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Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Intended status: Informational                           August 18, 2016
Expires: February 19, 2017


                    IPv6 Prefix Delegation for Hosts
                   draft-templin-v6ops-pdhost-04.txt

Abstract

   IPv6 prefixes are typically delegated to requesting routers which
   then use them to number their downstream-attached links and networks.
   The requesting router then acts as a router between the downstream-
   attached hosts and the upstream Internetwork, and can also act as a
   host under the weak end system model.  This document considers the
   case when the "requesting router" is actually a simple host which
   receives a delegated prefix that it can use solely for its own
   internal multi-addressing purposes under the strong end system model.
   This method can be applied in a wide variety of use cases to allow
   ample address availability without impacting link performance.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on February 19, 2017.

Copyright Notice

   Copyright (c) 2016 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   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 . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Multi-Addressing Considerations . . . . . . . . . . . . . . .   5
   4.  Multi-Addressing Alternatives for Delegated Prefixes  . . . .   5
   5.  MLD/DAD Implications  . . . . . . . . . . . . . . . . . . . .   6
   6.  IPv6 Neighbor Discovery Implications  . . . . . . . . . . . .   7
   7.  "Mixed Mode" Implications . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     11.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   IPv6 Prefix Delegation (PD) entails 1) the communication of a prefix
   from a delegating authority to a requesting node, 2) a representation
   of the prefix in the routing system, and 3) a control messaging
   service to maintain delegated prefix lifetimes.  Following
   delegation, the prefix is available for the requesting node's
   exclusive use and is not shared with any other nodes.  An example
   IPv6 PD service is DHCPv6 PD [RFC3315][RFC3633].

   Using services such as DHCPv6 PD, a Delegating Router 'D' delegates a
   prefix 'P' to a Requesting Node 'R'' as shown in Figure 1:
















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                        +---------------------+
                        |Delegating Router 'D'|
                        |   (Delegate 'P')    |
                        +----------+----------+
                                   |
                             .-(::::::::)
                           .-(:::: IP ::::)-.
                          (:: Internetwork ::)
                           `-(::::::::::::)-'
                              `-(::::::)-'
                                   | WAN Interface
                        +----------+----------+
                        |    (Receive 'P')    |
                        |  Requesting Node 'R'|
                        +----------+----------+
                                   | LAN Interface
       X----+-------------+--------+----+---------------+---X
            |             |      LAN    |               |
       +---++-+--+   +---++-+--+   +---++-+--+     +---++-+--+
       |   |A1|  |   |   |A2|  |   |   |A3|  |     |   |An|  |
       |   +--+  |   |   +--+  |   |   +--+  |     |   +--+  |
       | Host H1 |   | Host H2 |   | Host H3 | ... | Host Hn |
       +---------+   +---------+   +---------+     +---------+

                     Figure 1: Prefix Delegation Model

   In this figure, when Delegating Router 'D' delegates prefix 'P', the
   prefix is injected into the routing system in some fashion to ensure
   that IPv6 packets with destination addresses covered by 'P' are
   unconditionally forwarded to Requesting Node 'R'.  Meanwhile, 'R'
   receives 'P' via its "WAN" interface and sub-delegates 'P' to its
   downstream-attached links via one or more "LAN" interfaces.  Hosts
   'Hn' on a LAN interface subsequently receive addresses 'An' taken
   from 'P' via an address autoconfiguration service such as IPv6
   Stateless Address Autoconfiguration (SLAAC) [RFC4862].  'R' then acts
   as a router between hosts 'Hn' and correspondents reachable via the
   WAN interface.  'R' can also (or instead) act as a host under the
   weak end system model [RFC1122] if it can assign addresses taken from
   'P' to its own internal virtual interfaces (e.g., a loopback).

   This document considers the case when 'R' is actually a simple host,
   and receives a prefix delegation 'P' as if it were a router.  The
   host need not have any LAN interfaces, and can use the prefix solely
   for its own internal addressing purposes.  This could include
   assigning IPv6 adddresses taken from prefix 'P' to the WAN interface
   and then functioning as a host under the strong end system model
   [RFC1122] as shown in Figure 2:




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                        +---------------------+
                        |Delegating Router 'D'|
                        |   (Delegate 'P')    |
                        +----------+----------+
                                   |
                             .-(::::::::)
                           .-(:::: IP ::::)-.
                          (:: Internetwork ::)
                           `-(::::::::::::)-'
                              `-(::::::)-'
                                   | WAN Interface
                        +--+-+--+-++-+-----+--+
                        |A1| |A2| |A3| ... |An|
                        +--+ +--+ +--+     +--+
                        |    (Receive 'P')    |
                        | Requesting Node 'R' |
                        +---------------------+

                     Figure 2: Strong End System Model

   In the above diagram, Requesting Node 'R' receives prefix 'P' from
   Delegating Router 'D' the same as described above.  However, when 'R'
   receives 'P' it assigns addresses 'An' taken from 'P' to the WAN
   interface instead of sub-delegating 'P' to downstream attached LAN
   interfaces.  The major benefit for a host managing a delegated prefix
   in this fashion is multi-addressing.  With multi-addressing, the host
   can assign an unlimited supply of addresses to make them available
   for local applicaitons without requiring coordination with any other
   nodes.

   This approach is applicable to a wide variety of use cases.  For
   example, it can be used to coordinate the Virtual Private Network
   (VPN) interfaces of mobile devices (e.g., cellphones, tablets, laptop
   computers, etc.) that connect into a home enterprise network via
   public access networks.  In that case, the mobile device can assign
   addresses taken from prefix 'P' to the VPN interface so that
   applications would work the same as for a simple host connected to a
   LAN.  The approach can also be applied to aviation applications for
   both manned and unmanned aircraft where the aircraft is treated as a
   mobile host that needs to maintain stable IPv6 addresses even as it
   hands off between available aviation data links across various phases
   of flight.  The approach further applies to any prefix delegation use
   case where the prefix recipient wishes to act as a simple host, for
   example a cellular service customer device that receives a prefix
   delegation from their service provider.

   The following sections present multi-addressing considerations for
   hosts that employ prefix delegation mechanisms.



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2.  Terminology

   The terminology of the normative references apply.  The following
   terms are defined for the purposes of this document:

   shared prefix
      an IPv6 prefix that may be advertised to more than one node on the
      same link, e.g., in a Prefix Information Option (PIO) included in
      a Router Advertisement (RA) message [RFC4861].  The shared prefix
      property applies not only on multi-access links (e.g., Ethernet),
      but also on point-to-point links where the shared prefix is
      visible to both ends of the link.

   delegated prefix
      a prefix that is delegated to a requesting node solely for its own
      use, and is not delegated to any other nodes on the link.

3.  Multi-Addressing Considerations

   IPv6 allows nodes to assign multiple addresses to a single interface.
   [I-D.ietf-v6ops-host-addr-availability] discusses options for multi-
   addressing as well as use cases where multi-addressing may be
   desirable.  Address configuration options for multi-addressing
   include SLAAC [RFC4862], stateful DHCPv6 address configuration
   [RFC3315] and any other address formation methods (e.g., manual
   configuration).

   Nodes that use SLAAC and DHCPv6 address configuration configure
   addresses from a shared prefix and assign them to the link over which
   the prefix was received.  When this happens, the node is obliged to
   use Multicast Listener Discovery (MLD) to join the appropriate
   solicited-node multicast group(s) and to use the Duplicate Address
   Detection (DAD) algorithm [RFC4862] to ensure that no other node that
   receives the shared prefix configures a duplicate address.

   In contrast, a node that uses address configuration from a delegated
   prefix can assign addresses to the interface over which the prefix is
   received without invoking MLD/DAD, since the prefix has been
   delegated to the node for its own exclusive use and is not shared
   with any other nodes.

4.  Multi-Addressing Alternatives for Delegated Prefixes

   When a node receives a prefix delegation, it has many alternatives
   for the way in which it can provision the prefix.  [RFC7278]
   discusses alternatives for provisioning a prefix obtained by a User
   Equipment (UE) device under the 3rd Generation Partnership Program
   (3GPP) service model.  This document considers the more general case



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   when the node receives a prefix delegation in which the prefix is
   delegated for the exclusive use of the prefix recipient.

   When the node receives the prefix (e.g., a /64), it can sub-delegate
   the prefix to its LAN interfaces and configure one or more addresses
   for itself on a LAN interface.  The node also configures a default
   route that points to a router on the WAN link.  The node can then act
   as both a host for its own applications accodring to the weak end
   system model and a router for any downstream-attached hosts.  This
   approach is often known as the "tethered" configuration.

   When the node does not have any LAN interfaces, it may still wish to
   obtain a prefix for multi-addressing purposes.  In a first
   alternative, the node can receive the prefix acting as a requesting
   node over the WAN interface but then assign the prefix to an internal
   virtual interface (e.g., a loopback interface) and assign one or more
   addresses taken from the prefix to the virtual interface.  In that
   case, applications on the node can use the assigned addresses
   according to the weak end system model.

   In a second alternative, the node can receive the prefix as a
   requesting node over the WAN interface but then assign one or more
   addresses taken from the prefix to the WAN interface.  In that case,
   applications on the node can use the assigned addresses according to
   the strong end system model as shown in Figure 2.

   In both of these latter two cases, the node acts as a host internally
   even though it behaves as a router from the standpoint of prefix
   delegation and neighbor discovery over the WAN interface.  The host
   can configure as many addresses for itself as it wants.

5.  MLD/DAD Implications

   When a node configures addresses for itself using either SLAAC or
   DHCPv6 from a shared prefix, the node performs MLD/DAD by sending
   multicast messages to test whether there is another node on the link
   that configures a duplicate address from the shared prefix.  When
   there are many such addresses and/or many such nodes, this could
   result in substantial multicast traffic that affects all nodes on the
   link.

   When a node configures addresses for itself using a delegated prefix,
   the node can configure as many addresses as it wants but does not
   perform MLD/DAD for any of the addresses over the WAN interface.
   This means that arbitrarily many addresses can be assigned without
   causing any multicast messaging over the WAN link that could disturb
   other nodes.  Note however that nodes that assign addresses directly




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   to the WAN interface must be capable of disabling MLD/DAD on the WAN
   interface, i.e., by setting DupAddrDetectTransmits to zero [RFC4862].

6.  IPv6 Neighbor Discovery Implications

   The node acts as a simple host to send Router Solicitation messages
   over the WAN interface the same as described in Section 4.2 of
   [RFC7084].

   In order to maintain the appearance of a router (i.e., even though it
   is acting as a simple host), the node sets the "Router" flag to TRUE
   in any Neighbor Advertisement messages it sends.  This ensures that
   the "isRouter" flag in the neighbor cache entries of any neighbors
   remains TRUE.

   The node initially has only a default route pointing to a router on
   the WAN link.  This means that packets sent over the node's WAN
   interface will initially go through a default router even if there is
   a better first-hop node on the link.  In that case,a Redirect message
   can update the node's neighbor cache, and future packets can take the
   more direct route without disturbing the default router.  The
   Redirect can apply either to a singleton destination address, or to
   an entire destination prefix as described in AERO
   [I-D.templin-aerolink].

7.  "Mixed Mode" Implications

   In some instances, a node may receive both delegated and shared
   prefixes.  In that case, the node could avoid MLD/DAD for addresses
   configured from the delegated prefixes and employ MLD/DAD for
   addresses configured from he shared prefixes.  Note however that
   since DupAddrDetectTransmits applies on a per-interface (and not a
   per-prefix) basis any such considerations are out of scope since this
   document does not update any standards-track specifications.

8.  IANA Considerations

   This document introduces no IANA considerations.

9.  Security Considerations

   Security considerations are the same as specified for DHCPv6 Prefix
   Delegation in [RFC3633].








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10.  Acknowledgements

   This work was motivated by recent discussions on the v6ops list.
   Mark Smith pointed out the need to consider MLD as well as DAD for
   the assignment of addresses to interfaces.  Ricardo Pelaez-Negro,
   Edwin Cordeiro, Fred Baker and Naveen Lakshman provided useful
   comments that have greatly improved the draft.

11.  References

11.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <http://www.rfc-editor.org/info/rfc791>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <http://www.rfc-editor.org/info/rfc1122>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <http://www.rfc-editor.org/info/rfc2460>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

   [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,
              <http://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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc4862>.







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   [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
              Requirements for IPv6 Customer Edge Routers", RFC 7084,
              DOI 10.17487/RFC7084, November 2013,
              <http://www.rfc-editor.org/info/rfc7084>.

   [RFC7278]  Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6
              /64 Prefix from a Third Generation Partnership Project
              (3GPP) Mobile Interface to a LAN Link", RFC 7278,
              DOI 10.17487/RFC7278, June 2014,
              <http://www.rfc-editor.org/info/rfc7278>.

11.2.  Informative References

   [I-D.ietf-v6ops-host-addr-availability]
              Colitti, L., Cerf, D., Cheshire, S., and d.
              dschinazi@apple.com, "Host address availability
              recommendations", draft-ietf-v6ops-host-addr-
              availability-07 (work in progress), May 2016.

   [I-D.templin-aerolink]
              Templin, F., "Asymmetric Extended Route Optimization
              (AERO)", draft-templin-aerolink-70 (work in progress),
              July 2016.

Author's Address

   Fred L. Templin (editor)
   Boeing Research & Technology
   P.O. Box 3707
   Seattle, WA  98124
   USA

   Email: fltemplin@acm.org


















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