Network Working Group G. Montenegro Internet-Draft Microsoft Corporation Intended status: Standards Track N. Kushalnagar Expires: May 11, 2007 Intel Corp J. Hui D. Culler Arch Rock Corp November 7, 2006 Transmission of IPv6 Packets over IEEE 802.15.4 Networks draft-ietf-6lowpan-format-07 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 11, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document describes the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on IEEE 802.15.4 networks. Additional specifications include a simple header compression scheme Montenegro, et al. Expires May 11, 2007 [Page 1] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 using shared context and provisions for packet delivery in IEEE 802.15.4 meshes. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 1.2. Terms used . . . . . . . . . . . . . . . . . . . . . . . . 3 2. IEEE 802.15.4 mode for IP . . . . . . . . . . . . . . . . . . 3 3. Addressing Modes . . . . . . . . . . . . . . . . . . . . . . . 4 4. Maximum Transmission Unit . . . . . . . . . . . . . . . . . . 5 5. LoWPAN Adaptation Layer and Frame Format . . . . . . . . . . . 6 5.1. Link Fragmentation . . . . . . . . . . . . . . . . . . . . 9 5.2. Reassembly . . . . . . . . . . . . . . . . . . . . . . . . 10 6. Stateless Address Autoconfiguration . . . . . . . . . . . . . 11 7. IPv6 Link Local Address . . . . . . . . . . . . . . . . . . . 12 8. Unicast Address Mapping . . . . . . . . . . . . . . . . . . . 12 9. Multicast Address Mapping . . . . . . . . . . . . . . . . . . 14 10. Header Compression . . . . . . . . . . . . . . . . . . . . . . 14 10.1. Encoding of IPv6 Header Fields . . . . . . . . . . . . . . 15 10.2. Encoding of UDP Header Fields . . . . . . . . . . . . . . 17 10.3. Non-Compressed Fields . . . . . . . . . . . . . . . . . . 18 10.3.1. Non-Compressed IPv6 Fields . . . . . . . . . . . . . 18 10.3.2. Non-Compressed and partially compressed UDP fields . 19 11. Frame Delivery in a Link-Layer Mesh . . . . . . . . . . . . . 19 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 13. Security Considerations . . . . . . . . . . . . . . . . . . . 23 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 24 15.1. Normative References . . . . . . . . . . . . . . . . . . . 24 15.2. Informative References . . . . . . . . . . . . . . . . . . 25 Appendix A. Alternatives for Delivery of Frames in a Mesh . . . . 26 Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 29 Intellectual Property and Copyright Statements . . . . . . . . . . 30 Montenegro, et al. Expires May 11, 2007 [Page 2] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 1. Introduction The IEEE 802.15.4 standard [ieee802.15.4] targets low power personal area networks. This document defines the frame format for transmission of IPv6 [RFC2460] packets as well as the formation of IPv6 link-local addresses and statelessly autoconfigured addresses on top of IEEE 802.15.4 networks. Since IPv6 requires support of packet sizes much larger than the largest IEEE 802.15.4 frame size, an adaptation layer is defined. This document also defines mechanisms for header compression required to make IPv6 practical on IEEE 802.15.4 networks, and the provisions required for packet delivery in IEEE 802.15.4 meshes. However, a full specification of mesh routing (the specific protocol used, the interactions with neighbor discovery, etc) is out of scope of this document. 1.1. Requirements notation The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 1.2. Terms used AES: Advanced Encryption Scheme CSMA/CA: Carrier Sense Multiple Access / Collision Avoidance FFD: Full Function Device GTS: Guaranteed Time Service MTU: Maximum Transmission Unit MAC: Media Access Control PAN: Personal Area Network RFD: Reduced Function Device 2. IEEE 802.15.4 mode for IP IEEE 802.15.4 defines four types of frames: beacon frames, MAC command frames, acknowledgement frames and data frames. IPv6 packets MUST be carried on data frames. Data frames may optionally request that they be acknowledged. In keeping with [RFC3819] it is recommended that IPv6 packets be carried in frames for which acknowledgements are requested so as to aid link-layer recovery. IEEE 802.15.4 networks can either be nonbeacon-enabled or beacon- enabled [ieee802.15.4]. The latter is an optional mode in which devices are synchronized by a so-called coordinator's beacons. This allows the use of superframes within which a contention-free Guaranteed Time Service (GTS) is possible. This document does not require that IEEE networks run in beacon-enabled mode. In nonbeacon- Montenegro, et al. Expires May 11, 2007 [Page 3] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 enabled networks, data frames (including those carrying IPv6 packets) are sent via the contention-based channel access method of unslotted CSMA/CA. In nonbeacon-enabled networks, beacons are not used for synchronization. However, they are still useful for link-layer device discovery to aid in association and disassociation events. This document recommends that beacons be configured so as to aid these functions. A further recommendation is for these events to be available at the IPv6 layer to aid in detecting network attachment, a problem being worked on at the IETF at the time of this writing. The specification allows for frames in which either the source or destination addresses (or both) are elided. The mechanisms defined in this document require that both source and destination addresses be included in the IEEE 802.15.4 frame header. The source or destination PAN ID fields may also be included. 3. Addressing Modes IEEE 802.15.4 defines several addressing modes: it allows the use of either IEEE 64-bit extended addresses or (after an association event) 16-bit addresses unique within the PAN [ieee802.15.4]. This document supports both 64-bit extended addresses, and 16-bit short addresses. For use within 6LoWPANs, this document imposes additional constraints (beyond those imposed by IEEE 802.15.4) on the format of the 16-bit short addresses, as specified in Section 12. Short addresses being transient in nature, a word of caution is in order: since they are doled out by the PAN coordinator function during an association event, their validity and uniqueness is limited by the lifetime of that association. This can be cut short by expiration of the association or simply by any mishap occurring to the PAN coordinator. Because of the scalability issues posed by such a centralized allocation and single point of failure at the PAN coordinator, deployers should carefully weigh the tradeoffs (and implement the necessary mechanisms) of growing such networks based on short addresses. Of course, IEEE 64-bit extended addresses may not suffer from these drawbacks, but still share the remaining scalability issues concerning routing, discovery, configuration, etc. This document assumes that a PAN maps to a specific IPv6 link, hence it implies a unique prefix. Knowledge of the 16-bit PAN ID (e.g., by including it in the IEEE 802.15.4 headers) would enable automatically mapping it to the corresponding IPv6 prefix. One possible method is to concatenate the 16 bits of PAN ID to a /48 in order to obtain the 64-bit link prefix. Whichever method is used, the assumption in this document is that a given PAN ID maps to a unique IPv6 prefix. This Montenegro, et al. Expires May 11, 2007 [Page 4] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 complies with the recommendation that shared networks support link- layer subnet [RFC3819] broadcast. Strictly speaking, it is multicast not broadcast that exists in IPv6. However, multicast is not supported natively in IEEE 802.15.4. Hence, IPv6 level multicast packets MUST be carried as link-layer broadcast frames in IEEE 802.15.4 networks. This MUST be done such that the broadcast frames are only heeded by devices within the specific PAN of the link in question. As per section 126.96.36.199 in [ieee802.15.4], this is accomplished as follows: 1. A destination PAN identifier is included in the frame, and it MUST match the PAN ID of the link in question. 2. A short destination address is included in the frame, and it MUST match the broadcast address (0xffff). Additionally, support for mapping of IPv6 multicast addresses MAY be provided as per Section 9. A full specification of such functionality is out of scope of this document. As usual, hosts learn IPv6 prefixes via router advertisements as per [I-D.ietf-ipv6-2461bis]. The working group may pursue additional mechanisms as well. 4. Maximum Transmission Unit The MTU size for IPv6 packets over IEEE 802.15.4 is 1280 octets. However, a full IPv6 packet does not fit in an IEEE 802.15.4 frame. 802.15.4 protocol data units have different sizes depending on how much overhead is present [ieee802.15.4]. Starting from a maximum physical layer packet size of 127 octets (aMaxPHYPacketSize) and a maximum frame overhead of 25 (aMaxFrameOverhead), the resultant maximum frame size at the media access control layer is 102 octets. Link-layer security imposes further overhead, which in the maximum case (21 octets of overhead in the AES-CCM-128 case, versus 9 and 13 for AES-CCM-32 and AES-CCM-64, respectively) leaves only 81 octets available. This is obviously far below the minimum IPv6 packet size of 1280 octets, and in keeping with section 5 of the IPv6 specification [RFC2460], a fragmention and reassembly adaptation layer must be provided at the layer below IP. Such a layer is defined below in Section 5. Furthermore, since the IPv6 header is 40 octets long, this leaves only 41 octets for upper-layer protocols, like UDP. The latter uses 8 octets in the header which leaves only 33 octets for application data. Additionally, as pointed out above, there is a need for a fragmentation and reassembly layer, which will use even more octets. Montenegro, et al. Expires May 11, 2007 [Page 5] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 The above considerations lead to the following two observations: 1. The adaptation layer must be provided to comply with IPv6 requirements of minimum MTU. However, it is expected that (a) most applications of IEEE 802.15.4 will not use such large packets, and (b) small application payloads in conjunction with proper header compression will produce packets that fit within a single IEEE 802.15.4 frame. The justification for this adaptation layer is not just for IPv6 compliance, as it is quite likely that the packet sizes produced by certain application exchanges (e.g., configuration or provisioning) may require a small number of fragments. 2. Even though the above space calculation shows the worst case scenario, it does point out the fact that header compression is compelling to the point of almost being unavoidable. Since we expect that most (if not all) applications of IP over IEEE 802.15.4 will make use of header compression, it is defined below in Section 10. 5. LoWPAN Adaptation Layer and Frame Format All IP datagrams transported over IEEE 802.15.4 are prefixed by an encapsulation header stack with one of the formats illustrated below. Each header in the header stack contains a header type dispatch byte followed zero or more header fields. Whereas in an IPv6 header the stack would contain, in order, addressing options, hop-by-hop options, routing options, fragmentation options, destination options, and finally payload; in a lowpan header the analogous header sequence is mesh (L2 addressing) options, hop-by-hop options (including broadcast), fragmentation options, L3 addressing and upper-layer protocol options (including header compression). Previous version of this Format Draft used an unstacked header layout, which interwove fragmentation, header compression, mesh delivery, and broadcast aspects in a non-orthogonal structure. The stacked header structure offers the same functionality in a simpler, more compact, and more extensible framework. This version the draft preserves the earlier ordering of sections and concepts to maintain greatest continuity. Later versions may revise section ordering for a simpler presentation. Montenegro, et al. Expires May 11, 2007 [Page 6] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 The most basic format consists of a single dispatch byte followed by payload: -------------------- |dispatch |payload | -------------------- A basic datagram using uncompressed IPV6 addresses consists of: --------------------------------- |IPv6 disp| IPv6 header|payload| ---------------------------------- A basic datagram using header compression scheme HC1 consists of: ------------------------------- |HC1 disp|HC1 header|payload| ------------------------------- A Mesh routed, unfragmented datagram HC1 consists of: --------------------------------------------------- |Mesh disp|Mesh header|addressing header| payload | --------------------------------------------------- A unrouted, fragmented datagram consists of --------------------------------------------------- |Frag disp|Frag header|addressing header| payload | --------------------------------------------------- A Mesh routed, fragmented datagram using header compression scheme HC1 consists of: ---------------------------------------------------------------------- |Mesh disp|Mesh header|Frag disp|Frag header|HC1 disp|HC1 hdr|payload| ---------------------------------------------------------------------- A Mesh routed, Broadcast, unfragmented datagram consists of: ----------------------------------------------------------------------- |Mesh disp|Mesh header|BCast Disp | Bcast Hdr | address header|payload| ----------------------------------------------------------------------- If the datagram were fragmented, the fragmentation header would fall between the broadcast and addressing headers. Montenegro, et al. Expires May 11, 2007 [Page 7] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Figure 1: Lowpan Header Stacking For fragmentation and mesh headers, a portion of the header information is provided directly in the dispatch byte. These headers, if present, precede general header dispatch. The format for the three types of headers is as follows. General Header (addressing and all extensions) 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| dispatch | type specific additional header +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Fragmentation Header 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 0| frag | tag, size and offset info +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Mesh Header 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 1| mesh | originator, final, hop info +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: LoWPAN header type formats The dispatch byte may be treated as an unstructured namespace. Only a few symbols are required to represent current lowpan functionality. Although some additional savings could be achieved by encoding additional functionality into the dispatch byte, these measures would tend to constrain the ability to address future alternatives. Pattern Header Type +----------------------------------------------------------+ | 00000000 | NALP - Not-a-Lowpan frame | | 00000001 | IPv6_disp - uncompressed IPv6 Addresses | | 00000010 | HC1_disp - HC1 compressed IPv6 Addresses | | 00001000 | BC0 - Broadcast | | ... | | | 01111111 | ESC - Additional Dispatch byte follows | +----------------------------------------------------------+ Figure 3: Dispatch Type Bit Pattern Montenegro, et al. Expires May 11, 2007 [Page 8] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 The uncompressed IPv6 and HC1 header compression format is described in Section *10*. The mesh header is described in Section *11* The fragmentation header is described in the following secion. The encapsulation formats defined in this section, (subsequently referred to as the "LowPAN encapsulation") are the payload in the IEEE 802.15.4 MAC protocol data unit (PDU). The LoWPAN payload (e.g., an IPv6 packet) follows this encapsulation header. All protocol datagrams (e.g., IPv6, Compressed IPv6 headers, etc) SHALL be preceded by one of the LoWPAN encapsulation headers described above. This permits uniform software treatment of datagrams without regard to the mode of their transmission. 5.1. Link Fragmentation If an entire payload (e.g., IPv6) datagram fits within a single 802.15.4 frame, it is unfragmented and the LoWPAN encapsulation should contain no fragmentation header. If the datagram does not fit within a single IEEE 802.15.4 frame, it SHALL be broken into link fragments. The first link fragment SHALL contain a fragmentation header as shown below. 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 0|0| dgram_tag | dgram_size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: LoWPAN first fragment encapsulation header format The second and subsequent link fragments (up to and including the last) SHALL contain a fragmentation header that conforms to the format shown below. 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 0|1| dgram_tag | dgram_size | dgram_offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: LoWPAN subsequent fragment(s) encapsulation header format Field definitions are as follows: Montenegro, et al. Expires May 11, 2007 [Page 9] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 datagram_size: This 11 bit field encodes the size of the entire IP payload datagram. The value of datagram_size SHALL be the same for all link fragments of an IP payload datagram. For IPv6, this SHALL be 40 octets (the size of the uncompressed IPv6 header) more than the value of Payload Length in the IPv6 header [RFC2460]. Typically, this field needs to encode a maximum length of 1280 (IEEE 802.15.4 link MTU as defined in this document), and as much as 1500 (the default maximum IPv6 packet size if IPv6 fragmentation is in use). Therefore, this field is 11 bits long, which works in either case. NOTE: This field does not need to be in every packet, as one could send it with the first fragment and elide it subsequently. However, including it in every link fragment eases the task of reassembly in the event that a second (or subsequent) link fragment arrives before the first. In this case, the guarantee of learning the datagram_size as soon as any of the fragments arrives tells the receiver how much buffer space to set aside as it waits for the rest of the fragments. The format above trades off simplicity for efficiency. datagram_offset: This field is present only in the second and subsequent link fragments and SHALL specify the offset, in increments of 8 octets, of the fragment from the beginning of the payload datagram. The first octet of the datagram (e.g., the start of the IPv6 header) has an offset of zero; the implicit value of datagram_offset in the first link fragment is zero. This field is 8 bits long. datagram_tag: The value of datagram_tag (datagram tag) SHALL be the same for all link fragments of a payload (e.g., IPv6) datagram. The sender SHALL increment datagram_tag for successive, fragmented datagrams. The incremented value of datagram_tag SHALL wrap from 1023 back to zero. This field is 10 bits long, and its initial value is not defined. 5.2. Reassembly The recipient of link fragments SHALL use (1) the sender's 802.15.4 source address (or the Originator Address if a Mesh Delivery field is present), (2) the destination's 802.15.4 address (or the Final Destination address if a Mesh Delivery field is present), (3) datagram_size and (4) datagram_tag to identify all the link fragments that belong to a given datagram. Upon receipt of a link fragment, the recipient starts constructing the original unfragmented packet whose size is datagram_size. It Montenegro, et al. Expires May 11, 2007 [Page 10] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 uses the datagram_offset field to determine the location of the individual fragments within the original unfragmented packet. For example, it may place the data payload (except the encapsulation header) within a payload datagram reassembly buffer at the location specified by datagram_offset. The size of the reassembly buffer SHALL be determined from datagram_size. If a link fragment is received that overlaps another fragment as identified above and differs in either the size or datagram_offset of the overlapped fragment, the fragment(s) already accumulated in the reassembly buffer SHALL be discarded. A fresh reassembly may be commenced with the most recently received link fragment. Fragment overlap is determined by the combination of datagram_offset from the encapsulation header and "Frame Length" from the 802.15.4 PPDU packet header. Upon detection of a IEEE 802.15.4 Disassociation event, fragment recipients SHOULD discard all link fragments of all partially reassembled payload datagrams, and fragment senders SHOULD discard all not yet transmitted link fragments of all partially transmitted payload (e.g., IPv6) datagrams. Similarly, when a node first receives a fragment with a given datagram_tag, it starts a reassembly timer. When this time expires, if the entire packet has not been reassembled, the existing fragments SHOULD be discarded and the reassembly state SHOULD be flushed. The reassembly timeout MUST be set to a maximum of 60 seconds (this is also the timeout in the IPv6 reassembly procedure [RFC2460] ). 6. Stateless Address Autoconfiguration This section defines how to obtain an IPv6 interface identifier. The Interface Identifier [RFC3513] for an IEEE 802.15.4 interface may be based on the EUI-64 identifier [EUI64] assigned to the IEEE 802.15.4 device. In this case, the Interface Identifier is formed from the EUI-64 according to the "IPv6 over Ethernet" specification [RFC2464]. All 802.15.4 devices have an IEEE EUI-64 address, but 16-bit short addresses (Section 3 and Section 12) are also possible. In these cases, a "pseudo 48-bit address" is formed as follows. First, the left-most 32 bits are formed by concatenating 16 zero bits to the 16- bit PAN ID (alternatively, if no PAN ID is known, 16 zero bits may be used). This produces a 32-bit field as follows: Montenegro, et al. Expires May 11, 2007 [Page 11] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 16_bit_PAN:16_zero_bits Then, these 32 bits are concatenated with the 16-bit short address. This produces a 48-bit address as follows: 32_bits_as_specified_previously:16_bit_short_address The interface identifier is formed from this 48-bit address as per the "IPv6 over Ethernet" specification. However, in the resultant interface identifier, the "Universal/Local" (U/L) bit SHALL be set to 0 in keeping with the fact that this is not a globally unique value. For either address format, all zero addresses MUST NOT be used. A different MAC address set manually or by software MAY be used to derive the Interface Identifier. If such a MAC address is used, its global uniqueness property should be reflected in the value of the U/L bit. An IPv6 address prefix used for stateless autoconfiguration [I-D.ietf-ipv6-rfc2462bis] of an IEEE 802.15.4 interface MUST have a length of 64 bits. 7. IPv6 Link Local Address The IPv6 link-local address [RFC3513] for an IEEE 802.15.4 interface is formed by appending the Interface Identifier, as defined above, to the prefix FE80::/64. 10 bits 54 bits 64 bits +----------+-----------------------+----------------------------+ |1111111010| (zeros) | Interface Identifier | +----------+-----------------------+----------------------------+ Figure 6 8. Unicast Address Mapping The address resolution procedure for mapping IPv6 non-multicast addresses into IEEE 802.15.4 link-layer addresses follows the general description in section 7.2 of [I-D.ietf-ipv6-2461bis], unless otherwise specified. The Source/Target Link-layer Address option has the following forms when the link layer is IEEE 802.15.4 and the addresses are EUI-64 or Montenegro, et al. Expires May 11, 2007 [Page 12] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 16-bit short addresses, respectively. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length=2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- IEEE 802.15.4 -+ | EUI-64 | +- -+ | | +- Address -+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- Padding -+ | | +- (all zeros) -+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length=1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 16-bit short Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- Padding -+ | (all zeros) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 7 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 2 if using EUI-64 addresses, or 1 if using 16-bit short addresses. Montenegro, et al. Expires May 11, 2007 [Page 13] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 IEEE 802.15.4 Address: The 64-bit IEEE 802.15.4 address, or the 16- bit short address (as per the format in Section 9), in canonical bit order. This is the address the interface currently responds to. This address may be different from the built-in address used to derive the Interface Identifier, because of privacy or security (e.g., of neighbor discovery) considerations. 9. Multicast Address Mapping An IPv6 packet with a multicast destination address DST, consisting of the sixteen octets DST through DST, is transmitted to the following 802.15.4 16-bit multicast address: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1 0 0|DST* | DST | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 8 Here, DST* refers to the last 5 bits in octet DST, that is, bits 3-7 within DST. The initial 3-bit pattern of "100" follows the 16-bit address format for multicast addresses (Section 12). This allows for multicast support within 6LoWPAN networks, but the full specification of such support is out of scope of this document. Example mechanisms are: flooding, controlled flooding, unicasting to the PAN coordinator, etc. It is expected that this would be specified by the different mesh routing mechanisms. 10. Header Compression There is much published and in-progress standardization work on header compression. Nevertheless, header compression for IPv6 over IEEE 802.15.4 has differing constraints summarized as follows: Existing work assumes that there are many flows between any two devices. Here, we assume that most of the time there will be only one flow, and this allows a very simple and low context flavor of header compression. Given the very limited packet sizes, it is highly desirable to integrate layer 2 with layer 3 compression, something traditionally not done (although now changing due to the ROHC Montenegro, et al. Expires May 11, 2007 [Page 14] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 working group. It is expected that IEEE 802.15.4 devices will be deployed in multi-hop networks. However, header compression in a mesh departs from the usual point-to-point link scenario in which the compressor and decompressor are in direct and exclusive communication with each other. In an IEEE 802.15.4 network, it is highly desirable for a device to be able to send header compressed packets via any of its neighbors, with as little preliminary context-building as possible. Preliminary context is often required. If so, it is highly desirable to allow building it by not relying exclusively on the in-line negotiation phase. For example, if we assume there is some manual configuration phase that precedes deployment (perhaps with human involvement), then one should be able to leverage this phase to set up context such that the first packet sent will already be compressed. Any new packets formats required by header compression reuse the basic packet formats defined in Section 5 by using different values for the dispatch byte. 10.1. Encoding of IPv6 Header Fields By virtue of having joined the same 6lowpan network, devices share some state. This makes it possible to compress headers even in the absence of the customary context-building phase. Thus, the following common IPv6 header values may be compressed from the onset: Version is IPv6, both IPv6 source and destination are link local, the IPv6 bottom 64 bits can be inferred from the layer two source and destination, the packet length can be inferred either from layer two ("Frame Length" in the IEEE 802.15.4 PPDU) or from the "datagram_size" field in the fragment header (if present), both the Traffic Class and the Flow Label are zero, and the Next Header is UDP, ICMP or TCP. The only field in the IPv6 header that always needs to be carried in full is the Hop Limit (8 bits). Depending on how closely the packet matches this common case, different fields may not be compressible thus needing to be carried "in-line" as well (Section 10.3.1). This common IPv6 header (as mentioned above) can be compressed to 2 octets (1 octet for the HC1 encoding and 1 octet for the Hop Limit), instead of 40 octets. Such a packet is compressible via the LOWPAN_HC1 format by using a header dispatch type of HC1_disp followed by a LOWPAN_HC1 header "HC1 encoding" field (8 bits) to encode the different combinations as shown below. This header may be preceded by a fragmentation header, which may be preceded by a mesh header. Montenegro, et al. Expires May 11, 2007 [Page 15] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HC1 encoding | Non-Compressed fields follow... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 9: LOWPAN_HC1 (common compressed header encoding) As can be seen below (bit 7), an HC2 encoding may follow an HC1 octet. In this case, the non-compressed fields follow the HC2 encoding field Section 10.3. The address fields encoded by "HC1 encoding" are interpreted as follows: PI: Prefix carried in-line (Section 10.3.1). PC: Prefix compressed (link-local prefix assumed). II: Interface identifier carried in-line (Section 10.3.1). IC: Interface identifier elided (derivable from the corresponding link-layer address). If applied to the interface identifier of either the source or destination address when routing in a mesh (Section 11), the corresponding link-layer address is that found in the "Mesh Delivery" field (Figure 11). The "HC1 encoding" is shown below (starting with bit 0 and ending at bit 7): IPv6 source address (bits 0 and 1): 00: PI, II 01: PI, IC 10: PC, II 11: PC, IC IPv6 destination address (bits 2 and 3): 00: PI, II 01: PI, IC 10: PC, II 11: PC, IC Traffic Class and Flow Label (bit 4): 0: not compressed, full 8 bits for Traffic Class and 20 bits for Flow Label are sent 1: Traffic Class and Flow Label are zero Montenegro, et al. Expires May 11, 2007 [Page 16] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Next Header (bits 5 and 6): 00: not compressed, full 8 bits are sent 01: UDP 10: ICMP 11: TCP HC2 encoding(bit 7): 0: No more header compression bits 1: HC1 encoding immediately followed by more header compression bits per HC2 encoding format. Bits 5 and 6 determine which of the possible HC2 encodings apply (e.g., UDP, ICMP or TCP encodings). 10.2. Encoding of UDP Header Fields Bits 5 and 6 of the LOWPAN_HC1 allows compressing the Next Header field in the IPv6 header (for UDP, TCP and ICMP). Further compression of each of these protocol headers is also possible. This section explains how the UDP header itself may be compressed. The HC2 encoding in this section is the HC_UDP encoding, and it only applies if bits 5 and 6 in HC1 indicate that the protocol that follows the IPv6 header is UDP. The HC_UDP encoding (Figure 10) allows compressing the following fields in the UDP header: source port, destination port and length. The UDP header's checksum field is not compressed and is therefore carried in full. The scheme defined below allows compressing the UDP header to 4 octets instead of the original 8 octets. The only UDP header field whose value may be deduced from information available elsewhere is the Length. The other fields must be carried in-line either in full or in a partially compressed manner (Section 10.3.2). 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |HC_UDP encoding| Fields carried in-line follow... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 10: HC_UDP (UDP common compressed header encoding) The "HC_UDP encoding" for UDP is shown below (starting with bit 0 and ending at bit 7): Montenegro, et al. Expires May 11, 2007 [Page 17] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 UDP source port (bit 0): 0: Not compressed, carried "in-line" (Section 10.3.2) 1: Compressed to 4 bits. The actual 16-bit source port is obtained by calculating: P + short_port value. P is a predetermined port number with value TBD. The short_port is expressed as a 4-bit value which is carried "in-line" (Section 10.3.2) UDP destination port (bit 1): 0: Not compressed, carried "in-line" (Section 10.3.2) 1: Compressed to 4 bits. The actual 16-bit destination port is obtained by calculating: P + short_port value. P is a predetermined port number with value TBD. The short_port is expressed as a 4-bit value which is carried "in-line" (Section 10.3.2) Length (bit 2): 0: not compressed, carried "in-line" (Section 10.3.2) 1: compressed, length computed from IPv6 header length information. The value of the UDP length field is equal to the Payload Length from the IPv6 header, minus the length of any extension headers present between the IPv6 header and the UDP header. Reserved (bit 3 through 7) Note: TCP, ICMP HC2 formats TBD. 10.3. Non-Compressed Fields 10.3.1. Non-Compressed IPv6 Fields This scheme allows the IPv6 header to be compressed to different degrees. Hence, instead of the entire (standard) IPv6 header, only non-compressed fields need to be sent. The subsequent header (as specified by the Next Header field in the original IPv6 header) immediately follows the IPv6 non-compressed fields. Uncompressed IPv6 addressing is described by a addressing header consisting of a IPv6_disp dispatch byte followed by and additional header bytes and the uncompressed addresses, as described above. Such an addressing header may be preceded by a fragmentation header, which may be preceded by a mesh header. The non-compressed IPv6 field that MUST be always present is the Hop Limit (8 bits). This field MUST always follow the encoding fields (e.g., "HC1 encoding" as shown in Figure 9), perhaps including other future encoding fields). Other non-compressed fields MUST follow the Montenegro, et al. Expires May 11, 2007 [Page 18] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Hop Limit as implied by the "HC1 encoding" in the exact same order as shown above (Section 10.1): source address prefix (64 bits) and/or interface identifier (64 bits), destination address prefix (64 bits) and/or interface identifier (64 bits), Traffic Class (8 bits), Flow Label (20 bits) and Next Header (8 bits). The actual next header (e.g., UDP, TCP, ICMP, etc) follows the non-compressed fields. 10.3.2. Non-Compressed and partially compressed UDP fields This scheme allows the UDP header to be compressed to different degrees. Hence, instead of the entire (standard) UDP header, only non-compressed or partially compressed fields need to be sent. The non-compressed or partially compressed fields in the UDP header MUST always follow the IPv6 header and any of its associated in-line fields. Any UDP header in-line fields present MUST appear in the same order as the corresponding fields appear in a normal UDP header [RFC0768], e.g., source port, destination port, length and checksum. If either the source or destination ports are in "short_port" notation (as indicated in the compressed UDP header), then instead of taking 16 bits, the inline port numbers take 4 bits. 11. Frame Delivery in a Link-Layer Mesh Even though 802.15.4 networks are expected to commonly use mesh routing, the IEEE 802.15.4-2003 specification [ieee802.15.4] does not define such capability. In such cases, Full Function Devices (FFDs) run an ad hoc or mesh routing protocol to populate their routing tables (outside the scope of this document). In such mesh scenarios, two devices do not require direct reachability in order to communicate. Of these devices, the sender is known as the "Originator", and the receiver is known as the "Final Destination". An originator device may use other intermediate devices as forwarders towards the final destination. In order to achieve such frame delivery using unicast, it is necessary to include the link-layer addresses of the originator and final destinations, in addition to the hop-by-hop source and destination. This section defines how to effect delivery of layer 2 frames in a mesh, given a target "Final Destination" link-layer address. Mesh delivery is enabled by including a Mesh header prior to any other headers of the LoWPAN encapsulation (Section 5), unfragmented and fragmented, a full-blown IPv6 header, or a compressed IPv6 header as per Section 10, or any others defined elsewhere. If a node wishes to use a default mesh forwarder to deliver a packet Montenegro, et al. Expires May 11, 2007 [Page 19] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 (i.e., because it does not have direct reachability to the destination), it MUST include a Mesh header with the originator's link-layer address set to its own, and the final destination's link- layer address set to the packet's ultimate destination. It sets the source address in the 802.15.4 header to its own link-layer address, and puts the forwarder's link-layer address in the 802.15.4 header's destination address field. Finally, it transmits the packet. Similarly, if a node receives a frame with a Mesh header, it must look at the Mesh header's "Final Destination" field to determine the real destination. If the node is itself the final destination, it consumes the packet as per normal delivery. If it is not the final destination, the device then reduces the "Hops Left" field, and if the result is zero, discards the packet. Otherwise, the node consults its link-layer routing table, determines what the next hop towards the final destination should be, and puts that address in the destination address field of the 802.15.4 header. Finally, the node changes the source address in the 802.15.4 header to its own link- layer address and transmits the packet. Whereas a node must participate in a mesh routing protocol to be a forwarder, no such requirement exists for simply using mesh forwarding. Only "Full Function Devices" (FFDs) are expected to participate as routers in a mesh. "Reduced Function Devices" (RFDs) limit themselves to discovering FFDs and using them for all their forwarding, in a manner similar to how IP hosts typically use default routers to forward all their off-link traffic. For an RFD using mesh delivery, the "forwarder" is always the appropriate FFD. The "Mesh header" field consists of a Mesh dispatch byte followed by a mesh header. If Hops Left exceeds 14, it is encoded as the esc value of 0xF and followed by an additional Hops Left byte 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|1|O|F|HopsLft| Originator Address... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...Final Destination Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 11: Mesh Header Field definitions are as follows: Montenegro, et al. Expires May 11, 2007 [Page 20] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 O: This 1-bit field SHALL be zero if the Originator Address is an IEEE extended 64 bit address (EUI-64), or 1 if it is a short 16- bit addresses. F: This 1-bit field SHALL be zero if the Final Destination Address is an IEEE extended 64 bit address (EUI-64), or 1 if it is a short 16-bit addresses. Hops Left: This 6-bit field SHALL be decremented by each forwarding node before sending this packet towards its next hop. The packet is not forwarded any further if Hops Left is decremented to 0. Originator Address: This is the link-layer address of the Originator. Final Destination Address: This is the link-layer address of the Final Destination. Note that the 'O' and 'F' bits allow for a mix of 16 and 64-bit addresses. This is useful at least to allow for mesh layer "broadcast", as 802.15.4 broadcast addresses are defined as 16-bit short addresses. Additional mesh routing functionality is encoded using additional routing header immediately following the Mesh header. In particular, a broadcast header consists of a BC0 dispatch followed by a broadcast header consisting of a sequence number. 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0| BC0 |Sequence Number| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 12: Broadcast Header Field definitions are as follows: Sequence Number: This 8-bit field SHALL be incremented by the originator whenever it sends a new mesh broadcast or multicast packet. Full specification of how to handle this field is out of scope of this document. Further implications of such mesh-layer broadcast, e.g., whether it maps to a controlled flooding mechanism or its role in, say, topology discovery, is out of scope of this document. Montenegro, et al. Expires May 11, 2007 [Page 21] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Additional mesh routing capabilities, such as specifying the mesh routing protocol, source routing, and so on may be expressed by defining additional routing headers that preceed the fragmentation or addressing header in the header stack. 12. IANA Considerations This document creates two new IANA registries, as discussed below. Future assignments in these registries are to be coordinated via IANA under the policy of "Specification Required" [RFC2434]. It is expected that this policy will allow for other (non-IETF) organizations to more easily obtain assignments. This document creates a new IANA registry for the Dispatch type field shown in the header definitions Section 5. This document defines the values IPv6, LOWPAN_HC1 header compression, BC0 broadcast and two escapes values (not a LOWPAN frame and ESC to allow additional dispatch bytes). This document defines this field to be 8 bits long. The value 0 being reserved and not used, this allows for a total of 254 different values, which should be more than enough. This document creates a new IANA registry for the 16-bit short address fields as used in 6LoWPAN packets. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 16-bit short Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 13 This registry MUST include the addresses 0xffff (16-bit broadcast address accepted by all devices currently listening to the channel) and 0xfffe as defined in [ieee802.15.4]. Additionally, within 6LoWPAN networks, 16-bit short addresses MUST follow this format (referring to bit fields in the order from 0 to 7), where "x" is a place holder for an unspecified bit value: Range 1, Oxxxxxxxxxxxxxxx: The first bit (bit 0) SHALL be zero if the 16-bit address is a unicast address. This leaves 15 bits for the actual address. Montenegro, et al. Expires May 11, 2007 [Page 22] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Range 2, 100xxxxxxxxxxxxx: Bits 0,1 and 2 SHALL follow this pattern if the 16-bit address is a multicast address (see Section 9). This leaves 13 bits for the actual multicast address. Range 3, 101xxxxxxxxxxxxx: This pattern for bits 0,1 and 2 is reserved. Any future assignment shall follow the policy mentioned above. Range 4, 110xxxxxxxxxxxxx: This pattern for bits 0,1 and 2 is reserved. Any future assignment shall follow the policy mentioned above. Range 5, 111xxxxxxxxxxxxx: This pattern for bits 0,1 and 2 is reserved. Any future assignment shall follow the policy mentioned above. This document requests an IANA assignment of a port number P, for use with UDP header compression (Section 10.2). This port number P is used as the base to which the "short_port" 4-bit values are added in order to obtain the actual UDP port used. 13. Security Considerations The method of derivation of Interface Identifiers from EUI-64 MAC addresses is intended to preserve global uniqueness when possible. However, there is no protection from duplication through accident or forgery. Neighbor Discovery in IEEE 802.15.4 links may be susceptible to threats as detailed in [RFC3756]. Mesh routing is expected to be common in IEEE 802.15.4 networks. This implies additional threats due to ad hoc routing as per [KW03]. IEEE 802.15.4 provides some capability for link-layer security. Users are urged to make use of such provisions if at all possible and practical. Doing so will alleviate the threats referred to above. A sizeable portion of IEEE 802.15.4 devices is expected to always communicate within their PAN (i.e., within their link, in IPv6 terms). In response to cost and power consumption considerations, and in keeping with the IEEE 802.15.4 model of "Reduced Function Devices" (RFDs), these devices will typically implement the minimum set of features necessary. Accordingly, security for such devices may rely quite strongly on the mechanisms defined at the link-layer by IEEE 802.15.4. The latter, however, only defines the AES modes for authentication or encryption of IEEE 802.15.4 frames, and does not, in particular, specify key management (presumably group Montenegro, et al. Expires May 11, 2007 [Page 23] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 oriented). Other issues to address in real deployments relate to secure configuration and management. Whereas such a complete picture is out of scope of this document, it is imperative that IEEE 802.15.4 networks be deployed with such considerations in mind. Of course, it is also expected that some IEEE 802.15.4 devices (the so-called "Full Function Devices", or "FFDs") will implement coordination or integration functions. These may communicate regularly with off-link IPv6 peers (in addition to the more common on-link exchanges). Such IPv6 devices are expected to secure their end-to-end communications with the usual mechanisms (e.g., IPsec, TLS, etc). 14. Acknowledgements Thanks to the authors of RFC 2464 and RFC 2734, as parts of this document are patterned after theirs. Thanks to Geoff Mulligan for useful discussions which helped shape this document. Erik Nordmark's suggestions were instrumental for the header compression section. Also thanks to Shoichi Sakane, Samita Chakrabarti, Vipul Gupta, Carsten Bormann, Ki-Hyung Kim, Mario Mao, and Phil Levis. 15. References 15.1. Normative References [EUI64] "GUIDELINES FOR 64-BIT GLOBAL IDENTIFIER (EUI-64) REGISTRATION AUTHORITY", IEEE http://standards.ieee.org/ regauth/oui/tutorials/EUI64.html. [I-D.ietf-ipv6-2461bis] Narten, T., "Neighbor Discovery for IP version 6 (IPv6)", draft-ietf-ipv6-2461bis-09 (work in progress), October 2006. [I-D.ietf-ipv6-rfc2462bis] Thomson, S., "IPv6 Stateless Address Autoconfiguration", draft-ietf-ipv6-rfc2462bis-08 (work in progress), May 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 Montenegro, et al. Expires May 11, 2007 [Page 24] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 (IPv6) Specification", RFC 2460, December 1998. [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, December 1998. [RFC3513] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6) Addressing Architecture", RFC 3513, April 2003. [ieee802.15.4] IEEE Computer Society, "IEEE Std. 802.15.4-2003", October 2003. 15.2. Informative References [I-D.ietf-ipngwg-icmp-v3] Conta, A., "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", draft-ietf-ipngwg-icmp-v3-07 (work in progress), July 2005. [I-D.ietf-ipv6-node-requirements] Loughney, J., "IPv6 Node Requirements", draft-ietf-ipv6-node-requirements-11 (work in progress), August 2004. [KW03] Karlof, Chris and Wagner, David, "Secure Routing in Sensor Networks: Attacks and Countermeasures", Elsevier's AdHoc Networks Journal, Special Issue on Sensor Network Applications and Protocols vol 1, issues 2-3, September 2003. [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [RFC1042] Postel, J. and J. Reynolds, "Standard for the transmission of IP datagrams over IEEE 802 networks", STD 43, RFC 1042, February 1988. [RFC3439] Bush, R. and D. Meyer, "Some Internet Architectural Guidelines and Philosophy", RFC 3439, December 2002. [RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor Discovery (ND) Trust Models and Threats", RFC 3756, May 2004. [RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D., Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. Wood, "Advice for Internet Subnetwork Designers", BCP 89, Montenegro, et al. Expires May 11, 2007 [Page 25] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 RFC 3819, July 2004. Appendix A. Alternatives for Delivery of Frames in a Mesh Before settling on the mechanism finally adopted for delivery in a mesh (Section 11), several alternatives were considered. In addition to the hop-by-hop source and destination link-layer addresses, delivering a packet in a LoWPAN mesh requires the end-to-end originator and destination addresses. These could be expressed either as layer 2 or as layer 3 (i.e., IP ) addresses. In the latter case, there would be no need to provide any additional header support in this document (i.e., within the LoWPAN header itself). The link- layer destination address would point to the next hop destination address while the IP header destination address would point to the final destination (IP) address (possibly multiple hops away from the source), and similarly for the source addresses. Thus, while forwarding data, the single-hop source and destination addresses would change at each hop (always pointing to the node doing the forwarding and the "best" next link-layer hop, respectively), while the source and destination IP addresses would remain unchanged. Notice that if an IP packet is fragmented, the individual fragments may arrive at any node out of order. If the initial fragment (which contains the IP header) is delayed for some reason, a node that receives a subsequent fragment would lack the required information. It would be forced to wait until it receives the IP header (within the first fragment) before being able to forward the fragment any further. This imposes some additional buffering requirements on intermediate nodes. Additionally, such a specification would only work for one type of LoWPAN payload: IPv6. In general, it would have to be adapted for any other payload, and would require that payload to provide its own end-to-end addressing information. On the other hand, the approach finally followed (Section 11) creates a mesh at the LoWPAN layer (below layer 3). Accordingly, link-layer originator and final destination address are included within the LoWPAN header. This enables mesh delivery for any protocol or application layered on the LoWPAN adaptation layer (Section 5). For IPv6 as supported in this document, another advantage of expressing the originator and final destinations as layer 2 addresses is that the IPv6 addresses can be compressed as per the header compression specified in Section 10. Furthermore, the number of octets needed to maintain routing tables is reduced due to the smaller size of 802.15.4 addresses (either 64 bits or 16 bits) as compared to IPv6 addresses (128 bits). A disadvantage is that applications on top of IP do not address packets to link-layer destination addresses, but to IP (layer 3) destination addresses. Thus, given an IP address, there is a need to resolve the corresponding link-layer address. Montenegro, et al. Expires May 11, 2007 [Page 26] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Accordingly, a mesh routing specification needs to clarify the Neighbor Discovery implications, although in some special cases, it may be possible to derive a device's address at layer 2 from its address at layer 3 (and viceversa). Such complete specification is outside the scope of this document. Appendix B. Changes Changes up to version draft-ietf-6lowpan-format-06.txt are as follows: Conversion to stacked header layout analogous to IPv6 headers. Further clarification in the reassembly procedures. Editorial nits and corrections. Changes up to version draft-ietf-6lowpan-format-05.txt are as follows: Added some padding bits to the first and subsequent fragment formats to align on an octet boundary. Header compression may result in alignment not falling on an octet boundary. Since hardware typically cannot transmit units less than an octet, added text to the effect that one lays out the contiguous compressed headers and then zero bits SHOULD BE added as appropriate to align to an octet boundary. Added how to distinguish between the multicast and the unicast formats for the mesh delivery field. We use one of the 5 reserved bits to signal if the bcast/mcast mesh delivery format is being used, and we called it the 'B' ("broadcast") bit. So no change to the mesh delivery fields is required. Since the reserved bits are common to all three lowpan header formats, the 'B' bit applies to all. Changes from version draft-ietf-6lowpan-format-02.txt to version draft-ietf-6lowpan-format-03.txt are as follows: Interface Identifier derivation using 16-bit short addresses now using the PAN ID as well. Word of caution on the transient nature of 16 bit short addresses. Montenegro, et al. Expires May 11, 2007 [Page 27] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Reassembly now also keying on destination and datagram_size. Mesh delivery header now allowing mix of 16/64 bit addresses. This leaves 6 bits for hops_left (64 hops is plenty). Added optional Multicast Address mapping patterned after that of ethernet. Clarified that all zero addresses must not be used (for either 16 or 64 bit formats). Added address format section to IANA considerations to define unicast, multicast and reserved address formats. Added Mesh Broadcast or Multicast Delivery Field. Created a new section on Addressing Modes. Sundry editorial changes. Changes from version draft-ietf-6lowpan-format-01.txt to version draft-ietf-6lowpan-format-02.txt are as follows: Further details on broadcast by using PAN-specific broadcast. Sundry editorial changes. Changes from version draft-ietf-6lowpan-format-00.txt to version draft-ietf-6lowpan-format-01.txt are as follows: Added a reassembly timeout of 15 sec. Added support for 16-bit "short" addresses. datagram tag now at 10 bits protocol_type and datagram offset both went from 11 to 8 bits (which is still enough for the format, and which implies counting offset in units of 8 octets for the latter). Addition of the originator's link-layer source address to the "Mesh Delivery" header. Changed name of "Final Destination" header to "Mesh Delivery" header. Further clarification on mesh delivery. Montenegro, et al. Expires May 11, 2007 [Page 28] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Sundry editorial changes. Changes from version draft-montenegro-lowpan-ipv6-over-802.15.4-02.txt to version draft-ietf-6lowpan-format-00.txt are as follows: The LoWPAN encapsulation was modified to allow 11 bits of protocol type (prot_type field). Because of this, the minimum overhead grew from 1 octet to 2 octets. This was done in order to allow more protocol types as the previous format started with a field only 5 bits wide. Whereas growing it to 7 bits was possible in the future, this would always entail 2 octets of overhead for the longer protocol types to be used. The 'M' bit had been left out of the 3rd packet format (for subsequent fragments). Corrected this oversight. This means that the fragment tag lost one bit. Sundry editorial changes. Authors' Addresses Gabriel Montenegro Microsoft Corporation Email: firstname.lastname@example.org Nandakishore Kushalnagar Intel Corp Email: email@example.com Jonathan Hui Arch Rock Corp Email: firstname.lastname@example.org David E. Culler Arch Rock Corp Email: email@example.com Montenegro, et al. Expires May 11, 2007 [Page 29] Internet-Draft IPv6 over IEEE 802.15.4 November 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at firstname.lastname@example.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Montenegro, et al. Expires May 11, 2007 [Page 30]
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