rfc1688.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                         W. Simpson
Request for Comments: 1688                                    Daydreamer
Category: Informational                                      August 1994


                      IPng Mobility Considerations

Status of this Memo

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

Abstract

   This document was submitted to the IPng Area in response to RFC 1550.
   Publication of this document does not imply acceptance by the IPng
   Area of any ideas expressed within.  Comments should be submitted to
   the [e-mail] mailing list.  This RFC specifies
   criteria related to mobility for consideration in design and
   selection of the Next Generation of IP.

Table of Contents

   1.     Introduction ..........................................    2
   2.     Addressing ............................................    2
      2.1       Ownership .......................................    2
      2.2       Topology ........................................    3
      2.3       Manufacturer ....................................    3
      2.4       Numbering .......................................    3
      2.5       Configuration ...................................    3
   3.     Communication .........................................    3
      3.1       Topological Changes .............................    4
      3.2       Routing Updates .................................    4
      3.3       Path Optimization ...............................    5
      3.4       At Home .........................................    5
      3.5       Away From Home ..................................    5
   4.     Security ..............................................    5
      4.1       Authentication ..................................    5
      4.2       Anonymity .......................................    6
      4.3       Location Privacy ................................    6
      4.4       Content Privacy .................................    6
   5.     Bandwidth .............................................    6
      5.1       Administrative Messages .........................    7
      5.2       Response Time ...................................    7
      5.3       Header Prediction ...............................    8
   6.     Processing ............................................    8
      6.1       Fixed Location ..................................    8



Simpson                                                         [Page 1]

RFC 1688                     IPng Mobility                   August 1994


      6.2       Simple Fields ...................................    9
      6.3       Simple Tests ....................................    9
      6.4       Type, Length, Value .............................    9
   Acknowledgements .............................................    9
   Security Considerations ......................................    9
   Author's Address .............................................    9

1.  Introduction

   Current versions of the Internet Protocol make an implicit assumption
   that a node's point of attachment remains fixed.  Datagrams are sent
   to a node based on the location information contained in the node's
   IP address.

   If a node moves while keeping its IP address unchanged, its IP
   network number will not reflect its new point of attachment.  The
   routing protocols will not be able to route datagrams to it
   correctly.

   A number of considerations arise for routing these datagrams to a
   Mobile Node.

2.  Addressing

   Each Mobile Node must have at least one Home-Address which identifies
   it to other nodes.  This Home-Address must be globally unique.

2.1.  Ownership

   The presence of ownership information in the Home-Address would be
   beneficial.  A Mobile Node will be assigned a Home-Address by the
   organization that owns the machine, and will be able to use that
   Home-Address regardless of the current point of attachment.

   The ownership information must be organized in such a fashion to
   facilitate "inverse" lookup in the Domain Name Service, and other
   future services.

   Ownership information could be used by other nodes to ascertain the
   current topological location of the Mobile Node.

   Ownership information could also be used for generation of accounting
   records.








Simpson                                                         [Page 2]

RFC 1688                     IPng Mobility                   August 1994


2.2.  Topology

   There is no requirement that the Home-Address contain topological
   information.  Indeed, by the very nature of mobility, any such
   topological information is irrelevant.

   Topological information in the Home-Address must not hinder mobility,
   whether by prevention of relocation, or by wasting bandwidth or
   processing efficiency.

2.3.  Manufacturer

   There is no requirement that the Home-Address contain manufacturer
   information.

   Manufacturer information in the Home-Address must not hinder
   mobility, whether by prevention of relocation, or by wasting
   bandwidth or processing efficiency.

2.4.  Numbering

   The number of mobile nodes is expected to be constrained by the
   population of users within the lifetime of the IPng protocol.  The
   maximum world-wide sustainable population is estimated as 16e9,
   although during the lifetime of IPng the population is not expected
   to exceed 8e9.

   Each user is assumed to be mobile, and to have a maximum combined
   personal mobile and home network(s) on the order of 4e3 nodes.

   The expectation is that only 46 bits will be needed to densely number
   all mobile and home nodes.

   The size of addressing elements is also constrained by bandwidth
   efficiency and processing efficiency, as described later.

2.5.  Configuration

   Since the typical user would be unlikely to be aware of or willing
   and able to maintain 4e3 nodes, the assignment of Home-Addresses must
   be automatically configurable.  Registration of the nodes must be
   dynamic and transparent to the user, both at home and away from home.

3.  Communication

   A Mobile Node must continue to be capable of communicating directly
   with other nodes which do not implement mobility functions.




Simpson                                                         [Page 3]

RFC 1688                     IPng Mobility                   August 1994


   No protocol enhancements are required in hosts or routers that are
   not serving any of the mobility functions.  Similarly, no additional
   protocols are needed by a router (that is not acting as a Home Agent
   or a Foreign Agent) to route datagrams to or from a Mobile Node.

   A Mobile Node using its Home-Address must be able to communicate with
   other nodes after having been disconnected from the Internet, and
   then reconnected at a different point of attachment.

   A Mobile Node using its Home-Address must be able to communicate with
   other nodes while roaming between different points of attachment,
   without loss of transport connections.

3.1.  Topological Changes

   In order that transport connections be maintained while roaming,
   topological changes must not affect transport connections.

   For correspondent nodes which do not implement mobility functions,
   topological changes should not be communicated to the correspondent.

   For correspondent nodes which implement mobility functions, the
   correspondent should be capable of determining topological changes.

   Topological change information must be capable of insertion and
   removal by routers in the datagram path, as well as by the
   correspondent and Mobile Node.

3.2.  Routing Updates

   Mobile Nodes are expected to be able to change their point of
   attachment no more frequently than once per second.

   Changes in topology which occur more frequently must be handled at
   the link layer transparently to the internetwork layer.  It is
   further noted that engineering margins may require the link layer to
   handle all changes at a frequency in the neighborhood of 10 seconds.

   Changes in topology which occur less frequently must be immediately
   reflected in the mobility updates.  This may preclude the use of the
   Domain Name Service as the repository of mobility topological
   information.

   It must be noted that global routing updates do not operate at this
   frequency.  As old topological information may be obsoleted faster
   than global routing updates, access to the repository of mobility
   topological information must be independent of prior topological
   information.



Simpson                                                         [Page 4]

RFC 1688                     IPng Mobility                   August 1994


   The mobility specific repository should use ownership information in
   the Home-Address for access to the repository.

3.3.  Path Optimization

   Optimization of the path from a correspondent to a mobile node is not
   required.  However, such optimization is desirable.

   For correspondent nodes which implement mobility functions, the
   correspondent should be capable of determining the optimal path.

   The optimization mechanism is also constrained by security, bandwidth
   efficiency and processing efficiency, as described later.

3.4.  At Home

   Mobile Nodes do not require special "virtual" home network addresses.
   The assumption that extra addresses or multiple routers are available
   is unwarranted in small networks.

   Mobile Nodes must operate without special assistance from routers in
   order to communicate directly with other nodes on the home subnetwork
   link.