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IPv6 Operations Working Group (v6ops)                            F. Gont
Internet-Draft                                    SI6 Networks / UTN-FRH
Intended status: Best Current Practice                        G. Doering
Expires: September 14, 2017                                  SpaceNet AG
                                                         M. Garcia Corbo
                                                                 SITRANS
                                                                 G. Gont
                                                            SI6 Networks
                                                          March 13, 2017


          On the Dynamic/Automatic Configuration of IPv6 Hosts
                 draft-gont-v6ops-host-configuration-01

Abstract

   IPv6 has two different mechanisms for dynamic/automatic host
   configuration: SLAAC and DHCPv6.  These two mechanisms allow for the
   configuration of IPv6 addresses and a number of network parameters.
   While there is overlap in the parameters that can be configured via
   these two protocols, different implementations support only subsets
   of such parameters with either mechanism, or have no support for
   DHCPv6 at all.  This document analyzes a problem that arises from
   this situation, and mandates that all host implementations support
   RFC 6105 (DNS options for SLAAC) and the stateless DHCPv6
   functionality in RFC 3315.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 14, 2017.








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Copyright Notice

   Copyright (c) 2017 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
   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.

   This document may not be modified, and derivative works of it may not
   be created, and it may not be published except as an Internet-Draft.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Current Requirements regarding RDNSS and Stateless DHCPv6 . .   4
   4.  Requirements for IPv6 Hosts . . . . . . . . . . . . . . . . .   4
   5.  Requirements for IPv6 Routers . . . . . . . . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   IPv6 has two different mechanisms for dynamic/automatic host
   configuration: Stateless Address Autoconfiguration (SLAAC) [RFC4862]
   and Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315].
   SLAAC allows for distributed address assignment (where each host
   automatically configures its own IPv6 addresses) and basic network
   configuration (such as recursive DNS servers and DNS search lists).
   On the other hand, DHCPv6 provides for centralized address assignment
   (the DHCPv6 server leases IPv6 addresses to hosts) and richer network
   configuration (NTP servers, web proxys, etc.).

   Traditionally, SLAAC has been seen as a more lightweight mechanism,
   suitable for resource-constrained devices, while DHCPv6 has been seen
   more as heavy-weight and full-fledged mechanism.  We note that this



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   distinction is rather questionable, and is essentially meaningless
   for typical mobile devices or home appliances.

   Among the possible configuration information that can be conveyed
   with both SLAAC and DHCPv6 is DNS related configuration: recursive
   DNS servers and DNS search lists.  Configuring this information is
   probably as vital in practice as configuring IPv6 addresses, since
   for obvious reasons both humans and popular applications operate on
   names (rather than on IPv6 addresses).  The ability to convey this
   information has always been part of DHCPv6, while for the SLAAC case,
   support was added in a separate document that standardizes "IPv6
   Router Advertisement Options for DNS Configuration" [RFC6106].

   Unfortunately, different host and router implementations provide
   support for only a subset of these options.  For example, some host
   implementations (e.g., Android) support SLAAC DNS options [RFC6106],
   but do not support stateless DHCPv6.  On the other hand, other host
   implementations (e.g., Microsoft Windows) support stateless DHCPv6,
   but do not support [RFC6106].  Similarly, some router implementations
   support [RFC6106], while others do not.

   This represents a problem for IPv6 deployment, since:

   1.  in order to support most popular IPv6 host implementations, IPv6
       networks are required to support *both* SLAAC and DHCPv6.

   2.  some router implementations do not support [RFC6106] and hence
       support for the SLAAC DNS options may be impossible or require
       yet an additional network element or network service to support
       [RFC6106]

   We note that, in most cases, this problem is currently masked by the
   fact that most IPv6 deployments are actually dual-stack, and hence
   hosts can currently rely DNS-related information being obtained via
   IPv4-based DHCP.  However, at the point such deployments disable IPv4
   to become IPv6-only, the aforementioned problems will become evident,
   possibly as a surprise to network operators.

2.  Terminology

   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].








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3.  Current Requirements regarding RDNSS and Stateless DHCPv6

   Section 7.2.1 of [RFC6434] ("IPv6 Node Requirements") states:

      IPv6 nodes use DHCP [RFC3315] to obtain address configuration
      information (see Section 5.9.5) and to obtain additional (non-
      address) configuration.  If a host implementation supports
      applications or other protocols that require configuration that is
      only available via DHCP, hosts SHOULD implement DHCP.

   Since DNS information is (in theory) also available via RA messages,
   the aforementioned text essentially makes support for stateless
   DHCPv6 optional.

   Regarding SLAAC DNS options, [RFC6434] states, in Section 7.3,

   o  Implementations SHOULD implement the DNS RA option [RFC6106].

   which certainly is not clear whether it is referring to hosts,
   routers, or both.

   In any case, we note that [RFC6434] has been published on the
   "Informational" track, and hence implementations may completely
   ignore this RFC while still claiming full-compliance with all the
   relevant IETF standards.

   [RFC7084] ("Basic Requirements for IPv6 Customer Edge Routers")
   requires support for "DNS_SERVERS [RFC3646]" option and the SLAAC DNS
   options in the IPv6 CE Routers.  As with [RFC6434], it was published
   on the "Informational" track.

4.  Requirements for IPv6 Hosts

   IPv6 hosts MUST support the SLAAC DNS options specified in [RFC6106],
   and the stateless DHCPv6 mechanism specified in [RFC3315].

5.  Requirements for IPv6 Routers

   IPv6 routers MUST support the SLAAC DNS options specified in
   [RFC6106].

6.  IANA Considerations

   This document has no actions for IANA.  The RFC-Editor should remove
   this section prior to publication of this document as an RFC.






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7.  Security Considerations

   Host implementations supporting SLAAC are subject to a number of
   attacks based on forged ICMPv6 Router Advertisement [RFC4861]
   messages.  Such attacks can be mitigated by means of RA-Guard
   [RFC6105] [RFC7113].  Hosts supporting DHCPv6 are subject to a number
   of attacks based on forged DHCPv6-server messages.  Such attacks can
   be mitigated by means of DHCPv6-Shield [RFC7610].

8.  Acknowledgements

   The authors would like to thank Chuck Anderson, Brian Carpenter, Nick
   Hilliard, Philip Homburg, Mark Smith, Barbara Stark, and several
   participants of the v6ops wg (TBD) for providing valuable comments on
   earlier versions of this document.

   Fernando Gont would like to thank Nelida Garcia and Jorge Oscar Gont
   for their love and support, and Ivan Arce and Diego Armando Maradona
   for their inspiration.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [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>.

   [RFC6106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
              "IPv6 Router Advertisement Options for DNS Configuration",
              RFC 6106, DOI 10.17487/RFC6106, November 2010,
              <http://www.rfc-editor.org/info/rfc6106>.



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9.2.  Informative References

   [RFC6105]  Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
              Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
              DOI 10.17487/RFC6105, February 2011,
              <http://www.rfc-editor.org/info/rfc6105>.

   [RFC6434]  Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
              Requirements", RFC 6434, DOI 10.17487/RFC6434, December
              2011, <http://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,
              <http://www.rfc-editor.org/info/rfc7084>.

   [RFC7113]  Gont, F., "Implementation Advice for IPv6 Router
              Advertisement Guard (RA-Guard)", RFC 7113,
              DOI 10.17487/RFC7113, February 2014,
              <http://www.rfc-editor.org/info/rfc7113>.

   [RFC7610]  Gont, F., Liu, W., and G. Van de Velde, "DHCPv6-Shield:
              Protecting against Rogue DHCPv6 Servers", BCP 199,
              RFC 7610, DOI 10.17487/RFC7610, August 2015,
              <http://www.rfc-editor.org/info/rfc7610>.

Authors' Addresses

   Fernando Gont
   SI6 Networks / UTN-FRH
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706
   Argentina

   Phone: +54 11 4650 8472
   Email: fgont@si6networks.com
   URI:   http://www.si6networks.com


   Gert Doering
   SpaceNet AG
   Joseph-Dollinger-Bogen 14
   Muenchen  D-80807
   Germany

   Email: gert@space.net





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   Madeleine Garcia Corbo
   Servicios de Informacion del Transporte
   Neptuno 358
   Havana City  10400
   Cuba

   Email: madelen.garcia16@gmail.com


   Guillermo Gont
   SI6 Networks
   Evaristo Carriego 2644
   Haedo, Provincia de Buenos Aires  1706
   Argentina

   Phone: +54 11 4650 8472
   Email: ggont@si6networks.com
   URI:   https://www.si6networks.com

































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