rfc3493.txt

bind 9.3结合mysql数据库

Network Working Group                                        R. Gilligan
Request for Comments: 3493                                Intransa, Inc.
Obsoletes: 2553                                               S. Thomson
Category: Informational                                            Cisco
                                                                J. Bound
                                                               J. McCann
                                                         Hewlett-Packard
                                                              W. Stevens
                                                           February 2003


               Basic Socket Interface Extensions for 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 (2003).  All Rights Reserved.

Abstract

   The de facto standard Application Program Interface (API) for TCP/IP
   applications is the "sockets" interface.  Although this API was
   developed for Unix in the early 1980s it has also been implemented on
   a wide variety of non-Unix systems.  TCP/IP applications written
   using the sockets API have in the past enjoyed a high degree of
   portability and we would like the same portability with IPv6
   applications.  But changes are required to the sockets API to support
   IPv6 and this memo describes these changes.  These include a new
   socket address structure to carry IPv6 addresses, new address
   conversion functions, and some new socket options.  These extensions
   are designed to provide access to the basic IPv6 features required by
   TCP and UDP applications, including multicasting, while introducing a
   minimum of change into the system and providing complete
   compatibility for existing IPv4 applications.  Additional extensions
   for advanced IPv6 features (raw sockets and access to the IPv6
   extension headers) are defined in another document.










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Table of Contents

   1.  Introduction................................................3
   2.  Design Considerations.......................................4
       2.1  What Needs to be Changed...............................4
       2.2  Data Types.............................................6
       2.3  Headers................................................6
       2.4  Structures.............................................6
   3.  Socket Interface............................................6
       3.1  IPv6 Address Family and Protocol Family................6
       3.2  IPv6 Address Structure.................................7
       3.3  Socket Address Structure for 4.3BSD-Based Systems......7
       3.4  Socket Address Structure for 4.4BSD-Based Systems......9
       3.5  The Socket Functions...................................9
       3.6  Compatibility with IPv4 Applications..................10
       3.7  Compatibility with IPv4 Nodes.........................11
       3.8  IPv6 Wildcard Address.................................11
       3.9  IPv6 Loopback Address.................................13
       3.10 Portability Additions.................................14
   4.  Interface Identification...................................16
       4.1  Name-to-Index.........................................17
       4.2  Index-to-Name.........................................17
       4.3  Return All Interface Names and Indexes................18
       4.4  Free Memory...........................................18
   5.  Socket Options.............................................18
       5.1  Unicast Hop Limit.....................................19
       5.2  Sending and Receiving Multicast Packets...............19
       5.3  IPV6_V6ONLY option for AF_INET6 Sockets...............22
   6.  Library Functions..........................................22
       6.1  Protocol-Independent Nodename and
            Service Name Translation..............................23
       6.2  Socket Address Structure to Node Name
            and Service Name......................................28
       6.3  Address Conversion Functions..........................31
       6.4  Address Testing Macros................................33
   7.  Summary of New Definitions.................................33
   8.  Security Considerations....................................35
   9.  Changes from RFC 2553......................................35
   10. Acknowledgments............................................36
   11. References.................................................37
   12. Authors' Addresses.........................................38
   13. Full Copyright Statement...................................39









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1. Introduction

   While IPv4 addresses are 32 bits long, IPv6 addresses are 128 bits
   long.  The socket interface makes the size of an IP address quite
   visible to an application; virtually all TCP/IP applications for
   BSD-based systems have knowledge of the size of an IP address.  Those
   parts of the API that expose the addresses must be changed to
   accommodate the larger IPv6 address size.  IPv6 also introduces new
   features, some of which must be made visible to applications via the
   API.  This memo defines a set of extensions to the socket interface
   to support the larger address size and new features of IPv6.  It
   defines "basic" extensions that are of use to a broad range of
   applications.  A companion document, the "advanced" API [4], covers
   extensions that are of use to more specialized applications, examples
   of which include routing daemons, and the "ping" and "traceroute"
   utilities.

   The development of this API was started in 1994 in the IETF IPng
   working group.  The API has evolved over the years, published first
   in RFC 2133, then again in RFC 2553, and reaching its final form in
   this document.

   As the API matured and stabilized, it was incorporated into the Open
   Group's Networking Services (XNS) specification, issue 5.2, which was
   subsequently incorporated into a joint Open Group/IEEE/ISO standard
   [3].

   Effort has been made to ensure that this document and [3] contain the
   same information with regard to the API definitions.  However, the
   reader should note that this document is for informational purposes
   only, and that the official standard specification of the sockets API
   is [3].

   It is expected that any future standardization work on this API would
   be done by the Open Group Base Working Group [6].

   It should also be noted that this document describes only those
   portions of the API needed for IPv4 and IPv6 communications.  Other
   potential uses of the API, for example the use of getaddrinfo() and
   getnameinfo() with the AF_UNIX address family, are beyond the scope
   of this document.










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2. Design Considerations

   There are a number of important considerations in designing changes
   to this well-worn API:

   -  The API changes should provide both source and binary
      compatibility for programs written to the original API.  That is,
      existing program binaries should continue to operate when run on a
      system supporting the new API.  In addition, existing applications
      that are re-compiled and run on a system supporting the new API
      should continue to operate.  Simply put, the API changes for IPv6
      should not break existing programs.  An additional mechanism for
      implementations to verify this is to verify the new symbols are
      protected by Feature Test Macros as described in [3].  (Such
      Feature Test Macros are not defined by this RFC.)

   -  The changes to the API should be as small as possible in order to
      simplify the task of converting existing IPv4 applications to
      IPv6.

   -  Where possible, applications should be able to use this API to
      interoperate with both IPv6 and IPv4 hosts.  Applications should
      not need to know which type of host they are communicating with.

   -  IPv6 addresses carried in data structures should be 64-bit
      aligned.  This is necessary in order to obtain optimum performance
      on 64-bit machine architectures.

   Because of the importance of providing IPv4 compatibility in the API,
   these extensions are explicitly designed to operate on machines that
   provide complete support for both IPv4 and IPv6.  A subset of this
   API could probably be designed for operation on systems that support
   only IPv6.  However, this is not addressed in this memo.

2.1 What Needs to be Changed

   The socket interface API consists of a few distinct components:

   -  Core socket functions.

   -  Address data structures.

   -  Name-to-address translation functions.

   -  Address conversion functions.






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   The core socket functions -- those functions that deal with such
   things as setting up and tearing down TCP connections, and sending
   and receiving UDP packets -- were designed to be transport
   independent.  Where protocol addresses are passed as function
   arguments, they are carried via opaque pointers.  A protocol-specific
   address data structure is defined for each protocol that the socket
   functions support.  Applications must cast pointers to these
   protocol-specific address structures into pointers to the generic
   "sockaddr" address structure when using the socket functions.  These
   functions need not change for IPv6, but a new IPv6-specific address
   data structure is needed.

   The "sockaddr_in" structure is the protocol-specific data structure
   for IPv4.  This data structure actually includes 8-octets of unused
   space, and it is tempting to try to use this space to adapt the
   sockaddr_in structure to IPv6.  Unfortunately, the sockaddr_in
   structure is not large enough to hold the 16-octet IPv6 address as
   well as the other information (address family and port number) that
   is needed.  So a new address data structure must be defined for IPv6.

   IPv6 addresses are scoped [2] so they could be link-local, site,
   organization, global, or other scopes at this time undefined.  To
   support applications that want to be able to identify a set of
   interfaces for a specific scope, the IPv6 sockaddr_in structure must
   support a field that can be used by an implementation to identify a
   set of interfaces identifying the scope for an IPv6 address.

   The IPv4 name-to-address translation functions in the socket
   interface are gethostbyname() and gethostbyaddr().  These are left as
   is, and new functions are defined which support both IPv4 and IPv6.

   The IPv4 address conversion functions -- inet_ntoa() and inet_addr()
   -- convert IPv4 addresses between binary and printable form.  These
   functions are quite specific to 32-bit IPv4 addresses.  We have
   designed two analogous functions that convert both IPv4 and IPv6
   addresses, and carry an address type parameter so that they can be
   extended to other protocol families as well.

   Finally, a few miscellaneous features are needed to support IPv6.  A
   new interface is needed to support the IPv6 hop limit header field.
   New socket options are needed to control the sending and receiving of
   IPv6 multicast packets.

   The socket interface will be enhanced in the future to provide access
   to other IPv6 features.  Some of these extensions are described in
   [4].





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2.2 Data Types

   The data types of the structure elements given in this memo are
   intended to track the relevant standards.  uintN_t means an unsigned
   integer of exactly N bits (e.g., uint16_t).  The sa_family_t and
   in_port_t types are defined in [3].

2.3 Headers

   When function prototypes and structures are shown we show the headers
   that must be #included to cause that item to be defined.

2.4 Structures

   When structures are described the members shown are the ones that
   must appear in an implementation.  Additional, nonstandard members
   may also be defined by an implementation.  As an additional
   precaution nonstandard members could be verified by Feature Test
   Macros as described in [3].  (Such Feature Test Macros are not
   defined by this RFC.)

   The ordering shown for the members of a structure is the recommended
   ordering, given alignment considerations of multibyte members, but an
   implementation may order the members differently.

3. Socket Interface

   This section specifies the socket interface changes for IPv6.

3.1 IPv6 Address Family and Protocol Family

   A new address family name, AF_INET6, is defined in <sys/socket.h>.
   The AF_INET6 definition distinguishes between the original
   sockaddr_in address data structure, and the new sockaddr_in6 data
   structure.

   A new protocol family name, PF_INET6, is defined in <sys/socket.h>.
   Like most of the other protocol family names, this will usually be
   defined to have the same value as the corresponding address family
   name:

      #define PF_INET6        AF_INET6

   The AF_INET6 is used in the first argument to the socket() function
   to indicate that an IPv6 socket is being created.