Improved Recursive DNS Server Selection for Multi-Interfaced Nodes
RFC 6731

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Internet Engineering Task Force (IETF)                     T. Savolainen
Request for Comments: 6731                                         Nokia
Category: Standards Track                                        J. Kato
ISSN: 2070-1721                                                      NTT
                                                                T. Lemon
                                                           Nominum, Inc.
                                                           December 2012

   Improved Recursive DNS Server Selection for Multi-Interfaced Nodes

Abstract

   A multi-interfaced node is connected to multiple networks, some of
   which might be utilizing private DNS namespaces.  A node commonly
   receives recursive DNS server configuration information from all
   connected networks.  Some of the recursive DNS servers might have
   information about namespaces other servers do not have.  When a
   multi-interfaced node needs to utilize DNS, the node has to choose
   which of the recursive DNS servers to use.  This document describes
   DHCPv4 and DHCPv6 options that can be used to configure nodes with
   information required to perform informed recursive DNS server
   selection decisions.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6731.

Copyright Notice

   Copyright (c) 2012 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

Savolainen, et al.           Standards Track                    [Page 1]
RFC 6731              RDNSS Selection for MIF Nodes        December 2012

   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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  Private Namespaces and Problems for Multi-Interfaced Nodes . .  4
     2.1.  Fully Qualified Domain Names with Limited Scopes . . . . .  4
     2.2.  Network-Interface-Specific IP Addresses  . . . . . . . . .  5
     2.3.  A Problem Not Fully Solved by the Described Solution . . .  6
   3.  Deployment Scenarios . . . . . . . . . . . . . . . . . . . . .  7
     3.1.  CPE Deployment Scenario  . . . . . . . . . . . . . . . . .  7
     3.2.  Cellular Network Scenario  . . . . . . . . . . . . . . . .  7
     3.3.  VPN Scenario . . . . . . . . . . . . . . . . . . . . . . .  8
     3.4.  Dual-Stack Accesses  . . . . . . . . . . . . . . . . . . .  8
   4.  Improved RDNSS Selection . . . . . . . . . . . . . . . . . . .  8
     4.1.  Procedure for Prioritizing RDNSSes and Handling
           Responses  . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.2.  RDNSS Selection DHCPv6 Option  . . . . . . . . . . . . . . 11
     4.3.  RDNSS Selection DHCPv4 Option  . . . . . . . . . . . . . . 13
     4.4.  Scalability Considerations . . . . . . . . . . . . . . . . 15
     4.5.  Limitations on Use . . . . . . . . . . . . . . . . . . . . 15
     4.6.  Coexistence of Various RDNSS Configuration Tools . . . . . 16
     4.7.  Considerations on Follow-Up Queries  . . . . . . . . . . . 17
     4.8.  Closing Network Interfaces and Local Caches  . . . . . . . 17
   5.  Example of a Node Behavior . . . . . . . . . . . . . . . . . . 17
   6.  Considerations for Network Administrators  . . . . . . . . . . 19
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 20
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 20
     8.1.  Attack Vectors . . . . . . . . . . . . . . . . . . . . . . 20
     8.2.  Trust Levels of Network Interfaces . . . . . . . . . . . . 21
     8.3.  Importance of Following the Algorithm  . . . . . . . . . . 21
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 21
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 22
   Appendix A.  Possible Alternative Practices for RDNSS Selection  . 23