rfc1752.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

     oriented media such as ATM
   * datagram service - IPng preserves datagram service as its basic
     operational mode, it is possible that the use of path MTU discovery
     will complicate the use of datagrams in some cases
   * configuration ease - IPng will have easy and flexible address
     autoconfiguration which will support a wide variety of environments
     from nodes on an isolated network to nodes deep in a complex
     internet
   * security - IPng includes specific mechanisms for authentication and
     encryption at the internetwork layer; the security features do rely



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     on the presence of a yet to be defined key management system
   * unique names - IPng addresses may be used as globally unique names
     although they do have topological significance
   * access to standards - all of the IPng standards will be published
     as RFCs with unlimited distribution
   * multicast support - IPng specifically includes multicast support
   * extensibility - the use of extension headers and an expandable
     header option feature will allow the introduction of new features
     into IPng when needed in a way that minimizes the disruption of the
     existing network
   * service classes - the IPng header includes a Flow Label which may
     be used to differentiate requested service classes
   * mobility - the proposed IPv4 mobility functions will work with IPng
   * control protocol - IPng includes the familiar IPv4 control protocol
     features
   * tunneling support - encapsulation of IPng or other protocols within
     IPng is a basic capability described in the IPng specifications

11.2 IPv6

   The IANA has assigned version number 6 to IPng.  The protocol itself
   will be called IPv6.

   The remainder of this memo is used to describe IPv6 and its features.
   This description is an overview snapshot.  The standards documents
   themselves should be referenced for definitive specifications.  We
   also make a number of specific recommendations concerning the details
   of the proposed protocol, the procedures required to complete the
   definition of the protocol, and the IETF working groups we feel are
   necessary to accomplish the task.

12. IPv6 Overview

   IPv6 is a new version of the Internet Protocol, it has been designed
   as an evolutionary, rather than revolutionary, step from IPv4.
   Functions which are generally seen as working in IPv4 were kept in
   IPv6.  Functions which don't work or are infrequently used were
   removed or made optional.  A few new features were added where the
   functionality was felt to be necessary.

   The important features of IPv6 include: [Hinden94c]

   * expanded addressing and routing capabilities - The IP address size
     is increased from 32 bits to 128 bits providing support for a much
     greater number of addressable nodes, more levels of addressing
     hierarchy, and simpler auto-configuration of addresses.





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     The scaleability of multicast routing is improved by adding a
     "scope" field to multicast addresses.

     A new type of address, called a "cluster address" is defined to
     identify topological regions rather than individual nodes.  The use
     of cluster addresses in conjunction with the IPv6 source route
     capability allows nodes additional control over the path their
     traffic takes.

   * simplified header format - Some IPv4 header fields have been
     dropped or made optional to reduce the common-case processing cost
     of packet handling and to keep the bandwidth overhead of the IPv6
     header as low as possible in spite of the increased size of the
     addresses.  Even though the IPv6 addresses are four time longer
     than the IPv4 addresses, the IPv6 header is only twice the size of
     the IPv4 header.

   * support for extension headers and options - IPv6 options are placed
     in separate headers that are located in the packet between the IPv6
     header and the transport-layer header.  Since most IPv6 option
     headers are not examined or processed by any router along a
     packet's delivery path until it arrives at its final destination,
     this organization facilitates a major improvement in router
     performance for packets containing options.  Another improvement is
     that unlike IPv4, IPv6 options can be of arbitrary length and not
     limited to 40 bytes. This feature plus the manner in which they are
     processed, permits IPv6 options to be used for functions which were
     not practical in IPv4.

     A key extensibility feature of IPv6 is the ability to encode,
     within an option, the action which a router or host should perform
     if the option is unknown. This permits the incremental deployment
     of additional functionality into an operational network with a
     minimal danger of disruption.

   * support for authentication and privacy - IPv6 includes the
     definition of an extension which provides support for
     authentication and data integrity. This extension is included as a
     basic element of IPv6 and support for it will be required in all
     implementations.

     IPv6 also includes the definition of an extension to support
     confidentiality by means of encryption.  Support for this extension
     will be strongly encouraged in all implementations.







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   * support for autoconfiguration - IPv6 supports multiple forms of
     autoconfiguration, from "plug and play" configuration of node
     addresses on an isolated network to the full-featured facilities
     offered by DHCP.

   * support for source routes - IPv6 includes an extended function
     source routing header designed to support the Source Demand Routing
     Protocol (SDRP). The purpose of SDRP is to support source-initiated
     selection of routes to complement the route selection provided by
     existing routing protocols for both inter-domain and intra-domain
     routes. [Estrin94b]

   * simple and flexible transition from IPv4 - The IPv6 transition plan
     is aimed at meeting four basic requirements: [Gillig94a]

     - Incremental upgrade.  Existing installed IPv4 hosts and routers
       may be upgraded to IPv6 at any time without being dependent on
       any other hosts or routers being upgraded.
     - Incremental deployment.  New IPv6 hosts and routers can be
       installed at any time without any prerequisites.
     - Easy Addressing.  When existing installed IPv4 hosts or routers
       are upgraded to IPv6, they may continue to use their existing
       address.  They do not need to be assigned new addresses.
     - Low start-up costs.  Little or no preparation work is needed in
       order to upgrade existing IPv4 systems to IPv6, or to deploy new
       IPv6 systems.

   * quality of service capabilities - A new capability is added to
     enable the labeling of packets belonging to particular traffic
     "flows" for which the sender has requested special handling, such
     as non-default quality of service or "real-time" service.




















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12.1 IPv6 Header Format

   The IPv6 header, although longer than the IPv4 header, is
   considerably simplified.  A number of functions that were in the IPv4
   header have been relocated in extension headers or dropped.
   [Deering94b]

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version|                       Flow Label                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Payload Length        |  Next Header  |   Hop Limit   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                         Source Address                        +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Destination Address                      +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   * Version - Internet Protocol version number. IPng has been assigned
     version number 6. (4-bit field)

   * Flow Label - This field may be used by a host to label those
     packets for which it is requesting special handling by routers
     within a network, such as non-default quality of service or "real-
     time" service. (28-bit field)

   * Payload Length - Length of the remainder of the packet following
     the IPv6 header, in octets. To permit payloads of greater than 64K
     bytes, if the value in this field is 0 the actual packet length
     will be found in an Hop-by-Hop option. (16-bit unsigned integer)

   * Next Header - Identifies the type of header immediately following
     the IPv6 header.  The Next Header field uses the same values as the
     IPv4 Protocol field (8-bit selector field)






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   * Hop Limit - Used to limit the impact of routing loops. The Hop
     Limit field is decremented by 1 by each node that forwards the
     packet.  The packet is discarded if Hop Limit is decremented to
     zero. (8-bit unsigned integer)

   * Source Address - An address of the initial sender of the packet.
     (128 bit field)

   * Destination Address - An address of the intended recipient of the
     packet (possibly not the ultimate recipient, if an optional Routing
     Header is present). (128 bit field)

12.2 Extension Headers

   In IPv6, optional internet-layer information is encoded in separate
   headers that may be placed between the IPv6 header and the
   transport-layer header in a packet.  There are a small number of such
   extension headers, each identified by a distinct Next Header value.
   [From a number of the documents listed in Appendix C.]

   12.2.1 Hop-by-Hop Option Header

      The Hop-by-Hop Options header is used to carry optional
      information that must be examined by every node along a packet's
      delivery path.  The Hop-by-Hop Options header is identified by a
      Next Header value of 0 in the IPv6 header, and has the following
      format:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Next Header  |  Hdr Ext Len  |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+