)' [RFC6775] describes the neighbor discovery approach as adapted for use in several 6LoWPAN topologies, including the mesh topology. Bluetooth LE does not support mesh networks; hence, only those aspects that apply to a star topology are considered.
The following aspects of the Neighbor Discovery optimizations [RFC6775] are applicable to Bluetooth LE 6LNs:
- A Bluetooth LE 6LN MUST NOT register its link-local address. A Bluetooth LE 6LN MUST register its non-link-local addresses with the 6LBR by sending a Neighbor Solicitation (NS) message with the Address Registration Option (ARO) and process the Neighbor Advertisement (NA) accordingly. The NS with the ARO option MUST be sent irrespective of the method used to generate the IID. If the 6LN registers multiple addresses that are not based on Bluetooth device address for the same compression context, the header compression efficiency will decrease (see Section 3.2.4).
- For sending Router Solicitations and processing Router Advertisements, the Bluetooth LE 6LNs MUST follow Sections 5.3 and 5.4 of [RFC6775], respectively.
3.2.4. Header Compression
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Header compression as defined in RFC 6282 [RFC6282], which specifies the compression format for IPv6 datagrams on top of IEEE 802.15.4, is REQUIRED as the basis for IPv6 header compression on top of Bluetooth LE. All headers MUST be compressed according to the encoding formats described in RFC 6282 [RFC6282].
The Bluetooth LE's star topology structure and ARO can be exploited in order to provide a mechanism for address compression. The following text describes the principles of IPv6 address compression on top of Bluetooth LE.
The ARO option requires use of a 64-bit Extended Unique Identifier (EUI-64) [RFC6775]. In the case of Bluetooth LE, the field SHALL be filled with the 48-bit device address used by the Bluetooth LE node converted into 64-bit Modified EUI-64 format [RFC4291].
To enable efficient header compression, when the 6LBR sends a Router Advertisement, it MUST include a 6LoWPAN Context Option (6CO) [RFC6775] matching each address prefix advertised via a Prefix Information Option (PIO) [RFC4861] for use in stateless address autoconfiguration.
When a 6LN is sending a packet to a 6LBR, it MUST fully elide the source address if it is a link-local address. For other packets to or through a 6LBR with a non-link-local source address that the 6LN has registered with ARO to the 6LBR for the indicated prefix, the source address MUST be fully elided if it is the latest address that the 6LN has registered for the indicated prefix. If a source non- link-local address is not the latest registered, then the 64 bits of the IID SHALL be fully carried in-line (SAM=01), or if the first 48 bits of the IID match with the latest registered address, then the last 16 bits of the IID SHALL be carried in-line (SAM=10). That is, if SAC=0 and SAM=11, the 6LN MUST be using the link-local IPv6 address derived from the Bluetooth LE device address, and if SAC=1 and SAM=11, the 6LN MUST have registered the source IPv6 address with the prefix related to the compression context, and the 6LN MUST be referring to the latest registered address related to the compression context. The IPv6 address MUST be considered to be registered only after the 6LBR has sent a Neighbor Advertisement with an ARO having its status field set to success. The destination IPv6 address MUST be fully elided if the destination address is the 6LBR's link-local address based on the 6LBR's Bluetooth device address (DAC=0, DAM=11).
The destination IPv6 address MUST be fully or partially elided if context has been set up for the destination address, for example, DAC=0 and DAM=01 when destination prefix is link-local, and DAC=1 and DAM=01 if compression context has been configured for the destination prefix used.
When a 6LBR is transmitting packets to a 6LN, it MUST fully elide the source IID if the source IPv6 address is the link-local address based on the 6LBR's Bluetooth device address (SAC=0, SAM=11), and it MUST elide the source prefix or address if a compression context related to the IPv6 source address has been set up. The 6LBR also MUST fully elide the destination IPv6 address if it is the link-local address based on the 6LN's Bluetooth device address (DAC=0, DAM=11), or if the destination address is the latest registered by the 6LN with ARO for the indicated context (DAC=1, DAM=11). If the destination address is a non-link-local address and not the latest registered, then the 6LN MUST either include the IID part fully in-line (DAM=01) or, if the first 48 bits of the IID match to the latest registered address, then elide those 48 bits (DAM=10).
3.2.4.1. Remote Destination Example
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When a 6LN transmits an IPv6 packet to a remote destination using global Unicast IPv6 addresses, if a context is defined for the 6LN's global IPv6 address, the 6LN has to indicate this context in the corresponding source fields of the compressed IPv6 header as per Section 3.1 of RFC 6282 [RFC6282] and has to elide the full IPv6 source address previously registered with ARO (if using the latest registered address; otherwise, part or all of the IID may have to be transmitted in-line). For this, the 6LN MUST use the following settings in the IPv6 compressed header: SAC=1 and SAM=11. The CID may be set 0 or 1, depending on which context is used. In this case, the 6LBR can infer the elided IPv6 source address since 1) the 6LBR has previously assigned the prefix to the 6LNs; and 2) the 6LBR maintains a Neighbor Cache that relates the device address and the IID the device has registered with ARO. If a context is defined for the IPv6 destination address, the 6LN has to also indicate this context in the corresponding destination fields of the compressed IPv6 header, and elide the prefix of or the full destination IPv6 address. For this, the 6LN MUST set the DAM field of the compressed IPv6 header as DAM=01 (if the context covers a 64-bit prefix) or as DAM=11 (if the context covers a full 128-bit address). DAC MUST be set to 1. Note that when a context is defined for the IPv6 destination address, the 6LBR can infer the elided destination prefix by using the context.
When a 6LBR receives an IPv6 packet sent by a remote node outside the Bluetooth LE network, and the destination of the packet is a 6LN, if a context is defined for the prefix of the 6LN's global IPv6 address, the 6LBR has to indicate this context in the corresponding destination fields of the compressed IPv6 header. The 6LBR has to elide the IPv6 destination address of the packet before forwarding it, if the IPv6 destination address is inferable by the 6LN. For this, the 6LBR will set the DAM field of the IPv6 compressed header as DAM=11 (if the address is the latest 6LN has registered). DAC needs to be set to 1. If a context is defined for the IPv6 source address, the 6LBR needs to indicate this context in the source fields of the compressed IPv6 header and elide that prefix as well. For this, the 6LBR needs to set the SAM field of the IPv6 compressed header as SAM=01 (if the context covers a 64-bit prefix) or SAM=11 (if the context covers a full 128-bit address). SAC is to be set to 1.
3.2.4.2. Example of Registration of Multiple Addresses
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As described above, a 6LN can register multiple non-link-local addresses that map to the same compression context. From the multiple address registered, only the latest address can be fully elided (SAM=11, DAM=11), and the IIDs of previously registered addresses have to be transmitted fully in-line (SAM=01, DAM=01) or, in the best case, can be partially elided (SAM=10, DAM=10). This is illustrated in the example below:
1. The 6LN registers first address 2001:db8::1111:2222:3333:4444 to a 6LBR. At this point the address can be fully elided using SAC=1/SAM=11 or DAC=1/DAM=11. 2. The 6LN registers second address 2001:db8::1111:2222:3333:5555 to the 6LBR. As the second address is now the latest registered, it can be fully elided using SAC=1/SAM=11 or DAC=1/DAM=11. The first address can now be partially elided using SAC=1/SAM=10 or DAC=1/DAM=10, as the first 112 bits of the address are the same between the first and the second registered addresses.- Expiration of registration time for the first or the second address has no impact on the compression. Hence, even if the most recently registered address expires, the first address can only be partially elided (SAC=1/SAM=10, DAC=1/DAM=10). The 6LN can register a new address, or re-register an expired address, to become able to again fully elide an address.
3.2.5. Unicast and Multicast Address Mapping
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The Bluetooth LE Link Layer does not support multicast. Hence, traffic is always unicast between two Bluetooth LE nodes. Even in the case where a 6LBR is attached to multiple 6LNs, the 6LBR cannot do a multicast to all the connected 6LNs. If the 6LBR needs to send a multicast packet to all its 6LNs, it has to replicate the packet and unicast it on each link. However, this may not be energy efficient, and particular care must be taken if the central is battery powered. To further conserve power, the 6LBR MUST keep track of multicast listeners at Bluetooth LE link-level granularity (not at subnet granularity), and it MUST NOT forward multicast packets to 6LNs that have not registered as listeners for multicast groups the packets belong to. In the opposite direction, a 6LN always has to send packets to or through the 6LBR. Hence, when a 6LN needs to transmit an IPv6 multicast packet, the 6LN will unicast the corresponding Bluetooth LE packet to the 6LBR.
4. Security Considerations
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The transmission of IPv6 over Bluetooth LE links and IPv6 over IEEE 802.15.4 have similar requirements and concerns for security. Security considerations for the Bluetooth LE Link Layer are covered by the IPSP [IPSP].
Bluetooth LE Link Layer supports encryption and authentication by using the Counter with CBC-MAC (CCM) mechanism [RFC3610] and a 128-bit AES block cipher. Upper-layer security mechanisms may exploit this functionality when it is available. (Note: CCM does not consume octets from the maximum per-packet L2CAP data size, since the link-layer data unit has a specific field for them when they are used.)
Key management in Bluetooth LE is provided by the Security Manager Protocol (SMP), as defined in [BTCorev4.1].
The Direct Test Mode offers two setup alternatives: with and without accessible HCI. In designs with accessible HCI, the so-called upper tester communicates through the HCI (which may be supported by Universal Asynchronous Receiver Transmitter (UART), Universal Serial Bus (USB), and Secure Digital transports), with the Physical and Link Layers of the Bluetooth LE device under test. In designs without accessible HCI, the upper tester communicates with the device under test through a two-wire UART interface. The Bluetooth specification [BTCorev4.1] does not provide security mechanisms for the communication between the upper tester and the device under test in either case. Nevertheless, an attacker needs to physically connect a device (via one of the wired HCI types) to the device under test to be able to interact with the latter.
The IPv6 link-local address configuration described in Section 3.2.2 only reveals information about the 6LN to the 6LBR that the 6LBR already knows from the link-layer connection. This means that a device using Bluetooth privacy features reveals the same information in its IPv6 link-local addresses as in its device addresses. Respectively, a device not using privacy at the Bluetooth level will not have privacy at the IPv6 link-local address either. For non- link-local addresses, implementations are recommended not to embed the Bluetooth device address in the IID by default and instead support, for example, [RFC3315], [RFC3972], [RFC4941], [RFC5535], or [RFC7217].
A malicious 6LN may attempt to perform a denial-of-service attack on the Bluetooth LE network, for example, by flooding packets. This sort of attack is mitigated by the fact that link-local multicast is not bridged between Bluetooth LE links and by 6LBR being able to rate-limit packets sent by each 6LN by making smart use of the Bluetooth LE L2CAP credit-based flow-control mechanism.
5. References
5.1. Normative References
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[BTCorev4.1]
Bluetooth Special Interest Group, "Bluetooth Core Specification Version 4.1", December 2013, <https://www.bluetooth.org/en-us/specification/adopted- specifications>. [IPSP] Bluetooth Special Interest Group, "Bluetooth Internet Protocol Support Profile Specification Version 1.0.0", December 2014, <https://www.bluetooth.org/en- us/specification/adopted-specifications>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, <http://www.rfc-editor.org/info/rfc4291>. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, <http://www.rfc-editor.org/info/rfc4861>. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007, <http://www.rfc-editor.org/info/rfc4862>. [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, September 2011, <http://www.rfc-editor.org/info/rfc6282>. [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. Bormann, "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC 6775, DOI 10.17487/RFC6775, November 2012, <http://www.rfc-editor.org/info/rfc6775>. [RFC7136] Carpenter, B. and S. Jiang, "Significance of IPv6 Interface Identifiers", RFC 7136, DOI 10.17487/RFC7136, February 2014, <http://www.rfc-editor.org/info/rfc7136>.
5.2. Informative References
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[IEEE802] IEEE, "IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture", IEEE 802, DOI 10.1109/ieeestd.2002.93395, <http://ieeexplore.ieee.org/servlet/opac?punumber=7732>.[IEEE802.15.4]
IEEE, "IEEE Standard for Local and metropolitan area networks--Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs)", IEEE 802.15.4, DOI 10.1109/ieeestd.2011.6012487, <http://ieeexplore.ieee.org/servlet/ opac?punumber=6012485>. [RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July 2003, <http://www.rfc-editor.org/info/rfc3315>. [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September 2003, <http://www.rfc-editor.org/info/rfc3610>. [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, DOI 10.17487/RFC3633, December 2003, <http://www.rfc-editor.org/info/rfc3633>. [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, DOI 10.17487/RFC3972, March 2005, <http://www.rfc-editor.org/info/rfc3972>. [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, <http://www.rfc-editor.org/info/rfc4193>. [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, DOI 10.17487/RFC4903, June 2007, <http://www.rfc-editor.org/info/rfc4903>. [RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007, <http://www.rfc-editor.org/info/rfc4941>. [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, <http://www.rfc-editor.org/info/rfc4944>. [RFC5535] Bagnulo, M., "Hash-Based Addresses (HBA)", RFC 5535, DOI 10.17487/RFC5535, June 2009, <http://www.rfc-editor.org/info/rfc5535>. [RFC7217] Gont, F., "A Method for Generating Semantically Opaque Interface Identifiers with IPv6 Stateless Address Autoconfiguration (SLAAC)", RFC 7217, DOI 10.17487/RFC7217, April 2014, <http://www.rfc-editor.org/info/rfc7217>.
Acknowledgements
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The Bluetooth, Bluetooth Smart, and Bluetooth Smart Ready marks are registered trademarks owned by Bluetooth SIG, Inc.
Carsten Bormann, Samita Chakrabarti, Niclas Comstedt, Alissa Cooper, Elwyn Davies, Brian Haberman, Marcel De Kogel, Jouni Korhonen, Chris Lonvick, Erik Nordmark, Erik Rivard, Dave Thaler, Pascal Thubert, Xavi Vilajosana, and Victor Zhodzishsky provided valuable feedback for this document.
The authors would like to give special acknowledgements to Krishna Shingala, Frank Berntsen, and Bluetooth SIG's Internet Working Group for providing significant feedback and improvement proposals for this document.
Carles Gomez has been supported in part by the Spanish Government Ministerio de Economia y Competitividad through project TEC2012-32531, and FEDER.
Johanna Nieminen worked on this RFC in 2011-2012 while at Nokia and would like to thank Nokia for supporting the project.
Contributors
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Kanji Kerai, Jari Mutikainen, David Canfeng-Chen, and Minjun Xi from Nokia contributed significantly to this document.
Authors' Addresses
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Johanna Nieminen
TeliaSoneraEmail: johannamaria.nieminen@gmail.com Teemu Savolainen Nokia Visiokatu 3 Tampere 33720 Finland Email: teemu.savolainen@nokia.com
Markus Isomaki
Nokia
Karaportti 2-4
Espoo 02610
FinlandEmail: markus.isomaki@nokia.com Basavaraj Patil AT&T 1410 East Renner Road Richardson, TX 75082 United States Email: basavaraj.patil@att.com Zach Shelby ARM 150 Rose Orchard Way San Jose, CA 95134 United States Email: zach.shelby@arm.com Carles Gomez Universitat Politecnica de Catalunya/i2CAT C/Esteve Terradas, 7 Castelldefels 08860 Spain Email: carlesgo@entel.upc.edu