IPv6 Prefix Delegation for Hosts
draft-templin-v6ops-pdhost-15

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12                        
          13 14 15                                                      
Network Working Group                                    F. Templin, Ed.
Internet-Draft                              Boeing Research & Technology
Intended status: Informational                         September 6, 2017
Expires: March 10, 2018


                 IPv6 Prefix Delegation for End Systems
                   draft-templin-v6ops-pdhost-07.txt

Abstract

   IPv6 prefixes are typically delegated to requesting routers which
   then use them to number their downstream-attached links and networks.
   This document considers the case when the "requesting router" is
   actually an end system which receives a delegated prefix that it can
   use for its own sub-delegation and/or multi-addressing purposes.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Multi-Addressing Considerations . . . . . . . . . . . . . . .   5
   4.  Multi-Addressing Alternatives for Delegated Prefixes  . . . .   6
   5.  MLD/DAD Implications  . . . . . . . . . . . . . . . . . . . .   6
   6.  IPv6 Neighbor Discovery Implications  . . . . . . . . . . . .   7
   7.  ICMPv6 Implications . . . . . . . . . . . . . . . . . . . . .   7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   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 router to a requesting router, 2) a representation
   of the prefix in the delegating router's routing table, and 3) a
   control messaging service to maintain delegated prefix lifetimes.
   Following delegation, the prefix is available for the requesting
   router's exclusive use and is not shared with any other nodes.  An
   example IPv6 PD service is DHCPv6 PD [RFC3315][RFC3633].

   This document considers the case when the "requesting router" is
   actually an end system (ES) that can act as a router on behalf of its
   downstream networks and/or as a host on behalf of its local
   applications.  The following paragraphs present possibilities for ES
   behavior upon receipt of a delegated prefix.

   For ESes that connect downstream-attached ("tethered") networks, a
   Delegating Router 'D' delegates a prefix 'P' to a Requesting ES 'R''
   as shown in Figure 1:















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                        +---------------------+
                        |Delegating Router 'D'|
                        |   (Delegate 'P')    |
                        +----------+----------+
                                   |
                                   | Upstream Interface
                                   |
                        +----------+----------+
                        |    (Receive 'P')    |
                        |  Requesting ES 'R'  |
                        +----------+----------+
                                   | Downstream Interface
       X----+-------------+--------+----+---------------+---X
            |             |             |               |
       +---++-+--+   +---++-+--+   +---++-+--+     +---++-+--+
       |   |A1|  |   |   |A2|  |   |   |A3|  |     |   |An|  |
       |   +--+  |   |   +--+  |   |   +--+  |     |   +--+  |
       | Host H1 |   | Host H2 |   | Host H3 | ... | Host Hn |
       +---------+   +---------+   +---------+     +---------+

                    Figure 1: Tethered End System Model

   In this figure, when Delegating Router 'D' delegates prefix 'P', it
   inserts 'P' into its routing table with Requesting ES 'R' as the next
   hop.  Meanwhile, 'R' receives 'P' via its upstream interface and sub-
   delegates 'P' to its downstream external (physical) and/or internal
   (virtual) interfaces.  Hosts 'H(i)' on a downstream network
   subsequently receive addresses 'A(i)' taken from 'P' via an address
   autoconfiguration service such as IPv6 Stateless Address
   Autoconfiguration (SLAAC) [RFC4862].  'R' then acts as a router
   between hosts 'H(i)' and correspondents reachable via the upstream
   interface.

   This document also considers the case when 'R' does not have any
   downstream interfaces, and can use 'P' solely for its own internal
   addressing purposes.  In that case, 'R' assigns 'P' to a virtual
   interface (e.g., a loopback) so that unused portions of the prefix
   will be unreachable.

   'R' can then function under the weak end system model [RFC1122] by
   assigning addresses taken from 'P' to virtual interfaces (e.g., a
   loopback) as shown in Figure 2:









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                        +---------------------+
                        |Delegating Router 'D'|
                        |   (Delegate 'P')    |
                        +----------+----------+
                                   |
                                   | Upstream Interface
                                   |
                        +----------+----------+
                        |    (Receive 'P')    |
                        |  Requesting ES 'R'  |
                        +---------------------+
                        | Loopback Interface  |
                        +--+-+--+-++-+-----+--+
                        |A1| |A2| |A3| ... |An|
                        +--+-+--+-+--+-----+--+

                      Figure 2: Weak End System Model

   'R' could instead function under the strong end system model
   [RFC1122] by assigning IPv6 addresses taken from 'P' to the upstream
   interface as shown in Figure 3:

                        +---------------------+
                        |Delegating Router 'D'|
                        |   (Delegate 'P')    |
                        +----------+----------+
                                   |
                                   | Upstream Interface
                                   |
                        +--+-+--+-++-+-----+--+
                        |A1| |A2| |A3| ... |An|
                        +--+ +--+ +--+     +--+
                        |    (Receive 'P')    |
                        |  Requesting ES 'R'  |
                        +---------------------+

                     Figure 3: Strong End System Model

   The major benefit for an ES managing a delegated prefix in either the
   weak or strong end system models is multi-addressing.  With multi-
   addressing, the ES can configure an unlimited supply of addresses to
   make them available for local applications without requiring
   coordination with any other nodes on the upstream interface.

   The following sections present multi-addressing considerations for
   ESes 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:

   node
      a device that observes IPv6 node requirements [RFC6434].

   End System (ES)
      an IPv6 node that is capable of acting as a host from the
      perspective of local applications and as a router from the
      perspective of IPv6 ND and IPv6 prefix delegation.  The ES may
      also have an embedded gateway function as described in [RFC1122].

   shared prefix
      an IPv6 prefix that may be advertised to more than one node on the
      same link, e.g., in a Router Advertisement (RA) message Prefix
      Information Option (PIO) [RFC4861].

   individual prefix
      an IPv6 prefix that is advertised to exactly one node on the link,
      e.g., in a unicast RA message PIO.  (However, the node may have no
      way of knowing that the prefix is an individual prefix and not a
      shared one.)

   delegated prefix
      a prefix that is exclusively delegated to a requesting node for
      provisioning on its downstream links.

3.  Multi-Addressing Considerations

   IPv6 allows nodes to assign multiple addresses to a single interface.
   [RFC7934] 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).

   ESes that use SLAAC and/or DHCPv6 address configuration configure
   addresses from a shared or individual prefix and assign them to the
   upstream interface.  When it assigns the addresses, the ES is
   required 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 configures a duplicate address.

   In contrast, an ES that uses address configuration from a delegated
   prefix can assign addresses without invoking MLD/DAD on the upstream



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   interface, since the prefix has been delegated to the ES for its own
   exclusive use and is not shared with any other nodes.

4.  Multi-Addressing Alternatives for Delegated Prefixes

   When an ES 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 when
   the ES receives a prefix delegation in which the prefix is delegated
   for its own exclusive use.

   When the ES receives the prefix, it can distribute the prefix to
   downstream interfaces and configure one or more addresses for itself
   on a downstream interface.  The ES then acts as a router on behalf of
   its downstream-attached networks and configures a default route that
   points to a router via the upstream interface.

   The ES could instead use the delegated prefix for its own multi-
   addressing purposes.  In a first alternative, the ES can assign the
   prefix to a virtual interface (e.g., a loopback) and assign one or
   more addresses taken from the prefix to virtual interfaces.  In that
   case, applications on the ES can use the assigned addresses according
   to the weak end system model.

   In a second alternative, the ES can assign the prefix to a virtual
   interface and assign one or more addresses taken from the prefix to
   the upstream interface.  In that case, applications on the ES can use
   the assigned addresses according to the strong end system model.

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

5.  MLD/DAD Implications

   When an ES configures addresses for itself using either SLAAC or
   DHCPv6 from a shared or individual prefix, the ES performs MLD/DAD by
   sending multicast messages over the upstream interface to test
   whether there is another node on the link that configures a duplicate
   address.  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 an ES configures addresses for itself from a delegated prefix,
   the ES can configure as many addresses as it wants but does not



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   perform MLD/DAD for any of the addresses over the upstream interface.
   This means that the ES can assign arbitrarily many addresses without
   causing any multicast messaging over the upstream interface that
   could disturb other nodes.

6.  IPv6 Neighbor Discovery Implications

   The ES acts as a simple host to send Router Solicitation (RS)
   messages over the upstream interface (i.e., the same as described in
   Section 4.2 of [RFC7084]) but also 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 ES initially has only a default route pointing to a router via
   the upstream interface.  This means that packets sent over the ES's
   upstream 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 ES'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
   [I-D.templin-6man-rio-redirect].

7.  ICMPv6 Implications

   The Internet Control Message Protocol for IPv6 (ICMPv6) includes a
   set of control message types [RFC4443] including Destination
   Unreachable (DU).

   According to [RFC4443], routers SHOULD return DU messages (subject to
   rate limiting) with code 0 ("No route to destination") when a packet
   arrives for which there is no matching entry in the routing table,
   and with code 3 ("Address unreachable") when the IPv6 destination
   address cannot be resolved.

   According to [RFC4443], hosts SHOULD return DU messages (subject to
   rate limiting) with code 3 to internal applications when the IPv6
   destination address cannot be resolved, and with code 4 ("Port
   unreachable") if the IPv6 destination address is one of its own
   addresses but the transport protocol has no listener.

   An ES that obtains and manages a prefix delegation per this document
   returns DU messages the same as described for both routers and hosts
   above.






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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] and for IPv6 Neighbor Discovery in[RFC4861].

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, Naveen Lakshman and Ole Troan provided
   useful comments that have greatly improved the document.

11.  References

11.1.  Normative References

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://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,
              <https://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, <https://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, <https://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,
              <https://www.rfc-editor.org/info/rfc3633>.








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   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [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>.

   [RFC6434]  Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
              Requirements", RFC 6434, DOI 10.17487/RFC6434, December
              2011, <https://www.rfc-editor.org/info/rfc6434>.

   [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,
              <https://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,
              <https://www.rfc-editor.org/info/rfc7278>.

11.2.  Informative References

   [I-D.templin-6man-rio-redirect]
              Templin, F. and j. woodyatt, "Route Information Options in
              IPv6 Neighbor Discovery", draft-templin-6man-rio-
              redirect-04 (work in progress), August 2017.

   [RFC7934]  Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
              "Host Address Availability Recommendations", BCP 204,
              RFC 7934, DOI 10.17487/RFC7934, July 2016,
              <https://www.rfc-editor.org/info/rfc7934>.

Author's Address







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

   Email: fltemplin@acm.org












































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