6Lo Working Group                                                  G. Li
Internet-Draft                                                    D. Lou
Intended status: Experimental                                 L. Iannone
Expires: 21 April 2022                                            Huawei
                                                                  P. Liu
                                                            China Mobile
                                                         18 October 2021

   Native Short Addressing for Low power and Lossy Networks Expansion


   This document specifies mechanisms of NSA (Native Short Address) that
   enables IP packet transmission over links where the transmission of a
   full length address may not be desirable.  This document focuses on
   carrying IP packets across a LLN (Low power and Lossy Network), in
   which the nodes' location is fixed and changes in the logical
   topology are caused only by unstable radio connectivity (not physical
   mobility).  The specifications include NSA allocation, routing
   mechanisms, header format design including length-variable fields,
   and IPv6 interconnection support.

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 https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 21 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Li, et al.                Expires 21 April 2022                 [Page 1]

Internet-Draft                     NSA                      October 2021

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  NSA Allocation  . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  NSA Addresses and IPv6 Addresses  . . . . . . . . . . . .   9
     4.2.  Limitation of Number of Children Node . . . . . . . . . .  10
   5.  Routing for a NSA Network . . . . . . . . . . . . . . . . . .  10
     5.1.  Routing toward an NSA endpoint  . . . . . . . . . . . . .  11
     5.2.  Routing toward an external IPv6 node  . . . . . . . . . .  13
   6.  Benefits of Native Short Addressing . . . . . . . . . . . . .  13
   7.  NSA Header Format . . . . . . . . . . . . . . . . . . . . . .  14
   8.  NSA Control Message . . . . . . . . . . . . . . . . . . . . .  16
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     9.1.  Dispatch Type Field . . . . . . . . . . . . . . . . . . .  17
     9.2.  Allocation Function Registry  . . . . . . . . . . . . . .  17
     9.3.  ICMP NSA Control Message  . . . . . . . . . . . . . . . .  18
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  18
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     11.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   There is an ongoing massive expansion of the network edge that is
   driven by the "Internet of Things" (IoT) technology, especially over
   low-power links which often, in the past, did not support IP packet

   Particularly driven by the requirements stemming from Industry 4.0
   and Smart City deployments, more and more devices/things are
   connected to the Internet.  Sensors in plants/parking bays/mines,
   temperature/humidity/flash sensors in museums, normally are located
   in a fixed position and are networked by low power and lossy links.
   Comparing with traditional scenarios, scalability of the (edge)
   network along with lower power consumption are key technical
   requirements.  Moreover, large-scale Low power Lossy Networks (LLNs)

Li, et al.                Expires 21 April 2022                 [Page 2]

Internet-Draft                     NSA                      October 2021

   are expected to be able to carry IPv6 packets over their links,
   together with an efficient access to native IPv6 domains.  These kind
   of networks, do not necessarily imply nodes mobility [RFC5673],
   whilst some topology changes may still happen because of fluctuating
   radio link quality.

   The work in [SIXLOWPAN]/[SIXLO]/[LPWAN] Working Groups address many
   fundamental issues for those type of deployments.  Those deployments
   can be considered an instantiation of what [RFC8799] defines as
   "limited domains".  For instance, the 6lowpan compression technology
   ([RFC4944] and [RFC6282]) addresses the problem of IPv6 transmission
   over LLNs, making it possible to interconnect IPv6-based IoT networks
   and the Internet.  [RFC8138] introduces a framework for implementing
   multi-hop routing on an LLN using a compressed routing header, which
   works also with RPL (Routing Protocol for LLNs [RFC6550]).  This
   technique enables the ability to forward IPv6 packets within the
   domain without the need of decompression.  In addition, SCHC (Generic
   Framework for Static Context Header Compression and Fragmentation
   [RFC8724]) enables even more compression by using a common static

   The specifications in this document leverage on previous work, namely
   using the dispatch type field ([RFC4944], [RFC8025]) that allows to
   accommodate the proposed address format.  This means that except the
   addresses (source and destination) the other fields of the header
   will be compressed mostly according to LPWAN_IPHC.  The proposed
   addressing is independent of Unique Local Addresses [RFC4193], which
   has a dependency on specific link-layer conventions [RFC6282].  It is
   also different from stateful address allocation that requires all
   nodes to obtain addresses from a centralized DHCP server, which leads
   to long network startup time and consumption of extra bandwidth.
   Compared to RPL-based routing [RFC6550], NSA avoids the extra
   overhead of address assignment by integrating address assignment and
   tree forming together.  Furthermore, NSA provides shorter packet
   header than unstoring-mode RPL and much smaller routing table size
   than storing-mode RPL.

2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] and [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

Li, et al.                Expires 21 April 2022                 [Page 3]

Internet-Draft                     NSA                      October 2021

3.  Overview

   Native Short Address (NSA) is an efficient topology-based network
   layer address assignment mechanism that is performed in a
   decentralized fashion.  The NSA nodes are aware of its own IPv6
   address constructed by IPv6 prefix (by configuration) and NSA (see
   Section 5.2).  Inside the NSA domain, nodes communicate with each
   other using only NSA addresses.  It is a smaller address space
   compared to the huge IPv6 addressing space.  The NSA enables
   stateless forwarding in most cases.  When IPv6 communication occurs
   between nodes inside the NSA domain and external IPv6 nodes, the
   border router, which plays as well the role of "root" in the
   addressing tree, performs network layer translation (as per
   Section 5.2 and [RFC6282]).  The architecture of NSA network is
   showed in Figure 1.

                  /|\               Internet (IPv6)
                   |               --------+--------
     IPv6 Domain   |                       |
                   |                       |
                   |               +-------+-------+
   ----------------------------    | Border Router |
                   |               +---------------+
                   |                         O
                   |                O         O   O
                   |                  O  O
                   |             O                    O
     NSA Domain    |                           O
                   |          O      O  O          O    O   O
                   |               O
                   |                      O   O
                   |                                  O
                   |               O
                   |        Up to several thousands of nodes

            Figure 1: The architecture of general NSA networks.

   The overall design objective is centered on how to minimize the
   packet overhead and reduce the size of routing table to save
   communication energy in a large-scale IoT LLN network.  NSA
   eliminates compression/decompression of address and also reduces the
   amount of information synchronization messages, so it actually

Li, et al.                Expires 21 April 2022                 [Page 4]

Internet-Draft                     NSA                      October 2021

   reduces computation complexity during packets parsing and forwarding.
   To this end, NSA uses a context-independent address encoding
   mechanism.  It does not carry any field about address context in the
   packet.  It carries source and destination addresses by variable
   length fields whose size can be reduced to one octet each in the best
   case.  This allows the NSA packet header to be smaller than
   LOWPAN_IPHC's 7 octets (see Figure 2), down to 4 octets, representing
   around 40% reduction in the header size.  Considering that devices in
   the target limited domain are strongly constrained in resources,
   while still requiring to use a global unicast IPv6 address to
   identify them, 7 octets is the smallest size that LOWPAN_IPHC can
   achieve in a multi-hop environment, higher than the 2-3 octets
   necessary in a link-local communication [RFC6282].

     0   1   2   3   4   5   6   7      0   1   2   3   4   5   6   7
   +---+---+---+---+---+---+---+---+  +---+---+---+---+---+---+---+---+
   | 0 | 1 | 0 | 1 |   TF  |NH |HLM|  | 0 | 1 | 1 |  TF   |NH | HLIM  |
   +---+---+---+---+---+---+---+---+  +---+---+---+---+---+---+---+---+
   |Payload Length(variable length)|  |CID|SAC|  SAM  | M |DAC|  DAM  |
   +---+---+---+---+---+---+---+---+  +---+---+---+---+---+---+---+---+
   |I/O|AM |     Src(var len)      |  |      SCI      |      DCI      |
   +---+---+---+---+---+---+---+---+  +---+---+---+---+---+---+---+---+
   |        Dst (var len)          |  |                               |
   +---+---+---+---+---+---+---+---+  +         Source Address        +
                                      |                               |
                                      |                               |
                                      +       Destination Address     +
                                      |                               |

                                        b. IPHC best case header
      a. NSA best case header              with context-based encoding
                                           and global unicast address

         Figure 2: Best case of NSA and LOWPAN_IPHC packet header.

   There are three distinct NSA features that allow NSA to be efficient,

   1.  Native hort address allocation (see Section 4),

   2.  Stateless routing (see Section 5),

   3.  Compact header format design (see Section 7) that avoids context
       and compression.

Li, et al.                Expires 21 April 2022                 [Page 5]

Internet-Draft                     NSA                      October 2021

4.  NSA Allocation

   In an NSA network, there are 3 types of roles, namely:

   *  Root,

   *  Forwarder,

   *  Leaf.

   The basic rules of allocation include:

   *  Each node's address is prefixed by their parent's address.

   *  The forwarder runs an AF (Allocation Function) to generate its
      children's addresses.

   *  All nodes run the same AF in the same network instance.

   Normally, the root role is assigned to the border router when the LLN
   bootstraps.  An example of a possible result of an NSA deployment is
   shown in Figure 3.

                            root         +--------------------------+
                                1        | append more bits to form |
                                 O --    | brother's address        |
                               / |    \  +--------------------------+
                             /   | \    \
                            /    |   \    \-\
         +---------+ 10    /   11|     \      \
         |forwarder|     /            110\      \   111
         |node     |  O -        O        O        O
         +---------+/    \                | \
                   /  | \  \              |  \
                  /   |  \    \           O   O
                 /    |    \    \
             100/ 101 |  1010   1011   +--------------+
                                       |Prefix is '10'|
              O      O      O      O   +--------------+
             /|            /|
            / |           / |
           O  O          O  O

             Figure 3: An example of NSA addresses allocation.

   Each node acquiring a native short address needs to send an Address
   Request (AR) message to its link layer neighbors and wait for the
   response.  In the AR message, the node needs to designate a 'role'

Li, et al.                Expires 21 April 2022                 [Page 6]

Internet-Draft                     NSA                      October 2021

   value (forwarder or leaf) and the 'nodeid'.  Forwarder and Leaf roles
   can be assigned similarly to IEEE 802.15.4, which distinguishes
   between Full-Function Devices (FFD) and reduced function devices
   (RFD) (cf., [ZigBee]).  If a neighbor is neither a forwarder nor the
   root, it will drop the message silently.  Otherwise, the neighbor
   should calculate an address based on parameters in the AR message.
   After the neighbor node assigned an address for node, it stores the
   suffix of that address as the interface ID towards the node.  Then,
   it generates and sends Address Assignment (AA) message back.  Once a
   node receives a valid AA response, it uses that assigned address as
   its own network layer address, thus becomes a child of the address
   assigner.  It will then ignore replies from other neighbors.  If a
   node does not receive any response after an pre-defined interval, it
   will send the AR message again.  It is RECOMMENDED that nodes re-send
   the AR message up to 3 times, if no answer is received they SHOULD

   The allocation function AF(role,i) used in this document is defined
   in Figure 4.  Where every forwarder node should store and maintain
   two indexes, one for the children that are forwarders and one for the
   children that are leaves (starting at 0 for the first child in each
   role).  Let's call the first index 'f', as of forwarder, and the
   second 'l' as for leaves.  The '+' symbol indicates a concatenation
   operation; the b() operation indicates the binary string conversion
   operation with leading zeros trimmed (note that in this case b(0) is
   an empty string).

        AF(role, f, l) = 'address of the node performing the function'
                       + (role == leaf? b(l++):b(f++))
                       + (role == leaf?'1':'0'),
        in which, f and l are the indexes of respectively the forwarders
        and the leaves at this layer (starting at 0).

          Figure 4: Definition of the Allocation Function (AF) of
                           forwarder/root nodes.

   Taking the example of the topology in Figure 3, the proposed AF works
   as follows.

   At the top level, there are 4 children of root, two are forwarders
   and the other two are leaves.  Starting from the left most node and
   moving to the right, the root node applies the AF as follows:

   *  For the first child, which is a forwarder:

      -  A('forwarder', 0, 0) = '1'(root address) + b(0) + '0' = '1' +
         '' + '0' = 10

Li, et al.                Expires 21 April 2022                 [Page 7]

Internet-Draft                     NSA                      October 2021

      -  Index f is increased by one and is now equal 1 (f=1)

   *  For the second child, which is a leaf:

      -  A('leaf', 1, 0) = '1'(root address) + b(0) + '1' = '1' + '' +
         '1' = 11

      -  Index l is increased by one and is now equal 1 (l=1)

   *  For the third child, which is a forwarder:

      -  A('forwarder', 1, 1) = '1'(root address) + b(1) + '0' = '1' +
         '1' + '0' = 110

      -  Index f is increased by one and is now equal 2 (f=2)

   *  For the forth child, which is a leaf:

      -  A('leaf', 2, 1) = '1'(root address) + b(1) + '1' = '1' + '1' +
         '1' = 111

      -  Index l is increased by one and is now equal 2 (l=2)

   The first level addresses have now been assigned.  Let's now have a
   look how the node 10 (the first forwarder child of the root) applies
   the same Allocation function.  Note that node 10 will use its own 'f'
   and 'l' indexes initialized to 0.  Strarting again from the left most
   node, node 10 applies the AF as follows:

   *  For the first child, which is a forwarder:

      -  A('forwarder', 0, 0) = '10'(node address) + b(0) + '0' = '10' +
         '' + '0' = 100

      -  Index f is increased by one and is now equal 1 (f=1)

   *  For the second child, which is a leaf:

      -  A('leaf', 1, 0) = '10'(node address) + b(0) + '1' = '10' + '' +
         '1' = 101

      -  Index l is increased by one and is now equal 1 (l=1)

   *  For the third child, which is a forwarder:

      -  A('forwarder', 1, 1) = '10'(node address) + b(1) + '0' = '10' +
         '1' + '0' = 1010

Li, et al.                Expires 21 April 2022                 [Page 8]

Internet-Draft                     NSA                      October 2021

      -  Index f is increased by one and is now equal 2 (f=2)

   *  For the forth child, which is a leaf:

      -  A('leaf', 2, 1) = '10'(root address) + b(1) + '1' = '10' + '1'
         + '1' = 1011

      -  Index l is increased by one and is now equal 2 (l=2)

   Note how the children of the same parent all have the same prefix (10
   in this example).

   The Allocation Function can be different from the one defined in
   Figure 4, but all nodes know which one to use by configuration.  The
   use of one and only one AF is allowed in an NSA domain.  It is
   RECOMMENDED that implementations support at least the AF proposed in
   this document (cf.  Section 9).

4.1.  NSA Addresses and IPv6 Addresses

   Obtaining a full IPv6 address from a NSA address is pretty
   straightforward.  First the NSA address is concatenated to the
   configured IPv6 prefix.  Since the length of the NSA address is very
   likely smaller than 64 bits (the interface ID length in IPv6), the
   node needs to pad it with zeros ('0') used as most significative
   bits.  The full IPv6 address will look like: IPv6 prefix +
   "000...000" + NSA (or in IPv6 notation <IPv6 Prefix>::<NSA>).  The
   NSA is assigned by the root/forwarder as previously described.

   In an IPv6 communication, the node will derive the NSA address as the
   short source address from its own IPv6 address by simply removing the
   IPv6 prefix and all leading zeros before the NSA part.  The node will
   compare the destination IPv6 address with its own IPv6 address.  If
   they have the same prefix, it means that the destination is in the
   local NSA domain and its corresponding NSA address will be extracted
   as the short destination address (and the I/O Flag can be set
   accordingly).  Otherwise, it will be a communication towards the
   Internet.  In that case, a mapping mechanism implemented on the root
   node will generate a short address to be mapped to the full IPv6
   destination address.  As previously stated, the mapping mechanism is
   out of the scope of this document.

   Since the short mapped address is generated on the root, when the
   node first open the connection toward the external site, with a first
   packet, the destination address is set to the full, uncompressed,
   IPv6 address.  Once the packet arrives to the root node, performing
   the destination address lookup the root will notice that a full IPv6
   address is being used and will trigger the short address generation

Li, et al.                Expires 21 April 2022                 [Page 9]

Internet-Draft                     NSA                      October 2021

   mechanism and create a new mapping.  Such, mapping is communicated to
   the source node via a new dedicated ICMP message (see Section 8).
   Once the node originating the communication receives such a message
   it MUST use the mapped short address for any further communication.

4.2.  Limitation of Number of Children Node

   The maximum number of child nodes is determined by the specific AF
   used.  IEEE 802.15.5 has explored the use of a per-branch setup,
   which, however, incurs scalability problems [LEE10].  NSA allocation
   design is more flexible and extensible than the one proposed in IEEE
   802.15.5.  The AF used as example in this document does not need any
   specific setup network by network, though it is still limited by the
   maximum length of addresses.  For the special case of the parent
   connecting to huge amount of children, a variant of the proposed AF
   can be designed to fulfill the requirement.

5.  Routing for a NSA Network

   Internal and external communication in an NSA network works slightly
   different.  For internal communications, among NSA endpoints, packets
   carry native short addresses and no special operation is needed.  For
   external communications, the root is responsible to perform the
   translation between native short addresses and IPv6 addresses.  For
   instance, for a packet entering into the NSA domain, the root will
   extract the native short address of the destination from the suffix
   of the IPv6 address, by removing all leading '0's.  It will also map
   the source IPv6 address to a mapped native short address, in order to
   make it more efficient for communication inside the NSA domain.

   The root has to store the mapping between external IPv6 addresses and
   their assigned mapped Native Short Addresses.  The method of
   generating those mapping is out of scope of this document, however,
   the addressing space for the external NSA has to be maintained
   separate from the internal NSA address space.  Overlap are allowed
   since the two addressing space are distiguishable in the packets by
   the use of the I/O field, as explained later on.

   The following paragraphs will detail the routing operations for both
   internal and external communication.  The intra-network routing
   procedure depends on the specific AF used.  Here we will use the AF
   previously introduced (see Figure 4) to illustrate the routing

Li, et al.                Expires 21 April 2022                [Page 10]

Internet-Draft                     NSA                      October 2021

5.1.  Routing toward an NSA endpoint

   To perform forwarding operations, NSA nodes access the I/O field in
   the NSA header (see Section 7).  When its value is 1, the packet is
   destined to a internal NSA node, so it is an inner-domain packet.
   Otherwise, the packet is destined to an external IPv6 node, so it is
   called an outer-domain packet.  Intra-domain packets carry a native
   short addresses in the source and the destination address fields.
   More specifically the destination address field is the address of
   another node in the same NSA domain.  As such an NSA node performs
   the following sequence of actions, also see Figure 5:

   1.  Get destination address from packet (abbreviated to DA) and the
       current node's address (abbreviated to CA).  Go to step 2.

   2.  If length of DA is smaller than length of CA, send the packet to
       parent node, exit.  Otherwise, go to step 3.

   3.  If length of DA equals to length of CA, go to step 4.  Otherwise,
       go to step 5.

   4.  If DA and CA are the same, the packet arrived at destination,
       exit.  Otherwise, send the packet to parent node, exit.

   5.  Check whether CA is equal to the prefix of DA.  If yes, go to
       step 6.  Otherwise, send the packet to parent node, exit.

   6.  Calculate which child is the next hop address and forward packet
       to it.  With the AF propose in this document such operation
       reduces to reading the DA's bits starting from the position
       equals to the length of CA, then skip all '1' until the first '0'
       or the last bit of DA.  The sub-string obtained in such a way is
       the address of direct child of current node.

   7.  If any exception happens in the above steps, drop the packet and
       send error notification.

Li, et al.                Expires 21 April 2022                [Page 11]

Internet-Draft                     NSA                      October 2021

              /*\       DA:Destination Address
             |***|      CA:Current Node's Address
      |Parse DA from pkt|
      /                \  yes
     | Len(DA)<Len(CA)? |-------------------------------+
      \                /                                |
       +-------+------+                                 |
               | no                                     |
              \|/                                       |
       +-------+------+           +--------------+      |
      /                \  yes    /                \  no |
     | Len(DA)=Len(CA)? |------>|     CA == DA ?   |--->+
      \                /         \                /     |
       +-------+------+           +-------+------+      |
               | no                       | yes         |
              \|/                        /*\            |
       +-------+------+                 |***|           |
      /                \  no             \*/            |
     | CA==PrefixOf(DA)?|------------------------------>+
      \                /                                |
       +-------+------+                                 |
               | yes                                    |
              \|/                                      \|/
     +---------+---------+                    +---------+---------+
     | Calculate next-hop|                    | Forward to Parent |
     |         &         |                    +---------+---------+
     |      Forward      |                              |
     +---------+---------+                              |

             Figure 5: Flow Chart of Internal Routing Procedure

   In the case of packet arriving from the Internet (external IPv6
   domain toward the local NSA domain) header adaptation operation is
   performed by the root node.  Concerning the destination address, the
   root builds the native short address of the destination by removing
   the prefix and the leading '0's of the suffix of the destination

Li, et al.                Expires 21 April 2022                [Page 12]

Internet-Draft                     NSA                      October 2021

   address.  Meanwhile, it checks whether it exists already a mapping
   between the source address and a mapped NSA address to be used as
   source address in the NSA packet.  If not it creates one.  Then the
   root creates the inner-domain packet.  It uses the NSA address as
   destination setting the I/O field to 1 so to route the packet to as
   described above to the destination node.  The mapped NSA address is
   used as source address and the fact that is a Mapped Address is
   signaled by setting to 1 the MA field.

5.2.  Routing toward an external IPv6 node

   In the case that the I/O field (cf.  Section 7) is set to 0, the
   packet is destined to an external IPv6 node, it is an outer-domain
   packet.  As such the destination address is either a full IPv6
   address (for the first packet of a communication) or a mapped short
   address generated by the root node and not belonging to any node
   inside the NSA domain.

   All NSA nodes (except root) just send packets that are destined
   outside the local domain (I/O field equal 0) to their parent, not
   even looking at the actual destination address.  Eventually all
   packets will reach the root node, which acts as gateway.  The Root
   node is able to map the destination NSA address to the corresponding
   full IPv6 address.  Also, the root node is able to rebuild the full
   source IPv6 address by concatenating the IPv6 prefix and the NSA
   address as explained in Section 5.2.  Other fields of the header are
   also decompressed as described in Section 7.  A full IPv6 header
   replaces the original NSA header in the packet, which is then
   forwarded according to traditional IPv6 protocol.

6.  Benefits of Native Short Addressing

   The NSA use a single set of messages for address assignment and tree
   forming.  It is not more complex than RPL tree forming.  So, NSA
   saves the overhead of address assignment of RPL.

   Comparing to RPL with storing mode (see [RFC6550]), there is no need
   for a NSA node to generate and store routing table entries in the
   normal case.  One of the potential issues is the risk of renumbering
   of addresses when the topology changes.  The topology change could
   happen in two different scenarios, the high mobility scenario where
   nodes are moving quite often or even all the time (e.g.  UAV) and the
   unstable link connection scenario where the locations of nodes are
   fixed, but the connections are broken from time to time.  The later
   is usually called "logic topology change", which covers most of IoT
   scenarios, see [IoTSurvey].

Li, et al.                Expires 21 April 2022                [Page 13]

Internet-Draft                     NSA                      October 2021

   A "moving" node may possibly be the root of a whole sub-tree, with
   many children and grand-children, hence, renumbering would introduce
   a non-negligible cost.  Instead of "renumbering", the sub-tree rooted
   on the "moving" node, its address and the addresses of all its
   children and grand-children will be kept unchanged.  A specific entry
   in the routing tables of the original and new parent nodes will be
   created, in order to make the sub-tree still reachable.

   Herewith one example, also depicted in Figure Figure 6, node A with
   the address of 1000 somehow moves from node B (original parent) to
   node C (new parent).  In this case, the routing tables in B, C and
   their parents' nodes should be updated by adding a new route to
   "1000", the address of node A.  Meanwhile, the original parent (node
   B) should keep its original address assignment.  Comparing with
   renumbering the addresses of node A and its children, the cost of
   adding one new route to their parent nodes is much lower, although in
   this case, the NSA does not implement complete stateless routing.

          |     Add route:    |
          | to 1000, via 1010 |    1
          +-------------------+   O
                           *     /
     +-----------------+    *   /
     |     Add route:  |     * /
     | to 1000, via 10 |      O 10
     +-----------------+     / \
                        *   /    \
                         * /       \ 1010 (node C)
            (node B) 100  O         O
                          .       /  *
                          .     /     *-----------------+
                          .   /       |     Add route:  |
                          O /         | to 1000, direct |
                        1000 (node A) +-----------------+

           Figure 6: Add extra routes for "logic topology change

7.  NSA Header Format

   As explained in Section 4, the addresses in NSA are of variable
   length, in this section, we outline the design of the header format
   partially based on the format of 6lowpan, accommodating the variable
   length property in the packet.  The header format is shown in
   Figure 7.

Li, et al.                Expires 21 April 2022                [Page 14]

Internet-Draft                     NSA                      October 2021

      0                                       1
      0   1   2   3   4   5   6   7   8   9   0   1   2   3   4   5
    | 0 | 1 | 0 | 1 |  TF   |NH |HL | Payload Length(Variable Len)  |
    |I/O|MA |    SA(Variable Len)   |         DA(Variable Len)      |
    |                        In-line fields ...                     |

                   Figure 7: Header format of NSA packets

   The first 4 bits are new dispatch types that will be introduced in
   Section 9.

   *  TF: The same definition as in [RFC6282] Section 3.1.1.

   *  NH: The same definition as in [RFC6282] Section 3.1.1.

   *  HL: This field indicates the hop limit.  When HL is 0, a hop limit
      field defined in [RFC2460] locates in in-line fields, while HL is
      1 means no hop limit header in packet.

   *  Payload length is a variable length field.  It normally occupies
      an octet assuming most packets are smaller than 252 bytes.  For
      larger packets, payload length may expand to 2 to 3 octets.  The
      encoding method is defined as follows.  When the first octet has
      value of:

      -  0~252: Indicates how many octets the payload consist of.

      -  253: Indicates that there is an extra octet for payload length,
         with the actual length value equal to the last byte value plus

      -  254: Indicates that there is an extra two octets for payload
         length, with the actual length value equal to the value of the
         second byte multiple 256 plus value of the last byte plus 252.

      -  255: Reserved.

   *  I/O: Indicates whether this packet is destined to a inner-domain
      node (value '1') or an outer-domain node (value '0'), where the
      former means from an NSA or IPv6 node to a NSA destination, while
      the latter means to an external IPv6 node.

Li, et al.                Expires 21 April 2022                [Page 15]

Internet-Draft                     NSA                      October 2021

   *  MA: Indicates the source address is actually a Mapped Address
      generated by the root.  When it is '1', the source address of the
      packet is a mapped address of an external IPv6 address, while if
      it is '0', the source address of the packet is an NSA address.

   For length variable native short address encoding, for both Source
   Address (SA) and Destination Address (DA), the definition is:

   *  0~252: if the address value locates in this interval, one octet is
      used to encode the value

   *  253: indicates that the address is encoded in 2 octets.

   *  254: indicates that the following 4 octets encode the address.

   *  255: indicates that the following octet defines the length of
      address in octets, followed by the address value octets.

   The sequence of in-line fields is as per [RFC8200] section 3.

8.  NSA Control Message

   This documents specifies only one NSA Control Message, namely the NSA
   Mapped Address Advertisement described in Section 4.  The purpose of
   such a message is advertise the mapping of an IPv6 address into a NSA
   address.  The map is performed by the root node and sent to the node
   originating the communication.  The root keeps a copy of the mapping
   to be used for future packets.  The format is as follows:

     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
     |  Type         | Code = 0x00   | Reserved      | NSA Length    |
     |                                                               |
     |          Target IPv6 Address (Fixed length 128 bist)          |
     |                                                               |
     |                                                               |
     | Target NSA Address (Variable length) .... |

   *  Type: Type value identifying NSA Control Message.  Value to be
      assigned by IANA (cf.  Section 9)

   *  Code: This field identifies the specific control message.  In this
      case it is set to the value 0x00 "NSA Mapped Address for External
      IPv6 Address".

Li, et al.                Expires 21 April 2022                [Page 16]

Internet-Draft                     NSA                      October 2021

   *  Reserved: Set as 0 on transmission and ignore on reception.

   *  NSA Length: This field indicates the length of the Target NSA
      Address at the end of the message, expressed in octets.

   The "NSA Mapped Address for External IPv6 Address" is a variable
   length message, however, the first five fields of the message, namely
   Type, Codem Reserved, NSA Length, and Target IPv6 address, have a
   fixed length of 160 bits (20 octets), hence the length of the NSA
   address is sufficient to calculate the length of the entire packet:
   20 octets + "NSA length".

9.  IANA Considerations

9.1.  Dispatch Type Field

   This document requires IANA to assign the range 01010000 to 01011111
   in page 10 of the "Dispatch Type Field" registry as follows:

   | Bit Pattern |Page|         Header Type         | Reference     |
   | 0101TTNH    | 10 |  LOWPAN NSA IP(LOWPAN_NIP)  |[This Document]|

         Figure 8: LOWPAN Dispatch Type Field requested allocation

9.2.  Allocation Function Registry

   This section provides guidance to the Internet Assigned Numbers
   Authority (IANA) regarding registration of values related to the NSA
   specification, in accordance with BCP 26 [RFC8126].

   IANA is asked to create a registry named "Native Short Addresses
   (NSA) Parameters".

   Such registry should be populated with a one octet sub registry named
   "Allocation Function" and used to identify the AF used in a NSA
   deployment.  The sub registry is populated as follows:

         | Value   | AF Name                    | Reference       |
         | 0x00    | Native Allocation Function | [This Document] |
         |0x01-0xFF| Un-assigned                |                 |

Li, et al.                Expires 21 April 2022                [Page 17]

Internet-Draft                     NSA                      October 2021

   Values can be assigned by IANA on a "First Come, First Served" basis
   according to [RFC8126].

9.3.  ICMP NSA Control Message

   IANA is requested to allocate an ICMPv6 type value from the "ICMPv6
   Parameters" registry to be used by "NSA Control Message".

   Also IANA is requested to create an "NSA Control Codes" sub registry,
   for the Code field of the ICMPv6 NSA Control Message.

   New codes may be allocated through the "Specification Required"
   procedure as defined in [RFC8126].  The following code is currently
   defined (the others are to be marked as un-assigned):

   | Code | Description                                | Reference     |
   | 0x00 |NSA Mapped Address for External IPv6 Address|[This Document]|

10.  Security Considerations

   An extended security analysis will be provided in future revision of
   this document.  As of this point we consider that the security
   considerations of [RFC4944], [RFC6282] apply.

11.  References

11.1.  Normative References

   [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, <https://www.rfc-editor.org/info/rfc2460>.

   [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,

Li, et al.                Expires 21 April 2022                [Page 18]

Internet-Draft                     NSA                      October 2021

   [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,

   [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,

   [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,

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,

11.2.  Informative References

              Oliveira, A. and T. Vazão, "Low-power and lossy networks
              under mobility: A survey", Computer Networks Vol. 107, pp.
              339-352, DOI 10.1016/j.comnet.2016.03.018, October 2016,

   [LEE10]    Lee, M., Zhang, R., Zheng, J., Ahn, G., Zhu, C., Park, T.,
              Cho, S., Shin, C., and J. Ryu, "IEEE 802.15.5 WPAN mesh
              standard-low rate part: Meshing the wireless sensor
              networks", IEEE Journal on Selected Areas in
              Communications Vol. 28, pp. 973-983,
              DOI 10.1109/jsac.2010.100902, September 2010,

Li, et al.                Expires 21 April 2022                [Page 19]

Internet-Draft                     NSA                      October 2021

   [LPWAN]    "IPv6 over Low Power Wide-Area Networks (lpwan) WG", n.d.,

   [RFC4193]  Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
              Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,

   [RFC5673]  Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
              Phinney, "Industrial Routing Requirements in Low-Power and
              Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October
              2009, <https://www.rfc-editor.org/info/rfc5673>.

   [RFC8138]  Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
              "IPv6 over Low-Power Wireless Personal Area Network
              (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
              April 2017, <https://www.rfc-editor.org/info/rfc8138>.

   [RFC8724]  Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
              Zúñiga, "SCHC: Generic Framework for Static Context Header
              Compression and Fragmentation", RFC 8724,
              DOI 10.17487/RFC8724, April 2020,

   [RFC8799]  Carpenter, B. and B. Liu, "Limited Domains and Internet
              Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,

   [SIXLO]    "IPv6 over Networks of Resource-constrained Nodes (6lo)
              WG", n.d., <https://datatracker.ietf.org/wg/6lo/about/>.

              "IPv6 over Low power WPAN (6lowpan) - Concluded WG", n.d.,

   [ZigBee]   "ZigBee Wireless Networks and Transceivers",
              Elsevier book, DOI 10.1016/b978-0-7506-8393-7.x0001-5,

Authors' Addresses

   Guangpeng Li
   Huawei Technologies
   Beiqing Road, Haidian District

Li, et al.                Expires 21 April 2022                [Page 20]

Internet-Draft                     NSA                      October 2021

   Email: liguangpeng@huawei.com

   David Lou
   Huawei Technologies Duesseldorf GmbH
   Riesstrasse 25
   80992 Munich

   Email: zhe.lou@huawei.com

   Luigi Iannone
   Huawei Technologies France S.A.S.U.
   18, Quai du Point du Jour
   92100 Boulogne-Billancourt

   Email: luigi.iannone@huawei.com

   Peng Liu
   China Mobile
   No. 53, Xibianmen Inner Street, Xicheng District

   Email: liupengyjy@chinamobile.com

Li, et al.                Expires 21 April 2022                [Page 21]