Network Working Group J. Hui Internet-Draft D. Culler Intended status: Standards Track Arch Rock Corporation Expires: December 30, 2007 June 28, 2007 Stateless IPv6 Header Compression for Globally Routable Packets in 6LoWPAN Subnetworks draft-hui-6lowpan-hc1g-00 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 December 30, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document specifies a stateless IP header compression scheme for IPv6 packet delivery in 6LoWPAN subnetworks. The compression scheme focuses on LoWPAN nodes that may have global unicast addresses assigned to their interfaces. Hui & Culler Expires December 30, 2007 [Page 1]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 2. Header Compression . . . . . . . . . . . . . . . . . . . . . . 4 2.1. LOWPAN_HC1g Encoding of IPv6 Header Fields . . . . . . . . 5 2.2. LOWPAN_HC2 Encoding of UDP Header Fields . . . . . . . . . 7 2.3. ICMP and TCP Header Compression . . . . . . . . . . . . . 7 3. Modified IEEE EUI-64 Interface Identifiers . . . . . . . . . . 8 4. 16-bit Short Addresses . . . . . . . . . . . . . . . . . . . . 8 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Intellectual Property and Copyright Statements . . . . . . . . . . 12 Hui & Culler Expires December 30, 2007 [Page 2]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 1. Introduction The IEEE 802.15.4 standard specifies an MTU of 128 bytes, including the length byte [ieee802.15.4] on a 250 kbps wireless link. Because the link MTU is small, in fact smaller than the required 1280-byte MTU of IPv6 [RFC2460], and because bandwidth, memory, or power resources are critical in many IEEE 802.15.4 applications, 6LoWPAN has defined an adaptation layer to support layer 3 (LOWPAN_HC1) and layer 4 (LOWPAN_HC2) header compression, and sub-IP fragmentation, for packet delivery over IEEE 802.15.4 links [I-D.ietf-6lowpan-format]. Substantial portions of the headers are elided, where they can be derived by the receiver from information contained in the IEEE 802.15.4 frame with basic assumptions of shared context. The IPv6 addressing architecture supports a notion of scoping [RFC4291]. Addresses defined within a scope must not extend beyond their scope. Currently, IPv6 defines three unicast address scopes: link-local, site-local, and global. Link-local addresses are composed of a well-known 64-bit prefix and a 64-bit interface identifier. Link-local addresses are intended for addressing on a single link. They are commonly used for configuration protocols or communication between nodes when no router exists. Site-local addresses were originally intended for use within an administratively-defined domain, but their use has since been deprecated. Global addresses are intended for addressing any node connected to the IPv6 network, including nodes within a local scope once configured. A global address is composed of a n-bit global routing prefix, m-bit subnet identifier, and a 128-n-m-bit interface identifier. Global addresses not starting with a binary 000 are required to have a 64-bit interface identifier, where n+m=64. LOWPAN_HC1 supports eliding the prefix and/or interface identifier of IPv6 source and destination addresses, but only for the link-local prefix. Thus, for any LoWPAN node with a global unicast address assigned to its 802.15.4 interface and using it for communication, the full 128-bit address must be carried within packets to or from the node. Carrying full source and destination addresses in an IEEE 802.15.4 packet consumes a quarter of the link-layer's MTU. This overhead occurs in many important situations. For example, an IPv6 packet communicated between two nodes within a PAN, whether over a single L2 hop or multiple L2 mesh-routed hops, utilizes extensive header compression if their link-local addresses are specified, but the same communication between the same nodes foregoes HC1 header compression if their global address is specified. For monitoring networks, the data collection point is often a machine that is connected to the PAN by way of other non-802.15.4 links. Similarly, in automation and control settings, the controller is often a machine Hui & Culler Expires December 30, 2007 [Page 3]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 on existing IP links. Communication to and from nodes external to the PAN utilize global address, so no HC1 header compression is permitted, even when only a single IEEE 802.15.4 hop is involved. Even where no other kinds of links are involved, IP routing among nodes utilizing IEEE 803.15.4 links, as might occur among 802.15.4 subnets, perhaps using different PAN IDs, different channels, or different MACs, cannot utilize HC1 header compression, because the link-local address cannot be used. This document specifies a stateless header compression scheme for layer 3 (LOWPAN_HC1g) that allows compression of global unicast addresses and permits existing compression of the layer 4 header. Similar to LOWPAN_HC1, LOWPAN_HC1g recognizes that a prefix is shared throughout the PAN, but in the LOWPAN_HC1g case it is a shared global prefix, rather than the shared link local prefix. Indeed, link-local communication is important to protocols like IPv6 Neighbor Discovery [RFC2461] and LOWPAN_HC1 may be used to compress link-local addresses. 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. Header Compression The LOWPAN_HC1g header compression scheme proposed in this section maintains many of LOWPAN_HC1's design considerations. First, LOWPAN_HC1g is a very simple and low-context form of header compression. Second, it integrates layer 2 with layer 3 compression. Finally, it also allows LoWPAN devices to send header compressed packets via any of its neighbors, with as little preliminary context- building as possible. LOWPAN_HC1g operates directly on top of the basic LoWPAN header formats defined in Section 5 of the 6LoWPAN format document. LOWPAN_HC1g is identified by dispatch value 0x30, whereas LOWPAN_HC1 is identified by dispatch value 0x10. Layer 4 header compression uses LOWPAN_HC2; the only, yet significant, difference is where the layer 4 encoding bits appear in the header stack. In LOWPAN_HC1g, the LOWPAN_HC2 encoding bits immediately precede the uncompressed layer 4 fields. Typical LOWPAN_HC1g/HC2 header configurations are shown in Figure 1. Hui & Culler Expires December 30, 2007 [Page 4]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 +-------------------+--------------+--------------+----- | HC1g Header | Uncompressed | Uncompressed | Data | L4 Uncompressed | IP Fields | UDP Header | +-------------------+--------------+--------------+----- +-----------------+--------------+-------------+--------------+------ | HC1g Header | Uncompressed | HC2 Header | Uncompressed | Data | L4 Compressed | IP Fields | | UDP Fields | +-----------------+--------------+-------------+--------------+------ Figure 1: Typical LOWPAN_HC1g/HC2 Header Configurations 2.1. LOWPAN_HC1g Encoding of IPv6 Header Fields The LOWPAN_HC1g header compression scheme supports the expected common case on 6LoWPAN networks with no added overhead to LOWPAN_HC1. Version is IPv6, Payload Length is derived from the 802.15.4 header or "datagram_size" field from the fragmentation header, Traffic Class and Flow Label are zero, Next Header is UDP, ICMP, or TCP, one or both of IPv6 source and destination addresses are local to the PAN, and the source and destination interface identifiers are derived directly from the link-layer. The only field that cannot be compressed is the Hops Left field. Thus, in the local case, the IP header is compressed to 2 octets. To support compression of global unicast addresses, LOWPAN_HC1g assumes that a PAN is assigned one compressible 64-bit global IP prefix. When either the source or destination address matches the compressible global IP prefix, the prefix can be elided. Note that additional global IP prefixes may be assigned to an interface, but those prefixes are not compressible when using LOWPAN_HC1g. Additionally, if interfaces are assigned a 64-bit interface identifier, where the upper 49-bits is zero, the 64-bit global prefix and the upper 48-bits of the interface identifier may be elided. Such interface identifiers represent those with local scope, with the universal/global bit set to "0". The 49th bit is not elided to maintain alignment on octet boundaries. However, enforcing the 49th bit to be "0", borrows from the 16-bit short address encoding specified in I-D.ietf-6lowpan-format. [I-D.ietf-6lowpan-format] Section 4 discusses how the encoding can be useful for commonly-used multicast addresses. The address compression encoding in LOWPAN_HC1g has four possible forms: Hui & Culler Expires December 30, 2007 [Page 5]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 Full 128-bit Address: Full 128-bit IPv6 address carried unmodified in-line. Compressed 64-bit Address: 64-bit prefix elided, 64-bit interface identifier carried in-line. The 64-bit prefix is derived from the 64-bit prefix assigned to the PAN. Compressed 16-bit Address: 64-bit prefix elided, least significant 16 bits of 64-bit interface identifier inline. The 64-bit prefix is derived from the 64-bit prefix assigned to the PAN. The upper 48 bits of the interface identifier are assumed to be all zeros. Full 128-bit IPv6 address elided: The prefix identifier is derived from the 64-bit global prefix assigned to the PAN. The 64-bit interface identifier is derived either from the LoWPAN Mesh Addressing header or from the IEEE 802.15.4 link header. The link-layer addresses used to derive the 64-bit interface identifier is a short address, the short address describes the lower 16 bits of the interface identifier. The upper 48 bits are assumed to be all zeros. The LOWPAN_HC1g encoding field is shown in Figure 2. 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | SC | DC |VTF| NH |L4C| +---+---+---+---+---+---+---+---+ Figure 2: LOWPAN_HC1g Header Compression Encoding SC: IPv6 source address compression (bits 0 and 1): 00: Full 128-bit address 01: Compressed 64-bit address 10: Compressed 16-bit address 11: Full 128-bit IPv6 address elided DC: IPv6 destination address compression (bits 2 and 3): 00: Full 128-bit address 01: Compressed 64-bit address 10: Compressed 16-bit address 11: Full 128-bit IPv6 address elided VTF: Version, Traffic Class, and Flow Label (bit 4): 0: Full 4 bits for Version, 8 bits for Traffic Class, and 20 bits for Flow Label are carried in-line. 1: Version, Traffic Class, and Flow Label are elided and assumed to be zero. Hui & Culler Expires December 30, 2007 [Page 6]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 NH: Next Header (bits 5 and 6): 00: Next header field carried in-line. 01: UDP 10: ICMP 11: TCP L4C: Layer 4 Compression (bit 7): 0: Full layer 4 header is carried in-line. An HC2 encoding does not precede the layer 4 header. 1: Layer 4 header is compressed. An HC2 encoding follows the IP header but precedes the layer 4 header. Currently, this indicator only supports UDP compression. Of the fields in the IPv6 header, the uncompressed field that MUST always be carried in-line is Hop Limit. Payload Length MUST never appear, as it is always derived from the IEEE 802.15.4 header or the "datagram_size" field in the LoWPAN fragmentation header. All other fields, when carried in-line, MUST appear in the same order as specified in RFC 2460 [RFC2460]. When all fields are carried in- line, the header looks identical to a full IPv6 header without the Payload Length field. This differs from LOWPAN_HC1, where fields do not appear in this order. While it is possible to always assume IPv6 for the Version field, it is carried in-line whenever Traffic Class and Flow Label are carried in-line. Not doing so will result in field alignment not falling on an octet boundary. The actual next header specified by the LOWPAN_HC1g encoding immediately follows all IPv6 header fields carried in-line. 2.2. LOWPAN_HC2 Encoding of UDP Header Fields Bit 7 in the LOWPAN_HC1g encoding specifies whether or not the layer 4 header is compressed. If layer 4 compression is specified, then the LOWPAN_HC2g encoding replaces the uncompressed form of the layer 4 header. For UDP, the HC_UDP encoding scheme remains unchanged from the 6LoWPAN format document [I-D.ietf-6lowpan-format]. The only difference is that the HC_UDP encoding field immediately precedes the in-line UDP fields, rather than sitting between the HC1 encoding and in-line IPv6 fields. This co-locates the bits describing UDP headers with the in-line fields. 2.3. ICMP and TCP Header Compression This document does not specify a compression scheme for ICMP and TCP. Such compression schemes may be specified in the future. Hui & Culler Expires December 30, 2007 [Page 7]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 3. Modified IEEE EUI-64 Interface Identifiers For LOWPAN_HC1g to compress a 128-bit address down to 16-bits, two conditions must be satisfied: (i) the prefix matches the compressible global prefix assigned to the PAN and (ii) the upper 49-bits of the interface identifier must be zeros. This interface identifier is constructed in Modified EUI-64 format, MUST have scope limited to the assigned compressible global subnet-prefix, and MUST be subnet-prefix unique. Included in the upper 49-bits is the universal/local bit, which is set to "0" to indicate local scope. As suggested in RFC 4291 [RFC4291], possible approaches to select such a PAN-unique interface identifier may include: Manual Configuration Node Serial Number Other Node-Specific Token 4. 16-bit Short Addresses [I-D.ietf-6lowpan-format] specifies an encoding for 16-bit short addresses to be used in 6LoWPAN packets. The document reserves 0xffff (16-bit broadcast) and 0xfffe as defined in IEEE 802.15.4 [ieee802.15.4]. The document also specifies five different value ranges. The lower 32,768 values are reserved for unicast addresses and the next 8192 values are reserved for a link-layer multicast address mapping. This document allocates another range of 8192 values to be used for commonly used, well-known IPv6 multicast addresses. By creating a mapping between full 128-bit well-known multicast addresses to 16-bit short addresses, commonly-used multicast addresses can be compressed to 16-bits. The multicast mapping can be used with the 6LoWPAN Mesh Delivery header or a LoWPAN_HC1g header by specifying use of the 16- bit short address form. The encoding used for the 13-bits is as follows: 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Range| Scope | Mapped Group ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: LOWPAN_HC1g Header Compression Encoding Hui & Culler Expires December 30, 2007 [Page 8]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 Range: 3-bit range identifier which indicates the use of a mapped well-known IPv6 multicast address. Scope: 4-bit multicast scope as specified in RFC 4007 [RFC4007]. Mapped Group ID: 9-bit mapped multicast group identifier. The full 128-bit multicast address can be reconstructed from the 16- bit mapped multicast address. By definition, the 3-bit range identifier indicates the well-known multicast prefix (0xFF) in addition to a flags field set to all zeros (indicating a permanently assigned multicast address, that the multicast address is not assigned based on the network prefix, and that it doesn't embed the address of a Rendezvous Point). The 4-bit scope is carried in-line and the 112-bit group ID is derived from the 9-bit mapped group ID using a well-known mapping maintained by the Internet Assigned Numbers Authority (IANA). This document defines an initial mapping. Additional mappings between 9-bit mapped group IDs and 112-bit group IDs may be specified in the future. +-------+---------+-----------------------+ | 9-bit | 112-bit | Description | +-------+---------+-----------------------+ | 1 | 1 | All Nodes Addresses | | 2 | 2 | All Routers Addresses | +-------+---------+-----------------------+ 9-bit to 128-bit Group ID Mapping 5. IANA Considerations This document defines a new layer 3 header compression scheme for 6LoWPAN networks. The document allocate a new Dispatch type value of 0x30 that indicates the use of LOWPAN_HC1g. This document requests another range, preferably Range 3 in the 16- bit short address field specified in [I-D.ietf-6lowpan-format]. This document creates a new IANA registry for mapped well-known multicast addresses, mapping 112-bit group identifiers to compressed 9-bit ones. The registry MUST include the All Nodes Address (1) and the All Routers Address (2). 6. Security Considerations The definition of LOWPAN_HC1g permits the compression of header Hui & Culler Expires December 30, 2007 [Page 9]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 information on communication that could take place in its absence, albeit in a less efficient form. It recognizes that a IEEE 802.15.4 PAN may have associated with it a global prefix. How that global prefix is assigned and managed is beyond the scope of this document. All drafts are required to have a security considerations section. See RFC 3552 [RFC3552] for a guide. 7. References 7.1. Normative References [I-D.ietf-6lowpan-format] Montenegro, G., "Transmission of IPv6 Packets over IEEE 802.15.4 Networks", draft-ietf-6lowpan-format-13 (work in progress), April 2007. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and B. Zill, "IPv6 Scoped Address Architecture", RFC 4007, March 2005. [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. [ieee802.15.4] IEEE Computer Society, "IEEE Std. 802.15.4-2006", October 2006. 7.2. Informative References [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations", BCP 72, RFC 3552, July 2003. Hui & Culler Expires December 30, 2007 [Page 10]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 Authors' Addresses Jonathan W. Hui Arch Rock Corporation 657 Mission St. Ste. 600 San Francisco, California 94105 USA Phone: +415 692 0828 Email: jhui@archrock.com David E. Culler Arch Rock Corporation 657 Mission St. Ste. 600 San Francisco, California 94105 USA Phone: +415 692 0828 Email: dculler@archrock.com Hui & Culler Expires December 30, 2007 [Page 11]
Internet-Draft 6LoWPAN Compression of Global Addresses June 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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, THE IETF TRUST 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 ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Hui & Culler Expires December 30, 2007 [Page 12]