tech-invite   World Map     

3GPP     Specs     Glossaries     Architecture     IMS     UICC       IETF     RFCs     Groups     SIP     ABNFs       Search

RFC 8138

 
 
 

IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Routing Header

Part 2 of 2, p. 19 to 37
Prev Section

 


prevText      Top      ToC       Page 19 
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.

Top      Up      ToC       Page 20 
   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.

Top      Up      ToC       Page 21 
   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.

Top      Up      ToC       Page 22 
   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.

Top      Up      ToC       Page 23 
   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

Top      Up      ToC       Page 24 
   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

Top      Up      ToC       Page 25 
   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.

Top      Up      ToC       Page 26 
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.

Top      Up      ToC       Page 27 
   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].

Top      Up      ToC       Page 28 
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>.

Top      Up      ToC       Page 29 
   [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.

Top      Up      ToC       Page 30 
   [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.

Top      Up      ToC       Page 31 
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

Top      Up      ToC       Page 32 
   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].

Top      Up      ToC       Page 33 
   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

Top      Up      ToC       Page 34 
   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

Top      Up      ToC       Page 35 
   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

Top      Up      ToC       Page 36 
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.

Top      Up      ToC       Page 37 
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