IPv6 Router Advertisement Option for DNS Configuration
RFC 5006

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Network Working Group                                      J. Jeong, Ed.
Request for Comments: 5006                  ETRI/University of Minnesota
Category: Experimental                                           S. Park
                                                     SAMSUNG Electronics
                                                              L. Beloeil
                                                      France Telecom R&D
                                                          S. Madanapalli
                                                      Ordyn Technologies
                                                          September 2007

         IPv6 Router Advertisement Option for DNS Configuration

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Abstract

   This document specifies a new IPv6 Router Advertisement option to
   allow IPv6 routers to advertise DNS recursive server addresses to
   IPv6 hosts.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1.  Applicability Statements . . . . . . . . . . . . . . . . .  2
     1.2.  Coexistence of RDNSS Option and DHCP Option  . . . . . . .  2
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   5.  Neighbor Discovery Extension . . . . . . . . . . . . . . . . .  4
     5.1.  Recursive DNS Server Option  . . . . . . . . . . . . . . .  4
     5.2.  Procedure of DNS Configuration . . . . . . . . . . . . . .  5
       5.2.1.  Procedure in IPv6 Host . . . . . . . . . . . . . . . .  5
   6.  Implementation Considerations  . . . . . . . . . . . . . . . .  6
     6.1.  DNS Server List Management . . . . . . . . . . . . . . . .  6
     6.2.  Synchronization between DNS Server List and Resolver
           Repository . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  8
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     10.1. Normative References . . . . . . . . . . . . . . . . . . .  9
     10.2. Informative References . . . . . . . . . . . . . . . . . .  9

Jeong, et al.                 Experimental                      [Page 1]
RFC 5006          IPv6 RA Option for DNS Configuration    September 2007

1.  Introduction

   Neighbor Discovery (ND) for IP Version 6 and IPv6 Stateless Address
   Autoconfiguration provide ways to configure either fixed or mobile
   nodes with one or more IPv6 addresses, default routers and some other
   parameters [2][3].  To support the access to additional services in
   the Internet that are identified by a DNS name, such as a web server,
   the configuration of at least one recursive DNS server is also needed
   for DNS name resolution.

   It is infeasible for nomadic hosts, such as laptops, to be configured
   manually with a DNS resolver each time they connect to a different
   wireless LAN (WLAN) such as IEEE 802.11 a/b/g [12]-[15].  Normally,
   DHCP [6]-[8] is used to locate such resolvers.  This document
   provides an alternate, experimental mechanism which uses a new IPv6
   Router Advertisement (RA) option to allow IPv6 routers to advertise
   DNS recursive server addresses to IPv6 hosts.

1.1.  Applicability Statements

   The only standards-track DNS configuration mechanism in the IETF is
   DHCP, and its support in hosts and routers is necessary for reasons
   of interoperability.

   RA-based DNS configuration is a useful, optional alternative in
   networks where an IPv6 host's address is autoconfigured through IPv6
   stateless address autoconfiguration, and where the delays in
   acquiring server addresses and communicating with the servers are
   critical.  RA-based DNS configuration allows the host to acquire the
   nearest server addresses on every link.  Furthermore, it learns these
   addresses from the same RA message that provides configuration
   information for the link, thereby avoiding an additional protocol
   run.  This can be beneficial in some mobile environments, such as
   with Mobile IPv6 [10].

   The advantages and disadvantages of the RA-based approach are
   discussed in [9] along with other approaches, such as the DHCP and
   well-known anycast addresses approaches.

1.2.  Coexistence of RDNSS Option and DHCP Option

   The RDNSS (Recursive DNS Server) option and DHCP option can be used
   together [9].  To order the RA and DHCP approaches, the O (Other
   stateful configuration) flag can be used in the RA message [2].  If