Goals of Detecting Network Attachment in IPv6
RFC 4135

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Network Working Group                                           JH. Choi
Request for Comments: 4135                                   Samsung AIT
Category: Informational                                         G. Daley
                                                  CTIE Monash University
                                                             August 2005

             Goals of Detecting Network Attachment in IPv6

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   When a host establishes a new link-layer connection, it may or may
   not have a valid IP configuration for Internet connectivity.  The
   host may check for link change (i.e., determine whether a link change
   has occurred), and then, based on the result, it can automatically
   decide whether its IP configuration is still valid.  During link
   identity detection, the host may also collect necessary information
   to initiate a new IP configuration if the IP subnet has changed.  In
   this memo, this procedure is called Detecting Network Attachment
   (DNA).  DNA schemes should be precise, sufficiently fast, secure, and
   of limited signaling.

Table of Contents

   1. Introduction ....................................................2
   2. Problems in Detecting Network Attachment ........................3
      2.1. Wireless Link Properties ...................................3
      2.2. Link Identity Detection with a Single RA ...................3
      2.3. Delays .....................................................4
   3. Goals for Detecting Network Attachment ..........................5
      3.1. Goals List .................................................6
   4. Security Considerations .........................................6
   5. Acknowledgements ................................................7
   6. References ......................................................8
      6.1. Normative References .......................................8
      6.2. Informative References .....................................8

Choi & Daley                 Informational                      [Page 1]
RFC 4135                       DNA Goals                     August 2005

1.  Introduction

   When a host has established a new link-layer connection, it can send
   and receive some IPv6 packets on the link, including those used for
   configuration.  On the other hand, the host has Internet connectivity
   only when it is able to exchange packets with off-link destinations.

   When a link-layer connection is established or re-established, the
   host may not know whether its existing IP configuration is still
   valid for Internet connectivity.  A subnet change might have occurred
   when the host changed its point of attachment.

   In practice, the host doesn't know which of its addresses are valid
   on the newly attached link.  It also doesn't know whether its
   existing default router is on this link or whether its neighbor cache
   entries are valid.  Correct configuration of each of these components
   is necessary in order to send packets on and off the link.

   To examine the status of the existing configuration, a host may check
   whether a 'link change' has occurred.  In this document, the term
   'link' is as defined in RFC 2461 [1].  The notion 'link' is not
   identical with the notion 'subnet', as defined in RFC 3753 [2].  For
   example, there may be more than one subnet on a link, and a host
   connected to a link may be part of one or more of the subnets on the
   link.

   Today, a link change necessitates an IP configuration change.
   Whenever a host detects that it has remained at the same link, it can
   usually assume its IP configuration is still valid.  Otherwise, the
   existing one is no longer valid, and a new configuration must be
   acquired.  Therefore, to examine the validity of an IP configuration,
   all that is required is that the host checks for link change.

   In the process of checking for link change, a host may collect some
   of the necessary information for a new IP configuration, such as on-
   link prefixes.  So, when an IP subnet change has occurred, the host
   can immediately initiate the process of getting a new IP
   configuration.  This may reduce handoff delay and minimize signaling.

   Rapid attachment detection is required for a device that changes
   subnet while having on-going sessions.  This may be the case if a
   host is connected intermittently, is a mobile node, or has urgent
   data to transmit upon attachment to a link.

   Detecting Network Attachment (DNA) is the process by which a host
   collects the appropriate information and detects the identity of its
   currently attached link to ascertain the validity of its IP
   configuration.

Choi & Daley                 Informational                      [Page 2]