| 6Lo Working Group | Y. Choi, Ed. |
| Internet-Draft | Y-G. Hong |
| Intended status: Standards Track | ETRI |
| Expires: January 9, 2020 | J-S. Youn |
| Dongeui Univ | |
| D-K. Kim | |
| KNU | |
| J-H. Choi | |
| Samsung Electronics Co., | |
| July 8, 2019 |
Transmission of IPv6 Packets over Near Field Communication
draft-ietf-6lo-nfc-15
Near field communication (NFC) is a set of standards for smartphones and portable devices to establish radio communication with each other by touching them together or bringing them into proximity, usually no more than 10 cm apart. NFC standards cover communications protocols and data exchange formats, and are based on existing radio-frequency identification (RFID) standards including ISO/IEC 14443 and FeliCa. The standards include ISO/IEC 18092 and those defined by the NFC Forum. The NFC technology has been widely implemented and available in mobile phones, laptop computers, and many other devices. This document describes how IPv6 is transmitted over NFC using 6LoWPAN techniques.
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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 [ECMA-340]. 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. At the time of this writing, it has been used in devices such as mobile phones, running Android operating system, named with a feature called "Android Beam". It is expected for the other mobile phones, running other operating systems (e.g., iOS, etc.) to be equipped with NFC technology in the near future.
Considering exponential growth in the number of heterogeneous air interface technologies, NFC has been widely used like 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. NFC can provide secured communications with its short transmission range.
When the number of devices and things having different air interface technologies communicate with each other, IPv6 is an ideal internet protocol 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 [RFC4944] 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", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
NFC enables simple and two-way interaction between two 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-enabled devices are unique in that they can support three modes of operation: card emulation, peer-to-peer, and reader/writer. Only peer-to-peer in the three modes 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, the peer mode is used for ipv6-over-nfc. In addition, NFC-enabled devices can securely send IPv6 packets in wireless range 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 transmission of information between the peer devices. Figure 1 depicts the NFC P2P protocol stack with IPv6 bindings to LLCP.
For data communication in IPv6 over NFC, an IPv6 packet MUST be passed down to LLCP of NFC and transported to an Information (I) and an Unnumbered Information (UI) Field in Protocol Data Unit (PDU) of LLCP of the NFC-enabled peer device. LLCP does not support fragmentation and reassembly. For IPv6 addressing or address configuration, LLCP MUST provide related information, such as link layer addresses, to its upper layer. The LLCP to IPv6 protocol binding MUST 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 | |
| | |
+----------------------------------------+ ------------------
Figure 1: Protocol Stacks of NFC
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 Transmission, and Connection-less Transmission. 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. The Connection-oriented Transmission component is responsible for maintaining all connection-oriented data exchanges including connection set-up and termination. The Connectionless Transmission component is responsible for handling unacknowledged data exchanges.
According to NFC Logical Link Control Protocol v1.3, 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 are assigned by the local LLC to services registered by local service environment. In addition, address values between 20h and 3Fh are 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 Section 3.2, an IPv6 packet MUST be 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 contains 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 is 128 octets. The local and remote LLCs each establish and maintain distinct MIU values for each data link connection endpoint. Also, an LLC is 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 MIU value is 128 bytes. Otherwise, the MTU size in NFC LLCP MUST be calculated from the MIU value as follows:
MTU = MIU = 128 + MIUX.
According to [LLCP-1.3], Figure 2 shows an example of the MIUX parameter TLV. Each of TLV Type and TLV Length field is 1 byte, and TLV Value field is 2 bytes.
0 0 1 2 3
0 8 6 2 1
+----------+----------+------+-----------+
| Type | Length | Value |
+----------+----------+------+-----------+
| 00000010 | 00000010 | 1011 | 0x0~0x7FF |
+----------+----------+------+-----------+
Figure 2: Example of MIUX Parameter TLV
When the MIUX parameter is encoded as a TLV option, the TLV Type field MUST be 0x02 and the TLV Length field MUST be 0x02. The MIUX parameter MUST be encoded into the least significant 11 bits of the TLV Value field. The unused bits in the TLV Value field MUST be set to zero by the sender and ignored by the receiver. A maximum value of the TLV Value field can be 0x7FF, and a maximum size of the MTU in NFC LLCP is 2176 bytes including the 128 byte default of MIU. This value MUST be 0x480 to cover MTU of IPV6 if FAR is not used in IPv6 over NFC.
NFC technology also has considerations and requirements owing to low power consumption and allowed protocol overhead. 6LoWPAN standards [RFC4944], [RFC6775], and [RFC6282] 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 Section 4.3), Neighbor Discovery (see Section 4.5) and header compression (see Section 4.7).
Figure 3 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.
| |
| Upper Layer Protocols |
+----------------------------------------+
| IPv6 |
+----------------------------------------+
| Adaptation Layer for IPv6 over NFC |
+----------------------------------------+
| NFC Link Layer |
+----------------------------------------+
| NFC Physical Layer |
+----------------------------------------+
Figure 3: Protocol Stacks for IPv6 over NFC
The adaptation layer for IPv6 over NFC support neighbor discovery, stateless address auto-configuration, header compression, and fragmentation & reassembly.
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 [RFC4944]. 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 Section 4.8).
This document does NOT RECOMMEND using FAR over NFC link. In addition, the implementation for this specification MUST use MIUX extension to communicate the MTU of the link to the peer as defined in Section 3.4.
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 [RFC4862]. A 64-bit Interface identifier (IID) for an NFC interface is formed by utilizing the 6-bit NFC SSAP (see Section 3.3). In the viewpoint of address configuration, such an IID should guarantee a stable IPv6 address during the course of a single connection, 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 [RFC7136], interface identifiers of all unicast addresses for NFC-enabled devices are 64 bits long and constructed by using the generation algorithm of random (but stable) identifier (RID) (see Figure 4).
0 1 3 4 6
0 6 2 8 3
+---------+---------+---------+---------+
| Random (but stable) Identifier (RID) |
+---------+---------+---------+---------+
Figure 4: IID from NFC-enabled device
The RID is an output which is created by the algorithm, F() with input parameters. One of the parameters is Net_IFace, and NFC Link Layer address (i.e., SSAP) is a source of the NetIFace parameter. The 6-bit address of SSAP of NFC is easy and short to be targeted by attacks of third party (e.g., address scanning). The F() can provide secured and stable IIDs for NFC-enabled devices. In addition, an optional parameter, Network_ID is used to increase the randomness of the generated IID.
The IPv6 link-local address for an NFC-enabled device is formed by appending the IID, to the prefix FE80::/64, as depicted in Figure 5.
0 0 0 1
0 1 6 2
0 0 4 7
+----------+------------------+----------------------------+
|1111111010| zeros | Interface Identifier |
+----------+------------------+----------------------------+
| |
| <---------------------- 128 bits ----------------------> |
| |
Figure 5: IPv6 link-local address in NFC
The tool for a 6LBR to obtain an IPv6 prefix for numbering the NFC network can be accomplished via DHCPv6 Prefix Delegation ([RFC3633]). The "Interface Identifier" is used the secured and stable IIDs for NFC-enabled devices.
Neighbor Discovery Optimization for 6LoWPANs ([RFC6775]) 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:
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 Figure 6.
+---------------+---------------+--------------+
| IPHC Dispatch | IPHC Header | Payload |
+---------------+---------------+--------------+
Figure 6: A IPv6-over-NFC Encapsulated 6LOWPAN_IPHC Compressed IPv6 Datagram
The dispatch value is treated as an unstructured namespace. Only a single pattern is used to represent current IPv6-over-NFC functionality.
+------------+--------------------+-----------+
| Pattern | Header Type | Reference |
+------------+--------------------+-----------+
| 01 1xxxxx | 6LOWPAN_IPHC | [RFC6282] |
+------------+--------------------+-----------+
Figure 7: Dispatch Values
Other IANA-assigned 6LoWPAN Dispatch values do not apply to this specification.
Header compression as defined in [RFC6282], 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 [RFC6282] MUST be implemented. Further, implementations MUST also support Generic Header Compression (GHC) of [RFC7400].
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 Figure 8.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding(all zeros)| NFC Addr. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: NFC short address format
IPv6-over-NFC MUST NOT use fragmentation and reassembly (FAR) for the payloads as discussed in Section 3.4. The NFC link connection for IPv6 over NFC MUST be configured with an equivalent MIU size to fit the MTU of IPv6 Packet. The MIUX value is 0x480 in order to fit the MTU (1280 bytes) of a IPv6 packet if NFC devices support extension of the MTU. However, if the NFC device does not support extension, IPv6-over-NFC uses FAR with the default MTU (128 bytes), as defined in [RFC4944].
The address resolution procedure for mapping IPv6 non-multicast addresses into NFC link-layer addresses follows the general description in Section 4.6.1 and 7.2 of [RFC4861], 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. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Unicast address mapping
Option fields:
The NFC Link Layer does not support multicast. Therefore, packets are always transmitted by unicast between two NFC-enabled devices. 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.
NFC networks 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.
Figure 10 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 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.
************
6LN ------------------- 6LBR -----* Internet *------- CN
| (dis. 10 cm or less) | ************ |
| | |
| <-------- NFC -------> | <----- IPv6 packet ------> |
| (IPv6 over NFC packet) | |
Figure 10: NFC-enabled device network connected to the Internet
Two or more 6LNs are connected with a 6LBR, but each connection uses a different subnet. The 6LBR is acting as a router and forwarding packets between 6LNs and the Internet. Also, the 6LBR MUST ensure address collisions do not occur and forwards packets sent by one 6LN to another.
In some scenarios, the NFC-enabled device network may transiently be a simple isolated network as shown in the Figure 11.
6LN ---------------------- 6LR ---------------------- 6LN
| (10 cm or less) | (10 cm or less) |
| | |
| <--------- NFC --------> | <--------- NFC --------> |
| (IPv6 over NFC packet) | (IPv6 over NFC packet) |
Figure 11: Isolated NFC-enabled device network
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 work achieve a common objective. In an isolated NFC-enabled device network, when two or more 6LRs are connected with each other, and then they are acting like routers, the 6LR MUST ensure address collisions do not occur.
There are no IANA considerations related to this document.
This document does not RECOMMEND sending NFC packets over the Internet or any unsecured network.
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 uses an IPv6 interface identifier formed from a "Short Address" and a set of well-known constant bits for the modified EUI-64 format. However, NFC applications use short-lived connections, and the every connection is made with different address of NFC link with an extremely short-lived link.
This document does not RECOMMEND sending NFC packets over the Internet or any unsecured network. Especially, there can be a threat model in the scenario of Section 5.1. when the NFC-enabled device links to a NFC-enabled gateway for connectivity with the Internet, the gateway can be attacked. Even though IPv6 over NFC guarantees security between the two NFC devices, there can be another threat during packet forwarding.
We are grateful to the members of the IETF 6lo working group.
Michael Richardson, Suresh Krishnan, Pascal Thubert, Carsten Bormann, Alexandru Petrescu, James Woodyatt, Dave Thaler, Samita Chakrabarti, and Gabriel Montenegro have provided valuable feedback for this draft.