Transmission of IPv6 Packets over Near Field Communication

NFC is a set of short-range wireless technologies, typically requiring a distance of 10 cm or less. NFC operates at 13.56 MHz on ISO/IEC 18000-3 air interface and at rates ranging from 106 kbit/s to 424 kbit/s. NFC always involves an initiator and a target; the initiator actively generates an RF field that can power a passive target. This enables NFC targets to take very simple form factors such as tags, stickers, key fobs, or cards that do not require batteries. NFC peer-to-peer communication is possible, provided both devices are powered. NFC builds upon RFID systems by allowing two-way communication between endpoints, where earlier systems such as contactless smart cards were one-way only. It has been used in devices such as mobile phones, running Android operating system, named with a feature called "Android Beam". In addition, it is expected for the other mobile phones, running the other operating systems (e.g., iOS, etc.) to be equipped with NFC technology in the near future. Considering the potential for exponential growth in the number of heterogeneous air interface technologies, NFC would be widely used as one of the other air interface technologies, such as Bluetooth Low Energy (BT-LE), Wi-Fi, and so on. Each of the heterogeneous air interface technologies has its own characteristics, which cannot be covered by the other technologies, so various kinds of air interface technologies would co-exist together. Therefore, it is required for them to communicate with each other. NFC also has the strongest ability (e.g., secure communication distance of 10 cm) to prevent a third party from attacking privacy. When the number of devices and things having different air interface technologies communicate with each other, IPv6 is an ideal internet protocols owing to its large address space. Also, NFC would be one of the endpoints using IPv6. Therefore, this document describes how IPv6 is transmitted over NFC using 6LoWPAN techniques. RFC4944 specifies the transmission of IPv6 over IEEE 802.15.4. The NFC link also has similar characteristics to that of IEEE 802.15.4. Many of the mechanisms defined in RFC 4944 can be applied to the transmission of IPv6 on NFC links. This document specifies the details of IPv6 transmission over NFC links.

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 .

NFC technology enables simple and safe two-way interactions between electronic devices, allowing consumers to perform contactless transactions, access digital content, and connect electronic devices with a single touch. NFC complements many popular consumer level wireless technologies, by utilizing the key elements in existing standards for contactless card technology (ISO/IEC 14443 A&B and JIS-X 6319-4). NFC can be compatible with existing contactless card infrastructure and it enables a consumer to utilize one device across different systems. Extending the capability of contactless card technology, NFC also enables devices to share information at a distance that is less than 10 cm with a maximum communication speed of 424 kbps. Users can share business cards, make transactions, access information from a smart poster or provide credentials for access control systems with a simple touch. NFC's bidirectional communication ability is ideal for establishing connections with other technologies by the simplicity of touch. In addition to the easy connection and quick transactions, simple data sharing is also available.

NFC-enabled devices are unique in that they can support three modes of operation: card emulation, peer-to-peer, and reader/writer. Peer-to-peer mode enables two NFC-enabled devices to communicate with each other to exchange information and share files, so that users of NFC-enabled devices can quickly share contact information and other files with a touch. Therefore, an NFC-enabled device can securely send IPv6 packets to any corresponding node on the Internet when an NFC-enabled gateway is linked to the Internet.

IP can use the services provided by the Logical Link Control Protocol (LLCP) in the NFC stack to provide reliable, two-way transport of information between the peer devices. depicts the NFC P2P protocol stack with IPv6 bindings to LLCP. For data communication in IPv6 over NFC, an IPv6 packet SHALL be passed down to LLCP of NFC and transported to an Information Field in Protocol Data Unit (I PDU) of LLCP of the NFC-enabled peer device. LLCP does not support fragmentation and reassembly. For IPv6 addressing or address configuration, LLCP SHALL provide related information, such as link layer addresses, to its upper layer. The LLCP to IPv6 protocol binding SHALL transfer the SSAP and DSAP value to the IPv6 over NFC protocol. SSAP stands for Source Service Access Point, which is a 6-bit value meaning a kind of Logical Link Control (LLC) address, while DSAP means an LLC address of the destination NFC-enabled device.

| | | | Application Layer | Upper Layer Protocols | Transport Layer | | Network Layer | | | +----------------------------------------+ <------------------ | IPv6-LLCP Binding | | +----------------------------------------+ NFC | | Logical Link | Logical Link Control Protocol | Layer | (LLCP) | | +----------------------------------------+ <------------------ | | | | Activities | | | Digital Protocol | NFC | | Physical +----------------------------------------+ Layer | | | | RF Analog | | | | | +----------------------------------------+ <------------------ The LLCP consists of Logical Link Control (LLC) and MAC Mapping. The MAC Mapping integrates an existing RF protocol into the LLCP architecture. The LLC contains three components, such as Link Management, Connection-oriented Transport, and Connection-less Transport. The Link Management component is responsible for serializing all connection-oriented and connection-less LLC PDU (Protocol Data Unit) exchanges and for aggregation and disaggregation of small PDUs. This component also guarantees asynchronous balanced mode communication and provides link status supervision by performing the symmetry procedure. The Connection-oriented Transport component is responsible for maintaining all connection-oriented data exchanges including connection set-up and termination. The Connectionless Transport component is responsible for handling unacknowledged data exchanges.

According to NFCForum-TS-LLCP_1.3, NFC-enabled devices have two types of 6-bit addresses (i.e., SSAP and DSAP) to identify service access points. The several service access points can be installed on a NFC device. However, the SSAP and DSAP can be used as identifiers for NFC link connections with the IPv6 over NFC adaptation layer. Therefore, the SSAP can be used to generate an IPv6 interface identifier. Address values between 00h and 0Fh of SSAP and DSAP are reserved for identifying the well-known service access points, which are defined in the NFC Forum Assigned Numbers Register. Address values between 10h and 1Fh SHALL be assigned by the local LLC to services registered by local service environment. In addition, address values between 20h and 3Fh SHALL be assigned by the local LLC as a result of an upper layer service request. Therefore, the address values between 20h and 3Fh can be used for generating IPv6 interface identifiers.

As mentioned in , an IPv6 packet SHALL passed down to LLCP of NFC and transported to an Unnumbered Information Protocol Data Unit (UI PDU) and an Information Field in Protocol Data Unit (I PDU) of LLCP of the NFC-enabled peer device. The information field of an I PDU SHALL contain a single service data unit. The maximum number of octets in the information field is determined by the Maximum Information Unit (MIU) for the data link connection. The default value of the MIU for I PDUs SHALL be 128 octets. The local and remote LLCs each establish and maintain distinct MIU values for each data link connection endpoint. Also, an LLC MAY announce a larger MIU for a data link connection by transmitting an MIUX extension parameter within the information field. If no MIUX parameter is transmitted, the default MIU value of 128 SHALL be used. Otherwise, the MTU size in NFC LLCP SHALL calculate the MIU value as follows:

MIU = 128 + MIUX. When the MIUX parameter is encoded as a TLV, the TLV Type field SHALL be 0x02 and the TLV Length field SHALL be 0x02. The MIUX parameter SHALL be encoded into the least significant 11 bits of the TLV Value field. The unused bits in the TLV Value field SHALL be set to zero by the sender and SHALL be ignored by the receiver. However, a maximum value of the TLV Value field can be 0x7FF, and a maximum size of the MTU in NFC LLCP is 2176 bytes.

NFC technology also has considerations and requirements owing to low power consumption and allowed protocol overhead. 6LoWPAN standards RFC 4944, RFC 6775, and RFC 6282 provide useful functionality for reducing overhead which can be applied to NFC. This functionality consists of link-local IPv6 addresses and stateless IPv6 address auto-configuration (see ), Neighbor Discovery (see ) and header compression (see ).

illustrates IPv6 over NFC. Upper layer protocols can be transport layer protocols (TCP and UDP), application layer protocols, and others capable running on top of IPv6.

In the case of BT-LE, the Logical Link Control and Adaptation Protocol (L2CAP) supports fragmentation and reassembly (FAR) functionality; therefore, the adaptation layer for IPv6 over BT-LE does not have to conduct the FAR procedure. The NFC LLCP, in contrast, does not support the FAR functionality, so IPv6 over NFC needs to consider the FAR functionality, defined in RFC 4944. However, the MTU on an NFC link can be configured in a connection procedure and extended enough to fit the MTU of IPv6 packet (see ). The NFC link between two communicating devices is considered to be a point-to-point link only. Unlike in BT-LE, an NFC link does not support a star topology or mesh network topology but only direct connections between two devices. Furthermore, the NFC link layer does not support packet forwarding in link layer. Due to this characteristics, 6LoWPAN functionalities, such as addressing and auto-configuration, and header compression, need to be specialized into IPv6 over NFC.

An NFC-enabled device (i.e., 6LN) performs stateless address autoconfiguration as per RFC 4862. A 64-bit Interface identifier (IID) for an NFC interface is formed by utilizing the 6-bit NFC LLCP address (see ). In the viewpoint of address configuration, such an IID SHOULD guarantee a stable IPv6 address because each data link connection is uniquely identified by the pair of DSAP and SSAP included in the header of each LLC PDU in NFC. Following the guidance of RFC 7136, interface identifiers of all unicast addresses for NFC-enabled devices are 64 bits long and constructed in a modified EUI-64 format as shown in .

0 1 3 4 6 0 6 2 8 3 +----------------+----------------+----------------+-----------------+ |RRRRRRuRRRRRRRRR|RRRRRRRR11111111|11111110RRRRRRRR|RRRRRRRRRRRRRRRRR| +----------------+----------------+----------------+-----------------+ The 'R' bits are output values which MAY be created by mechanisms like hash functions with input values, i.e., the SSAP and other values (e.g., a prefix and a nonce) because the 6-bit address of SSAP is easy and short to be targeted by attacks of third party (e.g., address scanning). shows an example for IID creation. The F() means a mechanism to make a output value for 64-bit IID, and an parameter, "nonce" is an example input value for making the different output values.

IID = F( SHA-256(6-bit SSAP, 64-bit Prefix), 'u' bit, nonce ) In addition, the "Universal/Local" bit (i.e., the 'u' bit) of an NFC-enabled device address MUST be set to 0 RFC 4291.

Only if the NFC-enabled device address is known to be a public address, the "Universal/Local" bit be set to 1. The IPv6 link-local address for an NFC-enabled device is formed by appending the IID, to the prefix FE80::/64, as depicted in .

0 0 0 1 0 1 6 2 0 0 4 7 +----------+------------------+----------------------------+ |1111111010| zeros | Interface Identifier | +----------+------------------+----------------------------+ | | | <---------------------- 128 bits ----------------------> | | | The tool for a 6LBR to obtain an IPv6 prefix for numbering the NFC network is can be accomplished via DHCPv6 Prefix Delegation (RFC 3633).

Neighbor Discovery Optimization for 6LoWPANs (RFC 6775) describes the neighbor discovery approach in several 6LoWPAN topologies, such as mesh topology. NFC does not support a complicated mesh topology but only a simple multi-hop network topology or directly connected peer-to-peer network. Therefore, the following aspects of RFC 6775 are applicable to NFC: In a case that an NFC-enabled device (6LN) is directly connected to a 6LBR, an NFC 6LN MUST register its address with the 6LBR by sending a Neighbor Solicitation (NS) message with the Address Registration Option (ARO) and process the Neighbor Advertisement (NA) accordingly. In addition, if DHCPv6 is used to assign an address, Duplicate Address Detection (DAD) MAY not be required. For sending Router Solicitations and processing Router Advertisements the NFC 6LNs MUST follow Sections 5.3 and 5.4 of RFC 6775.

All IPv6-over-NFC encapsulated datagrams are prefixed by an encapsulation header stack consisting of a Dispatch value followed by zero or more header fields. The only sequence currently defined for IPv6-over-NFC is the LOWPAN_IPHC header followed by payload, as depicted in .

+---------------+---------------+--------------+ | IPHC Dispatch | IPHC Header | Payload | +---------------+---------------+--------------+ The dispatch value may be treated as an unstructured namespace. Only a single pattern is used to represent current IPv6-over-NFC functionality.

Header compression as defined in RFC 6282, which specifies the compression format for IPv6 datagrams on top of IEEE 802.15.4, is REQUIRED in this document as the basis for IPv6 header compression on top of NFC. All headers MUST be compressed according to RFC 6282 encoding formats. Therefore, IPv6 header compression in RFC 6282 MUST be implemented. Further, implementations MAY also support Generic Header Compression (GHC) of RFC 7400. If a 16-bit address is required as a short address, it MUST be formed by padding the 6-bit NFC link-layer (node) address to the left with zeros as shown in .

0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding(all zeros)| NFC Addr. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

NFC provides fragmentation and reassembly (FAR) for payloads from 128 bytes up to 2176 bytes as mentioned in . The MTU of a general IPv6 packet can fit into a single NFC link frame. Therefore, the FAR functionality as defined in RFC 4944, which specifies the fragmentation methods for IPv6 datagrams on top of IEEE 802.15.4, MAY NOT be required as the basis for IPv6 datagram FAR on top of NFC. The NFC link connection for IPv6 over NFC MUST be configured with an equivalent MIU size to fit the MTU of IPv6 Packet. If NFC devices support extension of the MTU, the MIUX value is 0x480 in order to fit the MTU (1280 bytes) of a IPv6 packet.

The address resolution procedure for mapping IPv6 non-multicast addresses into NFC link-layer addresses follows the general description in Section 7.2 of RFC 4861, unless otherwise specified. The Source/Target link-layer Address option has the following form when the addresses are 6-bit NFC link-layer (node) addresses.

0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- Padding (all zeros) -+ | | +- +-+-+-+-+-+-+ | | NFC Addr. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Option fields: Type: 1: for Source Link-layer address. 2: for Target Link-layer address. Length: This is the length of this option (including the type and length fields) in units of 8 octets. The value of this field is 1 for 6-bit NFC node addresses. NFC address: The 6-bit address in canonical bit order. This is the unicast address the interface currently responds to.

All IPv6 multicast packets MUST be sent to NFC Destination Address, 0x3F (broadcast) and be filtered at the IPv6 layer. When represented as a 16-bit address in a compressed header, it MUST be formed by padding on the left with a zero. In addition, the NFC Destination Address, 0x3F, MUST NOT be used as a unicast NFC address of SSAP or DSAP.

0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Padding(all zeros)|1 1 1 1 1 1| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

As two typical scenarios, the NFC network can be isolated and connected to the Internet.

One of the key applications of using IPv6 over NFC is securely transmitting IPv6 packets because the RF distance between 6LN and 6LBR is typically within 10 cm. If any third party wants to hack into the RF between them, it must come to nearly touch them. Applications can choose which kinds of air interfaces (e.g., BT-LE, Wi-Fi, NFC, etc.) to send data depending on the characteristics of the data. illustrates an example of an NFC-enabled device network connected to the Internet. The distance between 6LN and 6LBR is typically 10 cm or less. If there is any laptop computers close to a user, it will become the a 6LBR. Additionally, when the user mounts an NFC-enabled air interface adapter (e.g., portable NFC dongle) on the close laptop PC, the user's NFC-enabled device (6LN) can communicate with the laptop PC (6LBR) within 10 cm distance.

In some scenarios, the NFC-enabled device network may transiently be a simple isolated network as shown in the .

6LN ---------------------- 6LR ---------------------- 6LN | (10 cm or less) | (10 cm or less) | | | | | <--------- NFC --------> | <--------- NFC --------> | | (IPv6 over NFC packet) | (IPv6 over NFC packet) | In mobile phone markets, applications are designed and made by user developers. They may image interesting applications, where three or more mobile phones touch or attach each other to accomplish outstanding performance.

There are no IANA considerations related to this document.

When interface identifiers (IIDs) are generated, devices and users are required to consider mitigating various threats, such as correlation of activities over time, location tracking, device-specific vulnerability exploitation, and address scanning. IPv6-over-NFC is, in practice, not used for long-lived links for big size data transfer or multimedia streaming, but used for extremely short-lived links (i.e., single touch-based approaches) for ID verification and mobile payment. This will mitigate the threat of correlation of activities over time. IPv6-over-NFC uses an IPv6 interface identifier formed from a "Short Address" and a set of well-known constant bits (such as padding with '0's) for the modified EUI-64 format. However, the short address of NFC link layer (LLC) is not generated as a physically permanent value but logically generated for each connection. Thus, every single touch connection can use a different short address of NFC link with an extremely short-lived link. This can mitigate address scanning as well as location tracking and device-specific vulnerability exploitation. However, malicious tries for one connection of a long-lived link with NFC technology are not secure, so the method of deriving interface identifiers from 6-bit NFC Link layer addresses is intended to preserve global uniqueness when it is possible. Therefore, it requires a way to protect from duplication through accident or forgery and to define a way to include sufficient bit of entropy in the IPv6 interface identifier, such as random EUI-64.

We are grateful to the members of the IETF 6lo working group. Michael Richardson, Suresh Krishnan, Pascal Thubert, Carsten Bormann, and Alexandru Petrescu have provided valuable feedback for this draft.