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 27, 2017
Expires: March 31, 2018


         IPv6 Prefix Delegation for Hosts That Act Like Routers
                   draft-templin-v6ops-pdhost-11.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 of hosts that act like routers to
   receive delegated prefixes that they can use for their own sub-
   delegation and/or multi-addressing purposes.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on March 31, 2018.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Multi-Addressing Considerations . . . . . . . . . . . . . . .   6
   4.  Multi-Addressing Alternatives for Delegated Prefixes  . . . .   6
   5.  MLD/DAD Implications  . . . . . . . . . . . . . . . . . . . .   7
   6.  Dynamic Routing Protocol Implications . . . . . . . . . . . .   7
   7.  IPv6 Neighbor Discovery Implications  . . . . . . . . . . . .   7
   8.  ICMPv6 Implications . . . . . . . . . . . . . . . . . . . . .   8
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   8
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     12.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  11

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 between the delegating and requesting
   routers to maintain 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 the
   Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
   [RFC3315][RFC3633].

   This document considers the case when the requesting router is a node
   that acts as a host on behalf of its local applications and as a
   router on behalf of its downstream networks.  The following
   paragraphs present possibilities for node behavior upon receipt of a
   delegated prefix.

   For nodes that connect downstream-attached (aka "tethered") networks,
   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')    |
                        +----------+----------+
                                   |
                                   | Upstream link
                                   |
                        +----------+----------+
                        |  Upstream Interface |
                        +---------------------+
                        |                     |
                        | Requesting node 'R' |
                        |    (Receive 'P')    |
                        |                     |
                        +---------------------+
                        | Downstream Interface|
                        +--+-+--+-+--+-----+--+
                        |A1| |A2| |A3| ... |An|
                        +--+-+--+-++-+-----+--+
                                   |
                                   | Downstream link
                                   |
       X----+-------------+--------+----+---------------+---X
            |             |             |               |
       +---++-+--+   +---++-+--+   +---++-+--+     +---++-+--+
       |   |X1|  |   |   |X2|  |   |   |X3|  |     |   |Xn|  |
       |   +--+  |   |   +--+  |   |   +--+  |     |   +--+  |
       | Host H1 |   | Host H2 |   | Host H3 | ... | Host Hn |
       +---------+   +---------+   +---------+     +---------+

          <-------------- Tethered Network ------------->

                      Figure 1: Classic Routing Model

   In this figure, when Delegating Router 'D' delegates prefix 'P', it
   inserts 'P' into its routing table with Requesting node 'R' as the
   next hop.  Meanwhile, 'R' receives 'P' via an upstream interface and
   sub-delegates 'P' to its downstream external (physical) and/or
   internal (virtual) networks.  'R' assigns addresses 'A(i)' taken from
   'P' to downstream interfaces, and Hosts 'H(i)' on downstream networks
   assign addresses 'X(i)' taken from 'P' to their interfaces.  'R' then
   acts as a router between hosts 'H(i)' on downstream links and
   correspondents reachable via other interfaces.  'R' can also act as a
   host on behalf of its local applications.

   This document also considers the case when 'R' does not have any
   physical downstream interfaces, and can use 'P' solely for its own
   internal addressing purposes.  In that case, 'R' assigns 'P' to a



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   virtual interface (e.g., a loopback) that is seen as a downstream
   interface.

   'R' can then function under the weak end system model
   [RFC1122][RFC8028] by assigning addresses taken from 'P' to a virtual
   interface as shown in Figure 2:

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

                      Figure 2: Weak End System Model

   'R' could instead function under the strong end system model
   [RFC1122][RFC8028] by assigning IPv6 addresses taken from 'P' to an
   upstream interface as shown in Figure 3:



















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

                     Figure 3: Strong End System Model

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

   The following sections present considerations for nodes that employ
   prefix delegation mechanisms.

2.  Terminology

   The terminology of the normative references apply, and the terms
   "node", "host" and "router" are the same as defined in [RFC8200].

   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
      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,
      where the node may be unaware that the prefix is individual and
      may not participate in prefix maintenance procedures.




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   delegated prefix
      an IPv6 prefix that is explicitly delegated to a node for its own
      exclusive use, where the node is an active participant in prefix
      delegation and maintenance procedures.

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 StateLess Address
   AutoConfiguration (SLAAC) [RFC4862], DHCPv6 address configuration
   [RFC3315], manual configuration, etc.

   Nodes configure addresses from a shared or individual prefix and
   assign them to the upstream interface over which the prefix was
   received.  When the node assigns the addresses, it is required to use
   Multicast Listener Discovery (MLD) [RFC3810] 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, a node that configures addresses from a delegated prefix
   can assign them without invoking MLD/DAD on an upstream interface,
   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 provisioning 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 node receives a
   delegated prefix explicitly provided for its own exclusive use.

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

   The node could instead (or in addition) use portions of the delegated
   prefix for its own multi-addressing purposes.  In a first
   alternative, the node can assign as many addresses as it wants from
   the prefix to virtual interfaces.  In that case, applications running
   on the node can use the addresses according to the weak end system
   model.



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   In a second alternative, the node can assign as many addresses as it
   wants from the prefix to the upstream interface over which the prefix
   was received.  In that case, applications running on the node can use
   the addresses according to the strong end system model.

   In both of these latter two cases, the node assigns the prefix itself
   to a virtual interface so that unused addresses from the prefix are
   correctly identified as unreachable.  The node then acts as a host on
   behalf of its local applications even though neighbors on the
   upstream link see it as a router.

5.  MLD/DAD Implications

   When a node configures addresses for itself from a shared or
   individual prefix, it performs MLD/DAD by sending multicast messages
   over upstream interfaces 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 a node configures addresses for itself from a delegated prefix,
   it can configure as many addresses as it wants but does not perform
   MLD/DAD for any of the addresses over upstream interfaces.  This
   means that the node can configure arbitrarily many addresses without
   causing any multicast messaging over the upstream interface that
   could disturb other nodes.

6.  Dynamic Routing Protocol Implications

   The node can be configured to either participate or not participate
   in a dynamic routing protocol over the upstream interface, according
   to the deployment model.  When there are many nodes on the upstream
   link, dynamic routing protocol participation might be impractical due
   to scaling limitations, and may also be exacerbated by factors such
   as node mobility.

   Unless it participates in a dynamic routing protocol, the node
   initially has only a default route pointing to a neighbor via an
   upstream interface.  This means that packets sent by the node over an
   upstream interface will initially go through a default router even if
   there is a better first-hop node on the link.

7.  IPv6 Neighbor Discovery Implications

   The node acts as a simple host to send Router Solicitation (RS)
   messages over upstream interfaces (i.e., the same as described in
   Section 4.2 of [RFC7084]) but also sets the "Router" flag to TRUE in




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   any Neighbor Advertisement messages it sends.  The node does not send
   RA messages over upstream interfaces.

   The current first-hop router may send a Redirect message that updates
   the node's neighbor cache so that future packets can use a better
   first-hop node on the link.  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].

8.  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.

   Nodes that obtain and manage prefix delegations per this document
   observe the same procedures as described for both routers and hosts
   above.

9.  IANA Considerations

   This document introduces no IANA considerations.

10.  Security Considerations

   Security considerations for IPv6 Neighbor Discovery [RFC4861] and any
   applicable prefix delegation mechanisms apply to this document.

   Additionally, the node may receive unwanted IPv6 packets via an
   upstream interface that match a delegated prefix but do not match a
   configured IPv6 address.  In that case, the node drops the packets
   and observes the "Destination Unreachable - Address unreachable"
   procedures discussed in Section 8.

   The node may also receive IPv6 packets via an upstream interface that
   do not match any of the node's delegated prefixes.  In that case, the



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   node drops the packets and observes the "Destination Unreachable - No
   route to destination" procedures discussed in Section 8.  Dropping
   the packets is necessary to avoid a reflection attack that would
   cause the node to forward packets received from an upstream interface
   via the same or a different upstream interface.

11.  Acknowledgements

   This work was motivated by 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, Ole Troan, Bob Hinden, Brian
   Carpenter, Joel Halpern and Albert Manfredi provided useful comments
   that have greatly improved the document.

   This work is aligned with the NASA Safe Autonomous Systems Operation
   (SASO) program under NASA contract number NNA16BD84C.

   This work is aligned with the FAA as per the SE2025 contract number
   DTFAWA-15-D-00030.

   This work is aligned with the Boeing Information Technology (BIT)
   MobileNet program and the Boeing Research & Technology (BR&T)
   enterprise autonomy program.

12.  References

12.1.  Normative References

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

   [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>.

   [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
              Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
              DOI 10.17487/RFC3810, June 2004,
              <https://www.rfc-editor.org/info/rfc3810>.




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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>.

   [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>.

12.2.  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.

   [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>.

   [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>.

   [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>.



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   [RFC8028]  Baker, F. and B. Carpenter, "First-Hop Router Selection by
              Hosts in a Multi-Prefix Network", RFC 8028,
              DOI 10.17487/RFC8028, November 2016,
              <https://www.rfc-editor.org/info/rfc8028>.

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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