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 22, 2017
Expires: March 26, 2018


                 IPv6 Prefix Delegation for End Systems
                   draft-templin-v6ops-pdhost-10.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 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 . . . . . . . . . . . . . . .   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  . . . . . . . . . . . .   8
   8.  ICMPv6 Implications . . . . . . . . . . . . . . . . . . . . .   8
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   9
   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
   actually an end system (ES) that can act as a router on behalf of its
   downstream networks and 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 (aka "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 link
                                   |
                        +----------+----------+
                        |  Upstream Interface |
                        +---------------------+
                        |                     |
                        |  Requesting ES '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 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 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 interface connections to the
   downstream link.  'R' then acts as a router between hosts 'H(i)' on
   downstream links and correspondents reachable via other interfaces.

   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), and acts as a router that
   forwards packets between the upstream and virtual interfaces.

   '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 ES '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 ES 'R'  |
                        |    (Receive 'P')    |
                        |                     |
                        +---------------------+
                        |   Virtual Interface |
                        +---------------------+

                     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 upstream interfaces.

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

2.  Terminology

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

   node, host, router
      the same as defined in [RFC8200].

   End System (ES)
      a node that acts as a host on behalf of its local applications and
      as a router on behalf of its downstream interface(s), but does not
      forward packets received on an upstream interface via the same or
      a different upstream interface (see: Security Considerations).

   shared prefix





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      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
      (e.g., in an RA PIO), where the node is a passive recipient of the
      prefix.

   delegated prefix
      an IPv6 prefix that is conveyed to an ES for its own exclusive
      use, where the ES is an active participant in the 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], stateful DHCPv6 address
   configuration [RFC3315], manual configuration, etc.

   ESes configure addresses from a shared or individual prefix and
   assign them to the upstream interface over which the prefix was
   received.  When it assigns the addresses, the ES 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, an ES that uses address configuration from a delegated
   prefix can assign addresses without invoking MLD/DAD on an upstream
   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
   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 ES receives a
   prefix delegation in which the prefix is explicitly 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



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   on downstream interfaces.  The ES then acts as a router on behalf of
   its downstream-attached networks and configures a default route via a
   neighbor on an upstream interface.

   The ES could instead (or in addition) use portions of the delegated
   prefix for its own multi-addressing purposes.  In a first
   alternative, the ES can assign the prefix to a virtual interface and
   assign one or more addresses taken from the prefix to virtual
   interfaces.  In that case, ES applications 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 over which the prefix was received.  In that
   case, ES applications 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 on behalf of
   its local applications and as a router from the standpoint of packet
   forwarding, prefix delegation and neighbor discovery over upstream
   interfaces.  The ES can configure as many addresses for itself as it
   wants.

5.  MLD/DAD Implications

   When an ES configures addresses for itself from a shared or
   individual prefix, the ES 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 an ES configures addresses for itself from a delegated prefix,
   the ES 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 ES 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 ES 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 ESes on the upstream link,
   dynamic routing protocol participation might be impractical due to
   scaling limitations, and may also be exacerbated by factors such as
   ES mobility.




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   Unless it participates in a dynamic routing protocol, the ES
   initially has only a default route pointing to a neighbor via an
   upstream interface.  This means that packets sent by the ES 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 ES 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
   any Neighbor Advertisement messages it sends.  The ES does not send
   RA messages over upstream interfaces.

   The current first-hop router may send a Redirect message that updates
   the ES'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.

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

9.  IANA Considerations

   This document introduces no IANA considerations.






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10.  Security Considerations

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

   Additionally, the ES 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 ES drops the packets and
   observes the "Destination Unreachable - Address unreachable"
   procedures in Section 8.

   The ES may also receive IPv6 packets via an upstream interface that
   do not match any of the ES's delegated prefixes.  In that case, the
   ES drops the packets and observes the "Destination Unreachable - No
   route to destination" procedures in Section 8.  This is necessary to
   avoid reflection attacks that would cause the ES to forward packets
   received from an upstream interface via the same or a different
   upstream interface.

11.  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, Ole Troan, Bob Hinden,
   Brian Carpenter, Joel Halpern and Albert Manfredi provided useful
   comments that have greatly improved the document.

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>.






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   [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>.

   [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>.



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   [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>.

   [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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