GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc8138

Internet Engineering Task Force (IETF) P. Thubert, Ed. Request for Comments: 8138 Cisco Category: Standards Track C. Bormann ISSN: 2070-1721 Uni Bremen TZI

                                                            L. Toutain
                                                        IMT Atlantique
                                                             R. Cragie
                                                                   ARM
                                                            April 2017
    IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN)
                           Routing Header

Abstract

 This specification introduces a new IPv6 over Low-Power Wireless
 Personal Area Network (6LoWPAN) dispatch type for use in 6LoWPAN
 route-over topologies, which initially covers the needs of Routing
 Protocol for Low-Power and Lossy Networks (RPL) data packet
 compression (RFC 6550).  Using this dispatch type, this specification
 defines a method to compress the RPL Option (RFC 6553) information
 and Routing Header type 3 (RFC 6554), an efficient IP-in-IP
 technique, and is extensible for more applications.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc8138.

Thubert, et al. Standards Track [Page 1] RFC 8138 6LoWPAN Routing Header April 2017

Copyright Notice

 Copyright (c) 2017 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Thubert, et al. Standards Track [Page 2] RFC 8138 6LoWPAN Routing Header April 2017

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   7
 3.  Using the Page Dispatch . . . . . . . . . . . . . . . . . . .   7
   3.1.  New Routing Header Dispatch (6LoRH) . . . . . . . . . . .   7
   3.2.  Placement of 6LoRH Headers  . . . . . . . . . . . . . . .   8
     3.2.1.  Relative to Non-6LoRH Headers . . . . . . . . . . . .   8
     3.2.2.  Relative to Other 6LoRH Headers . . . . . . . . . . .   8
 4.  6LoWPAN Routing Header General Format . . . . . . . . . . . .   9
   4.1.  Elective Format . . . . . . . . . . . . . . . . . . . . .  10
   4.2.  Critical Format . . . . . . . . . . . . . . . . . . . . .  10
   4.3.  Compressing Addresses . . . . . . . . . . . . . . . . . .  11
     4.3.1.  Coalescence . . . . . . . . . . . . . . . . . . . . .  11
     4.3.2.  DODAG Root Address Determination  . . . . . . . . . .  12
 5.  The SRH-6LoRH Header  . . . . . . . . . . . . . . . . . . . .  13
   5.1.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . .  13
   5.2.  SRH-6LoRH General Operation . . . . . . . . . . . . . . .  14
     5.2.1.  Uncompressed SRH Operation  . . . . . . . . . . . . .  14
     5.2.2.  6LoRH-Compressed SRH Operation  . . . . . . . . . . .  15
     5.2.3.  Inner LOWPAN_IPHC Compression . . . . . . . . . . . .  15
   5.3.  The Design Point of Popping Entries . . . . . . . . . . .  16
   5.4.  Compression Reference for SRH-6LoRH Header Entries  . . .  17
   5.5.  Popping Headers . . . . . . . . . . . . . . . . . . . . .  18
   5.6.  Forwarding  . . . . . . . . . . . . . . . . . . . . . . .  19
 6.  The RPL Packet Information 6LoRH (RPI-6LoRH)  . . . . . . . .  19
   6.1.  Compressing the RPLInstanceID . . . . . . . . . . . . . .  21
   6.2.  Compressing the SenderRank  . . . . . . . . . . . . . . .  21
   6.3.  The Overall RPI-6LoRH Encoding  . . . . . . . . . . . . .  21
 7.  The IP-in-IP 6LoRH Header . . . . . . . . . . . . . . . . . .  24
 8.  Management Considerations . . . . . . . . . . . . . . . . . .  26
 9.  Security Considerations . . . . . . . . . . . . . . . . . . .  27
 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
   10.1.  Reserving Space in 6LoWPAN Dispatch Page 1 . . . . . . .  27
   10.2.  New Critical 6LoWPAN Routing Header Type Registry  . . .  28
   10.3.  New Elective 6LoWPAN Routing Header Type Registry  . . .  28
 11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  28
   11.1.  Normative References . . . . . . . . . . . . . . . . . .  28
   11.2.  Informative References . . . . . . . . . . . . . . . . .  29
 Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  31
   A.1.  Examples Compressing the RPI  . . . . . . . . . . . . . .  31
   A.2.  Example of a Downward Packet in Non-Storing Mode  . . . .  32
   A.3.  Example of SRH-6LoRH Life Cycle . . . . . . . . . . . . .  34
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  36
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  37

Thubert, et al. Standards Track [Page 3] RFC 8138 6LoWPAN Routing Header April 2017

1. Introduction

 The design of Low-Power and Lossy Networks (LLNs) is generally
 focused on saving energy, a very constrained resource in most cases.
 The other constraints, such as the memory capacity and the duty
 cycling of the LLN devices, derive from that primary concern.  Energy
 is often available from primary batteries that are expected to last
 for years, or it is scavenged from the environment in very limited
 quantities.  Any protocol that is intended for use in LLNs must be
 designed with the primary concern of saving energy as a strict
 requirement.
 Controlling the amount of data transmission is one possible venue to
 save energy.  In a number of LLN standards, the frame size is limited
 to much smaller values than the guaranteed IPv6 Maximum Transmission
 Unit (MTU) of 1280 bytes.  In particular, an LLN that relies on the
 classical Physical Layer (PHY) of IEEE 802.15.4 [IEEE.802.15.4] is
 limited to 127 bytes per frame.  The need to compress IPv6 packets
 over IEEE 802.15.4 led to the writing of "Compression Format for IPv6
 Datagrams over IEEE 802.15.4-Based Networks" [RFC6282].
 Innovative route-over techniques have been and still are being
 developed for routing inside an LLN.  Generally, such techniques
 require additional information in the packet to provide loop
 prevention and to indicate information such as flow identification,
 source routing information, etc.
 For reasons such as security and the capability to send ICMPv6 errors
 (see "Internet Control Message Protocol (ICMPv6) for the Internet
 Protocol Version 6 (IPv6) Specification" [RFC4443]) back to the
 source, an original packet must not be tampered with, and any
 information that must be inserted in or removed from an IPv6 packet
 must be placed in an extra IP-in-IP encapsulation.
 This is the case when the additional routing information is inserted
 by a router on the path of a packet, for instance, the root of a
 mesh, as opposed to the source node, with the Non-Storing mode of the
 "RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks"
 [RFC6550].
 This is also the case when some routing information must be removed
 from a packet that flows outside the LLN.

Thubert, et al. Standards Track [Page 4] RFC 8138 6LoWPAN Routing Header April 2017

 "When to use RFC 6553, RFC 6554 and IPv6-in-IPv6" [RPL-INFO] details
 different cases where IPv6 headers defined in the RPL Option for
 Carrying RPL Information in Data-Plane Datagrams [RFC6553], Header
 for Source Routes with RPL [RFC6554], and IPv6-in-IPv6 encapsulation,
 are inserted or removed from packets in LLN environments operating
 RPL.
 When using RFC 6282 [RFC6282], the outer IP header of an IP-in-IP
 encapsulation may be compressed down to 2 octets in stateless
 compression and down to 3 octets in stateful compression when context
 information must be added.
    0                                       1
    0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
  | 0 | 1 | 1 |  TF   |NH | HLIM  |CID|SAC|  SAM  | M |DAC|  DAM  |
  +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
            Figure 1: LOWPAN_IPHC Base Encoding (RFC 6282)
 The stateless compression of an IPv6 address can only happen if the
 IPv6 address can de deduced from the Media Access Control (MAC)
 addresses, meaning that the IP endpoint is also the MAC-layer
 endpoint.  This is usually not the case in a RPL network, which is
 generally a multi-hop route-over (i.e., operated at Layer 3) network.
 A better compression, which does not involve variable compressions
 depending on the hop in the mesh, can be achieved based on the fact
 that the outer encapsulation is usually between the source (or
 destination) of the inner packet and the root.  Also, the inner IP
 header can only be compressed by RFC 6282 [RFC6282] if all the fields
 preceding it are also compressed.  This specification makes the inner
 IP header the first header to be compressed by RFC 6282 [RFC6282],
 and it keeps the inner packet encoded the same way whether or not it
 is encapsulated, thus preserving existing implementations.
 As an example, RPL [RFC6550] is designed to optimize the routing
 operations in constrained LLNs.  As part of this optimization, RPL
 requires the addition of RPL Packet Information (RPI) in every
 packet, as defined in Section 11.2 of RFC 6550 [RFC6550].
 "The Routing Protocol for Low-Power and Lossy Networks (RPL) Option
 for Carrying RPL Information in Data-Plane Datagrams" [RFC6553]
 specification indicates how the RPI can be placed in a RPL Option
 (RPL-OPT) that is placed in an IPv6 Hop-by-Hop header.
 This representation demands a total of 8 bytes, while, in most cases,
 the actual RPI payload requires only 19 bits.  Since the Hop-by-Hop
 header must not flow outside of the RPL domain, it must be inserted

Thubert, et al. Standards Track [Page 5] RFC 8138 6LoWPAN Routing Header April 2017

 in packets entering the domain and be removed from packets that leave
 the domain.  In both cases, this operation implies an IP-in-IP
 encapsulation.
 Additionally, in the case of the Non-Storing Mode of Operation (MOP),
 RPL requires a Source Routing Header (SRH) in all packets that are
 routed down a RPL graph.  For that purpose, "An IPv6 Routing Header
 for Source Routes with the Routing Protocol for Low-Power and Lossy
 Networks (RPL)" [RFC6554] defines the type 3 Routing Header for IPv6
 (RH3).
  1. —–+——— ^

| Internet |

              |                                    | Native IPv6
           +-----+                                 |
           |     | Border Router (RPL Root)      + | +
           |     |                               | | |
           +-----+                               | | | tunneled
              |                                  | | | using
        o    o   o    o                          | | | IPv6-in-
    o o   o  o   o  o  o o   o                   | | | IPv6 and
   o  o o  o o    o   o   o  o  o                | | | RPL SRH
   o   o    o  o     o  o    o  o  o             | | |
  o  o   o  o   o         o   o o                | | |
  o          o             o     o               + v +
                    LLN
            Figure 2: IP-in-IP Encapsulation within the LLN
 With Non-Storing RPL, even if the source is a node in the same LLN,
 the packet must first reach up the graph to the root so that the root
 can insert the SRH to go down the graph.  In any fashion, whether the
 packet was originated in a node in the LLN or outside the LLN, and
 regardless of whether or not the packet stays within the LLN, as long
 as the source of the packet is not the root itself, the source-
 routing operation also implies an IP-in-IP encapsulation at the root
 in order to insert the SRH.
 "An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4"
 [IPv6-ARCH] specifies the operation of IPv6 over the mode of
 operation described in "Using IEEE 802.15.4e Time-Slotted Channel
 Hopping (TSCH) in the Internet of Things (IoT): Problem Statement"
 [RFC7554].  The architecture requires the use of both RPL and the 6lo
 adaptation layer over IEEE 802.15.4.  Because it inherits the
 constraints on frame size from the MAC layer, 6TiSCH cannot afford to
 allocate 8 bytes per packet on the RPI, hence the requirement for
 6LoWPAN header compression of the RPI.

Thubert, et al. Standards Track [Page 6] RFC 8138 6LoWPAN Routing Header April 2017

 An extensible compression technique is required that simplifies
 IP-in-IP encapsulation when it is needed and optimally compresses
 existing routing artifacts found in RPL LLNs.
 This specification extends the 6lo adaptation layer framework
 ([RFC4944] [RFC6282]) so as to carry routing information for route-
 over networks based on RPL.  It includes the formats necessary for
 RPL and is extensible for additional formats.

2. Terminology

 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 RFC
 2119 [RFC2119].
 This document uses the terms from, and is consistent with, "Terms
 Used in Routing for Low-Power and Lossy Networks" [RFC7102] and RPL
 [RFC6550].
 The terms "route-over" and "mesh-under" are defined in RFC 6775
 [RFC6775].
 Other terms in use in LLNs are found in "Terminology for Constrained-
 Node Networks" [RFC7228].
 The term "byte" is used in its now customary sense as a synonym for
 "octet".

3. Using the Page Dispatch

 The "IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN)
 Paging Dispatch" [RFC8025] specification extends the 6lo adaptation
 layer framework ([RFC4944] [RFC6282]) by introducing a concept of
 "context" in the 6LoWPAN parser, a context being identified by a Page
 number.  The specification defines 16 Pages.
 This document operates within Page 1, which is indicated by a
 dispatch value of binary 11110001.

3.1. New Routing Header Dispatch (6LoRH)

 This specification introduces a new 6LoWPAN Routing Header (6LoRH) to
 carry IPv6 routing information.  The 6LoRH may contain source routing
 information such as a compressed form of SRH, as well as other sorts
 of routing information such as the RPI and IP-in-IP encapsulation.

Thubert, et al. Standards Track [Page 7] RFC 8138 6LoWPAN Routing Header April 2017

 The 6LoRH is expressed in a 6loWPAN packet as a Type-Length-Value
 (TLV) field, which is extensible for future use.
 It is expected that a router that does not recognize the 6LoRH
 general format detailed in Section 4 will drop the packet when a
 6LoRH is present.
 This specification uses the bit pattern 10xxxxxx in Page 1 for the
 new 6LoRH Dispatch.  Section 4 describes how RPL artifacts in data
 packets can be compressed as 6LoRH headers.

3.2. Placement of 6LoRH Headers

3.2.1. Relative to Non-6LoRH Headers

 In a zone of a packet where Page 1 is active (that is, once the Page
 1 Paging Dispatch is parsed, and until another Paging Dispatch is
 parsed as described in the 6LoWPAN Paging Dispatch specification
 [RFC8025]), the parsing of the packet MUST follow this specification
 if the 6LoRH Bit Pattern (see Section 3.1) is found.
 With this specification, the 6LoRH Dispatch is only defined in
 Page 1, so it MUST be placed in the packet in a zone where the Page 1
 context is active.
 Because a 6LoRH header requires a Page 1 context, it MUST always be
 placed after any Fragmentation Header and/or Mesh Header as defined
 in RFC 4944 [RFC4944].
 A 6LoRH header MUST always be placed before the LOWPAN_IPHC as
 defined in RFC 6282 [RFC6282].  It is designed in such a fashion that
 placing or removing a header that is encoded with 6LoRH does not
 modify the part of the packet that is encoded with LOWPAN_IPHC,
 whether or not there is an IP-in-IP encapsulation.  For instance, the
 final destination of the packet is always the one in the LOWPAN_IPHC,
 whether or not there is a Routing Header.

3.2.2. Relative to Other 6LoRH Headers

 The "Internet Protocol, Version 6 (IPv6) Specification" [RFC2460]
 defines chains of headers that are introduced by an IPv6 header and
 terminated by either another IPv6 header (IP-in-IP) or an Upper-Layer
 Protocol (ULP) header.  When an outer header is stripped from the
 packet, the whole chain goes with it.  When one or more headers are
 inserted by an intermediate router, that router normally chains the
 headers and encapsulates the result in IP-in-IP.

Thubert, et al. Standards Track [Page 8] RFC 8138 6LoWPAN Routing Header April 2017

 With this specification, the chains of headers MUST be compressed in
 the same order as they appear in the uncompressed form of the packet.
 This means that if there is more than one nested IP-in-IP
 encapsulation, the first IP-in-IP encapsulation, with all its chain
 of headers, is encoded first in the compressed form.
 In the compressed form of a packet that has a Source Route or a Hop-
 by-Hop (HbH) Options Header [RFC2460] after the inner IPv6 header
 (e.g., if there is no IP-in-IP encapsulation), these headers are
 placed in the 6LoRH form before the 6LOWPAN_IPHC that represents the
 IPv6 header (see Section 3.2.1).  If this packet gets encapsulated
 and some other SRH or HbH Options Headers are added as part of the
 encapsulation, placing the 6LoRH headers next to one another may
 present an ambiguity on which header belongs to which chain in the
 uncompressed form.
 In order to disambiguate the headers that follow the inner IPv6
 header in the uncompressed form from the headers that follow the
 outer IP-in-IP header, it is REQUIRED that the compressed IP-in-IP
 header is placed last in the encoded chain.  This means that the
 6LoRH headers that are found after the last compressed IP-in-IP
 header are to be inserted after the IPv6 header that is encoded with
 the 6LOWPAN_IPHC when decompressing the packet.
 With regard to the relative placement of the SRH and the RPI in the
 compressed form, it is a design point for this specification that the
 SRH entries are consumed as the packet progresses down the LLN (see
 Section 5.3).  In order to make this operation simpler in the
 compressed form, it is REQUIRED that in the compressed form, the
 addresses along the source route path are encoded in the order of the
 path, and that the compressed SRH are placed before the compressed
 RPI.

4. 6LoWPAN Routing Header General Format

 The 6LoRH uses the Dispatch Value Bit Pattern of 10xxxxxx in Page 1.
 The Dispatch Value Bit Pattern is split in two forms of 6LoRH:
    Elective (6LoRHE), which may skipped if not understood
    Critical (6LoRHC), which may not be ignored
 For each form, a Type field is used to encode the type of 6LoRH.
 Note that there is a different registry for the Type field of each
 form of 6LoRH.

Thubert, et al. Standards Track [Page 9] RFC 8138 6LoWPAN Routing Header April 2017

 This means that a value for the Type that is defined for one form of
 6LoRH may be redefined in the future for the other form.

4.1. Elective Format

 The 6LoRHE uses the Dispatch Value Bit Pattern of 101xxxxx.  A 6LoRHE
 may be ignored and skipped in parsing.  If it is ignored, the 6LoRHE
 is forwarded with no change inside the LLN.
     0                   1
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-       ...        -+
    |1|0|1| Length  |      Type     |                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-       ...        -+
                                     <--    Length    -->
               Figure 3: Elective 6LoWPAN Routing Header
 Length:  Length of the 6LoRHE expressed in bytes, excluding the first
       2 bytes.  This enables a node to skip a 6LoRHE header that it
       does not support and/or cannot parse, for instance, if the Type
       is not recognized.
 Type: Type of the 6LoRHE

4.2. Critical Format

 The 6LoRHC uses the Dispatch Value Bit Pattern of 100xxxxx.
 A node that does not support the 6LoRHC Type MUST silently discard
 the packet.
 Note: A situation where a node receives a message with a Critical
 6LoWPAN Routing Header that it does not understand should not occur
 and is an administrative error, see Section 8.
   0                   1
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-              ...               -+
  |1|0|0|   TSE   |      Type     |                                  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-              ...               -+
                                   <-- Length implied by Type/TSE -->
               Figure 4: Critical 6LoWPAN Routing Header

Thubert, et al. Standards Track [Page 10] RFC 8138 6LoWPAN Routing Header April 2017

 Type-Specific Extension (TSE):  The meaning depends on the Type,
       which must be known in all of the nodes.  The interpretation of
       the TSE depends on the Type field that follows.  For instance,
       it may be used to transport control bits, the number of
       elements in an array, or the length of the remainder of the
       6LoRHC expressed in a unit other than bytes.
 Type: Type of the 6LoRHC

4.3. Compressing Addresses

 The general technique used in this document to compress an address is
 first to determine a reference that has a long prefix match with this
 address and then elide that matching piece.  In order to reconstruct
 the compressed address, the receiving node will perform the process
 of coalescence described in Section 4.3.1.
 One possible reference is the root of the RPL Destination-Oriented
 Directed Acyclic Graph (DODAG) that is being traversed.  It is used
 by 6LoRH as the reference to compress an outer IP header in case of
 an IP-in-IP encapsulation.  If the root is the source of the packet,
 this technique allows one to fully elide the source address in the
 compressed form of the IP header.  If the root is not the
 encapsulator, then the Encapsulator Address may still be compressed
 using the root as a reference.  How the address of the root is
 determined is discussed in Section 4.3.2.
 Once the address of the source of the packet is determined, it
 becomes the reference for the compression of the addresses that are
 located in compressed SRH headers that are present inside the IP-in-
 IP encapsulation in the uncompressed form.

4.3.1. Coalescence

 An IPv6 compressed address is coalesced with a reference address by
 overriding the N rightmost bytes of the reference address with the
 compressed address, where N is the length of the compressed address,
 as indicated by the Type of the SRH-6LoRH header in Figure 7.
 The reference address MAY be a compressed address as well, in which
 case, it MUST be compressed in a form that is of an equal or greater
 length than the address that is being coalesced.
 A compressed address is expanded by coalescing it with a reference
 address.  In the particular case of a Type 4 SRH-6LoRH, the address
 is expressed in full and the coalescence is a complete override as
 illustrated in Figure 5.

Thubert, et al. Standards Track [Page 11] RFC 8138 6LoWPAN Routing Header April 2017

 RRRRRRRRRRRRRRRRRRR  A reference address, which may be
                      compressed or not
             CCCCCCC  A compressed address, which may be
                      shorter or the same as the reference
 RRRRRRRRRRRRCCCCCCC  A coalesced address, which may be the
                      same compression as the reference
                    Figure 5: Coalescing Addresses

4.3.2. DODAG Root Address Determination

 Stateful address compression requires that some state is installed in
 the devices to store the compression information that is elided from
 the packet.  That state is stored in an abstract context table, and
 some form of index is found in the packet to obtain the compression
 information from the context table.
 With RFC 6282 [RFC6282], the state is provided to the stack by the
 6LoWPAN Neighbor Discovery Protocol (NDP) [RFC6775].  NDP exchanges
 the context through the 6LoWPAN Context Option in Router
 Advertisement (RA) messages.  In the compressed form of the packet,
 the context can be signaled in a Context Identifier Extension.
 With this specification, the compression information is provided to
 the stack by RPL, and RPL exchanges it through the DODAGID field in
 the DAG Information Object (DIO) messages, as described in more
 detail below.  In the compressed form of the packet, the context can
 be signaled by the RPLInstanceID in the RPI.
 With RPL [RFC6550], the address of the DODAG root is known from the
 DODAGID field of the DIO messages.  For a Global Instance, the
 RPLInstanceID that is present in the RPI is enough information to
 identify the DODAG that this node participates with and its
 associated root.  But, for a Local Instance, the address of the root
 MUST be explicit, either in some device configuration or signaled in
 the packet, as the source or the destination address, respectively.
 When implicit, the address of the DODAG root MUST be determined as
 follows:
    If the whole network is a single DODAG, then the root can be well-
    known and does not need to be signaled in the packets.  But, since
    RPL does not expose that property, it can only be known by a
    configuration applied to all nodes.

Thubert, et al. Standards Track [Page 12] RFC 8138 6LoWPAN Routing Header April 2017

    Else, the router that encapsulates the packet and compresses it
    with this specification MUST also place an RPI in the packet as
    prescribed by RPL to enable the identification of the DODAG.  The
    RPI must be present even in the case when the router also places
    an SRH header in the packet.
 It is expected that the RPL implementation maintains an abstract
 context table, indexed by Global RPLInstanceID, that provides the
 address of the root of the DODAG that this node participates in for
 that particular RPL Instance.

5. The SRH-6LoRH Header

5.1. Encoding

 A Source Routing Header 6LoRH (SRH-6LoRH) provides a compressed form
 for the SRH, as defined in RFC 6554 [RFC6554], for use by RPL
 routers.
 One or more SRH-6LoRH header(s) MAY be placed in a 6LoWPAN packet.
 If a non-RPL router receives a packet with an SRH-6LoRH header, there
 was a routing or a configuration error (see Section 8).
 The desired reaction for the non-RPL router is to drop the packet, as
 opposed to skipping the header and forwarding the packet.
 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates it
 is Critical.  Routers that understand the 6LoRH general format
 detailed in Section 4 cannot ignore a 6LoRH header of this type and
 will drop the packet if it is unknown to them.
     0                   1
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-    -+-    -+ ... +-    -+
    |1|0|0|  Size   |6LoRH Type 0..4| Hop1 | Hop2 |     | HopN |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-    -+-    -+ ... +-    -+
              Where N = Size + 1
                        Figure 6: The SRH-6LoRH
 The 6LoRH Type of an SRH-6LoRH header indicates the compression level
 used for that header.
 The fields following the 6LoRH Type are compressed addresses
 indicating the consecutive hops and are ordered from the first to the
 last hop.

Thubert, et al. Standards Track [Page 13] RFC 8138 6LoWPAN Routing Header April 2017

 All the addresses in a given SRH-6LoRH header MUST be compressed in
 an identical fashion, so the Length of the compressed form is the
 same for all.
 In order to get different degrees of compression, multiple
 consecutive SRH-6LoRH headers MUST be used.
 Type 0 means that the address is compressed down to one byte, whereas
 Type 4 means that the address is provided in full in the SRH-6LoRH
 with no compression.  The complete list of Types of SRH-6LoRH and the
 corresponding compression level are provided in Figure 7:
   +-----------+----------------------+
   |   6LoRH   | Length of compressed |
   |   Type    | IPv6 address (bytes) |
   +-----------+----------------------+
   |    0      |       1              |
   |    1      |       2              |
   |    2      |       4              |
   |    3      |       8              |
   |    4      |      16              |
   +-----------+----------------------+
                     Figure 7: The SRH-6LoRH Types
 In the case of an SRH-6LoRH header, the TSE field is used as a Size,
 which encodes the number of hops minus 1; so a Size of 0 means one
 hop, and the maximum that can be encoded is 32 hops.  (If more than
 32 hops need to be expressed, a sequence of SRH-6LoRH elements can be
 employed.)  The result is that the Length, in bytes, of an SRH-6LoRH
 header is:
 2 + Length_of_compressed_IPv6_address * (Size + 1)

5.2. SRH-6LoRH General Operation

5.2.1. Uncompressed SRH Operation

 In the uncompressed form, when the root generates or forwards a
 packet in Non-Storing mode, it needs to include a Source Routing
 Header [RFC6554] to signal a strict source route path to a final
 destination down the DODAG.
 All the hops along the path, except the first one, are encoded in
 order in the SRH.  The last entry in the SRH is the final
 destination; the destination in the IPv6 header is the first hop
 along the source route path.  The intermediate hops perform a swap

Thubert, et al. Standards Track [Page 14] RFC 8138 6LoWPAN Routing Header April 2017

 and the Segments Left field indicates the active entry in the Routing
 Header [RFC2460].
 The current destination of the packet, which is the termination of
 the current segment, is indicated at all times by the destination
 address of the IPv6 header.

5.2.2. 6LoRH-Compressed SRH Operation

 The handling of the SRH-6LoRH is different: there is no swap, and a
 forwarding router that corresponds to the first entry in the first
 SRH-6LoRH, upon reception of a packet, effectively consumes that
 entry when forwarding.  This means that the size of a compressed
 source-routed packet decreases as the packet progresses along its
 path and that the routing information is lost along the way.  This
 also means that an SRH encoded with 6LoRH is not recoverable and
 cannot be protected.
 When compressed with this specification, all the remaining hops MUST
 be encoded in order in one or more consecutive SRH-6LoRH headers.
 Whether or not there is an SRH-6LoRH header present, the address of
 the final destination is indicated in the LOWPAN_IPHC at all times
 along the path.  Examples of this are provided in Appendix A.
 The current destination (termination of the current segment) for a
 compressed source-routed packet is indicated in the first entry of
 the first SRH-6LoRH.  In strict source routing, that entry MUST match
 an address of the router that receives the packet.
 The last entry in the last SRH-6LoRH is the last router on the way to
 the final destination in the LLN.  This router can be the final
 destination if it is found desirable to carry a whole IP-in-IP
 encapsulation all the way.  Else, it is the RPL parent of the final
 destination, or a router acting at 6LoWPAN Router (6LR) [RFC6775] for
 the destination host, and it is advertising the host as an external
 route to RPL.
 If the SRH-6LoRH header is contained in an IP-in-IP encapsulation,
 the last router removes the whole chain of headers.  Otherwise, it
 removes the SRH-6LoRH header only.

5.2.3. Inner LOWPAN_IPHC Compression

 6LoWPAN ND [RFC6282] is designed to support more than one IPv6
 address per node and per Interface Identifier (IID); an IID is
 typically derived from a MAC address to optimize the LOWPAN_IPHC
 compression.

Thubert, et al. Standards Track [Page 15] RFC 8138 6LoWPAN Routing Header April 2017

 Link-local addresses are compressed with stateless address
 compression (S/DAC=0).  The other addresses are derived from
 different prefixes, and they can be compressed with stateful address
 compression based on a context (S/DAC=1).
 But, stateless compression is only defined for the specific link-
 local prefix as opposed to the prefix in an encapsulating header.
 And with stateful compression, the compression reference is found in
 a context, as opposed to an encapsulating header.
 The result is that, in the case of an IP-in-IP encapsulation, it is
 possible to compress an inner source (respective destination) IP
 address in a LOWPAN_IPHC based on the encapsulating IP header only if
 stateful (context-based) compression is used.  The compression will
 operate only if the IID in the source (respective destination) IP
 address in the outer and inner headers match, which usually means
 that they refer to the same node.  This is encoded as S/DAC = 1 and
 S/AM=11.  It must be noted that the outer destination address that is
 used to compress the inner destination address is the last entry in
 the last SRH-6LoRH header.

5.3. The Design Point of Popping Entries

 In order to save energy and to optimize the chances of transmission
 success on lossy media, it is a design point for this specification
 that the entries in the SRH that have been used are removed from the
 packet.  This creates a discrepancy from the art of IPv6, where
 Routing Headers are mutable but recoverable.
 With this specification, the packet can be expanded at any hop into a
 valid IPv6 packet, including an SRH, and compressed back.  But the
 packet, as decompressed along the way, will not carry all the
 consumed addresses that packet would have if it had been forwarded in
 the uncompressed form.
 It is noted that:
    The value of keeping the whole RH in an IPv6 header is for the
    receiver to reverse it to use the symmetrical path on the way
    back.
    It is generally not a good idea to reverse a Routing Header.  The
    RH may have been used to stay away from the shortest path for some
    reason that is only valid on the way in (segment routing).
    There is no use in reversing an RH in the present RPL
    specifications.

Thubert, et al. Standards Track [Page 16] RFC 8138 6LoWPAN Routing Header April 2017

    Point-to-Point (P2P) RPL reverses a path that was learned
    reactively as a part of the protocol operation, which is probably
    a cleaner way than a reversed echo on the data path.
    Reversing a header is discouraged (by RFC 2460 [RFC2460]) for
    Redirected Header Option (RHO) unless it is authenticated, which
    requires an Authentication Header (AH).  There is no definition of
    an AH operation for SRH, and there is no indication that the need
    exists in LLNs.
    AH does not protect the RH on the way.  AH is a validation at the
    receiver with the sole value of enabling the receiver to reverse
    it.
    A RPL domain is usually protected by L2 security, which secures
    both RPL itself and the RH in the packets at every hop.  This is a
    better security than that provided by AH.
 In summary, the benefit of saving energy and lowering the chances of
 loss by sending smaller frames over the LLN are seen as overwhelming
 compared to the value of possibly reversing the header.

5.4. Compression Reference for SRH-6LoRH Header Entries

 In order to optimize the compression of IP addresses present in the
 SRH headers, this specification requires that the 6LoWPAN layer
 identifies an address that is used as a reference for the
 compression.
 With this specification, the Compression Reference for the first
 address found in an SRH header is the source of the IPv6 packet, and
 then the reference for each subsequent entry is the address of its
 predecessor once it is uncompressed.
 With RPL [RFC6550], an SRH header may only be present in Non-Storing
 mode, and it may only be placed in the packet by the root of the
 DODAG, which must be the source of the resulting IPv6 packet
 [RFC2460].  In this case, the address used as Compression Reference
 is the address of the root.
 The Compression Reference MUST be determined as follows:
    The reference address may be obtained by configuration.  The
    configuration may indicate either the address in full or the
    identifier of a 6LoWPAN Context that carries the address
    [RFC6775], for instance, one of the 16 Context Identifiers used in
    LOWPAN_IPHC [RFC6282].

Thubert, et al. Standards Track [Page 17] RFC 8138 6LoWPAN Routing Header April 2017

    Else, if there is no IP-in-IP encapsulation, the source address in
    the IPv6 header that is compressed with LOWPAN_IPHC is the
    reference for the compression.
    Else, if the IP-in-IP compression specified in this document is
    used and the Encapsulator Address is provided, then the
    Encapsulator Address is the reference.
    Else, meaning that the IP-in-IP compression specified in this
    document is used and the encapsulator is implicitly the root, the
    address of the root is the reference.

5.5. Popping Headers

 Upon reception, the router checks whether the address in the first
 entry of the first SRH-6LoRH is one of its own addresses.  If that is
 the case, the router MUST consume that entry before forwarding, which
 is an action of popping from a stack, where the stack is effectively
 the sequence of entries in consecutive SRH-6LoRH headers.
 Popping an entry of an SRH-6LoRH header is a recursive action
 performed as follows:
    If the Size of the current SRH-6LoRH header is 1 or more
    (indicating that there are at least 2 entries in the header), the
    router removes the first entry and decrements the Size by 1.
    If the Size of the current SRH-6LoRH header is 0 (indicating that
    there is only 1 entry in the header) and there is no subsequent
    SRH-6LoRH after this, then the current SRH-6LoRH is removed.
    If the Size of the current SRH-6LoRH header is 0 and there is a
    subsequent SRH-6LoRH and the Type of the subsequent SRH-6LoRH is
    equal to or greater than the Type of the current SRH-6LoRH header
    (indicating the same or lesser compression yielding the same or
    larger compressed forms), then the current SRH-6LoRH is removed.
    If the Size of the current SRH-6LoRH header is 0 and there is a
    subsequent SRH-6LoRH and the Type of the subsequent SRH-6LoRH is
    less the Type of the current SRH-6LoRH header, the first entry of
    the subsequent SRH-6LoRH is removed and coalesced with the first
    entry of the current SRH-6LoRH.
    At the end of the process, if there are no more SRH-6LoRH in the
    packet, then the processing node is the last router along the
    source route path.
 An example of this operation is provided in Appendix A.3.

Thubert, et al. Standards Track [Page 18] RFC 8138 6LoWPAN Routing Header April 2017

5.6. Forwarding

 When receiving a packet with an SRH-6LoRH, a router determines the
 IPv6 address of the current segment endpoint.
 If strict source routing is enforced and this router is not the
 segment endpoint for the packet, then this router MUST drop the
 packet.
 If this router is the current segment endpoint, then the router pops
 its address as described in Section 5.5 and continues processing the
 packet.
 If there is still an SRH-6LoRH, then the router determines the new
 segment endpoint and routes the packet towards that endpoint.
 Otherwise, the router uses the destination in the inner IP header to
 forward or accept the packet.
 The segment endpoint of a packet MUST be determined as follows:
    The router first determines the Compression Reference as discussed
    in Section 4.3.1.
    The router then coalesces the Compression Reference with the first
    entry of the first SRH-6LoRH header as discussed in Section 5.4.
    If the SRH-6LoRH header is Type 4, then the coalescence is a full
    override.
 Since the Compression Reference is an uncompressed address, the
 coalesced IPv6 address is also expressed in the full 128 bits.

6. The RPL Packet Information 6LoRH (RPI-6LoRH)

 Section 11.2 of the RPL document [RFC6550] specifies the RPL Packet
 Information (RPI) as a set of fields that are placed by RPL routers
 in IP packets to identify the RPL Instance, detect anomalies, and
 trigger corrective actions.
 In particular, the SenderRank, which is the scalar metric computed by
 a specialized Objective Function such as described in RFC 6552
 [RFC6552], indicates the Rank of the sender and is modified at each
 hop.  The SenderRank field is used to validate that the packet
 progresses in the expected direction, either upwards or downwards,
 along the DODAG.

Thubert, et al. Standards Track [Page 19] RFC 8138 6LoWPAN Routing Header April 2017

 RPL defines the "The Routing Protocol for Low-Power and Lossy
 Networks (RPL) Option for Carrying RPL Information in Data-Plane
 Datagrams" [RFC6553] to transport the RPI, which is carried in an
 IPv6 Hop-by-Hop Options Header [RFC2460], typically consuming 8 bytes
 per packet.
 With RFC 6553 [RFC6553], the RPL Option is encoded as 6 octets, which
 must be placed in a Hop-by-Hop header that consumes two additional
 octets for a total of 8 octets.  To limit the header's range to just
 the RPL domain, the Hop-by-Hop header must be added to (or removed
 from) packets that cross the border of the RPL domain.
 The 8-byte overhead is detrimental to LLN operation, particularly
 with regard to bandwidth and battery constraints.  These bytes may
 cause a containing frame to grow above maximum frame size, leading to
 Layer 2 or 6LoWPAN [RFC4944] fragmentation, which in turn leads to
 even more energy expenditure and issues discussed in "LLN Fragment
 Forwarding and Recovery" [FORWARD-FRAG].
 An additional overhead comes from the need, in certain cases, to add
 an IP-in-IP encapsulation to carry the Hop-by-Hop header.  This is
 needed when the router that inserts the Hop-by-Hop header is not the
 source of the packet so that an error can be returned to the router.
 This is also the case when a packet originated by a RPL node must be
 stripped from the Hop-by-Hop header to be routed outside the RPL
 domain.
 For that reason, this specification defines an IP-in-IP-6LoRH header
 in Section 7, but it must be noted that removal of a 6LoRH header
 does not require manipulation of the packet in the LOWPAN_IPHC, and
 thus, if the source address in the LOWPAN_IPHC is the node that
 inserted the IP-in-IP-6LoRH header, then this situation alone does
 not mandate an IP-in-IP-6LoRH header.
 Note: It was found that some implementations omit the RPI for packets
 going down the RPL graph in Non-Storing mode, even though RPL
 indicates that the RPI should be placed in the packet.  With this
 specification, the RPI is important to indicate the RPLInstanceID, so
 the RPI should not be omitted.
 As a result, a RPL packet may bear only an RPI-6LoRH header and no
 IP-in-IP-6LoRH header.  In that case, the source and destination of
 the packet are specified by the LOWPAN_IPHC.
 As with RFC 6553 [RFC6553], the fields in the RPI include an 'O', an
 'R', and an 'F' bit, an 8-bit RPLInstanceID (with some internal
 structure), and a 16-bit SenderRank.

Thubert, et al. Standards Track [Page 20] RFC 8138 6LoWPAN Routing Header April 2017

 The remainder of this section defines the RPI-6LoRH header, which is
 a Critical 6LoWPAN Routing Header that is designed to transport the
 RPI in 6LoWPAN LLNs.

6.1. Compressing the RPLInstanceID

 RPL Instances are discussed in Section 5 of the RPL specification
 [RFC6550].  A number of simple use cases do not require more than one
 RPL Instance, and in such cases, the RPL Instance is expected to be
 the Global Instance 0.  A global RPLInstanceID is encoded in a
 RPLInstanceID field as follows:
     0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+
    |0|     ID      |  Global RPLInstanceID in 0..127
    +-+-+-+-+-+-+-+-+
       Figure 8: RPLInstanceID Field Format for Global Instances
 For the particular case of the Global Instance 0, the RPLInstanceID
 field is all zeros.  This specification allows the compressor to
 elide a RPLInstanceID field that is all zeros and defines an I flag
 that, when set, signals that the field is elided.

6.2. Compressing the SenderRank

 The SenderRank is the result of the DAGRank operation on the Rank of
 the sender; here, the DAGRank operation is defined in Section 3.5.1
 of the RPL specification [RFC6550] as:
    DAGRank(rank) = floor(rank/MinHopRankIncrease)
 If MinHopRankIncrease is set to a multiple of 256, the least
 significant eight bits of the SenderRank will be all zeroes; by
 eliding those, the SenderRank can be compressed into a single byte.
 This idea is used in RFC 6550 [RFC6550], by defining
 DEFAULT_MIN_HOP_RANK_INCREASE as 256, and in RFC 6552 [RFC6552],
 which defaults MinHopRankIncrease to DEFAULT_MIN_HOP_RANK_INCREASE.
 This specification allows for the SenderRank to be encoded as either
 1 or 2 bytes and defines a K flag that, when set, signals that a
 single byte is used.

6.3. The Overall RPI-6LoRH Encoding

 The RPI-6LoRH header provides a compressed form for the RPL RPI.
 Routers that need to forward a packet with a RPI-6LoRH header are
 expected to be RPL routers that support this specification.

Thubert, et al. Standards Track [Page 21] RFC 8138 6LoWPAN Routing Header April 2017

 If a non-RPL router receives a packet with a RPI-6LoRH header, there
 was a routing or a configuration error (see Section 8).
 The desired reaction for the non-RPL router is to drop the packet as
 opposed to skip the header and forward the packet, which could end up
 forming loops by reinjecting the packet in the wrong RPL Instance.
 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates it
 is Critical.  Routers that understand the 6LoRH general format
 detailed in Section 4 cannot ignore a 6LoRH header of this type and
 will drop the packet if it is unknown to them.
 Since the RPI-6LoRH header is a Critical header, the TSE field does
 not need to be a length expressed in bytes.  Here, the field is fully
 reused for control bits that encode the O, R, and F flags from the
 RPI, as well as the I and K flags that indicate the compression
 format.
 The RPI-6LoRH is Type 5.
 The RPI-6LoRH header is immediately followed by the RPLInstanceID
 field, unless that field is fully elided, and then the SenderRank,
 which is either compressed into one byte or fully in-lined as 2
 bytes.  The I and K flags in the RPI-6LoRH header indicate whether
 the RPLInstanceID is elided and/or the SenderRank is compressed.
 Depending on these bits, the Length of the RPI-6LoRH may vary as
 described hereafter.
     0                   1                   2
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  ...  -+-+-+
    |1|0|0|O|R|F|I|K| 6LoRH Type=5  |   Compressed fields  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+  ...  -+-+-+
                Figure 9: The Generic RPI-6LoRH Format
 O, R, and F bits:  The O, R, and F bits are defined in Section 11.2
       of RFC 6550 [RFC6550].
 I flag:  If it is set, the RPLInstanceID is elided and the
       RPLInstanceID is the Global RPLInstanceID 0.  If it is not set,
       the octet immediately following the Type field contains the
       RPLInstanceID as specified in Section 5.1 of RFC 6550
       [RFC6550].
 K flag:  If it is set, the SenderRank is compressed into 1 octet,
       with the least significant octet elided.  If it is not set, the
       SenderRank is fully inlined as 2 octets.

Thubert, et al. Standards Track [Page 22] RFC 8138 6LoWPAN Routing Header April 2017

 In Figure 10, the RPLInstanceID is the Global RPLInstanceID 0, and
 the MinHopRankIncrease is a multiple of 256, so the least significant
 byte is all zeros and can be elided:
     0                   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|O|R|F|1|1| 6LoRH Type=5  | SenderRank    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              I=1, K=1
               Figure 10: The Most Compressed RPI-6LoRH
 In Figure 11, the RPLInstanceID is the Global RPLInstanceID 0, but
 both bytes of the SenderRank are significant so it cannot be
 compressed:
     0                   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|0|O|R|F|1|0| 6LoRH Type=5  |        SenderRank             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              I=1, K=0
                 Figure 11: Eliding the RPLInstanceID
 In Figure 12, the RPLInstanceID is not the Global RPLInstanceID 0,
 and the MinHopRankIncrease is a multiple of 256:
     0                   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|0|O|R|F|0|1| 6LoRH Type=5  | RPLInstanceID |  SenderRank   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              I=0, K=1
                   Figure 12: Compressing SenderRank

Thubert, et al. Standards Track [Page 23] RFC 8138 6LoWPAN Routing Header April 2017

 In Figure 13, the RPLInstanceID is not the Global RPLInstanceID 0,
 and both bytes of the SenderRank are significant:
     0                   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|0|O|R|F|0|0| 6LoRH Type=5  | RPLInstanceID |    Sender-...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ...-Rank      |
    +-+-+-+-+-+-+-+-+
              I=0, K=0
           Figure 13: The Least Compressed Form of RPI-6LoRH

7. The IP-in-IP 6LoRH Header

 The IP-in-IP 6LoRH (IP-in-IP-6LoRH) header is an Elective 6LoWPAN
 Routing Header that provides a compressed form for the encapsulating
 IPv6 Header in the case of an IP-in-IP encapsulation.
 An IP-in-IP encapsulation is used to insert a field such as a Routing
 Header or an RPI at a router that is not the source of the packet.
 In order to send an error back regarding the inserted field, the
 address of the router that performs the insertion must be provided.
 The encapsulation can also enable the last router prior to the
 Destination to remove a field such as the RPI, but this can be done
 in the compressed form by removing the RPI-6LoRH, so an IP-in-IP-
 6LoRH encapsulation is not required for that sole purpose.
 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates it
 is Elective.  This field is not Critical for routing since it does
 not indicate the destination of the packet, which is either encoded
 in an SRH-6LoRH header or in the inner IP header.  A 6LoRH header of
 this type can be skipped if not understood (per Section 4), and the
 6LoRH header indicates the Length in bytes.
   0                   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|1| Length  | 6LoRH Type 6  |  Hop Limit    | Encaps. Address  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-       ...      -+
                     Figure 14: The IP-in-IP-6LoRH

Thubert, et al. Standards Track [Page 24] RFC 8138 6LoWPAN Routing Header April 2017

 The Length of an IP-in-IP-6LoRH header is expressed in bytes and MUST
 be at least 1, to indicate a Hop Limit (HL) that is decremented at
 each hop.  When the HL reaches 0, the packet is dropped per RFC 2460
 [RFC2460].
 If the Length of an IP-in-IP-6LoRH header is exactly 1, then the
 Encapsulator Address is elided, which means that the encapsulator is
 a well-known router, for instance, the root in a RPL graph.
 The most efficient compression of an IP-in-IP encapsulation that can
 be achieved with this specification is obtained when an endpoint of
 the packet is the root of the RPL DODAG associated to the RPL
 Instance that is used to forward the packet, and the root address is
 known implicitly as opposed to signaled explicitly in the data
 packets.
 If the Length of an IP-in-IP-6LoRH header is greater than 1, then an
 Encapsulator Address is placed in a compressed form after the Hop
 Limit field.  The value of the Length indicates which compression is
 performed on the Encapsulator Address.  For instance, a Length of 3
 indicates that the Encapsulator Address is compressed to 2 bytes.
 The reference for the compression is the address of the root of the
 DODAG.  The way the address of the root is determined is discussed in
 Section 4.3.2.
 With RPL, the destination address in the IP-in-IP header is
 implicitly the root in the RPL graph for packets going upwards; in
 Storing mode, it is the destination address in the LOWPAN_IPHC for
 packets going downwards.  In Non-Storing mode, there is no implicit
 value for packets going downwards.
 If the implicit value is correct, the destination IP address of the
 IP-in-IP encapsulation can be elided.  Else, the destination IP
 address of the IP-in-IP header is transported in an SRH-6LoRH header
 as the first entry of the first of these headers.
 If the final destination of the packet is a leaf that does not
 support this specification, then the chain of 6LoRH headers must be
 stripped by the RPL/6LR router to which the leaf is attached.  In
 that example, the destination IP address of the IP-in-IP header
 cannot be elided.
 In the special case where a 6LoRH header is used to route 6LoWPAN
 fragments, the destination address is not accessible in the
 LOWPAN_IPHC on all fragments and can be elided only for the first
 fragment and for packets going upwards.

Thubert, et al. Standards Track [Page 25] RFC 8138 6LoWPAN Routing Header April 2017

8. Management Considerations

 Though it is possible to decompress a packet at any hop, this
 specification is optimized to enable that a packet is forwarded in
 its compressed form all the way, and it makes sense to deploy
 homogeneous networks where all nodes, or no nodes at all, use the
 compression technique detailed therein.
 This specification aims at a simple implementation running in
 constrained nodes, so it does indeed expect a homogeneous network
 and, as a consequence, it does not provide a method to determine the
 level of support by the next hops at forwarding time.
 Should an extension to this specification provide such a method,
 forwarding nodes could compress or decompress the RPL artifacts
 appropriately and enable a backward compatibility between nodes that
 support this specification and nodes that do not.
 It results that this specification does not attempt to enable such
 backwards compatibility.  It does not require extraneous code to
 exchange and handle error messages to automatically correct mismatch
 situations either.
 When a packet is expected to carry a 6LoRH header but does not, the
 node that discovers the issue is expected to send an ICMPv6 error
 message to the root.  It should be sent at an adapted rate-limitation
 and with a type 4 (indicating a "Parameter Problem") and a code 0
 (indicating an "Unrecognized Next Header field encountered").  The
 relevant portion of the received packet should be embedded and the
 offset therein where the 6LoRH header was expected should be pointed
 out.
 When a packet is received with a 6LoRH header that is not recognized,
 the node that discovers the issue is expected to send an ICMPv6 error
 message to the root.  It should be sent at an adapted rate-limitation
 and with a type 4 (indicating a "Parameter Problem") and a code 1
 (indicating an "Unrecognized Next Header type encountered").  The
 relevant portion of the received packet should be embedded and the
 offset therein where the 6LoRH header was expected should be pointed
 out.
 In both cases, the node SHOULD NOT place a 6LoRH header as defined in
 this specification in the resulting message, and the node should
 either omit the RPI or place it uncompressed after the IPv6 header.
 Additionally, in both cases, an alternate management method may be
 preferred in order to notify the network administrator that there is
 a configuration error.

Thubert, et al. Standards Track [Page 26] RFC 8138 6LoWPAN Routing Header April 2017

 Keeping the network homogeneous is either a deployment issue, by
 deploying only devices with a same capability, or a management issue,
 by configuring all devices to either use or not use a certain level
 of this compression technique and its future additions.
 In particular, the situation where a node receives a message with a
 Critical 6LoWPAN Routing Header that it does not understand is an
 administrative error whereby the wrong device is placed in a network,
 or the device is misconfigured.
 When a mismatch situation is detected, it is expected that the device
 raises some management alert indicating the issue, e.g., that it has
 to drop a packet with a Critical 6LoRH.

9. Security Considerations

 The security considerations of RFC 4944 [RFC4944], RFC 6282
 [RFC6282], and RFC 6553 [RFC6553] apply.
 Using a compressed format as opposed to the full in-line format is
 logically equivalent and is believed not to create an opening for a
 new threat when compared to RFC 6550 [RFC6550], RFC 6553 [RFC6553],
 and RFC 6554 [RFC6554], noting that, even though intermediate hops
 are removed from the SRH header as they are consumed, a node may
 still identify that the rest of the source-routed path includes a
 loop or not (see the "Security" section of RFC 6554).  It must be
 noted that if the attacker is not part of the loop, then there is
 always a node at the beginning of the loop that can detect it and
 remove it.

10. IANA Considerations

10.1. Reserving Space in 6LoWPAN Dispatch Page 1

 This specification reserves Dispatch Value Bit Patterns within the
 6LoWPAN Dispatch Page 1 as follows:
    10 1xxxxx: for Elective 6LoWPAN Routing Headers
    10 0xxxxx: for Critical 6LoWPAN Routing Headers
 Additionally, this document creates two IANA registries: one for the
 Critical 6LoWPAN Routing Header Type and one for the Elective 6LoWPAN
 Routing Header Type, each with 256 possible values, from 0 to 255, as
 described below.
 Future assignments are made by IANA using the "RFC Required"
 procedure [RFC5226].

Thubert, et al. Standards Track [Page 27] RFC 8138 6LoWPAN Routing Header April 2017

10.2. New Critical 6LoWPAN Routing Header Type Registry

 This document creates an IANA registry titled "Critical 6LoWPAN
 Routing Header Type" and assigns the following values:
    0-4: SRH-6LoRH [RFC8138]
    5: RPI-6LoRH [RFC8138]

10.3. New Elective 6LoWPAN Routing Header Type Registry

 This document creates an IANA registry titled "Elective 6LoWPAN
 Routing Header Type" and assigns the following value:
    6: IP-in-IP-6LoRH [RFC8138]

11. References

11.1. Normative References

 [IEEE.802.15.4]
            IEEE, "IEEE Standard for Low-Rate Wireless Networks",
            IEEE 802.15.4-2015, DOI 10.1109/IEEESTD.2016.7460875,
            <http://ieeexplore.ieee.org/document/7460875/>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
            December 1998, <http://www.rfc-editor.org/info/rfc2460>.
 [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
            Control Message Protocol (ICMPv6) for the Internet
            Protocol Version 6 (IPv6) Specification", RFC 4443,
            DOI 10.17487/RFC4443, March 2006,
            <http://www.rfc-editor.org/info/rfc4443>.
 [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
            "Transmission of IPv6 Packets over IEEE 802.15.4
            Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
            <http://www.rfc-editor.org/info/rfc4944>.

Thubert, et al. Standards Track [Page 28] RFC 8138 6LoWPAN Routing Header April 2017

 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            DOI 10.17487/RFC5226, May 2008,
            <http://www.rfc-editor.org/info/rfc5226>.
 [RFC6282]  Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
            Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
            DOI 10.17487/RFC6282, September 2011,
            <http://www.rfc-editor.org/info/rfc6282>.
 [RFC6550]  Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
            Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
            JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
            Low-Power and Lossy Networks", RFC 6550,
            DOI 10.17487/RFC6550, March 2012,
            <http://www.rfc-editor.org/info/rfc6550>.
 [RFC6552]  Thubert, P., Ed., "Objective Function Zero for the Routing
            Protocol for Low-Power and Lossy Networks (RPL)",
            RFC 6552, DOI 10.17487/RFC6552, March 2012,
            <http://www.rfc-editor.org/info/rfc6552>.
 [RFC6553]  Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
            Power and Lossy Networks (RPL) Option for Carrying RPL
            Information in Data-Plane Datagrams", RFC 6553,
            DOI 10.17487/RFC6553, March 2012,
            <http://www.rfc-editor.org/info/rfc6553>.
 [RFC6554]  Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
            Routing Header for Source Routes with the Routing Protocol
            for Low-Power and Lossy Networks (RPL)", RFC 6554,
            DOI 10.17487/RFC6554, March 2012,
            <http://www.rfc-editor.org/info/rfc6554>.
 [RFC8025]  Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
            Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
            RFC 8025, DOI 10.17487/RFC8025, November 2016,
            <http://www.rfc-editor.org/info/rfc8025>.

11.2. Informative References

 [FORWARD-FRAG]
            Thubert, P., Ed. and J. Hui, "LLN Fragment Forwarding and
            Recovery", Work in Progress, draft-thubert-6lo-forwarding-
            fragments-05, April 2017.

Thubert, et al. Standards Track [Page 29] RFC 8138 6LoWPAN Routing Header April 2017

 [IPv6-ARCH]
            Thubert, P., Ed., "An Architecture for IPv6 over the TSCH
            mode of IEEE 802.15.4", Work in Progress,
            draft-ietf-6tisch-architecture-11, January 2017.
 [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
            Bormann, "Neighbor Discovery Optimization for IPv6 over
            Low-Power Wireless Personal Area Networks (6LoWPANs)",
            RFC 6775, DOI 10.17487/RFC6775, November 2012,
            <http://www.rfc-editor.org/info/rfc6775>.
 [RFC7102]  Vasseur, JP., "Terms Used in Routing for Low-Power and
            Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
            2014, <http://www.rfc-editor.org/info/rfc7102>.
 [RFC7228]  Bormann, C., Ersue, M., and A. Keranen, "Terminology for
            Constrained-Node Networks", RFC 7228,
            DOI 10.17487/RFC7228, May 2014,
            <http://www.rfc-editor.org/info/rfc7228>.
 [RFC7554]  Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
            IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
            Internet of Things (IoT): Problem Statement", RFC 7554,
            DOI 10.17487/RFC7554, May 2015,
            <http://www.rfc-editor.org/info/rfc7554>.
 [RPL-INFO] Robles, M., Richardson, M., and P. Thubert, "When to use
            RFC 6553, 6554 and IPv6-in-IPv6", Work in Progress,
            draft-ietf-roll-useofrplinfo-14, April 2017.

Thubert, et al. Standards Track [Page 30] RFC 8138 6LoWPAN Routing Header April 2017

Appendix A. Examples

A.1. Examples Compressing the RPI

 The example in Figure 15 illustrates the 6LoRH compression of a
 classical packet in Storing mode in all directions, as well as in
 Non-Storing mode for a packet going up the DODAG following the
 default route to the root.  In this particular example, a
 fragmentation process takes place per RFC 4944 [RFC4944], and the
 fragment headers must be placed in Page 0 before switching to Page 1:
 +-  ...  -+-  ...  -+-+ ... -+- ... +-+-+ ... -+-+-+-+-+-+-+-+-+-+...
 |Frag type|Frag hdr |11110001|  RPI-  |IP-in-IP| LOWPAN_IPHC | ...
 |RFC 4944 |RFC 4944 | Page 1 | 6LoRH  | 6LoRH  |             |
 +-  ...  -+-  ...  -+-+ ... -+- ... +-+-+ ... -+-+-+-+-+-+-+-+-+-+...
                                                 <-  RFC 6282  ->
                                                  No RPL artifact
 +-  ...  -+-  ...  -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+...
 |Frag type|Frag hdr |
 |RFC 4944 |RFC 4944 |  Payload (cont)
 +-  ...  -+-  ...  -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+...
 +-  ...  -+-  ...  -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+...
 |Frag type|Frag hdr |
 |RFC 4944 |RFC 4944 |  Payload (cont)
 +-  ...  -+-  ...  -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+...
             Figure 15: Example Compressed Packet with RPI
 In Storing mode, if the packet stays within the RPL domain, then it
 is possible to save the IP-in-IP encapsulation, in which case, only
 the RPI is compressed with a 6LoRH, as illustrated in Figure 16 in
 the case of a non-fragmented ICMP packet:
 +- ...  -+-+- ... -+-+-+-+ ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+...
 |11110001| RPI-6LoRH |  NH = 0      | NH = 58  |  ICMP message ...
 |Page 1  |  Type 5   | 6LOWPAN_IPHC | (ICMP)   |  (no compression)
 +- ...  -+-+- ... -+-+-+-+ ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+...
                       <-      RFC 6282       ->
                           No RPL artifact
        Figure 16: Example ICMP Packet with RPI in Storing Mode

Thubert, et al. Standards Track [Page 31] RFC 8138 6LoWPAN Routing Header April 2017

 The format in Figure 16 is logically equivalent to the uncompressed
 format illustrated in Figure 17:
 +-+-+-+- ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
 |  IPv6 Header  | Hop-by-Hop |  RPI in       |  ICMP message ...
 |  NH = 58      | Header     |  RPL Option   |
 +-+-+-+- ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...
             Figure 17: Uncompressed ICMP Packet with RPI
 For a UDP packet, the transport header can be compressed with 6LoWPAN
 HC [RFC6282] as illustrated in Figure 18:
 +-+ ... -+-+-...-+-+- ... -+-+-+-+ ... -+-+-+ ... -+-+-+-+-+...
 |11110001| RPI-  | NH=1        |11110CPP| Compressed | UDP
 |Page 1  | 6LoRH | LOWPAN_IPHC | UDP    | UDP header | Payload
 +-+ ... -+-+-...-+-+- ... -+-+-+-+ ... -+-+-+ ... -+-+-+-+-+...
                   <-         RFC 6282              ->
                              No RPL artifact
             Figure 18: Uncompressed ICMP Packet with RPI
 If the packet is received from the Internet in Storing mode, then the
 root is supposed to encapsulate the packet to insert the RPI.  The
 resulting format would be as represented in Figure 19:

+-+ … -+-+-…-+-+– … -+-+-+-+- … -+-+ … -+-+-+ … -+-+-+… |11110001| RPI- | IP-in-IP | NH=1 |11110CPP| Compressed | UDP |Page 1 | 6LoRH | 6LoRH | LOWPAN_IPHC | UDP | UDP header | Payld +-+ … -+-+-…-+-+– … -+-+-+-+- … -+-+ … -+-+-+ … -+-+-+…

                            <-         RFC 6282              ->
                                       No RPL artifact
          Figure 19: RPI Inserted by the Root in Storing Mode

A.2. Example of a Downward Packet in Non-Storing Mode

 The example illustrated in Figure 20 is a classical packet in Non-
 Storing mode for a packet going down the DODAG following a source-
 routed path from the root.  Say that we have four forwarding hops to
 reach a destination.  In the uncompressed form, when the root
 generates the packet, the last 3 hops are encoded in a Routing Header
 Type 3 (SRH) and the first hop is the destination of the packet.  The
 intermediate hops perform a swap; the hop count indicates the current
 active hop as defined in RFC 2460 [RFC2460] and RFC 6554 [RFC6554].

Thubert, et al. Standards Track [Page 32] RFC 8138 6LoWPAN Routing Header April 2017

 When compressed with this specification, the 4 hops are encoded in
 SRH-6LoRH when the root generates the packet, and the final
 destination is left in the LOWPAN_IPHC.  There is no swap; the
 forwarding node that corresponds to the first entry effectively
 consumes it when forwarding, which means that the size of the encoded
 packet decreases and that the hop information is lost.
 If the last hop in an SRH-6LoRH is not the final destination, then it
 removes the SRH-6LoRH before forwarding.
 In the particular example illustrated in Figure 20, all addresses in
 the DODAG are assigned from the same /112 prefix and the last 2
 octets encoding an identifier such as an IEEE 802.15.4 short address.
 In that case, all addresses can be compressed to 2 octets, using the
 root address as reference.  There will be one SRH_6LoRH header with,
 in this example, three compressed addresses:

+-+ … -+-+ … +-+- … -+-+- … +-+-+-+ … +-+-+ … -+ … +-… |11110001|SRH-6LoRH| RPI- | IP-in-IP | NH=1 |11110CPP| UDP | UDP |Page 1 |Type1 S=2| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld +-+ … -+-+ … +-+- … -+-+– … -+-+-+ … +-+-+ … -+ … +-…

          <-8bytes->                  <-        RFC 6282      ->
                                              No RPL artifact
             Figure 20: Example Compressed Packet with SRH
 One may note that the RPI is provided.  This is because the address
 of the root that is the source of the IP-in-IP header is elided and
 inferred from the RPLInstanceID in the RPI.  Once found from a local
 context, that address is used as a Compression Reference to expand
 addresses in the SRH-6LoRH.
 With the RPL specifications available at the time of writing, the
 root is the only node that may incorporate an SRH in an IP packet.
 When the root forwards a packet that it did not generate, it has to
 encapsulate the packet with IP-in-IP.
 But, if the root generates the packet towards a node in its DODAG,
 then it should avoid the extra IP-in-IP as illustrated in Figure 21:
 +- ...  -+-+-+ ... +-+-+-+ ... -+-+-+-+-+-+-+-++-+- ... -+-+-+-+-+...
 |11110001| SRH-6LoRH | NH=1       | 11110CPP  | Compressed | UDP
 |Page 1  | Type1 S=3 | LOWPAN_IPHC| LOWPAN-NHC| UDP header | Payload
 +- ...  -+-+-+ ... +-+-+-+ ... -+-+-+-+-+-+-+-++-+- ... -+-+-+-+-+...
                                        <-        RFC 6282        ->
      Figure 21: Compressed SRH 4*2bytes Entries Sourced by Root

Thubert, et al. Standards Track [Page 33] RFC 8138 6LoWPAN Routing Header April 2017

 Note: The RPI is not represented, though RPL [RFC6550] generally
 expects it.  In this particular case, since the Compression Reference
 for the SRH-6LoRH is the source address in the LOWPAN_IPHC, and the
 routing is strict along the source route path, the RPI does not
 appear to be absolutely necessary.
 In Figure 21, all the nodes along the source route path share the
 same /112 prefix.  This is typical of IPv6 addresses derived from an
 IEEE802.15.4 short address, as long as all the nodes share the same
 PAN-ID.  In that case, a Type 1 SRH-6LoRH header can be used for
 encoding.  The IPv6 address of the root is taken as reference, and
 only the last 2 octets of the address of the intermediate hops are
 encoded.  The Size of 3 indicates 4 hops, resulting in an SRH-6LoRH
 of 10 bytes.

A.3. Example of SRH-6LoRH Life Cycle

 This section illustrates the operation specified in Section 5.6 of
 forwarding a packet with a compressed SRH along an A->B->C->D source
 route path.  The operation of popping addresses is exemplified at
 each hop.
 Packet as received by node A
 ----------------------------
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA AAAA AAAA
   Type 1 SRH-6LoRH Size = 0                  BBBB
   Type 2 SRH-6LoRH Size = 1             CCCC CCCC
                                         DDDD DDDD
  Step 1: Popping BBBB, the first entry of the next SRH-6LoRH
  Step 2: If larger value (2 vs. 1), the SRH-6LoRH is removed
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA AAAA AAAA
   Type 2 SRH-6LoRH Size = 1             CCCC CCCC
                                         DDDD DDDD
  Step 3: Recursion ended; coalescing BBBB with the first entry
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA AAAA BBBB
  Step 4: Routing based on next segment endpoint to B
                    Figure 22: Processing at Node A

Thubert, et al. Standards Track [Page 34] RFC 8138 6LoWPAN Routing Header April 2017

 Packet as received by node B
 ----------------------------
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA AAAA BBBB
   Type 2 SRH-6LoRH Size = 1             CCCC CCCC
                                         DDDD DDDD
  Step 1: Popping CCCC CCCC, the first entry of the next SRH-6LoRH
  Step 2: Removing the first entry and decrementing the Size (by 1)
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA AAAA BBBB
   Type 2 SRH-6LoRH Size = 0             DDDD DDDD
  Step 3: Recursion ended; coalescing CCCC CCCC with the first entry
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA CCCC CCCC
  Step 4: Routing based on next segment endpoint to C
                    Figure 23: Processing at Node B
 Packet as received by node C
 ----------------------------
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA CCCC CCCC
   Type 2 SRH-6LoRH Size = 0             DDDD DDDD
  Step 1: Popping DDDD DDDD, the first entry of the next SRH-6LoRH
  Step 2: The SRH-6LoRH is removed
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA CCCC CCCC
  Step 3: Recursion ended; coalescing DDDD DDDDD with the first entry
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA DDDD DDDD
  Step 4: Routing based on next segment endpoint to D
                    Figure 24: Processing at Node C
 Packet as received by node D
 ----------------------------
   Type 3 SRH-6LoRH Size = 0   AAAA AAAA DDDD DDDD
  Step 1: The SRH-6LoRH is removed
  Step 2: No more header; routing based on inner IP header
                    Figure 25: Processing at Node D

Thubert, et al. Standards Track [Page 35] RFC 8138 6LoWPAN Routing Header April 2017

Acknowledgements

 The authors wish to thank Tom Phinney, Thomas Watteyne, Tengfei
 Chang, Martin Turon, James Woodyatt, Samita Chakrabarti, Jonathan
 Hui, Gabriel Montenegro, and Ralph Droms for constructive reviews to
 the design in the 6lo working group.  The overall discussion involved
 participants to the 6MAN, 6TiSCH, and ROLL WGs; thank you all.
 Special thanks to Michael Richardson and Ines Robles (the Chairs of
 the ROLL WG), Brian Haberman (the Internet Area AD), and Alvaro
 Retana and Adrian Farrel (Routing Area ADs) for driving this complex
 effort across working groups and areas.

Thubert, et al. Standards Track [Page 36] RFC 8138 6LoWPAN Routing Header April 2017

Authors' Addresses

 Pascal Thubert (editor)
 Cisco Systems
 Building D - Regus
 45 Allee des Ormes
 BP1200
 MOUGINS - Sophia Antipolis  06254
 France
 Phone: +33 4 97 23 26 34
 Email: pthubert@cisco.com
 Carsten Bormann
 Universitaet Bremen TZI
 Postfach 330440
 Bremen  D-28359
 Germany
 Phone: +49-421-218-63921
 Email: cabo@tzi.org
 Laurent Toutain
 IMT Atlantique
 2 rue de la Chataigneraie
 CS 17607
 Cesson-Sevigne Cedex  35576
 France
 Email: Laurent.Toutain@IMT-Atlantique.fr
 Robert Cragie
 ARM Ltd.
 110 Fulbourn Road
 Cambridge  CB1 9NJ
 United Kingdom
 Email: robert.cragie@arm.com

Thubert, et al. Standards Track [Page 37]

/data/webs/external/dokuwiki/data/pages/rfc/rfc8138.txt · Last modified: 2017/04/11 23:05 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki