6lo P. Thubert, Ed.
Internet-Draft Cisco
Intended status: Standards Track C. Bormann
Expires: July 17, 2016 Uni Bremen TZI
L. Toutain
R. Cragie
January 14, 2016

6LoWPAN Routing Header And Paging Dispatches


This specification introduces a new 6LoWPAN dispatch type for use in 6LoWPAN Route-Over topologies, that initially covers the needs of RPL (RFC6550) data packets compression. Using this dispatch type, this specification defines a method to compress RPL Option (RFC6553) information and Routing Header type 3 (RFC6554), an efficient IP-in-IP technique and is extensible for more applications.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on July 17, 2016.

Copyright Notice

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Table of Contents

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 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 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 [IEEE802154] is limited to 127 bytes per frame. The need to compress IPv6 packets over IEEE 802.15.4 led to the 6LoWPAN Header Compression [RFC6282] work (6LoWPAN-HC).

Innovative Route-over techniques have been and are still being developed for routing inside a LLN. In a general fashion, 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 ICMP errors 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 a mesh root, as opposed to the source node. This is also the case when some routing information must be removed from a packet that flows outside the LLN. When to use RFC 6553, 6554 and IPv6-in-IPv6 [I-D.robles-roll-useofrplinfo] details different cases where RFC 6553, RFC 6554 and IPv6-in-IPv6 encapsulation is required to set the bases to help defining the compression of RPL routing information in LLN environments.

When using [RFC6282] the outter IP header of an IP-in-IP encapsulation may be compressed down to 2 octets in stateless compression and down to 3 octets in case of a stateful compression when a 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 (RFC6282).

The Stateless Compression of an IPv6 addresses can only happen if the IPv6 address can de deduced from the MAC addresses, meaning that the IP end point is also the MAC-layer endpoint. This is generally not the case in a RPL network which is generally a multi-hop route-over (operated at Layer-3) network. A better compression, that does not involve variable compressions depending on the hop in the mesh, can be achieved based on the fact that the outter 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 [RFC6282] if all the fields up to it are also compressed. This specification makes it so that the inner IP header is the first header that is compressed by [RFC6282], and conserves the inner packet encoded the same way whether it is encapsulated or not, conserving existing implementation.

As an example, the Routing Protocol for Low Power and Lossy Networks [RFC6550] (RPL) 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 [RFC6550].

The RPL Option for Carrying RPL Information in Data-Plane Datagrams [RFC6553] specification indicates how the RPI can be placed in a RPL Option for use in an IPv6 Hop-by-Hop header. This representation demands a total of 8 bytes when 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 removed from packets that leave the domain, and be inserted in packets entering the domain. In both cases, this operation implies an IP-in-IP encapsulation.

           ------+---------                            ^
                 |          Internet                   |
                 |                                     | Native IPv6
              +-----+                                  |
              |     | Border Router (RPL Root)    ^    |    ^
              |     |                             |    |    |
              +-----+                             |    |    | IPv6 in
                 |                                |    |    | IPv6
           o    o   o    o                        |    |    | + RPI
       o o   o  o   o  o  o o   o                 |    |    |  or RH3
      o  o o  o o    o   o   o  o  o              |    |    |
      o   o    o  o     o  o    o  o  o           |    |    |
     o  o   o  o   o         o   o o              v    v    v
     o          o             o     o

Figure 2: IP-in-IP Encapsulation within the LLN.

Additionally, in the case of the Non-Storing Mode of Operation (MOP), RPL requires a Routing Header type 3 (RH3) as defined in the IPv6 Routing Header for Source Routes with RPL [RFC6554] specification, for all packets that are routed down a RPL graph. 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 RH3 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 the packet stays within the LLN or not, 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 RH3.

6TiSCH [I-D.ietf-6tisch-architecture] specifies the operation of IPv6 over the TimeSlotted Channel Hopping [RFC7554] (TSCH) mode of operation of IEEE 802.15.4. The architecture requires the use of both RPL and the 6lo adaptation layer over IEEE 802.15.4. Because it inherits the constraints on the frame size from the MAC layer, 6TiSCH cannot afford to spend 8 bytes per packet on the RPI. Hence the requirement for a 6LoWPAN header compression of the RPI.

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. The specification 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 [RFC2119].

The Terminology used in this document is consistent with and incorporates that described in `Terminology in Low power And Lossy Networks’ [RFC7102] and [RFC6550].

The terms Route-over and Mesh-under are defined in [RFC6775].

Other terms in use in LLNs are found in [RFC7228].

The term “byte” is used in its now customary sense as a synonym for “octet”.

3. Using the Page Dispatch

The6LoWPAN Paging Dispatch [I-D.ietf-paging-dispatch] 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 draft operates within the 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 RH3, as well as other sorts of routing information such as the RPL Packet Information and IP-in-IP encapsulation.

The 6LoRH is expressed in a 6loWPAN packet as a Type-Length-Value (TLV) field, which is extensible for future use.

This specification uses the bit pattern 10xxxxxx in Page 1 for the new 6LoRH Dispatch and Section 4 describes how RPL artifacts in data packets can be compressed as 6LoRH headers.

3.2. Placement Of The 6LoRH

In a zone of a packet where Page 1 is active, which means once a Page 1 Paging Dispatch is parsed, and as long as no other Paging Dispatch is parsed, the parsing of the packet MUST follow this specification if the 6LoRH Bit Pattern 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.

One or more 6LoRH header(s) MAY be placed in a 6LoWPAN packet. A 6LoRH header MUST always be placed before the LOWPAN_IPHC as defined in 6LoWPAN Header Compression [RFC6282].

A 6LoRH header being always placed in a Page 1 context, it MUST always be placed after any Fragmentation Header and/or Mesh Header [RFC4944].

4. 6LoWPAN Routing Header General Format

The 6LoRH reuses in Page 1 the Dispatch Value Bit Pattern of 10xxxxxx.

The Dispatch Value Bit Pattern is split in two forms of 6LoRH:

  • Elective (6LoRHE) that may skipped if not understood

  • Critical (6LoRHC) that may not be ignored

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 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 known.

Type of the 6LoRHE

4.2. Critical Format

The 6LoRHC uses the Dispatch Value Bit Pattern of 100xxxxx.

A node which does not support the 6LoRHC Type MUST silently discard the packet.

Note: The situation where a node receives a message with a Critical 6LoWPAN Routing Header that it does not understand is a critical administrative error whereby the wrong device is placed in a network. It makes no sense to overburden the constrained device with code that would cause ICMP error to the source. Rather, it is expected that the device will raise some management alert indicating that it cannot operate in this network for that reason. It results that there is no provision for the exchange of error messages for this situation; it should be avoided by judicious use of administrative control and/or capability indications by the device manufacturer.

  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.


Type Specific Extension. 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 of the 6LoRHC

5. The Routing Header Type 3 (RH3) 6LoRH

The Routing Header type 3 (RH3) 6LoRH (RH3-6LoRH) is a Critical 6LoWPAN Routing Header that provides a compressed form for the RH3, as defined in [RFC6554] for use by RPL routers. Routers that need to forward a packet with a RH3-6LoRH are expected to be RPL routers and are expected to support this specification. If a non-RPL router receives a packet with a RH3-6LoRH, this means that there was a routing error and the packet should be dropped so the Type cannot be ignored.

    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 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-    -+-    -+ ... +-    -+

         Size indicates the number of compressed addresses

Figure 5: The RH3-6LoRH.

The values for the RH3-6LoRH Type are an enumeration, 0 to 4. The form of compression is indicated by the Type. The unit (as a number of bytes) in which the Size is expressed depends on the Type as described in Figure 6:

  |   Type    | Size Unit |
  |    0      |      1    |
  |    1      |      2    |
  |    2      |      4    |
  |    3      |      8    |
  |    4      |     16    |

Figure 6: The RH3-6LoRH Types.

In the case of a RH3-6LoRH, 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 RH3-6LoRH can be employed.)

The Next Hop is indicated in the first entry of the first RH3-6LoRH. Upon reception, the router checks whether it owns the address indicated as Next Hop, which MUST be the case in a strict source routing environment. If it is so, the entry is removed from the RH3-6LoRH and the Size is decremented. If the Size is now zero, the whole RH3-6LoRH is removed. If there is no more RH3-6LoRH, the processing node is the last router on the way, which may or may not be collocated with the final destination.

The last hop in the last RH3-6LoRH is the last router on the way to the destination in the LLN. In a classical RPL network, all nodes are routers so the last hop is effectively the destination as well. But in the general case, even when there is a RH3-6LoRH header present, the address of the final destination is always indicated in the LoWPAN_IPHC [RFC6282].

If some bits of the first address in the RH3-6LoRH can be derived from the final destination in the LoWPAN_IPHC, then that address may be compressed, otherwise it is expressed as a full IPv6 address of 128 bits. Next addresses only need to express the delta from the previous address.

All addresses in a given RH3-6LoRH header are compressed in a same fashion, down to the same number of bytes per address. In order to get different forms of compression, multiple consecutive RH3-6LoRH must be used.

6. The RPL Packet Information 6LoRH

[RFC6550], Section 11.2, specifies the RPL Packet Information (RPI) as a set of fields that are placed by RPL routers in IP packets for the purpose of Instance Identification, as well as Loop Avoidance and Detection.

In particular, the SenderRank, which is the scalar metric computed by an specialized Objective Function such as [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.

RPL defines the 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 eight bytes per packet.

With [RFC6553], the RPL option is encoded as six Octets; it must be placed in a Hop-by-Hop header that consumes two additional octets for a total of eight. In order to limit its range to the inside 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 the LLN operation, in particular with regards 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 causes even more energy spending and issues discussed in the LLN Fragment Forwarding and Recovery [I-D.thubert-6lo-forwarding-fragments].

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.

This specification defines an IPinIP-6LoRH in Section 7 for that purpose, but it must be noted that stripping a 6LoRH does not require a manipulation of the packet in the LOWPAN_IPHC, and thus, if the source address in the LOWPAN_IPHC is the node that inserted the IPinIP-6LoRH then this alone does not mandate an IPinIP-6LoRH.

Note: A typical packet in RPL non-storing mode going down the RPL graph requires an IP-in-IP encapsulating the RH3, whereas the RPI is usually (and quite illegally) omitted, unless it is important to indicate the RPLInstanceID. To match this structure, an optimized IP-in-IP 6LoRH is defined in Section 7.

As a result, a RPL packet may bear only an RPI-6LoRH and no IPinIP-6LoRH. In that case, the source and destination of the packet are located in the LOWPAN_IPHC.

As with [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.

The remainder of this section defines the RPI-6LoRH, 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 [RFC6550], Section 5. A number of simple use cases do not require more than one instance, and in such cases, the 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 7: RPLInstanceID Field Format for Global Instances.

For the particular case of the global Instance 0, the RPLInstanceID field is all zeros. This specification allows to elide a RPLInstanceID field that is all zeros, and defines a 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 [RFC6550], Section 3.5.1, as:

  • DAGRank(rank) = floor(rank/MinHopRankIncrease)

If MinHopRankIncrease is set to a multiple of 256, the least significant 8 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 [RFC6550] by defining DEFAULT_MIN_HOP_RANK_INCREASE as 256 and in [RFC6552] that defaults MinHopRankIncrease to DEFAULT_MIN_HOP_RANK_INCREASE.

This specification allows to encode the SenderRank as either one or two 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 provides a compressed form for the RPL RPI. Routers that need to forward a packet with a RPI-6LoRH are expected to be RPL routers and expected to support this specification. If a non-RPL router receives a packet with a RPI-6LoRH, this means that there was a routing error and the packet should be dropped so the Type cannot be ignored.

Since the I flag is not set, the TSE field does not need to be a length expressed in bytes. The field is fully reused for control bits so as to encode the O, R and F flags from the RPI, and the I and K flags that indicate the compression that is taking place.

The Type for the RPI-6LoRH is 5.

The RPI-6LoRH 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 the whole 2 bytes. The I and K flags in the RPI-6LoRH indicate whether the RPLInstanceID is elided and/or the SenderRank is compressed and 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 8: The Generic RPI-6LoRH Format.

O, R, and F bits:

The O, R, and F bits as defined in [RFC6550], Section 11.2.
I bit:

If it is set, the Instance ID 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 [RFC6550] section 5.1.
K bit:

If it is set, the SenderRank is be compressed into one octet, and the lowest significant octet is elided. If it is not set, the SenderRank, is fully inlined as 2 octets.

In Figure 9, 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 9: The most compressed RPI-6LoRH.

In Figure 10, the RPLInstanceID is the Global RPLInstanceID 0, but both bytes of the SenderRank are significant so it can not 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 10: Eliding the RPLInstanceID.

In Figure 11, 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 11: Compressing SenderRank.

In Figure 12, 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 12: Least compressed form of RPI-6LoRH.

7. The IP-in-IP 6LoRH

The IP-in-IP 6LoRH (IPinIP-6LoRH) 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 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 IPinIP-6LoRH encapsulation is not required for that sole purpose.

This field is not critical for routing so the Type can be ignored, and the TSE field contains 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 13: The IPinIP-6LoRH.

The Length of an IPinIP-6LoRH 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 [RFC2460]

If the Length of an IPinIP-6LoRH 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.

If the Length of an IPinIP-6LoRH is strictly more 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 Size of 3 indicates that the Encapsulator Address is compressed to 2 bytes.

When it cannot be elided, the destination IP address of the IP-in-IP header is transported in a RH3-6LoRH as the first address of the list.

With RPL, the destination address in the IP-in-IP header is implicitly the root in the RPL graph for packets going upwards, and the destination address in the IPHC for packets going downwards. If the implicit value is correct, the destination IP address of the IP-in-IP encapsulation can be elided.

If the final destination of the packet is a leaf that does not support this specification, then the chain of 6LoRH 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 the 6LoRH is used to route 6LoWPAN fragments, the destination address is not accessible in the IPHC on all fragments and can be elided only for the first fragment and for packets going upwards.

8. Security Considerations

The security considerations of [RFC4944], [RFC6282], and [RFC6553] apply.

Using a compressed format as opposed to the full in-line format is logically equivalent and does not create an opening for a new threat when compared to [RFC6550], [RFC6553] and [RFC6554].

9. IANA Considerations

9.1. Reserving Space in 6LoWPAN Dispatch Page 1

This specification reserves the Dispatch Value Bit Patterns of 10xxxxxx within the 6LoWPAN Dispatch Page 1.

9.2. Nex 6LoWPAN Routing Header Type Registry

This document creates a IANA registry for the 6LoWPAN Routing Header Type, and assigns the following values:

  • 0..4 : RH3-6LoRH [RFCthis]

  • 5 : RPI-6LoRH [RFCthis]

  • 6 : IPinIP-6LoRH [RFCthis]

10. Acknowledgments

The authors wish to thank 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 the chairs of the ROLL WG, Michael Richardson and Ines Robles, and Brian Haberman, Internet Area A-D, and Adrian Farrel, Routing Area A-D, for driving this complex effort across Working Groups and Areas.

11. References

11.1. Normative References

[I-D.ietf-paging-dispatch] Thubert, P., "6LoWPAN Paging Dispatch", Internet-Draft draft-ietf-paging-dispatch-00, January 2016.
[IEEE802154] IEEE standard for Information Technology, "IEEE std. 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area Networks", 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998.
[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.
[RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, DOI 10.17487/RFC6282, September 2011.
[RFC6550] Winter, T., Thubert, P., 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.
[RFC6552] Thubert, P., "Objective Function Zero for the Routing Protocol for Low-Power and Lossy Networks (RPL)", RFC 6552, DOI 10.17487/RFC6552, March 2012.
[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.
[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.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 2014.
[RFC7228] Bormann, C., Ersue, M. and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014.

11.2. Informative References

[I-D.ietf-6tisch-architecture] Thubert, P., "An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4", Internet-Draft draft-ietf-6tisch-architecture-09, November 2015.
[I-D.robles-roll-useofrplinfo] Robles, I., Richardson, M. and P. Thubert, "When to use RFC 6553, 6554 and IPv6-in-IPv6", Internet-Draft draft-robles-roll-useofrplinfo-02, October 2015.
[I-D.thubert-6lo-forwarding-fragments] Thubert, P. and J. Hui, "LLN Fragment Forwarding and Recovery", Internet-Draft draft-thubert-6lo-forwarding-fragments-02, November 2014.
[RFC6775] Shelby, Z., 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.
[RFC7554] Watteyne, T., 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.

Appendix A. Examples

The example in Figure 14 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 [RFC4944], and the fragment headers must be placed in Page 0 before switching to Page 1:

+-  ...  -+-  ...  -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+- ... 
|Frag type|Frag hdr |11110001| IPinIP |  RPI   | Dispatch + LOWPAN_IPHC 
|RFC 4944 |RFC 4944 | Page 1 | 6LoRH  | 6LoRH  | RFC 6282
+-  ...  -+-  ...  -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+- ...
                                                <-      RFC 6282     ->
                                                    No RPL artifact

Figure 14: Example Compressed Packet with RPI.

The example illustrated in Figure 15 is a classical packet in non-Storing mode for a packet going down the DODAG following a source routed path from the root; in this particular example, addresses in the DODAG are assigned to share a same /112 prefix, for instance taken from a /64 subnet with the first 6 octets of the suffix set to a constant such as all zeroes. In that case, all addresses but the first can be compressed to 2 octets, which means that there will be 2 RH3_6LoRH headers, one to store the first complete address and the one to store the sequence of addresses compressed to 2 octets (in this example, 3 of them):

+- ...  -+- ...  -+-+-+- ... -+-+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+- ... 
|11110001| IPinIP | RH3(128bits)| RH3(3*16bits)| Dispatch + LOWPAN_IPHC 
|Page 1  | 6LoRH  | 6LoRH       | 6LoRH        | RFC 6282
+- ...  -+- ... +-+-+-+- ... -+-+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+- ...
                                                <-      RFC 6282     -> 
                                                    No RPL artifact

Figure 15: Example Compressed Packet with RH3.

Note: the RPI is not represented since most implementations actually refrain from placing it in a source routed packet though [RFC6550] generally expects it.

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 Institut MINES TELECOM; TELECOM Bretagne 2 rue de la Chataigneraie CS 17607 Cesson-Sevigne Cedex, 35576 France EMail: Laurent.Toutain@telecom-bretagne.eu
Robert Cragie ARM Ltd. 110 Fulbourn Road Cambridge, CB1 9NJ UK EMail: robert.cragie@gridmerge.com