| 6Lo Working Group | C. Gomez |
| Internet-Draft | S. Darroudi |
| Intended status: Standards Track | Universitat Politecnica de Catalunya |
| Expires: January 3, 2019 | T. Savolainen |
| DarkMatter | |
| M. Spoerk | |
| Graz University of Technology | |
| July 2, 2018 |
IPv6 Mesh over BLUETOOTH(R) Low Energy using IPSP
draft-ietf-6lo-blemesh-03
RFC 7668 describes the adaptation of 6LoWPAN techniques to enable IPv6 over Bluetooth low energy networks that follow the star topology. However, recent Bluetooth specifications allow the formation of extended topologies as well. This document specifies the mechanisms needed to enable IPv6 over mesh networks composed of Bluetooth low energy links established by using the Bluetooth Internet Protocol Support Profile.
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This Internet-Draft will expire on January 3, 2019.
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Bluetooth low energy (hereinafter, Bluetooth LE) was first introduced in the Bluetooth 4.0 specification. Bluetooth LE (which has been marketed as Bluetooth Smart) is a low-power wireless technology designed for short-range control and monitoring applications. Bluetooth LE is currently implemented in a wide range of consumer electronics devices, such as smartphones and wearable devices. Given the high potential of this technology for the Internet of Things, the Bluetooth Special Interest Group (Bluetooth SIG) and the IETF have produced specifications in order to enable IPv6 over Bluetooth LE, such as the Internet Protocol Support Profile (IPSP) [IPSP], and RFC 7668, respectively. Bluetooth 4.0 only supports Bluetooth LE networks that follow the star topology. In consequence, RFC 7668 was specifically developed and optimized for that type of network topology. However, subsequent Bluetooth specifications allow the formation of extended topologies [BTCorev4.1], such as the mesh topology. The functionality described in RFC 7668 is not sufficient and would fail to enable IPv6 over mesh networks composed of Bluetooth LE links. This document specifies the mechanisms needed to enable IPv6 over mesh networks composed of Bluetooth LE links. This specification also allows to run IPv6 over Bluetooth LE star topology networks, albeit without all the topology-specific optimizations contained in RFC 7668.
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.
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) can both be adopted by a 6LN, a 6LR or a 6LBR.
Bluetooth LE defines two Generic Access Profile (GAP) roles of relevance herein: the Bluetooth LE central role and the Bluetooth LE peripheral role. A device in the central role, which is 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 hereinafter. Bluetooth 4.1 introduced the possibility for a peripheral to be connected to more than one central simultaneously, therefore allowing extended topologies beyond the star topology for a Bluetooth LE network. In addition, a device may simultaneously be a central in a set of link layer connections, as well as a peripheral in others. On the other hand, the IPSP enables discovery of IP-enabled devices and the establishment of a link layer connection for transporting IPv6 packets. The IPSP defines the Node and Router roles for devices that consume/originate IPv6 packets and for devices that can route IPv6 packets, respectively. Consistently with Bluetooth 4.1, a device may implement both roles simultaneously.
This document assumes a mesh network composed of Bluetooth LE links, where link layer connections are established between neighboring IPv6-enabled devices (see Section 3.3.2, item 3.b)). The IPv6 forwarding devices of the mesh have to implement both Node and Router roles, while simpler leaf-only nodes can implement only the Node role. In an IPv6-enabled mesh of Bluetooth LE links, a node is a neighbor of another node, and vice versa, if a link layer connection has been established between both by using the IPSP functionality for discovery and link layer connection establishment for IPv6 packet transport.
+------------------------------------+
| Application |
+---------+ +------------------------------------+
| IPSS | | UDP/TCP/other |
+---------+ +------------------------------------+
| GATT | | IPv6 |routing| |
+---------+ +------------------------------------+
| ATT | | 6Lo for IPv6 mesh over Bluetooh LE |
+---------+--+------------------------------------+
| Bluetooth LE L2CAP |
- - +-------------------------------------------------+- - - HCI
| Bluetooth LE Link Layer |
+-------------------------------------------------+
| Bluetooth LE Physical |
+-------------------------------------------------+
Figure 1: Protocol stack for IPv6 mesh over Bluetooth LE.
Figure 1 illustrates the protocol stack for IPv6 mesh over Bluetooth LE networks. There are two main differences with the IPv6 over Bluetooth LE stack in RFC 7668: a) the adaptation layer below IPv6 (labelled as "6Lo for IPv6 mesh of Bluetooth LE") is now adapted for mesh networks of Bluetooth LE links, and b) the protocol stack for IPv6 mesh networks of Bluetooth LE links includes IPv6 routing functionality.
/
.--------------------------------. /
/ 6LR 6LN 6LN \ /
/ \ \ \ \ /
| \ \ \ | /
| 6LN ----- 6LR --------- 6LR ------ 6LBR ----- | Internet
| <--Link--> <---Link--->/<--Link->/ | |
\ / / / \
\ 6LN ---- 6LR ----- 6LR / \
'--------------------------------' \
\
<------------ Subnet -----------------><---- IPv6 connection -->
to the Internet
Figure 2: Example of an IPv6 mesh over a Bluetooth LE network connected to the Internet
For IPv6 mesh over Bluetooth LE, a multilink model has been chosen, as further illustrated in Figure 2. 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 this specification, 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].
One or more 6LBRs are connected to the Internet. 6LNs are connected to the network through a 6LR or a 6LBR. A prefix is used on the whole subnet.
IPv6 mesh networks over Bluetooth LE MUST follow a route-over approach. This document does not specify the routing protocol to be used in an IPv6 mesh over Bluetooth LE.
6LN, 6LR and 6LBR IPv6 addresses in an IPv6 mesh over Bluetooth LE are configured as per section 3.2.2 of RFC 7668.
Multihop DAD functionality as defined in section 8.2 of RFC 6775, or some substitute mechanism (see section 3.3.2), MUST be supported.
'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. The route-over functionality of RFC 6775 MUST be supported.
The following aspects of the Neighbor Discovery optimizations [RFC6775] are applicable to Bluetooth LE 6LNs:
1. A Bluetooth LE 6LN MUST NOT register its link-local address. A Bluetooth LE host MUST register its non-link-local addresses with its routers 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. The ARO option requires use of an EUI-64 identifier [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].
If the 6LN registers for a same compression context multiple addresses that are not based on Bluetooth device address, the header compression efficiency will decrease.
2. For sending Router Solicitations and processing Router Advertisements the Bluetooth LE hosts MUST, respectively, follow Sections 5.3 and 5.4 of the [RFC6775].
3. The router behavior for 6LRs and 6LBRs is described in Section 6 of RFC 6775. However, as per this specification: a) Routers SHALL NOT use multicast NSs to discover other routers' link layer addresses. b) As per section 6.2 of RFC 6775, in a dynamic configuration scenario, a 6LR comes up as a non-router and waits to receive a Router Advertisement for configuring its own interface address first, before setting its interfaces to be advertising interfaces and turning into a router. In order to support such operation in an IPv6-enabled mesh of Bluetooth LE links, a 6LR first uses the IPSP Node role only. Once the 6LR has established a connection with another node previously running as a router, and receives a Router Advertisement from that router, the 6LR configures its own interface address, it turns into a router, and it runs as an IPSP Router. A 6LBR uses the IPSP Router role since the 6LBR is initialized. See an example in the Appendix.
4. Border router behavior is described in Section 7 of RFC 6775.
RFC 6775 defines substitutable mechanisms for distributing prefixes and context information (section 8.1 of RFC 6775), as well as for Duplicate Address Detection across a route-over 6LoWPAN (section 8.2 of RFC 6775). Implementations of this specification MUST support the features described in sections 8.1 and 8.2 of RFC 6775 unless some alternative ("substitute") from some other specification is supported.
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 RFC 6282 [RFC6282] encoding formats.
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.
The specific optimizations of RFC 7668 for header compression, which exploit the star topology and ARO, cannot be generalized in a mesh network composed of Bluetooth LE links. Still, a subset of those optimizations can be applied in some cases in such a network. In particular, the latter comprise link-local interactions, non-link- local packet transmissions originated and performed by a 6LN, and non-link-local packets transmitted (but not necessarily originated) by the neighbor of a 6LN to that 6LN. For the rest of packet transmissions, context-based compression MAY be used.
When a device transmits a packet to a neighbor, the sender MUST fully elide the source IID if the source IPv6 address is the link-local address based on the sender's Bluetooth device address (SAC=0, SAM=11). The sender also MUST fully elide the destination IPv6 address if it is the link-local-address based on the neighbor's Bluetooth device address (DAC=0, DAM=11).
When a 6LN transmits a packet, with a non-link-local source address that the 6LN has registered with ARO in the next-hop router 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 (SAC=1, SAM=11). If the source non-link-local address is not the latest registered by the 6LN, then the 64-bits of the IID SHALL be fully carried in-line (SAC=1, SAM=01) or if the first 48-bits of the IID match with the latest address registered by the 6LN, then the last 16-bits of the IID SHALL be carried in-line (SAC=1, SAM=10).
When a router transmits a packet to a neighboring 6LN, with a non-link-local destination address, the router MUST fully elide the destination IPv6 address 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).
The Bluetooth LE Link Layer does not support multicast. Hence, traffic is always unicast between two Bluetooth LE neighboring nodes. If a node needs to send a multicast packet to several neighbors, 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 node is battery powered. A router (i.e. a 6LR or a 6LBR) MUST keep track of neighboring multicast listeners, and it MUST NOT forward multicast packets to neighbors that have not registered as listeners for multicast groups the packets belong to.
There are no IANA considerations related to this document.
The security considerations in RFC 7668 apply.
IPv6 mesh networks over Bluetooth LE require a routing protocol to find end-to-end paths. Unfortunately, the routing protocol may generate additional opportunities for threats and attacks to the network.
RFC 7416 [RFC 7416] provides a systematic overview of threats and attacks on the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL), as well as countermeasures. In that document, described threats and attacks comprise threats due to failures to authenticate, threats due to failure to keep routing information, threats and attacks on integrity, and threats and attacks on availability. Reported countermeasures comprise confidentiality attack, integrity attack, and availability attack countermeasures.
While this specification does not state the routing protocol to be used in IPv6 mesh over Bluetooth LE networks, the guidance of RFC 7416 is useful when RPL is used in such scenarios. Furthermore, such guidance may partly apply for other routing protocols as well.
Carlo Alberto Boano (Graz University of Technology) contributed to the design and validation of this document.
The Bluetooth, Bluetooth Smart and Bluetooth Smart Ready marks are registered trademarks owned by Bluetooth SIG, Inc.
The authors of this document are grateful to all RFC 7668 authors, since this document borrows many concepts (albeit, with necessary extensions) from RFC 7668.
The authors also thank Alain Michaud, Mark Powell and Martin Turon for their comments, which helped improve the document.
Carles Gomez has been supported in part by the Spanish Government Ministerio de Economia y Competitividad through project TEC2012-32531, and FEDER.
This appendix provides an example of Bluetooth LE connection establishment and use of IPSP roles in an IPv6-enabled mesh of Bluetooth LE links that uses dynamic configuration. The example follows text in Section 3.3.2, item 3.b).
The example assumes a network with one 6LBR, two 6LRs and three 6LNs, as shown in Figure 3. Connectivity between the 6LNs and the 6LBR is only possible via the 6LRs.
The following text describes the different steps as time evolves, in the example. Note that other sequences of events that may lead to the same final scenario are also possible.
At the beginning, the 6LBR starts running as an IPSP Router, whereas the rest of devices are not yet initialized (Step 1). Next, the 6LRs start running as IPSP Nodes, i.e., they use Bluetooth LE advertisement packets to announce their presence and support of IPv6 capabilities (Step 2). The 6LBR (already running as an IPSP Router) discovers the presence of the 6LRs and establishes one Bluetooth LE connection with each 6LR (Step 3). After establishment of those link layer connections (and after reception of Router Advertisements from the 6LBR), Step 4, the 6LRs start operating as routers, and also initiate the IPSP Router role (note: whether the IPSP Node role is kept running simultaneously is an implementation decision). Then, 6LNs start running the IPSP Node role (Step 5). Finally, the 6LRs discover presence of the 6LNs and establish connections with the latter (Step 6).
Step 1
******
6LBR
(IPSP: Router)
6LR 6LR
(not initialized) (not initialized)
6LN 6LN 6LN
(not initialized) (not initialized) (not initialized)
Step 2
******
6LBR
(IPSP: Router)
6LR 6LR
(IPSP: Node) (IPSP: Node)
6LN 6LN 6LN
(not initialized) (not initialized) (not initialized)
Step 3
******
6LBR
(IPSP: Router)
Bluetooth LE connection --> / \
/ \
6LR 6LR
(IPSP: Node) (IPSP: Node)
6LN 6LN 6LN
(not initialized) (not initialized) (not initialized)
Step 4
******
6LBR
(IPSP: Router)
/ \
/ \
6LR 6LR
(IPSP: Router) (IPSP: Router)
6LN 6LN 6LN
(not initialized) (not initialized) (not initialized)
Step 5
******
6LBR
(IPSP: Router)
/ \
/ \
6LR 6LR
(IPSP: Router) (IPSP: Router)
6LN 6LN 6LN
(IPSP: Node) (IPSP: Node) (IPSP: Node)
Step 6
******
6LBR
(IPSP: Router)
/ \
/ \
6LR 6LR
(IPSP: Router) (IPSP: Router)
/ \ / \
/ \ / \
/ \ / \
6LN 6LN 6LN
(IPSP: Node) (IPSP: Node) (IPSP: Node)
Figure 3: An example of connection establishment and use of IPSP roles in an IPv6-enabled mesh of Bluetooth LE links.
| [RFC4903] | Thaler, D., "Multi-Link Subnet Issues", RFC 4903, DOI 10.17487/RFC4903, June 2007. |
| [RFC7416] | Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A. and M. Richardson, "A Security Threat Analysis for the Routing Protocol for Low-Power and Lossy Networks (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015. |