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Network Working Group                                          D. Shytyi
Internet-Draft                  Societe Francaise du Radiotelephone(SFR)
Intended status: Informational                                  G. Campo
Expires: March 28, 2019
                                                             A. Petrescu
                                                               CEA, LIST
                                                      September 24, 2018


      DHCPv6_PD, PDP and NDP Implementation in IoT Router (DANIR)
                    draft-shytyi-v6ops-danir-02.txt

Abstract

   This document provides a description of the implementation of Dynamic
   Host Configuration Protocol version 6 Prefix Delegation, Neighbour
   Discovery Protocol and of the use of the Packet Data Protocol in an
   Internet of Things Router.  This Internet of Things Router is
   connected on a cellular network; it is a DHCPv6-PD Client and it
   requests a /56 pool of prefixes from the server; the DHCPv6-PD server
   is placed in the PGW and is a part of the cellular infrastructure.
   After the pool of prefixes is delegated, the Internet of Things
   Router derives sub-prefixes from the prefix pool; each one of these
   sub-prefixes is aimed at one ingress interface.

   After the Internet of Things Router finishes the network prefix
   assignment procedure, it advertises the network prefixes on the
   ingress links by using the Neighbour Discovery protocol.  Finally,
   when Hosts receive the sub-prefixes via Router Adverticement
   messages, they configure the Global Unique Address with the Stateless
   Address Auto-configuration protocol.

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 March 28, 2019.



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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Environment . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   8
     4.1.  Solicitation of the network prefix pool . . . . . . . . .   9
       4.1.1.  The Packet Data Protocol  . . . . . . . . . . . . . .   9
       4.1.2.  The Dynamic Host Configuration Protocol version 6
               with Prefix Delegation  . . . . . . . . . . . . . . .   9
       4.1.3.  Option: PPP use . . . . . . . . . . . . . . . . . . .  12
     4.2.  Assignment of the network prefixes on the links . . . . .  12
     4.3.  Advertisement of the network prefixes . . . . . . . . . .  15
     4.4.  Recommendations . . . . . . . . . . . . . . . . . . . . .  16
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   This document describes the implementation of the Dynamic Host
   Configuration Protocol vestion 6 with Prefix Delegation (DHCPv6_PD),
   Neighbour Discovery Protocol (NDP) and usage of the Packet Data
   Protocol (PDP) in an Internet of Things (IoT) Router.

   The use of DHCPv6 Prefix Delegation in LTE networks is overviewed in
   [RFC6653].  It misses several important aspects.

   The router MUST be a node that forwards IP version 6 packets not
   explicitly addressed to itself [RFC8200].  Thus, it has more than one



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   link to perform the forwarding.  With multiple links, the need of
   multiple global unique network prefixes (GUNPs) , assigned to those
   links, appears.  To assign the GUNPs to the links, the Requesting IoT
   Router Solicits the pool of GUNPs.

   First, the Requesting IoT Router solicits the pool of the GUNP from
   the Delegating Router.

   After the pool is received, the Requesting IoT Router (1) derives
   GUNPs and (2) performs address autoconfiguration.  During the
   autoconfiguration process the Requesting IoT Router assigns the GUNPs
   to the links.  When the IoT Router finishes the GUNPs assignment
   procedure, it starts to advertise the GUNPs on the links with NDP
   [RFC4861].  Meanwhile, the Hosts that are connected to the Requesting
   IoT Router run the SLAAC mechanism to perform the GUA IP version 6
   autoconfiguration.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   Router - is a node, that performs forwarding.  Router node is not a
   final destination of forwarded packets.

   Delegating Router - is a node, DHCPv6 server, that chooses prefix(es)
   for delegation and advertises them to the Requesting Router
   [RFC3633].

   Requesting IoT Router - is a node that behaves as DHCPv6 client.  It
   requests the network prefix(es) and assigns network prefix(es) to the
   interfaces [RFC6653].

   Host - is a node that is not a router.

   Link - is an entity that enables link layer communication of nodes.

   Interface - node connection to the link.

   Link-local address - is an address with usage that is limited by a
   link.

   Global Unique Address (GUA) - is an address that is globally
   available and globally unique.






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3.  Overview

   This section provides an overview of the actions performed on the
   Delegating Router, Requesting IoT Router and host to perform address
   assignment on the interfaces with different GUNP.  The process of IP
   version 6 address assignment starts with advertising of the GUNP pool
   from the Delegating Router to the Requesting IoT Router.  To perform
   such a solicitation, the Requesting IoT Router runs the DHCPv6_PD.


                           +-----------------+
                           |                 |
                           |    Delegating   |
                           |     router      |
                           |                 |
                           | (DHCPv6 server) |
                           +-----------------+
                                   |
                                   |DHCPv6_PD network prefix
                           POOL    |2001:DB8:XYZU:TVWZ::/56
                                   |
                                   | GUA Prefix_0 /64
                                   |interface_0
                   +-------------------------------+
                   |                               |
                   |          Requesting           |
                   |          IoT router           |
                   |                               |
                   |(DHCPv6_PDclient + RADVDserver)|
                   +-------------------------------+
                   |interface_1    |interface_2    |interface_3
                   |               |               |
             GUNP  |Prefix_1 /64   |Prefix_2 /64   |Prefix_3 /64
                   |SLAAC GUA      |SLAAC GUA      |SLAAC GUA
           +-------------+  +------------+  +-------------+
           |             |  |            |  |             |
           |   Host 1    |  |   Host 2   |  |    Host 3   |
           |             |  |            |  |             |
           +-------------+  +------------+  +-------------+


   (In the above figure the scenario with 3 hosts connected to the
   Requesting IoT router is presented.  Normally there are no number
   limitations of connected hosts.)

   When the DHCPv6 message exchange is performed, the Requesting IoT
   Router receives the pool of IPv6 GUNPs.  After the pool of GUNPs is
   received, the Requesting IoT Router performs the autoconfiguration.



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   Precisely, when the Requesting IoT Router's interface is attached on
   the link, the Requesting IoT Router assigns to this link the GUNP
   taken from GUNP pool.  The Requesting IoT Router performs the GUNP
   assignment procedure for multiple links over the interfaces.
   Finally, this mechanism offers the automated assignment of GUNPs to
   the links.  At the moment of autoconfiguration, the Requesting IoT
   Router's interfaces are already assigned with link local addresses.

   The next step of the autoconfiguration phase SHOULD be performed
   using the Neighbor Discovery protocol.  The latter advertises the
   network's configuration on the links with different interfaces thus
   with different GUNPs.  To perform the GUNPs advertisement, the
   Requesting IoT ROuter sends the "Router Advertisement Messages" via
   its interfaces.  The Router Avertisement Messages carry the GUNPs
   that are further used by the stateless autoconfiguration mechanism
   (SLAAC).  There exists an open source implementation of Neighbor
   Discovery protocol - RADVD sever.  With RADVD it is possible to
   configure hosts interfaces connected to the router's interfaces in
   automatic manner.  It MAY be possible thanks to the fact that hosts
   run the SLAAC.

   The IP version 6 stateless autoconfiguration mechanism enables hosts
   to perform the address autoconfiguration.  The SLAAC mechanism SHOULD
   be used when it is enough to have random unique IP version 6
   addresses [RFC4862].  The length of the IP version 6 address is N
   bytes.  The first part of the address (128-N bits) consists of the
   GUNP information associated with a link.  The network prefix is
   advertised by the IoT Router on the link.  The second part of the
   address (8 bytes) consists of interface identifier on the link.  The
   interface identifier SHOULD be generated locally and randomly.


     +---------------------------------------+------------------------+
     |            128 - N bits               |       N bits           |
     +---------------------------------------+------------------------+
     |            link prefix                |  interface identifier  |
     +----------------------------------------------------------------+


   (In the above figure, an IP version 6 address scheme is presented
   [RFC4862].)

3.1.  Environment

   This section describes the location of the Delegating Router and the
   Requesting IoT Router in the cellular provider's infrastructure
   model.  The model is not a real cellular provider infrastructure.




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   After the DHCPv6 packet leaves the cellular interface of the IoT
   Requesting Router via wireless OFDMA link, it reaches the element of
   the access network which connects to the user equipment (UEs) -
   eNodeB station.

   Further, the packet MAY be transmitted to the Serving Gateway (SGW),
   as all the user's IP packets.  SGW is used to enable the UE movement
   between eNodeBs.  When the UE moves between eNodeBs, the SGW keeps
   information about the bearers.

   The final destination of the DHCPv6 packet is the Packet Data Network
   Gateway, that is responsible for IP address allocation for the UE and
   for filtering of down-link user's IP packets into the different QoS-
   based bearers.

   The model of the infrastructure described in this this section is a
   simplified example.  Real infrastructure construction could contain
   multiple SGW and eNodeBs and network equipment (that is not described
   in the current example) with respect of existing standards [RFC6459].
































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                     +---------------+       |
                     |      PGW      |       |
                     |   Delegating  |       |
                     |     Router    |       |
                     +---------------+       |
                             |               |
                             |               |
                     +---------------+       |
                     |      SGW      |       | Cellular infrastructure
                     +---------------+       |
                             |               |
                             |               |
                     +---------------+       |
                     |    eNodeB     |       |
                     +---------------+       |
                             |               |
                             |               |
                             ~               ~  Wireless OFDMA 3G/4G
                             |               |
                     +---------------+       |
                     |   +-------+   |       |
                     |   | Modem |   |       |
                     |   +-------+   |       |
                     |       |       |       |
                     |   +-------+   |       |
                     |   |  ARM  |   |       |
                     |   +-------+   |       |
                     |   Requesting  |       |  User Equipment
                     |      IoT      |       |
                     |     Router    |       |
                     +---------------+       |


   (The above figure descibes the model of the path followed by a DHCPv6
   packet from IoT requesting router to the Delegating PGW router.  The
   model is not a real infrastructure.)

   Additional experiments with using of USB dongle were performed.  The
   following figure illustrates the successful DHCPv6-PD test on Orange
   with dongle.  It uses a Huawei E392 USB dongle on laptop (and not the
   Sierra Wireless mangOH Red).










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                     +---------------+       |
                     |      PGW      |       |
                     |   Delegating  |       |
                     |     Router    |       |
                     +---------------+       |
                             |               |
                             |               |
                     +---------------+       |
                     |      SGW      |       | Cellular infrastructure
                     +---------------+       |
                             |               |
                             |               |
                     +---------------+       |
                     |    eNodeB     |       |
                     +---------------+       |
                             |               |
                             |               |
                             ~               ~  Wireless OFDMA 3G/4G
                             |               |
                     +---------------+       |
                     |   +--------+  |       |
                     |   |  E392  |  |       |
                     |   |  USB   |  |       |
                     |   | dongle |  |       |
                     |   +--------+  |       |
                     |       |       |       | User Equipment
                     |   +--------+  |       |
                     |   | Laptop |  |       |
                     |   +--------+  |       |
                     |               |       |
                     +---------------+       |



4.  Specification

   This section presents the process that starts with delegation of
   Network Prefix pool 2001:DB8:XXXX:XX::/56 from the Delegation Router
   and finishes with the configuration of IPv6 prefixes on the hosts
   interfaces.  Each Requesting IoT router's interface acts on a unique
   link.  The Host's interfaces, connected to the Requesting IoT router,
   acts on the same unique links as the Requesting IoT router's
   interfaces.








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4.1.  Solicitation of the network prefix pool

4.1.1.  The Packet Data Protocol

   This section describes how the Requesting IoT Router obtains the GUA
   address on the Recipient Interface (RI) (OFDMA interface, 3GPP
   interface).  The message "Activate PDP context Accept" is useful for
   forming the Globally Unique Address on the RI.

   The Packet Data Protocol [ETSI102361] contains the following types of
   DLL (Data Link Layer) bearer service data transmissions: unconfirmed
   data transmission; confirmed data (data transmission; response
   transmission.)  The Packet Data Protocol contains the following types
   of layer 3 bearer service data transmissions: Internet Protocol;
   Short Data.  These layer 3 bearer services are built on the top of
   DLL services.



                    ARM     Modem      eNodeB     SGW  PGW
                    |        |          |         |    |
                    |        |  PDP     |         |PDP |
                    |        |--------->|         |--->|
                    |        |          |         |    |
                    |        |<---------|         |<---|
                    |        |          |         |    |
                    |        |          |         |    |



4.1.2.  The Dynamic Host Configuration Protocol version 6 with Prefix
        Delegation

   To perform the pool solicitation, the Prefix Delegation options of
   the Dynamic Host Configuration Protocol version 6 (DHCPv6) are used
   [I-D.ietf-dhc-rfc3315bis].

   The Requesting IoT Router sends the DHCPv6 "Solicit" packet to the
   Delegating Router via the wireless link.  The DHCPv6 "Solicit" packet
   consists of Client Identifier, Transaction ID, Elapsed time and
   Identity Association for Prefix Delegation (IA_PD) options.  The
   initial "Solicit" packet triggers the 4 message exchange, that
   finishes with the reception of the GUNPs pool by the Requesting IoT
   Router.







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                +------------+                          +----------+
                | Requesting |                          |   PGW    |
                |    IoT     |                          |Delegating|
                |  Router    |                          |  Router  |
                +------------+                          +----------+
                      |                                       |
                      |                                       |
                      |1 Solicit                              |
                      |-------------->                        |
                      |                                       |
                      |                       2 Advertise     |
                      |                       <---------------|
                      |                                       |
                      |3 Request                              |
                      |-------------->                        |
                      |                                       |
                      |                                       |
                      |                       4 Reply         |
                      |                       <---------------|
                      |                                       |
                      |                                       |
                      |                                       |



   (In the above figure the full DHCPv6 message exchange mechanism
   between the ARM part of UE and PGW is presented.)

   The IA_PD option consists of the Identity Association (IA) - group
   identifier [RFC3633], parameters (IA id, times to extend the
   lifetimes of prefixes and prefixes allocated to the IA).  The full
   description of the IA_PD option is presented in the RFC3633
   [RFC3633].


















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        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         OPTION_IA_PD          |         option-length         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         IAID (4 octets)                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              T1                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              T2                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       .                                                               .
       .                          IA_PD-options                        .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   (in the above figure the DHCPv6 IA_PD option format [RFC3633].)

   The IA_PD-options field carries the IA_PD Prefix Option.  The IA_PD
   Prefix Option carries the recommended preferred/valid life time and
   IPv6 prefix with prefix length.  The additional fields allocated for
   the options for the advertised GUNP [RFC3633].


        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |        OPTION_IAPREFIX        |         option-length         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      preferred-lifetime                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        valid-lifetime                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | prefix-length |                                               |
       +-+-+-+-+-+-+-+-+          IPv6 prefix                          |
       |                           (16 octets)                         |
       |                                                               |
       |                                                               |
       |                                                               |
       |               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               |                                               .
       +-+-+-+-+-+-+-+-+                                               .
       .                       IAprefix-options                        .
       .                                                               .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+





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   (in the above figure the DHCPv6 IA_PD Prefix option format is
   presented [RFC3633].

   The PGW (Delegating Router) advertises, through the usage of a DHCPv6
   packet, an IPv6 pool 2001:DB8::/56 to the Requesting IoT Router.  The
   packet SHOULD be sent from the cellular infrastructure to the
   Requesting IoT Router, via the wireless link.  The full message
   exchange consists of: Solicit, Advertise, Request and Reply messages.

   The "Request", "Reply" messages are used to add/remove/update the
   assigned prefixes to IA_PDs.

   The Hop Limit of packets that contain the DHCPv6 data MUST be 255 to
   satisfy the properties of the cellular infrastructure.  To reach the
   PGW from the UE the DHCPv6 packets are encapsulated by SGW into UDP/
   IPv4 packets; this encapsulation is for the GTP-U tunnel.  The
   corresponding decapsulation mechanism decreases the Hop Limit; when
   the Hop Limit reaches value 0 the packet is discarded; to avoid this
   situation it is required to put the Hop Limit value of the DHCPv6
   Solicit equal to 255.

4.1.3.  Option: PPP use

   It is possible to use IPv6-over-PPP protocol [RFC1661], with LCP,
   between the ARM and the modem.  This protocol helps with forming an
   IPv6 link-local address on the IoT Router's RI.



                    ARM     Modem      eNodeB     SGW  PGW
                    |        |          |         |    |
                    |------->|          |         |    |
                    |PPP LCP |          |         |    |
                    |<-------|          |         |    |
                    |        |          |         |    |
                    |        |          |         |    |
                    |        |          |         |    |



4.2.  Assignment of the network prefixes on the links

   The receipt of the IA_PD Prefix option triggers the GUA
   autoconfiguration on the Requesting IoT Router's interfaces.  The
   Recipient Interface (RI) receives a message with the IA_PD prefix
   option and does not perform the autoconfiguration on the current
   stage.




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   All interfaces, except RI, now follow the GUA autoconfiguration
   procedure.  The number of interfaces that should follow the procedure
   could be specified in the configuration file of the Requesting IoT
   Router.

   The GUA interface autoconfiguration procedure in the Requesting IoT
   Router is done by assigning the network addresses from different
   GUNPs to the links.  The assignment of network addresses is performed
   using the 2001:DB8:XXXX:XX::/56 network pool.  Therefore, the
   Requesting IoT Router operates on multiple links (ingress links).

   The IoT Router derives several GUNPs from the received pool.  For
   example, from the pool 2001:db8:XYZU:TVWZ::/56 the GUNPs
   2001:db8:XYZU:TV01::/64 and 2001:db8:XYZU:TV02::/64 are derived.

   Further, the GUNPs are aimed at links.  For example, the GUNP
   2001:DB8:XXXX:XX01::/64 is aimed at the interface 1, and
   2001:DB8:XXXX:XX02::/64 at the interface 2; further,
   2001:DB8:XXXX:XXff::/64 corresponds to the interface interface 256.
































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           ++=======================++
           II                       II
           II                       II
           II                       II
           II                       II                               |H
           II        Prefix 1     +-----+          Link 1            |o
           II       +-------+     |  I1 |............................|s
           II       |  /64  |     +-----+  |                         |t
           II       |       |       II     |2001:DB8:XXXX:XX01::/64  |
           II       |       +--------------+                         |1
           II       |               II
           II       |               II
           II       |               II
           II       |               II                               |H
    /56  +-----+    |Prefix 2     +-----+          Link 2            |o
   ......|  I0 |----+-------+     |  I2 |............................|s
         +-----+    |  /64  |     +-----+  |                         |t
           II       |       |       II     |2001:DB8:XXXX:XX02::/64  |
           II       |       +--------------+                         |2
           II       |               II
           II       |               II
           II       |               II
           II       |               II                               |H
           II       |Prefix 3     +-----+          Link 3            |o
           II       +-------+     |  I3 |............................|s
           II          /64  |     +-----+  |                         |t
           II               |       II     |2001:DB8:XXXX:XX::/64  |
           II               +--------------+                         |3
           II                       II
           II                       II
           ++=======================++
              Requesting IoT Router


   (In the above figure the Requesting IoT Router, with 4 links, is
   presented).

   There are 2 cases that could be considered.  The first one is: all
   interfaces (except the RI) of the Requesting IoT Router could be
   assigned with the corresponding GUNPs.  In the second case, a list of
   manually selected interfaces is obtained.  Finally interfaces in the
   list are assigned with GUNPs.  The interfaces numbers represent their
   position in alphabetically ordered list by the names that operating
   system assigned to them during the initialization.

   During the final step of the GUA autoconfiguration in the Requesting
   IoT Router, the assignment of the IPv6 network addresses to the
   interfaces is performed.  The IPv6 network addresses have the current



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   format: 2001:DB8::XXXX:XXYY:1/56, where YY - is a value that
   represents the number of the interface.  When the GUA
   autoconfiguration on the Requesting IoT Router is finished, the
   Requesting IoT Router advertises via its interfaces the GUNPs to the
   Hosts.

4.3.  Advertisement of the network prefixes

   Finally, the Requesting IoT Router runs the Neighbour Discovery
   Protocol.  The Neighbour Discovery Protocol messages allow to
   advertise the configuration to the hosts.  To send the configuration
   parameters from the Requesting IoT Router to the hosts, the "Router
   Advertisement" type messages are used [RFC4861].  Usually the "Router
   Advertisement" messages are triggered by the "Router Solicit"
   messages sent from the Hosts to the Requesting IoT Router [RFC4861].

   The "Router Advertisement" message includes the "Prefix Information"
   option.  It is located in the "Options part" of the "Router
   Advertisement" message.  The position of the "Prefix Information"
   option is presented in the figure below.


        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      |          Checksum             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Cur Hop Limit |M|O|  Reserved |       Router Lifetime         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Reachable Time                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                          Retrans Timer                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Options ...         PREFIX INFORMATION
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-


   (Figure above presents the Router Advertisement message format
   [RFC4861])

   The "Prefix Information" option carries the GUNP value and length.
   These configuration parameters provide on-link GUNPs, used for SLAAC
   auto configuration.  The Prefix Length is a number that describes the
   number of bits which are used to identify the GUNP.  And each GUNP
   represents the sub-network.






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        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      |    Length     | Prefix Length |L|A| Reserved1 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Valid Lifetime                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Preferred Lifetime                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           Reserved2                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                            Prefix                             +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


4.4.  Recommendations

   First recommendation we suggest for DHCP is to use port different
   from 547 because it is blocked in many cases.  Insted we propose to
   use another one, like 25474.  Different approach to address this
   problem is to develop a method to dynamically negotiate such port
   number.

   Second recommendation may have to do with Hop Limit and multicast
   scope in DHCP Solicit messages.  It is reasonable to set the value of
   Hop Limit to 16.  It will allow to put DHCP servers _outside_ the
   cellular network domain.

   Third recommendation is that link layer protocol used to make IPv6
   addresses in 3GPP network should be documented - and agreed - at
   IETF, not only at 3GPP.  Thus document will be a base for
   disscussions about IPv6 and User Equipments (UE).

5.  Security Considerations

   At this time, no security considerations are addressed by this memo.

6.  IANA Considerations

   No request to IANA at this time.





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7.  Acknowledgements

   The authors would like to thank (in alphabetical order) Michael
   Mathias Boc, Giorgio Campo, David Frey and Artiol Kalca for their
   valuable comments related to the Linux Network stack, the Legato OS
   recipies and the cross-compilation for the ARM architecture.  Also
   the authors would like to acknowledge the contribution of Fred Baker,
   Michele Russo and Ole Troan for valuable comments during the review
   of this memo.

8.  Normative References

   [ETSI102361]
              ETSI, "ETSI TS 102 361-3 v1.1.7 (2007-12): Electromagnetic
              compatibility and Radio spectrum Matters; Digital Mobile
              Radio Systems; DRM data protocol.".

   [I-D.ietf-dhc-rfc3315bis]
              Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A.,
              Richardson, M., Jiang, S., Lemon, T., and T. Winters,
              "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
              bis", draft-ietf-dhc-rfc3315bis-13 (work in progress),
              April 2018.

   [RFC1661]  Simpson, W., Ed., "The Point-to-Point Protocol (PPP)",
              STD 51, RFC 1661, DOI 10.17487/RFC1661, July 1994,
              <https://www.rfc-editor.org/info/rfc1661>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3633]  Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
              Host Configuration Protocol (DHCP) version 6", RFC 3633,
              DOI 10.17487/RFC3633, December 2003,
              <https://www.rfc-editor.org/info/rfc3633>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,
              <https://www.rfc-editor.org/info/rfc4861>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.




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   [RFC6459]  Korhonen, J., Ed., Soininen, J., Patil, B., Savolainen,
              T., Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
              Partnership Project (3GPP) Evolved Packet System (EPS)",
              RFC 6459, DOI 10.17487/RFC6459, January 2012,
              <https://www.rfc-editor.org/info/rfc6459>.

   [RFC6653]  Sarikaya, B., Xia, F., and T. Lemon, "DHCPv6 Prefix
              Delegation in Long-Term Evolution (LTE) Networks",
              RFC 6653, DOI 10.17487/RFC6653, July 2012,
              <https://www.rfc-editor.org/info/rfc6653>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

Authors' Addresses

   Dmytro Shytyi
   Societe Francaise du Radiotelephone(SFR)
   Paris area , Ile-de-France
   France

   Email: ietf.dmytro@shytyi.net
   URI:   http://dmytro.shytyi.net https://shytyi.net


   Giorgio Campo


   Alexandre Petrescu
   CEA, LIST
   CEA Saclay
   Gif-sur-Yvette , Ile-de-France   91190
   France

   Phone: +33169089223
   Email: Alexandre.Petrescu@cea.fr













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