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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 5121

Network Working Group                                    Basavaraj Patil
Internet-Draft                                    Nokia Siemens Networks
Intended status: Standards Track                               Frank Xia
Expires: May 15, 2008                                    Behcet Sarikaya
                                                              Huawei USA
                                                                JH. Choi
                                                             Samsung AIT
                                                        Syam Madanapalli
                                                      Ordyn Technologies
                                                       November 12, 2007


     Transmission of IPv6 via the IPv6 CS over IEEE 802.16 Networks
                  draft-ietf-16ng-ipv6-over-ipv6cs-11

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on May 15, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   IEEE Std 802.16 is an air interface specification for fxed and mobile
   Broadband Wireless Access Systems.  Service specific convergence



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   sublayers to which upper layer protocols interface are a part of the
   IEEE 802.16 MAC (Medium Access Control).  The Packet convergence
   sublayer is used for the transport of all packet-based protocols such
   as Internet Protocol (IP) and, IEEE 802.3 LAN/MAN CSMA/CD Access
   Method (Ethernet).  IPv6 packets can be sent and received via the IP
   specific part of the packet convergence sublayer.  This document
   specifies the addressing and operation of IPv6 over the IP specific
   part of the packet CS for hosts served by a network that utilizes the
   IEEE Std 802.16 air interface.  It recommends the assignment of a
   unique prefix (or prefixes) to each host and allows the host to use
   multiple identifiers within that prefix, including support for
   randomly generated interface identifiers.


Table of Contents

   1.  Conventions used in this document  . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  IEEE 802.16 convergence sublayer support for IPv6  . . . . . .  5
     4.1.  IPv6 encapsulation over the IP CS of the MAC . . . . . . .  8
   5.  Generic network architecture using the 802.16 air interface  .  9
   6.  IPv6 link  . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     6.1.  IPv6 link in 802.16  . . . . . . . . . . . . . . . . . . . 10
     6.2.  IPv6 link establishment in 802.16  . . . . . . . . . . . . 11
     6.3.  Maximum transmission unit in 802.16  . . . . . . . . . . . 12
   7.  IPv6 prefix assignment . . . . . . . . . . . . . . . . . . . . 12
   8.  Router Discovery . . . . . . . . . . . . . . . . . . . . . . . 13
     8.1.  Router Solicitation  . . . . . . . . . . . . . . . . . . . 13
     8.2.  Router Advertisement . . . . . . . . . . . . . . . . . . . 13
     8.3.  Router lifetime and periodic router advertisements . . . . 13
   9.  IPv6 addressing for hosts  . . . . . . . . . . . . . . . . . . 14
     9.1.  Interface Identifier . . . . . . . . . . . . . . . . . . . 14
     9.2.  Duplicate address detection  . . . . . . . . . . . . . . . 14
     9.3.  Stateless address autoconfiguration  . . . . . . . . . . . 15
     9.4.  Stateful address autoconfiguration . . . . . . . . . . . . 15
   10. Multicast Listener Discovery . . . . . . . . . . . . . . . . . 15
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   13. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 15
   14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     14.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     14.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix A.  WiMAX network architecture and IPv6 support . . . . . 17
   Appendix B.  IPv6 link in WiMAX  . . . . . . . . . . . . . . . . . 19
   Appendix C.  IPv6 link establishment in WiMAX  . . . . . . . . . . 20
   Appendix D.  Maximum transmission unit in WiMAX  . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21



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   Intellectual Property and Copyright Statements . . . . . . . . . . 22


















































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1.  Conventions used in this document

   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].


2.  Introduction

   IEEE 802.16e is an air interface for fixed and mobile broadband
   wireless access systems.  The IEEE 802.16 standard specifies the air
   interface, including the medium access control (MAC) layer and
   multiple physical layer (PHY) specifications.  It can be deployed in
   licensed as well as unlicensed spectrum.  While the PHY and MAC are
   specified in IEEE 802.16, the details of IPv4 and IPv6 operation over
   the air interface are not included.  This document specifies the
   operation of IPv6 over the IEEE 802.16 air interface.

   IPv6 packets can be carried over the IEEE Std 802.16 specified air
   interface via :

   1.  the IP specific part of the Packet CS or,
   2.  the 802.3 [802.3] specific part of the Packet CS

   The scope of this specification is limited to the operation of IPv6
   over IP CS only.

   The IEEE 802.16 [802.16] specification includes the Phy and MAC
   details.  The convergence sublayers are a part of the MAC.  The
   packet convergence sublayer includes the IP specific part which is
   used by the IPv6 layer.

   The mobile station(MS)/host is attached to an access router via a
   base station (BS).  The host and the BS are connected via the IEEE
   Std 802.16 air interface at the link and physical layers.  The IPv6
   link from the MS terminates at an access router which may be a part
   of the BS or an entity beyond the BS.  The base station is a layer 2
   entity (from the perspective of the IPv6 link between the MS and AR)
   and relays the IPv6 packets between the AR and the host via a point-
   to-point connection over the air interface.


3.  Terminology

   The terminology in this document is based on the definitions in IP
   over 802.16 Problem Statement and Goals [I-D.ietf-16ng-ps-goals].





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   o  IP CS - The IP specific part of the packet convergence sublayer is
      refered to as IP CS.  IPv6 CS and IP CS are used interchangeably.
   o  Subscriber station (SS), Mobile Station (MS), Mobile Node (MN) -
      The term subscriber station, mobile station and mobile node are
      used interchangeably in this document and mean the same, i.e an IP
      host.


4.  IEEE 802.16 convergence sublayer support for IPv6

   The IEEE 802.16 MAC specifies two main service specific convergence
   sublayers:

   1.  ATM Convergence sublayer
   2.  Packet Convergence sublayer

   The Packet CS is used for the transport of packet based protocols
   which include:

   1.  IEEE Std 802.3(Ethernet)
   2.  Internet Protocol (IPv4 and IPv6)

   The service specific CS resides on top of the MAC Common Part
   Sublayer (CPS) as shown in figure 1.  The service specific CS is
   responsible for:

   o  accepting packets (PDUs) from the upper layer,
   o  performing classification of the packet/PDU based on a set of
      classifiers that are defined which are service specific,
   o  delivering the CS PDU to the appropriate service flow and
      transport connection and,
   o  receiving PDUs from the peer entity.

   Payload header suppression (PHS) is also a function of the CS but is
   optional.

   The figure below shows the concept of the service specific CS in
   relation to the MAC:













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     -----------------------------\
     |  ATM CS     | Packet CS   | \
     -----------------------------  \
     |  MAC Common Part Sublayer |   \
     | (Ranging, scheduling, etc)|    802.16 MAC
     -----------------------------   /
     |        Security           |  /
     |(Auth, encryption,key mgmt)| /
     -----------------------------/
     |         PHY               |
     -----------------------------


                       Figure 1: The IEEE 802.16 MAC

   Classifiers for each of the specific upper-layer protocols, i.e
   Ethernet and IP, are defined in the IEEE 802.16 specification, which
   enable the packets from the upper layer to be processed by the
   appropriate service specific part of the packet CS.  IPv6 can be
   transported directly over the IP specific part of the packet CS (IP
   CS).  IPv4 packets also are transported over the IP specific part of
   the packet CS.  The classifiers used by IP CS enable the
   differentiation of IPv4 and IPv6 packets and their mapping to
   specific transport connections over the air-interface.

   The figure below shows the options for IPv6 transport over the packet
   CS of IEEE 802.16:

                                      +-------------------+
                                      |    IPv6           |
         +-------------------+        +-------------------+
         |    IPv6           |        |    Ethernet       |
         +-------------------+        +-------------------+
         |  IP Specific      |        |  802.3 Specific   |
         | part of Packet CS |        | part of Packet CS |
         |...................|        |...................|
         |    MAC            |        |    MAC            |
         +-------------------+        +-------------------+
         |    PHY            |        |    PHY            |
         +-------------------+        +-------------------+

         (1) IPv6 over                (2) IPv6 over
             IP specific part             802.3/Ethernet
             of Packet CS                 Specific part
                                          of Packet CS






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     Figure 2: IPv6 over IP and 802.3 specific parts of the Packet CS

   The figure above shows that while there are multiple methods by which
   IPv6 can be transmitted over an 802.16 air interface, the scope of
   this document is limited to IPv6 operation over IP CS only.
   Transmission of IP over Ethernet is specified in
   [I-D.ietf-16ng-ip-over-ethernet-over-802.16].  Transmission of IPv4
   over IP CS is specified by the 16ng WG in
   [I-D.ietf-16ng-ipv4-over-802-dot-16-ipcs].

   It should be noted that immediately after ranging (802.16 air
   interface procedure) and exchange of SBC-REQ/RSP messages (802.16
   specific), the MS and BS exchange their capabilities via REG-REQ
   (Registration Request) and REG-RSP (Registration Response) 802.16 MAC
   messages.  These management frames negotiate parameters such as the
   Convergence Sublayer supported by the MS and BS.  By default, Packet,
   IPv4 and 802.3/Ethernet are supported.  IPv6 via the IP CS is
   supported by the MS and the BS only when the IPv6 support bit in the
   capability negotiation messages (REG-REQ and REG-RSP) implying such
   support is indicated in the parameter "Classification/PHS options and
   SDU (Service Data Unit) encapsulation support" (Refer to [802.16]).
   Additionally during the establishment of the transport connection for
   transporting IPv6 packets, the DSA-REQ (Dynamic Service Addition) and
   DSA-RSP messages between the BS and MS indicate via the CS-
   Specification TLV the CS that the connection being setup shall use.
   When the IPv6 packet is preceded by the IEEE 802.16 six byte MAC
   header there is no specific indication in the MAC header itself about
   the payload type.  The processing of the packet is based entirely on
   the classifiers.  Based on the classification rules, the MAC layer
   selects an appropriate transport connection for the transmission of
   the packet.  An IPv6 packet is transported over a transport
   connection that is specifically established for carrying such
   packets.

   Transmission of IPv6 as explained above is possible via multiple
   methods, i.e, via IP CS or via Ethernet interfaces.  Every Internet
   host connected via an 802.16 link :

   1.  MUST be able to send and receive IPv6 packets via IP CS when the
       MS and BS indicate IPv6 protocol support over IP CS
   2.  MUST be able to send and receive IPv6 packets over the Ethernet
       (802.3) specific part of the packet CS when the MS and BS
       indicate IPv6 protocol support over Ethernet CS.  However when
       the MS and BS indicate IPv6 protocol support over both IP CS and
       Ethernet CS, the MS and BS MUST use IP CS for sending and
       receiving IPv6 packets.

   When the MS and BS support IPv6 over IP CS, it MUST be used as the



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   default mode for transporting IPv6 packets over IEEE 802.16 and the
   recommendations in this document followed.  Inability to negotiate a
   common convergence sublayer for IPv6 transport between the MS and BS
   will result in failure to setup the transport connection and thereby
   render the host unable to send and receive IPv6 packets.  In the case
   of a host which implements more than one method of transporting IPv6
   packets, the default choice of which method to use (i.e IPv6 over the
   IP CS or IPv6 over 802.3) is IPv6 over IP CS when the BS also
   supports such capability.

4.1.  IPv6 encapsulation over the IP CS of the MAC

   The IPv6 payload when carried over the IP specific part of the Packet
   CS is encapsulated by the 6 byte IEEE 802.16 generic MAC header.  The
   format of the IPv6 packet encapsulated by the generic MAC header is
   shown in the figure below.  The format of the 6 byte MAC header is
   described in the [802.16] specification.  The CRC (cyclic redundancy
   check) is optional.  It should be noted that the actual MAC address
   is not included in the MAC header.



             ---------/ /-----------
             |    MAC SDU          |
             --------/ /------------
                     ||
                     ||
      MSB            \/                                    LSB
      ---------------------------------------------------------
      | Generic MAC header|  IPv6 Payload              | CRC  |
      ---------------------------------------------------------


                       Figure 3: IPv6 encapsulation

   For transmission of IPv6 packets via the IP CS over IEEE 802.16, the
   IPv6 layer interfaces with the 802.16 MAC directly.  The IPv6 layer
   delivers the IPv6 packet to the Packet CS of the IEEE 802.16 MAC.
   The packet CS defines a set of classifiers that are used to determine
   how to handle the packet.  The IP classifiers that are used at the
   MAC operate on the fields of the IP header and the transport protocol
   and these include the IP Traffic class, Next header field, Masked IP
   source and destination addresses and, Protocol source and destination
   port ranges.  Next header in this case refers to the last header of
   the IP header chain.  Parsing these classifiers, the MAC maps an
   upper layer packet to a specific service flow and transport
   connection to be used.  The MAC encapsulates the IPv6 packet in the 6
   byte MAC header (MAC SDU) and transmits it.  The figure below shows



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   the operation on the downlink, i.e the transmission from the BS to
   the host.  The reverse is applicable for the uplink transmission.




     -----------                               ----------
     | IPv6 Pkt|                               |IPv6 Pkt|
     -----------                               ----------
        | |                                      /|\
        | |                                       |
     --[SAP]---------------------       ---------[SAP]--------
     ||-| |----------|          |       |        /|\         |
     || \ /        0---->[CID1] |       |     --- |--------  |
     || Downlink   0\/-->[CID2] |       |     |Reconstruct|  |
     || classifiers0/\-->[....] |       |     | (undo PHS)|  |
     ||            0---->[CIDn] |       |     ---   -------  |
     ||--------------|          |       |        /|\         |
     |                          |       |         |          |
     |  {SDU, CID,..}           |       |    {SDU, CID,..}   |
     |       |                  |       |        /|\         |
     |       v                  |       |         |          |
     ------[SAP]-----------------       |-------[SAP]---------
     |     802.16 MAC CPS       |------>|   802.16 MAC CPS   |
     ----------------------------       ----------------------
              BS                                  MS


               Figure 4: IPv6 packet transmission: Downlink


5.  Generic network architecture using the 802.16 air interface

   In a network that utilizes the 802.16 air interface the host/MS is
   attached to an IPv6 access router (AR) in the network.  The BS is a
   layer 2 entity only.  The AR can be an integral part of the BS or the
   AR could be an entity beyond the BS within the access network.  An AR
   nay be attached to multiple BS' in a network.  IPv6 packets between
   the MS and BS are carried over a point-to-point transport connection
   which is identified by a unique connection identifier (CID).  The
   transport connection is a MAC layer link between the MS and the BS.
   The figures below describe the possible network architectures and are
   generic in nature.  More esoteric architectures are possible but not
   considered in the scope of this document.  Option A:







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           +-----+    CID1     +--------------+
           | MS1 |------------/|     BS/AR    |-----[Internet]
           +-----+           / +--------------+
              .         /---/
              .     CIDn
           +-----+    /
           | MSn |---/
           +-----+


            Figure 5: The IPv6 AR as an integral part of the BS

   Option B:




         +-----+   CID1    +-----+          +-----------+
         | MS1 |----------/| BS1 |----------|     AR    |-----[Internet]
         +-----+         / +-----+          +-----------+
            .           /        ____________
            .     CIDn /        ()__________()
         +-----+      /            L2 Tunnel
         | MSn |-----/
         +-----+


               Figure 6: The IPv6 AR is separate from the BS

   The above network models serve as examples and are shown to
   illustrate the point to point link between the MS and the AR.


6.  IPv6 link

   Neighbor Discovery for IP Version 6 [RFC4861] defines link as a
   communication facility or medium over which nodes can communicate at
   the link layer, i.e., the layer immediately below IP .  A link is
   bounded by routers that decrement the Hop limit field in the IPv6
   header.  When an MS moves within a link, it can keep using its IP
   addresses.  This is a layer 3 definition and note that the definition
   is not identical with the definition of the term '(L2) link' in IEEE
   802 standards.

6.1.  IPv6 link in 802.16

   In 802.16, the Transport Connection between an MS and a BS is used to
   transport user data, i.e.  IPv6 packets in this case.  A Transport



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   Connection is represented by a CID (Connection Identifier) and
   multiple Transport Connections can exist between an MS and BS.

   When an AR and a BS are colocated, the collection of Transport
   Connections to an MS is defined as a single link.  When an AR and a
   BS are separated, it is recommended that a tunnel is established
   between the AR and a BS whose granularity is no greater than 'per MS'
   or 'per service flow' ( An MS can have multiple service flows which
   are identified by a service flow ID).  Then the tunnel(s) for an MS,
   in combination with the MS's Transport connections, forms a single
   point-to-point link.

   The collection of service flows (tunnels) to an MS is defined as a
   single link.  Each link that use the same higher layer protocol has
   only an MS and an AR.  Each MS belongs to a different link.  A
   different prefix should be assigned to each unique link.  This link
   is fully consistent with a standard IP link, without exception and
   conforms with the definition of a point-to-point link in Neighbor
   discovery for IPv6 [RFC4861].  Hence the point-to-point link model
   for IPv6 operation over the IP specific part of the Packet CS in
   802.16 SHOULD be used.  A unique IPv6 prefix(es) per link (MS/host)
   MUST be assigned.

6.2.  IPv6 link establishment in 802.16

   In order to enable the sending and receiving of IPv6 packets between
   the MS and the AR, the link between the MS and the AR via the BS
   needs to be established.  This section illustrates the link
   establishment procedure.

   The MS goes through the network entry procedure as specified by
   802.16.  A high level description of the network entry procedure is
   as follows:

   1.  MS performs initial ranging with the BS.  Ranging is a process by
       which an MS becomes time aligned with the BS.  The MS is
       synchronized with the BS at the successful completion of ranging
       and is ready to setup a connection.
   2.  The MS and BS exchange basic capabilities that are necessary for
       effective communication during the initialization using SBC-REQ/
       RSP (802.16 specific) messages.
   3.  The MS progresses to an authentication phase.  Authentication is
       based on PKMv2 as defined in the IEEE Std 802.16 specification.
   4.  On successful completion of authentication, the MS performs
       802.16 registration with the network.
   5.  MS and BS perform capability exchange as per 802.16 procedures.
       Protocol support is indicated in this exchange.  The CS
       capability parameter indicates which classification/PHS options



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       and SDU encapsulation the MS supports.  By default, Packet, IPv4
       and 802.3/Ethernet shall be supported, thus absence of this
       parameter in REG-REQ (802.16 message) means that named options
       are supported by the MS/SS.  Support for IPv6 over the IP
       specific part of the packet CS is indicated by Bit#2 of the CS
       capability parameter (Refer to [802.16]).
   6.  The MS MUST request the establishment of a service flow for IPv6
       packets over IP CS if the MS and BS have confirmed capability for
       supporting IPv6 over IP CS.  The service flow MAY also be
       triggered by the network as a result of pre-provisioning.  The
       service flow establishes a link between the MS and the AR over
       which IPv6 packets can be sent and received.
   7.  The AR and MS SHOULD send router advertisements and solicitations
       as specified in Neighbor discovery,[RFC4861].

   The above flow does not show the actual 802.16 messages that are used
   for ranging, capability exchange or service flow establishment.
   Details of these are in [802.16].

6.3.  Maximum transmission unit in 802.16

   The MTU value for IPv6 packets on an 802.16 link is configurable.
   The default MTU for IPv6 packets over an 802.16 link MUST be 1500
   octets.

   The 802.16 MAC PDU (Protocol Data Unit) is composed of a 6 byte
   header followed by an optional payload and an optional CRC covering
   the header and the payload.  The length of the PDU is indicated by
   the Len parameter in the Generic MAC Header.  The Len parameter has a
   size of 11 bits.  Hence the total MAC PDU size is 2048 bytes.  The
   IPv6 payload size can vary.  In certain deployment scenarios the MTU
   value can be greater than the default.  Neighbor Discovery for IPv6
   [RFC4861] defines an MTU option that an AR can advertise, via router
   advertisement (RA), to a Mobile Node (MN).  If an AR advertises an
   MTU via the RA MTU option, the MN SHOULD use the MTU from the RA.
   Nodes that implement Path MTU discovery [RFC1981] MAY use the
   mechanism to determine the MTU for the IPv6 packets.


7.  IPv6 prefix assignment

   The MS and the AR are connected via a point-to-point connection at
   the IPv6 layer.  Hence each MS can be considered to be on a separate
   subnet.  A CPE (Customer Premise Equipment) type of device which
   serves multiple IPv6 hosts, may be the end point of the connection.
   Hence one or more /64 prefixes SHOULD be assigned to a link.  The
   prefixes are advertised with the on-link (L-bit) flag set as
   specified in [RFC4861].  The size and number of the prefixes is a



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   configuration issue.  Also, DHCP or AAA-based prefix delegation MAY
   be used to provide one or more prefixes to MS for an AR connected
   over 802.16.  The other properties of the prefixes are also dealt
   with via configuration.


8.  Router Discovery

8.1.  Router Solicitation

   On completion of the establishment of the IPv6 link, the MS may send
   a router solicitation message to solicit a Router Advertisement
   message from the AR to acquire necessary information as per the
   neighbor discovery for IPv6 specification [RFC4861].  An MS that is
   network attached may also send router solicitations at any time.
   Movement detection at the IP layer of an MS in many cases is based on
   receiving periodic router advertisements.  An MS may also detect
   changes in its attachment via link triggers or other means.  The MS
   can act on such triggers by sending router solicitations.  The router
   solicitation is sent over the IPv6 link that has been previously
   established.  The MS sends router solicitations to the all-routers
   multicast address.  It is carried over the point-to-point link to the
   AR via the BS.  The MS does not need to be aware of the link-local
   address of the AR in order to send a router solicitation at any time.
   The use of router advertisements as a means for movement detection is
   not recommended for MNs connected via 802.16 links as the frequency
   of periodic router advertisements can be high.

8.2.  Router Advertisement

   The AR SHOULD send a number (configurable value) of router
   advertisements as soon as the IPv6 link is established, to the MS.
   The AR sends unsolicited router advertisements periodically as per
   [RFC4861].  The interval between periodic router advertisements is
   however greater than the specification in Neighbor discovery for
   IPv6, and is discussed in the following section.

8.3.  Router lifetime and periodic router advertisements

   The router lifetime SHOULD be set to a large value, preferably in
   hours.  This document over-rides the specification for the value of
   the router lifetime in Neighbor Discovery for IP Version 6 (IPv6)
   [RFC4861].  The AdvDefaultLifetime in the router advertisement MUST
   be either zero or between MaxRtrAdvInterval and 43200 seconds.  The
   default value is 2 * MaxRtrAdvInterval.

   802.16 hosts have the capability to transition to an idle mode in
   which case the radio link between the BS and MS is torn down.  Paging



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   is required in case the network needs to deliver packets to the MS.
   In order to avoid waking a mobile which is in idle mode and consuming
   resources on the air interface, the interval between periodic router
   advertisements SHOULD be set quite high.  The MaxRtrAdvInterval value
   specified in this document over-rides the recommendation in Neighbor
   Discovery for IP Version 6 (IPv6) [RFC4861].  The MaxRtrAdvInterval
   MUST be no less than 4 seconds and no greater than 21600 seconds.
   The default value for MaxRtrAdvInterval is 10800 seconds.


9.  IPv6 addressing for hosts

   The addressing scheme for IPv6 hosts in 802.16 networks follows the
   IETFs recommendation for hosts specified in IPv6 Node Requirement,
   RFC 4294.  The IPv6 node requirements RFC4294 [RFC4294] specifies a
   set of RFCs that are applicable for addressing and the same is
   applicable for hosts that use 802.16 as the link layer for
   transporting IPv6 packets.

9.1.  Interface Identifier

   The MS has a 48-bit globally unique MAC address as specified in
   802.16 [802.16].  This MAC address MUST be used to generate the
   modified EUI-64 format-based interface identifier as specified in the
   IP Version 6 Addressing Architecture [RFC4291].  The modified EUI-64
   interface identifier is used in stateless address autoconfiguration.
   As in other links that support IPv6, EUI-64 based interface
   identifiers are not mandatory and other mechanisms, such as random
   interface identifiers, Privacy Extensions for Stateless Address
   Autoconfiguration in IPv6 [RFC3041] MAY also be used.

9.2.  Duplicate address detection

   DAD SHOULD be performed as per Neighbor Discovery for IP Version 6,
   [RFC4861] and, IPv6 Stateless Address Autoconfiguration, [RFC4862].
   The IPv6 link over 802.16 is specified in this document as a point-
   to-point link.  Based on this criteria, it may be redundant to
   perform DAD on a global unicast address that is configured using the
   EUI-64 or generated as per RFC3041 [RFC3041] for the interface as
   part of the IPv6 stateless address autoconfiguration protocol
   [RFC4862] as long as the following two conditions are met:

   1.  The prefixes advertised through the router advertisement messages
       by the access router terminating the 802.16 IPv6 link are unique
       to that link.
   2.  The access router terminating the 802.16 IPv6 link does not
       autoconfigure any IPv6 global unicast addresses from the prefix
       that it advertises.



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9.3.  Stateless address autoconfiguration

   When stateless address autoconfiguration is performed, it MUST be
   performed as specified in [RFC4861] and, [RFC4862].

9.4.  Stateful address autoconfiguration

   When stateful address autoconfiguration is performed, it MUST be
   performed as specified in [RFC4861] and, [RFC3315].


10.  Multicast Listener Discovery

   Multicast Listener Discovery Version 2 (MLDv2) for IPv6 [RFC4861]
   SHOULD be supported as specified by the hosts and routers attached to
   each other via an 802.16 link.  The access router which has hosts
   attached to it via a Point-to-point link over an 802.16 SHOULD NOT
   send periodic queries if the host is in idle/dormant mode.  The AR
   can obtain information about the state of a host from the paging
   controller in the network.


11.  IANA Considerations

   This draft does not require any actions from IANA.


12.  Security Considerations

   This document does not introduce any new vulnerabilities to IPv6
   specifications or operation.  The security of the 802.16 air
   interface is the subject of [802.16].  It should be noted that 802.16
   provides capability to cipher the traffic carried over the transport
   connections.  A traffic encryption key (TEK) is generated by the MS
   and BS on completion of successful authentication and is used to
   secure the traffic over the air interface.  An MS may still use IPv6
   security mechanisms even in the presence of security over the 802.16
   link.  In addition, the security issues of the network architecture
   spanning beyond the 802.16 base stations is the subject of the
   documents defining such architectures, such as WiMAX Network
   Architecture [WiMAXArch] in Sections 7.2 and 7.3 of Stage 2 Part 2.


13.  Acknowledgments

   The authors would like to acknowledge the contributions of the 16NG
   working group chairs Soohong Daniel Park and Gabriel Montenegro as
   well as Jari Arkko, Jonne Soininen, Max Riegel, Prakash Iyer, DJ



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   Johnston, Dave Thaler, Bruno Sousa, Alexandru Petrescu, Margaret
   Wasserman and Pekka Savola for their review and comments.  Review and
   comments by Phil Barber have also helped in improving the document
   quality.


14.  References

14.1.  Normative References

   [802.16]   "IEEE Std 802.16e: IEEE Standard for Local and
              metropolitan area networks, Amendment for Physical and
              Medium Access Control Layers for Combined Fixed and Mobile
              Operation in Licensed Bands", October 2005, <http://
              standards.ieee.org/getieee802/download/802.16e-2005.pdf>.

   [RFC1981]  McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
              for IP version 6", RFC 1981, August 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement  Levels", RFC 2119, March 1997,
              <ftp://ftp.isi.edu/in-notes/rfc2119>.

   [RFC3810]  Vida, R. and L. Costa, "Multicast Listener Discovery
              Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              September 2007.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862, September 2007.

14.2.  Informative References

   [802.3]    "IEEE Std 802.3-2005: IEEE Standard for Information
              technology-Telecommunications and information exchange
              between systems-Local and metropolitan area networks--
              Specific requirements Part 3: Carrier Sense Multiple
              Access with Collision Detection (CSMA/CD) Access Method
              and Physical Layer Specifications", December 2005,
              <http://standards.ieee.org/getieee802/802.3.html>.

   [I-D.ietf-16ng-ip-over-ethernet-over-802.16]
              Jeon, H., "Transmission of IP over Ethernet over IEEE



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              802.16 Networks",
              draft-ietf-16ng-ip-over-ethernet-over-802.16-02 (work in
              progress), July 2007.

   [I-D.ietf-16ng-ipv4-over-802-dot-16-ipcs]
              Madanapalli, S., "Transmission of IPv4 packets over IEEE
              802.16's IP Convergence Sublayer",
              draft-ietf-16ng-ipv4-over-802-dot-16-ipcs-00 (work in
              progress), May 2007.

   [I-D.ietf-16ng-ps-goals]
              Jee, J., "IP over 802.16 Problem Statement and Goals",
              draft-ietf-16ng-ps-goals-02 (work in progress),
              August 2007.

   [RFC3041]  Narten, T. and R. Draves, "Privacy Extensions for
              Stateless Address Autoconfiguration in IPv6", RFC 3041,
              January 2001.

   [RFC3315]  Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
              and M. Carney, "Dynamic Host Configuration Protocol for
              IPv6 (DHCPv6)", RFC 3315, July 2003.

   [RFC4294]  Loughney, J., "IPv6 Node Requirements", RFC 4294,
              April 2006.

   [WMF]      "http://www.wimaxforum.org".

   [WiMAXArch]
              "WiMAX End-to-End Network Systems Architecture http://
              www.wimaxforum.org/technology/documents/
              WiMAX_End-to-End_Network_Systems_Architecture_Stage_2-
              3_Release_1.1.0.zip", September 2007.


Appendix A.  WiMAX network architecture and IPv6 support

   The WiMAX (Worldwide Interoperability for Microwave Access) forum
   [WMF] has defined a network architecture in which the air interface
   is based on the IEEE 802.16 standard.  The addressing and operation
   of IPv6 described in this document is applicable to the WiMAX network
   as well.

   WiMAX is an example architecture of a network that uses the 802.16
   specification for the air interface.  WiMAX networks are also in the
   process of being deployed in various parts of the world and the
   operation of IPv6 within a WiMAX network is explained in this
   appendix.



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   The WiMAX network architecture consists of the Access Service Network
   (ASN) and the Connectivity Service Network (CSN).  The ASN is the
   access network which includes the BS and the AR in addition to other
   functions such as AAA, Mobile IP Foreign agent, Paging controller,
   Location Register etc.  The ASN is defined as a complete set of
   network functions needed to provide radio access to a WiMAX
   subscriber.  The ASN is the access network to which the MS attaches.
   The IPv6 access router is an entity within the ASN.  The term ASN is
   specific to the WiMAX network architecture.  The CSN is the entity
   that provides connectivity to the Internet and includes functions
   such as Mobile IP Home agent and AAA.  The figure below shows the
   WiMAX reference model:



                        -------------------
                        | ----      ASN   |                    |----|
         ----           | |BS|\ R6 -------|    |---------|     | CSN|
         |MS|-----R1----| ---- \---|ASN-GW| R3 |  CSN    | R5  |    |
         ----           |  |R8  /--|------|----|         |-----|Home|
                        | ---- /          |    |  visited|     | NSP|
                        | |BS|/           |    |   NSP   |     |    |
                        | ----            |    |---------|     |    |
                        |       NAP       |         \          |----|
                        -------------------          \---|        /
                                |                        |       /
                                |                     (--|------/----)
                                |R4                  (                )
                                |                   (      ASP network )
                            ---------                ( or Internet    )
                            |  ASN  |                 (              )
                            ---------                   (----------)



                  Figure 7: WiMAX Network reference model

   Three different types of ASN realizations called profiles are defined
   by the architecture.  ASNs of profile types A and C include BS' and
   ASN-gateway(s) (ASN-GW) which are connected to each other via an R6
   interface.  An ASN of profile type B is one in which the
   functionality of the BS and other ASN functions are merged together.
   No ASN-GW is specifically defined in a profile B ASN.  The absence of
   the R6 interface is also a profile B specific characteristic.  The MS
   at the IPv6 layer is associated with the AR in the ASN.  The AR may
   be a function of the ASN-GW in the case of profiles A and C and is a
   function in the ASN in the case of profile B. When the BS and the AR
   are separate entities and linked via the R6 interface, IPv6 packets



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   between the BS and the AR are carried over a GRE tunnel.  The
   granularity of the GRE tunnel should be on a per MS basis or on a per
   service flow basis (an MS can have multiple service flows, each of
   which are identified uniquely by a service flow ID).  The protocol
   stack in WiMAX for IPv6 is shown below:


   |-------|
   | App   |- - - - - - - - - - - - - - - - - - - - - - - -(to app peer)
   |       |
   |-------|                                   /------      -------
   |       |                                  / IPv6 |      |     |
   | IPv6  |- - - - - - - - - - - - - - - -  /       |      |     |-->
   |       |      ---------------    -------/        |      | IPv6|
   |-------|      |    \Relay/  |    |      |        |- - - |     |
   |       |      |     \   /   |    | GRE  |        |      |     |
   |       |      |      \ /GRE | -  |      |        |      |     |
   |       |- - - |       |-----|    |------|        |      |     |
   | IPv6CS|      |IPv6CS | IP  | -  | IP   |        |      |     |
   | ..... |      |...... |-----|    |------|--------|      |-----|
   |  MAC  |      | MAC   | L2  | -  | L2   |  L2    |- - - | L2  |
   |-------|      |------ |-----|    |----- |--------|      |-----|
   |  PHY  |- - - | PHY   | L1  | -  | L1   |  L1    |- - - | L1  |
    --------      ---------------    -----------------      -------

      MS             BS                   AR/ASN-GW          CSN Rtr



                      Figure 8: WiMAX protocol stack

   As can be seen from the protocol stack description, the IPv6 end-
   points are constituted in the MS and the AR.  The BS provides lower
   layer connectivity for the IPv6 link.


Appendix B.  IPv6 link in WiMAX

   WiMAX is an example of a network based on the IEEE Std 802.16 air
   interface.  This section describes the IPv6 link in the context of a
   WiMAX network.  The MS and the AR are connected via a combination of
   :

   1.  The transport connection which is identified by a Connection
       Identifier (CID) over the air interface, i.e the MS and BS and,
   2.  A GRE tunnel between the BS and AR which transports the IPv6
       packets




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   From an IPv6 perspective the MS and the AR are connected by a point-
   to-point link.  The combination of transport connection over the air
   interface and the GRE tunnel between the BS and AR creates a (point-
   to-point) tunnel at the layer below IPv6.

   The collection of service flows (tunnels) to an MS is defined as a
   single link.  Each link has only an MS and an AR.  Each MS belongs to
   a different link.  No two MSs belong to the same link.  A different
   prefix should be assigned to each unique link.  This link is fully
   consistent with a standard IP link, without exception and conforms
   with the definition of a point-to-point link in [RFC4861].


Appendix C.  IPv6 link establishment in WiMAX

   The mobile station performs initial network entry as specified in
   802.16.  On successful completion of the network entry procedure the
   ASN gateway/AR triggers the establishment of the initial service flow
   (ISF) for IPv6 towards the MS.  The ISF is a GRE tunnel between the
   ASN-GW/AR and the BS.  The BS in turn requests the MS to establish a
   transport connection over the air interface.  The end result is a
   transport connection over the air interface for carrying IPv6 packets
   and a GRE tunnel between the BS and AR for relaying the IPv6 packets.
   On successful completion of the establishment of the ISF, IPv6
   packets can be sent and received between the MS and AR.  The ISF
   enables the MS to communicate with the AR for host configuration
   procedures.  After the establishment of the ISF, the AR can send a
   router advertisement to the MS.  An MS can establish multiple service
   flows with different QoS characteristics.  The ISF can be considered
   as the primary service flow.  The ASN-GW/ AR treats each ISF, along
   with the other service flows to the same MS, as a unique link which
   is managed as a (virtual) interface.


Appendix D.  Maximum transmission unit in WiMAX

   The WiMAX forum [WMF] has specified the Max SDU size as 1522 octets.
   Hence the IPv6 path MTU can be 1500 octets.  However because of the
   overhead of the GRE tunnel used to transport IPv6 packets between the
   BS and AR and the 6 byte MAC header over the air interface, using a
   value of 1500 would result in fragmentation of packets.  It is
   recommended that the default MTU for IPv6 be set to 1400 octets for
   the MS in WiMAX networks.  Note that the 1522 octet specification is
   a WiMAX forum specification and not the size of the SDU that can be
   transmitted over 802.16, which has a higher limit.






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Authors' Addresses

   Basavaraj Patil
   Nokia Siemens Networks
   6000 Connection Drive
   Irving, TX  75039
   USA

   Email: basavaraj.patil@nsn.com


   Frank Xia
   Huawei USA
   1700 Alma Dr. Suite 100
   Plano, TX  75075

   Email: xiayangsong@huawei.com


   Behcet Sarikaya
   Huawei USA
   1700 Alma Dr. Suite 100
   Plano, TX  75075

   Email: sarikaya@ieee.org


   JinHyeock Choi
   Samsung AIT
   Networking Technology Lab
   P.O.Box 111
   Suwon, Korea  440-600

   Email: jinchoe@samsung.com


   Syam Madanapalli
   Ordyn Technologies
   1st Floor, Creator Building, ITPL.
   Off Airport Road
   Bangalore, India  560066

   Email: smadanapalli@gmail.com








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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
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