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rfc:rfc2553

Network Working Group R. Gilligan Request for Comments: 2553 FreeGate Obsoletes: 2133 S. Thomson Category: Informational Bellcore

                                                              J. Bound
                                                                Compaq
                                                            W. Stevens
                                                            Consultant
                                                            March 1999
             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 (1999).  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 [4].

Gilligan, et. al. Informational [Page 1] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

Table of Contents

 1. Introduction.................................................3
 2. Design Considerations........................................3
 2.1 What Needs to be Changed....................................4
 2.2 Data Types..................................................5
 2.3 Headers.....................................................5
 2.4 Structures..................................................5
 3. Socket Interface.............................................6
 3.1 IPv6 Address Family and Protocol Family.....................6
 3.2 IPv6 Address Structure......................................6
 3.3 Socket Address Structure for 4.3BSD-Based Systems...........7
 3.4 Socket Address Structure for 4.4BSD-Based Systems...........8
 3.5 The Socket Functions........................................9
 3.6 Compatibility with IPv4 Applications.......................10
 3.7 Compatibility with IPv4 Nodes..............................10
 3.8 IPv6 Wildcard Address......................................11
 3.9 IPv6 Loopback Address......................................12
 3.10 Portability Additions.....................................13
 4. Interface Identification....................................16
 4.1 Name-to-Index..............................................16
 4.2 Index-to-Name..............................................17
 4.3 Return All Interface Names and Indexes.....................17
 4.4 Free Memory................................................18
 5. Socket Options..............................................18
 5.1 Unicast Hop Limit..........................................18
 5.2 Sending and Receiving Multicast Packets....................19
 6. Library Functions...........................................21
 6.1 Nodename-to-Address Translation............................21
 6.2 Address-To-Nodename Translation............................24
 6.3 Freeing memory for getipnodebyname and getipnodebyaddr.....26
 6.4 Protocol-Independent Nodename and Service Name Translation.26
 6.5 Socket Address Structure to Nodename and Service Name......29
 6.6 Address Conversion Functions...............................31
 6.7 Address Testing Macros.....................................32
 7. Summary of New Definitions..................................33
 8. Security Considerations.....................................35
 9. Year 2000 Considerations....................................35
 Changes From RFC 2133..........................................35
 Acknowledgments................................................38
 References.....................................................39
 Authors' Addresses.............................................40
 Full Copyright Statement.......................................41

Gilligan, et. al. Informational [Page 2] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

1. Introduction

 While IPv4 addresses are 32 bits long, IPv6 interfaces are identified
 by 128-bit addresses.  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 (e.g., traffic class and flowlabel), 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.

2. Design Considerations

 There are a number of important considerations in designing changes
 to this well-worn API:
  1. 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
      additonal mechanism for implementations to verify this is to
      verify the new symbols are protected by Feature Test Macros as
      described in IEEE Std 1003.1.  (Such Feature Test Macros are not
      defined by this RFC.)
  1. The changes to the API should be as small as possible in order

to simplify the task of converting existing IPv4 applications to

      IPv6.
  1. 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.
  1. 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.

Gilligan, et. al. Informational [Page 3] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

2.1 What Needs to be Changed

 The socket interface API consists of a few distinct components:
  1. Core socket functions.
  1. Address data structures.
  1. Name-to-address translation functions.
  1. Address conversion functions.
 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 name-to-address translation functions in the socket interface are
 gethostbyname() and gethostbyaddr().  These are left as is and new
 functions are defined to support IPv4 and IPv6.  Additionally, the
 POSIX 1003.g draft [3] specifies a new nodename-to-address
 translation function which is protocol independent.  This function
 can also be used with IPv4 and IPv6.

Gilligan, et. al. Informational [Page 4] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 The 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.
 New interfaces are needed to support the IPv6 traffic class, flow
 label, and hop limit header fields.  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.  These extensions are described in [4].

2.2 Data Types

 The data types of the structure elements given in this memo are
 intended to be examples, not absolute requirements.  Whenever
 possible, data types from Draft 6.6 (March 1997) of POSIX 1003.1g are
 used: uintN_t means an unsigned integer of exactly N bits (e.g.,
 uint16_t).  We also assume the argument data types from 1003.1g when
 possible (e.g., the final argument to setsockopt() is a size_t
 value).  Whenever buffer sizes are specified, the POSIX 1003.1 size_t
 data type is used (e.g., the two length arguments to getnameinfo()).

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 IEEE Std 1003.1.  (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.

Gilligan, et. al. Informational [Page 5] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

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 PF_INET6 is used in the first argument to the socket() function
 to indicate that an IPv6 socket is being created.

3.2 IPv6 Address Structure

 A new in6_addr structure holds a single IPv6 address and is defined
 as a result of including <netinet/in.h>:
    struct in6_addr {
        uint8_t  s6_addr[16];      /* IPv6 address */
    };
 This data structure contains an array of sixteen 8-bit elements,
 which make up one 128-bit IPv6 address.  The IPv6 address is stored
 in network byte order.
 The structure in6_addr above is usually implemented with an embedded
 union with extra fields that force the desired alignment level in a
 manner similar to BSD implementations of "struct in_addr". Those
 additional implementation details are omitted here for simplicity.
 An example is as follows:

Gilligan, et. al. Informational [Page 6] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 struct in6_addr {
      union {
          uint8_t  _S6_u8[16];
          uint32_t _S6_u32[4];
          uint64_t _S6_u64[2];
      } _S6_un;
 };
 #define s6_addr _S6_un._S6_u8

3.3 Socket Address Structure for 4.3BSD-Based Systems

 In the socket interface, a different protocol-specific data structure
 is defined to carry the addresses for each protocol suite.  Each
 protocol- specific data structure is designed so it can be cast into a
 protocol- independent data structure -- the "sockaddr" structure.
 Each has a "family" field that overlays the "sa_family" of the
 sockaddr data structure.  This field identifies the type of the data
 structure.
 The sockaddr_in structure is the protocol-specific address data
 structure for IPv4.  It is used to pass addresses between applications
 and the system in the socket functions.  The following sockaddr_in6
 structure holds IPv6 addresses and is defined as a result of including
 the <netinet/in.h> header:

struct sockaddr_in6 {

  sa_family_t     sin6_family;    /* AF_INET6 */
  in_port_t       sin6_port;      /* transport layer port # */
  uint32_t        sin6_flowinfo;  /* IPv6 traffic class & flow info */
  struct in6_addr sin6_addr;      /* IPv6 address */
  uint32_t        sin6_scope_id;  /* set of interfaces for a scope */

};

 This structure is designed to be compatible with the sockaddr data
 structure used in the 4.3BSD release.
 The sin6_family field identifies this as a sockaddr_in6 structure.
 This field overlays the sa_family field when the buffer is cast to a
 sockaddr data structure.  The value of this field must be AF_INET6.
 The sin6_port field contains the 16-bit UDP or TCP port number.  This
 field is used in the same way as the sin_port field of the
 sockaddr_in structure.  The port number is stored in network byte
 order.

Gilligan, et. al. Informational [Page 7] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 The sin6_flowinfo field is a 32-bit field that contains two pieces of
 information: the traffic class and the flow label.  The contents and
 interpretation of this member is specified in [1].  The sin6_flowinfo
 field SHOULD be set to zero by an implementation prior to using the
 sockaddr_in6 structure by an application on receive operations.
 The sin6_addr field is a single in6_addr structure (defined in the
 previous section).  This field holds one 128-bit IPv6 address.  The
 address is stored in network byte order.
 The ordering of elements in this structure is specifically designed
 so that when sin6_addr field is aligned on a 64-bit boundary, the
 start of the structure will also be aligned on a 64-bit boundary.
 This is done for optimum performance on 64-bit architectures.
 The sin6_scope_id field is a 32-bit integer that identifies a set of
 interfaces as appropriate for the scope of the address carried in the
 sin6_addr field.  For a link scope sin6_addr sin6_scope_id would be
 an interface index.  For a site scope sin6_addr, sin6_scope_id would
 be a site identifier.  The mapping of sin6_scope_id to an interface
 or set of interfaces is left to implementation and future
 specifications on the subject of site identifiers.
 Notice that the sockaddr_in6 structure will normally be larger than
 the generic sockaddr structure.  On many existing implementations the
 sizeof(struct sockaddr_in) equals sizeof(struct sockaddr), with both
 being 16 bytes.  Any existing code that makes this assumption needs
 to be examined carefully when converting to IPv6.

3.4 Socket Address Structure for 4.4BSD-Based Systems

 The 4.4BSD release includes a small, but incompatible change to the
 socket interface.  The "sa_family" field of the sockaddr data
 structure was changed from a 16-bit value to an 8-bit value, and the
 space saved used to hold a length field, named "sa_len".  The
 sockaddr_in6 data structure given in the previous section cannot be
 correctly cast into the newer sockaddr data structure.  For this
 reason, the following alternative IPv6 address data structure is
 provided to be used on systems based on 4.4BSD.  It is defined as a
 result of including the <netinet/in.h> header.

Gilligan, et. al. Informational [Page 8] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

struct sockaddr_in6 {

  uint8_t         sin6_len;       /* length of this struct */
  sa_family_t     sin6_family;    /* AF_INET6 */
  in_port_t       sin6_port;      /* transport layer port # */
  uint32_t        sin6_flowinfo;  /* IPv6 flow information */
  struct in6_addr sin6_addr;      /* IPv6 address */
  uint32_t        sin6_scope_id;  /* set of interfaces for a scope */

};

 The only differences between this data structure and the 4.3BSD
 variant are the inclusion of the length field, and the change of the
 family field to a 8-bit data type.  The definitions of all the other
 fields are identical to the structure defined in the previous
 section.
 Systems that provide this version of the sockaddr_in6 data structure
 must also declare SIN6_LEN as a result of including the
 <netinet/in.h> header.  This macro allows applications to determine
 whether they are being built on a system that supports the 4.3BSD or
 4.4BSD variants of the data structure.

3.5 The Socket Functions

 Applications call the socket() function to create a socket descriptor
 that represents a communication endpoint.  The arguments to the
 socket() function tell the system which protocol to use, and what
 format address structure will be used in subsequent functions.  For
 example, to create an IPv4/TCP socket, applications make the call:
    s = socket(PF_INET, SOCK_STREAM, 0);
 To create an IPv4/UDP socket, applications make the call:
    s = socket(PF_INET, SOCK_DGRAM, 0);
 Applications may create IPv6/TCP and IPv6/UDP sockets by simply using
 the constant PF_INET6 instead of PF_INET in the first argument.  For
 example, to create an IPv6/TCP socket, applications make the call:
    s = socket(PF_INET6, SOCK_STREAM, 0);
 To create an IPv6/UDP socket, applications make the call:
    s = socket(PF_INET6, SOCK_DGRAM, 0);

Gilligan, et. al. Informational [Page 9] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 Once the application has created a PF_INET6 socket, it must use the
 sockaddr_in6 address structure when passing addresses in to the
 system.  The functions that the application uses to pass addresses
 into the system are:
    bind()
    connect()
    sendmsg()
    sendto()
 The system will use the sockaddr_in6 address structure to return
 addresses to applications that are using PF_INET6 sockets.  The
 functions that return an address from the system to an application
 are:
    accept()
    recvfrom()
    recvmsg()
    getpeername()
    getsockname()
 No changes to the syntax of the socket functions are needed to
 support IPv6, since all of the "address carrying" functions use an
 opaque address pointer, and carry an address length as a function
 argument.

3.6 Compatibility with IPv4 Applications

 In order to support the large base of applications using the original
 API, system implementations must provide complete source and binary
 compatibility with the original API.  This means that systems must
 continue to support PF_INET sockets and the sockaddr_in address
 structure.  Applications must be able to create IPv4/TCP and IPv4/UDP
 sockets using the PF_INET constant in the socket() function, as
 described in the previous section.  Applications should be able to
 hold a combination of IPv4/TCP, IPv4/UDP, IPv6/TCP and IPv6/UDP
 sockets simultaneously within the same process.
 Applications using the original API should continue to operate as
 they did on systems supporting only IPv4.  That is, they should
 continue to interoperate with IPv4 nodes.

3.7 Compatibility with IPv4 Nodes

 The API also provides a different type of compatibility: the ability
 for IPv6 applications to interoperate with IPv4 applications.  This
 feature uses the IPv4-mapped IPv6 address format defined in the IPv6
 addressing architecture specification [2].  This address format

Gilligan, et. al. Informational [Page 10] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 allows the IPv4 address of an IPv4 node to be represented as an IPv6
 address.  The IPv4 address is encoded into the low-order 32 bits of
 the IPv6 address, and the high-order 96 bits hold the fixed prefix
 0:0:0:0:0:FFFF.  IPv4- mapped addresses are written as follows:
    ::FFFF:<IPv4-address>
 These addresses can be generated automatically by the
 getipnodebyname() function when the specified host has only IPv4
 addresses (as described in Section 6.1).
 Applications may use PF_INET6 sockets to open TCP connections to IPv4
 nodes, or send UDP packets to IPv4 nodes, by simply encoding the
 destination's IPv4 address as an IPv4-mapped IPv6 address, and
 passing that address, within a sockaddr_in6 structure, in the
 connect() or sendto() call.  When applications use PF_INET6 sockets
 to accept TCP connections from IPv4 nodes, or receive UDP packets
 from IPv4 nodes, the system returns the peer's address to the
 application in the accept(), recvfrom(), or getpeername() call using
 a sockaddr_in6 structure encoded this way.
 Few applications will likely need to know which type of node they are
 interoperating with.  However, for those applications that do need to
 know, the IN6_IS_ADDR_V4MAPPED() macro, defined in Section 6.7, is
 provided.

3.8 IPv6 Wildcard Address

 While the bind() function allows applications to select the source IP
 address of UDP packets and TCP connections, applications often want
 the system to select the source address for them.  With IPv4, one
 specifies the address as the symbolic constant INADDR_ANY (called the
 "wildcard" address) in the bind() call, or simply omits the bind()
 entirely.
 Since the IPv6 address type is a structure (struct in6_addr), a
 symbolic constant can be used to initialize an IPv6 address variable,
 but cannot be used in an assignment.  Therefore systems provide the
 IPv6 wildcard address in two forms.
 The first version is a global variable named "in6addr_any" that is an
 in6_addr structure.  The extern declaration for this variable is
 defined in <netinet/in.h>:
    extern const struct in6_addr in6addr_any;

Gilligan, et. al. Informational [Page 11] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 Applications use in6addr_any similarly to the way they use INADDR_ANY
 in IPv4.  For example, to bind a socket to port number 23, but let
 the system select the source address, an application could use the
 following code:
    struct sockaddr_in6 sin6;
     . . .
    sin6.sin6_family = AF_INET6;
    sin6.sin6_flowinfo = 0;
    sin6.sin6_port = htons(23);
    sin6.sin6_addr = in6addr_any;  /* structure assignment */
     . . .
    if (bind(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1)
            . . .
 The other version is a symbolic constant named IN6ADDR_ANY_INIT and
 is defined in <netinet/in.h>.  This constant can be used to
 initialize an in6_addr structure:
    struct in6_addr anyaddr = IN6ADDR_ANY_INIT;
 Note that this constant can be used ONLY at declaration time.  It can
 not be used to assign a previously declared in6_addr structure.  For
 example, the following code will not work:
    /* This is the WRONG way to assign an unspecified address */
    struct sockaddr_in6 sin6;
     . . .
    sin6.sin6_addr = IN6ADDR_ANY_INIT; /* will NOT compile */
 Be aware that the IPv4 INADDR_xxx constants are all defined in host
 byte order but the IPv6 IN6ADDR_xxx constants and the IPv6
 in6addr_xxx externals are defined in network byte order.

3.9 IPv6 Loopback Address

 Applications may need to send UDP packets to, or originate TCP
 connections to, services residing on the local node.  In IPv4, they
 can do this by using the constant IPv4 address INADDR_LOOPBACK in
 their connect(), sendto(), or sendmsg() call.
 IPv6 also provides a loopback address to contact local TCP and UDP
 services.  Like the unspecified address, the IPv6 loopback address is
 provided in two forms -- a global variable and a symbolic constant.

Gilligan, et. al. Informational [Page 12] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 The global variable is an in6_addr structure named
 "in6addr_loopback."  The extern declaration for this variable is
 defined in <netinet/in.h>:
    extern const struct in6_addr in6addr_loopback;
 Applications use in6addr_loopback as they would use INADDR_LOOPBACK
 in IPv4 applications (but beware of the byte ordering difference
 mentioned at the end of the previous section).  For example, to open
 a TCP connection to the local telnet server, an application could use
 the following code:
    struct sockaddr_in6 sin6;
     . . .
    sin6.sin6_family = AF_INET6;
    sin6.sin6_flowinfo = 0;
    sin6.sin6_port = htons(23);
    sin6.sin6_addr = in6addr_loopback;  /* structure assignment */
     . . .
    if (connect(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1)
            . . .
 The symbolic constant is named IN6ADDR_LOOPBACK_INIT and is defined
 in <netinet/in.h>.  It can be used at declaration time ONLY; for
 example:
    struct in6_addr loopbackaddr = IN6ADDR_LOOPBACK_INIT;
 Like IN6ADDR_ANY_INIT, this constant cannot be used in an assignment
 to a previously declared IPv6 address variable.

3.10 Portability Additions

 One simple addition to the sockets API that can help application
 writers is the "struct sockaddr_storage". This data structure can
 simplify writing code portable across multiple address families and
 platforms.  This data structure is designed with the following goals.
  1. It has a large enough implementation specific maximum size to

store the desired set of protocol specific socket address data

      structures. Specifically, it is at least large enough to
      accommodate sockaddr_in and sockaddr_in6 and possibly other
      protocol specific socket addresses too.
    - It is aligned at an appropriate boundary so protocol specific
      socket address data structure pointers can be cast to it and
      access their fields without alignment problems. (e.g. pointers
      to sockaddr_in6 and/or sockaddr_in can be cast to it and access
      fields without alignment problems).

Gilligan, et. al. Informational [Page 13] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

  1. It has the initial field(s) isomorphic to the fields of the

"struct sockaddr" data structure on that implementation which

      can be used as a discriminants for deriving the protocol in use.
      These initial field(s) would on most implementations either be a
      single field of type "sa_family_t" (isomorphic to sa_family
      field, 16 bits) or two fields of type uint8_t and sa_family_t
      respectively, (isomorphic to sa_len and sa_family_t, 8 bits
      each).
 An example implementation design of such a data structure would be as
 follows.

/* * Desired design of maximum size and alignment */ #define _SS_MAXSIZE 128 /* Implementation specific max size */ #define _SS_ALIGNSIZE (sizeof (int64_t))

                       /* Implementation specific desired alignment */

/* * Definitions used for sockaddr_storage structure paddings design. */ #define _SS_PAD1SIZE (_SS_ALIGNSIZE - sizeof (sa_family_t)) #define _SS_PAD2SIZE (_SS_MAXSIZE - (sizeof (sa_family_t)+

                            _SS_PAD1SIZE + _SS_ALIGNSIZE))

struct sockaddr_storage {

  sa_family_t  __ss_family;     /* address family */
  /* Following fields are implementation specific */
  char      __ss_pad1[_SS_PAD1SIZE];
            /* 6 byte pad, this is to make implementation
            /* specific pad up to alignment field that */
            /* follows explicit in the data structure */
  int64_t   __ss_align;     /* field to force desired structure */
             /* storage alignment */
  char      __ss_pad2[_SS_PAD2SIZE];
            /* 112 byte pad to achieve desired size, */
            /* _SS_MAXSIZE value minus size of ss_family */
            /* __ss_pad1, __ss_align fields is 112 */

};

 On implementations where sockaddr data structure includes a "sa_len",
 field this data structure would look like this:

/* * Definitions used for sockaddr_storage structure paddings design. */ #define _SS_PAD1SIZE (_SS_ALIGNSIZE -

                          (sizeof (uint8_t) + sizeof (sa_family_t))

#define _SS_PAD2SIZE (_SS_MAXSIZE - (sizeof (sa_family_t)+

Gilligan, et. al. Informational [Page 14] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

                            _SS_PAD1SIZE + _SS_ALIGNSIZE))

struct sockaddr_storage {

  uint8_t      __ss_len;        /* address length */
  sa_family_t  __ss_family;     /* address family */
  /* Following fields are implementation specific */
  char         __ss_pad1[_SS_PAD1SIZE];
                /* 6 byte pad, this is to make implementation
                /* specific pad up to alignment field that */
                /* follows explicit in the data structure */
  int64_t      __ss_align;  /* field to force desired structure */
                /* storage alignment */
  char         __ss_pad2[_SS_PAD2SIZE];
                /* 112 byte pad to achieve desired size, */
                /* _SS_MAXSIZE value minus size of ss_len, */
                /* __ss_family, __ss_pad1, __ss_align fields is 112 */

};

 The above example implementation illustrates a data structure which
 will align on a 64 bit boundary. An implementation specific field
 "__ss_align" along "__ss_pad1" is used to force a 64-bit alignment
 which covers proper alignment good enough for needs of sockaddr_in6
 (IPv6), sockaddr_in (IPv4) address data structures.  The size of
 padding fields __ss_pad1 depends on the chosen alignment boundary.
 The size of padding field __ss_pad2 depends on the value of overall
 size chosen for the total size of the structure. This size and
 alignment are represented in the above example by implementation
 specific (not required) constants _SS_MAXSIZE (chosen value 128) and
 _SS_ALIGNMENT (with chosen value 8).  Constants _SS_PAD1SIZE (derived
 value 6) and _SS_PAD2SIZE (derived value 112) are also for
 illustration and not required.  The implementation specific
 definitions and structure field names above start with an underscore
 to denote implementation private namespace.  Portable code is not
 expected to access or reference those fields or constants.
 The sockaddr_storage structure solves the problem of declaring
 storage for automatic variables which is large enough and aligned
 enough for storing socket address data structure of any family. For
 example, code with a file descriptor and without the context of the
 address family can pass a pointer to a variable of this type where a
 pointer to a socket address structure is expected in calls such as
 getpeername() and determine the address family by accessing the
 received content after the call.
 The sockaddr_storage structure may also be useful and applied to
 certain other interfaces where a generic socket address large enough
 and aligned for use with multiple address families may be needed. A
 discussion of those interfaces is outside the scope of this document.

Gilligan, et. al. Informational [Page 15] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 Also, much existing code assumes that any socket address structure
 can fit in a generic sockaddr structure.  While this has been true
 for IPv4 socket address structures, it has always been false for Unix
 domain socket address structures (but in practice this has not been a
 problem) and it is also false for IPv6 socket address structures
 (which can be a problem).
 So now an application can do the following:
    struct sockaddr_storage __ss;
    struct sockaddr_in6 *sin6;
    sin6 = (struct sockaddr_in6 *) &__ss;

4. Interface Identification

 This API uses an interface index (a small positive integer) to
 identify the local interface on which a multicast group is joined
 (Section 5.3).  Additionally, the advanced API [4] uses these same
 interface indexes to identify the interface on which a datagram is
 received, or to specify the interface on which a datagram is to be
 sent.
 Interfaces are normally known by names such as "le0", "sl1", "ppp2",
 and the like.  On Berkeley-derived implementations, when an interface
 is made known to the system, the kernel assigns a unique positive
 integer value (called the interface index) to that interface.  These
 are small positive integers that start at 1.  (Note that 0 is never
 used for an interface index.) There may be gaps so that there is no
 current interface for a particular positive interface index.
 This API defines two functions that map between an interface name and
 index, a third function that returns all the interface names and
 indexes, and a fourth function to return the dynamic memory allocated
 by the previous function.  How these functions are implemented is
 left up to the implementation.  4.4BSD implementations can implement
 these functions using the existing sysctl() function with the
 NET_RT_IFLIST command.  Other implementations may wish to use ioctl()
 for this purpose.

4.1 Name-to-Index

 The first function maps an interface name into its corresponding
 index.
    #include <net/if.h>
    unsigned int  if_nametoindex(const char *ifname);

Gilligan, et. al. Informational [Page 16] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 If the specified interface name does not exist, the return value is
 0, and errno is set to ENXIO.  If there was a system error (such as
 running out of memory), the return value is 0 and errno is set to the
 proper value (e.g., ENOMEM).

4.2 Index-to-Name

 The second function maps an interface index into its corresponding
 name.
    #include <net/if.h>
    char  *if_indextoname(unsigned int ifindex, char *ifname);
 The ifname argument must point to a buffer of at least IF_NAMESIZE
 bytes into which the interface name corresponding to the specified
 index is returned.  (IF_NAMESIZE is also defined in <net/if.h> and
 its value includes a terminating null byte at the end of the
 interface name.) This pointer is also the return value of the
 function.  If there is no interface corresponding to the specified
 index, NULL is returned, and errno is set to ENXIO, if there was a
 system error (such as running out of memory), if_indextoname returns
 NULL and errno would be set to the proper value (e.g., ENOMEM).

4.3 Return All Interface Names and Indexes

 The if_nameindex structure holds the information about a single
 interface and is defined as a result of including the <net/if.h>
 header.
    struct if_nameindex {
      unsigned int   if_index;  /* 1, 2, ... */
      char          *if_name;   /* null terminated name: "le0", ... */
    };
 The final function returns an array of if_nameindex structures, one
 structure per interface.
    struct if_nameindex  *if_nameindex(void);
 The end of the array of structures is indicated by a structure with
 an if_index of 0 and an if_name of NULL.  The function returns a NULL
 pointer upon an error, and would set errno to the appropriate value.
 The memory used for this array of structures along with the interface
 names pointed to by the if_name members is obtained dynamically.
 This memory is freed by the next function.

Gilligan, et. al. Informational [Page 17] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

4.4 Free Memory

 The following function frees the dynamic memory that was allocated by
 if_nameindex().
    #include <net/if.h>
    void  if_freenameindex(struct if_nameindex *ptr);
 The argument to this function must be a pointer that was returned by
 if_nameindex().
 Currently net/if.h doesn't have prototype definitions for functions
 and it is recommended that these definitions be defined in net/if.h
 as well and the struct if_nameindex{}.

5. Socket Options

 A number of new socket options are defined for IPv6.  All of these
 new options are at the IPPROTO_IPV6 level.  That is, the "level"
 parameter in the getsockopt() and setsockopt() calls is IPPROTO_IPV6
 when using these options.  The constant name prefix IPV6_ is used in
 all of the new socket options.  This serves to clearly identify these
 options as applying to IPv6.
 The declaration for IPPROTO_IPV6, the new IPv6 socket options, and
 related constants defined in this section are obtained by including
 the header <netinet/in.h>.

5.1 Unicast Hop Limit

 A new setsockopt() option controls the hop limit used in outgoing
 unicast IPv6 packets.  The name of this option is IPV6_UNICAST_HOPS,
 and it is used at the IPPROTO_IPV6 layer.  The following example
 illustrates how it is used:
    int  hoplimit = 10;
    if (setsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS,
                   (char *) &hoplimit, sizeof(hoplimit)) == -1)
        perror("setsockopt IPV6_UNICAST_HOPS");
 When the IPV6_UNICAST_HOPS option is set with setsockopt(), the
 option value given is used as the hop limit for all subsequent
 unicast packets sent via that socket.  If the option is not set, the
 system selects a default value.  The integer hop limit value (called
 x) is interpreted as follows:

Gilligan, et. al. Informational [Page 18] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

    x < -1:        return an error of EINVAL
    x == -1:       use kernel default
    0 <= x <= 255: use x
    x >= 256:      return an error of EINVAL
 The IPV6_UNICAST_HOPS option may be used with getsockopt() to
 determine the hop limit value that the system will use for subsequent
 unicast packets sent via that socket.  For example:
    int  hoplimit;
    size_t  len = sizeof(hoplimit);
    if (getsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS,
                   (char *) &hoplimit, &len) == -1)
        perror("getsockopt IPV6_UNICAST_HOPS");
    else
        printf("Using %d for hop limit.\n", hoplimit);

5.2 Sending and Receiving Multicast Packets

 IPv6 applications may send UDP multicast packets by simply specifying
 an IPv6 multicast address in the address argument of the sendto()
 function.
 Three socket options at the IPPROTO_IPV6 layer control some of the
 parameters for sending multicast packets.  Setting these options is
 not required: applications may send multicast packets without using
 these options.  The setsockopt() options for controlling the sending
 of multicast packets are summarized below.  These three options can
 also be used with getsockopt().
    IPV6_MULTICAST_IF
       Set the interface to use for outgoing multicast packets.  The
       argument is the index of the interface to use.
       Argument type: unsigned int
    IPV6_MULTICAST_HOPS
       Set the hop limit to use for outgoing multicast packets.  (Note
       a separate option - IPV6_UNICAST_HOPS - is provided to set the
       hop limit to use for outgoing unicast packets.)
       The interpretation of the argument is the same as for the
       IPV6_UNICAST_HOPS option:

Gilligan, et. al. Informational [Page 19] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

         x < -1:        return an error of EINVAL
         x == -1:       use kernel default
         0 <= x <= 255: use x
         x >= 256:      return an error of EINVAL
         If IPV6_MULTICAST_HOPS is not set, the default is 1
         (same as IPv4 today)
       Argument type: int
    IPV6_MULTICAST_LOOP
       If a multicast datagram is sent to a group to which the sending
       host itself belongs (on the outgoing interface), a copy of the
       datagram is looped back by the IP layer for local delivery if
       this option is set to 1.  If this option is set to 0 a copy
       is not looped back.  Other option values return an error of
       EINVAL.
       If IPV6_MULTICAST_LOOP is not set, the default is 1 (loopback;
       same as IPv4 today).
       Argument type: unsigned int
 The reception of multicast packets is controlled by the two
 setsockopt() options summarized below.  An error of EOPNOTSUPP is
 returned if these two options are used with getsockopt().
    IPV6_JOIN_GROUP
       Join a multicast group on a specified local interface.  If the
       interface index is specified as 0, the kernel chooses the local
       interface.  For example, some kernels look up the multicast
       group in the normal IPv6 routing table and using the resulting
       interface.
       Argument type: struct ipv6_mreq
    IPV6_LEAVE_GROUP
       Leave a multicast group on a specified interface.
       Argument type: struct ipv6_mreq
 The argument type of both of these options is the ipv6_mreq structure,
 defined as a result of including the <netinet/in.h> header;

Gilligan, et. al. Informational [Page 20] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 struct ipv6_mreq {
     struct in6_addr ipv6mr_multiaddr; /* IPv6 multicast addr */
     unsigned int    ipv6mr_interface; /* interface index */
 };
 Note that to receive multicast datagrams a process must join the
 multicast group and bind the UDP port to which datagrams will be
 sent.  Some processes also bind the multicast group address to the
 socket, in addition to the port, to prevent other datagrams destined
 to that same port from being delivered to the socket.

6. Library Functions

 New library functions are needed to perform a variety of operations
 with IPv6 addresses.  Functions are needed to lookup IPv6 addresses
 in the Domain Name System (DNS).  Both forward lookup (nodename-to-
 address translation) and reverse lookup (address-to-nodename
 translation) need to be supported.  Functions are also needed to
 convert IPv6 addresses between their binary and textual form.
 We note that the two existing functions, gethostbyname() and
 gethostbyaddr(), are left as-is.  New functions are defined to handle
 both IPv4 and IPv6 addresses.

6.1 Nodename-to-Address Translation

 The commonly used function gethostbyname() is inadequate for many
 applications, first because it provides no way for the caller to
 specify anything about the types of addresses desired (IPv4 only,
 IPv6 only, IPv4-mapped IPv6 are OK, etc.), and second because many
 implementations of this function are not thread safe.  RFC 2133
 defined a function named gethostbyname2() but this function was also
 inadequate, first because its use required setting a global option
 (RES_USE_INET6) when IPv6 addresses were required, and second because
 a flag argument is needed to provide the caller with additional
 control over the types of addresses required.
 The following function is new and must be thread safe:
 #include <sys/socket.h>
 #include <netdb.h>
 struct hostent *getipnodebyname(const char *name, int af, int flags
                                     int *error_num);
 The name argument can be either a node name or a numeric address
 string (i.e., a dotted-decimal IPv4 address or an IPv6 hex address).
 The af argument specifies the address family, either AF_INET or

Gilligan, et. al. Informational [Page 21] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 AF_INET6. The error_num value is returned to the caller, via a
 pointer, with the appropriate error code in error_num, to support
 thread safe error code returns.  error_num will be set to one of the
 following values:
    HOST_NOT_FOUND
       No such host is known.
    NO_ADDRESS
       The server recognised the request and the name but no address is
       available.  Another type of request to the name server for the
       domain might return an answer.
    NO_RECOVERY
       An unexpected server failure occurred which cannot be recovered.
    TRY_AGAIN
       A temporary and possibly transient error occurred, such as a
       failure of a server to respond.
 The flags argument specifies the types of addresses that are searched
 for, and the types of addresses that are returned.  We note that a
 special flags value of AI_DEFAULT (defined below) should handle most
 applications.
 That is, porting simple applications to use IPv6 replaces the call
    hptr = gethostbyname(name);
 with
    hptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num);
 and changes any subsequent error diagnosis code to use error_num
 instead of externally declared variables, such as h_errno.
 Applications desiring finer control over the types of addresses
 searched for and returned, can specify other combinations of the
 flags argument.

Gilligan, et. al. Informational [Page 22] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 A flags of 0 implies a strict interpretation of the af argument:
  1. If flags is 0 and af is AF_INET, then the caller wants only

IPv4 addresses. A query is made for A records. If successful,

      the IPv4 addresses are returned and the h_length member of the
      hostent structure will be 4, else the function returns a NULL
      pointer.
  1. If flags is 0 and if af is AF_INET6, then the caller wants only

IPv6 addresses. A query is made for AAAA records. If

      successful, the IPv6 addresses are returned and the h_length
      member of the hostent structure will be 16, else the function
      returns a NULL pointer.
 Other constants can be logically-ORed into the flags argument, to
 modify the behavior of the function.
  1. If the AI_V4MAPPED flag is specified along with an af of

AF_INET6, then the caller will accept IPv4-mapped IPv6

      addresses.  That is, if no AAAA records are found then a query
      is made for A records and any found are returned as IPv4-mapped
      IPv6 addresses (h_length will be 16).  The AI_V4MAPPED flag is
      ignored unless af equals AF_INET6.
  1. The AI_ALL flag is used in conjunction with the AI_V4MAPPED

flag, and is only used with the IPv6 address family. When AI_ALL

      is logically or'd with AI_V4MAPPED flag then the caller wants
      all addresses: IPv6 and IPv4-mapped IPv6.  A query is first made
      for AAAA records and if successful, the IPv6 addresses are
      returned. Another query is then made for A records and any found
      are returned as IPv4-mapped IPv6 addresses. h_length will be 16.
      Only if both queries fail does the function return a NULL pointer.
      This flag is ignored unless af equals AF_INET6.
  1. The AI_ADDRCONFIG flag specifies that a query for AAAA records

should occur only if the node has at least one IPv6 source

      address configured and a query for A records should occur only
      if the node has at least one IPv4 source address configured.
      For example, if the node has no IPv6 source addresses
      configured, and af equals AF_INET6, and the node name being
      looked up has both AAAA and A records, then:
          (a) if only AI_ADDRCONFIG is specified, the function
              returns a NULL pointer;
          (b) if AI_ADDRCONFIG | AI_V4MAPPED is specified, the A
              records are returned as IPv4-mapped IPv6 addresses;

Gilligan, et. al. Informational [Page 23] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 The special flags value of AI_DEFAULT is defined as
    #define  AI_DEFAULT  (AI_V4MAPPED | AI_ADDRCONFIG)
 We noted that the getipnodebyname() function must allow the name
 argument to be either a node name or a literal address string (i.e.,
 a dotted-decimal IPv4 address or an IPv6 hex address).  This saves
 applications from having to call inet_pton() to handle literal
 address strings.
 There are four scenarios based on the type of literal address string
 and the value of the af argument.
 The two simple cases are:
 When name is a dotted-decimal IPv4 address and af equals AF_INET, or
 when name is an IPv6 hex address and af equals AF_INET6.  The members
 of the returned hostent structure are: h_name points to a copy of the
 name argument, h_aliases is a NULL pointer, h_addrtype is a copy of
 the af argument, h_length is either 4 (for AF_INET) or 16 (for
 AF_INET6), h_addr_list[0] is a pointer to the 4-byte or 16-byte
 binary address, and h_addr_list[1] is a NULL pointer.
 When name is a dotted-decimal IPv4 address and af equals AF_INET6,
 and flags equals AI_V4MAPPED, an IPv4-mapped IPv6 address is
 returned:  h_name points to an IPv6 hex address containing the IPv4-
 mapped IPv6 address, h_aliases is a NULL pointer, h_addrtype is
 AF_INET6, h_length is 16, h_addr_list[0] is a pointer to the 16-byte
 binary address, and h_addr_list[1] is a NULL pointer.  If AI_V4MAPPED
 is set (with or without AI_ALL) return IPv4-mapped otherwise return
 NULL.
 It is an error when name is an IPv6 hex address and af equals
 AF_INET.  The function's return value is a NULL pointer and error_num
 equals HOST_NOT_FOUND.

6.2 Address-To-Nodename Translation

 The following function has the same arguments as the existing
 gethostbyaddr() function, but adds an error number.
    #include <sys/socket.h> #include <netdb.h>
    struct hostent *getipnodebyaddr(const void *src, size_t len,
                                        int af, int *error_num);

Gilligan, et. al. Informational [Page 24] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 As with getipnodebyname(), getipnodebyaddr() must be thread safe.
 The error_num value is returned to the caller with the appropriate
 error code, to support thread safe error code returns.  The following
 error conditions may be returned for error_num:
    HOST_NOT_FOUND
       No such host is known.
    NO_ADDRESS
       The server recognized the request and the name but no address
       is available.  Another type of request to the name server for
       the domain might return an answer.
    NO_RECOVERY
       An unexpected server failure occurred which cannot be
       recovered.
    TRY_AGAIN
       A temporary and possibly transient error occurred, such as a
       failure of a server to respond.
 One possible source of confusion is the handling of IPv4-mapped IPv6
 addresses and IPv4-compatible IPv6 addresses, but the following logic
 should apply.
    1.  If af is AF_INET6, and if len equals 16, and if the IPv6
        address is an IPv4-mapped IPv6 address or an IPv4-compatible
        IPv6 address, then skip over the first 12 bytes of the IPv6
        address, set af to AF_INET, and set len to 4.
    2.  If af is AF_INET, lookup the name for the given IPv4 address
        (e.g., query for a PTR record in the in-addr.arpa domain).
    3.  If af is AF_INET6, lookup the name for the given IPv6 address
        (e.g., query for a PTR record in the ip6.int domain).
    4.  If the function is returning success, then the single address
        that is returned in the hostent structure is a copy of the
        first argument to the function with the same address family
        that was passed as an argument to this function.

Gilligan, et. al. Informational [Page 25] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 All four steps listed are performed, in order.  Also note that the
 IPv6 hex addresses "::" and "::1" MUST NOT be treated as IPv4-
 compatible addresses, and if the address is "::", HOST_NOT_FOUND MUST
 be returned and a query of the address not performed.
 Also for the macro in section 6.7 IN6_IS_ADDR_V4COMPAT MUST return
 false for "::" and "::1".

6.3 Freeing memory for getipnodebyname and getipnodebyaddr

 The hostent structure does not change from its existing definition.
 This structure, and the information pointed to by this structure, are
 dynamically allocated by getipnodebyname and getipnodebyaddr.  The
 following function frees this memory:
    #include <netdb.h>
    void freehostent(struct hostent *ptr);

6.4 Protocol-Independent Nodename and Service Name Translation

 Nodename-to-address translation is done in a protocol-independent
 fashion using the getaddrinfo() function that is taken from the
 Institute of Electrical and Electronic Engineers (IEEE) POSIX 1003.1g
 (Protocol Independent Interfaces) draft specification [3].
 The official specification for this function will be the final POSIX
 standard, with the following additional requirements:
  1. getaddrinfo() (along with the getnameinfo() function described

in the next section) must be thread safe.

  1. The AI_NUMERICHOST is new with this document.
  1. All fields in socket address structures returned by

getaddrinfo() that are not filled in through an explicit

       argument (e.g., sin6_flowinfo and sin_zero) must be set to 0.
       (This makes it easier to compare socket address structures.)
  1. getaddrinfo() must fill in the length field of a socket address

structure (e.g., sin6_len) on systems that support this field.

 We are providing this independent description of the function because
 POSIX standards are not freely available (as are IETF documents).
    #include <sys/socket.h>
    #include <netdb.h>

Gilligan, et. al. Informational [Page 26] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

    int getaddrinfo(const char *nodename, const char *servname,
                    const struct addrinfo *hints,
                    struct addrinfo **res);
 The addrinfo structure is defined as a result of including the
 <netdb.h> header.
struct addrinfo {
  int     ai_flags;     /* AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST */
  int     ai_family;    /* PF_xxx */
  int     ai_socktype;  /* SOCK_xxx */
  int     ai_protocol;  /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
  size_t  ai_addrlen;   /* length of ai_addr */
  char   *ai_canonname; /* canonical name for nodename */
  struct sockaddr  *ai_addr; /* binary address */
  struct addrinfo  *ai_next; /* next structure in linked list */
};
 The return value from the function is 0 upon success or a nonzero
 error code.  The following names are the nonzero error codes from
 getaddrinfo(), and are defined in <netdb.h>:
    EAI_ADDRFAMILY  address family for nodename not supported
    EAI_AGAIN       temporary failure in name resolution
    EAI_BADFLAGS    invalid value for ai_flags
    EAI_FAIL        non-recoverable failure in name resolution
    EAI_FAMILY      ai_family not supported
    EAI_MEMORY      memory allocation failure
    EAI_NODATA      no address associated with nodename
    EAI_NONAME      nodename nor servname provided, or not known
    EAI_SERVICE     servname not supported for ai_socktype
    EAI_SOCKTYPE    ai_socktype not supported
    EAI_SYSTEM      system error returned in errno
 The nodename and servname arguments are pointers to null-terminated
 strings or NULL.  One or both of these two arguments must be a non-
 NULL pointer.  In the normal client scenario, both the nodename and
 servname are specified.  In the normal server scenario, only the
 servname is specified.  A non-NULL nodename string can be either a
 node name or a numeric host address string (i.e., a dotted-decimal
 IPv4 address or an IPv6 hex address).  A non-NULL servname string can
 be either a service name or a decimal port number.
 The caller can optionally pass an addrinfo structure, pointed to by
 the third argument, to provide hints concerning the type of socket
 that the caller supports.  In this hints structure all members other
 than ai_flags, ai_family, ai_socktype, and ai_protocol must be zero
 or a NULL pointer.  A value of PF_UNSPEC for ai_family means the

Gilligan, et. al. Informational [Page 27] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 caller will accept any protocol family.  A value of 0 for ai_socktype
 means the caller will accept any socket type.  A value of 0 for
 ai_protocol means the caller will accept any protocol.  For example,
 if the caller handles only TCP and not UDP, then the ai_socktype
 member of the hints structure should be set to SOCK_STREAM when
 getaddrinfo() is called.  If the caller handles only IPv4 and not
 IPv6, then the ai_family member of the hints structure should be set
 to PF_INET when getaddrinfo() is called.  If the third argument to
 getaddrinfo() is a NULL pointer, this is the same as if the caller
 had filled in an addrinfo structure initialized to zero with
 ai_family set to PF_UNSPEC.
 Upon successful return a pointer to a linked list of one or more
 addrinfo structures is returned through the final argument.  The
 caller can process each addrinfo structure in this list by following
 the ai_next pointer, until a NULL pointer is encountered.  In each
 returned addrinfo structure the three members ai_family, ai_socktype,
 and ai_protocol are the corresponding arguments for a call to the
 socket() function.  In each addrinfo structure the ai_addr member
 points to a filled-in socket address structure whose length is
 specified by the ai_addrlen member.
 If the AI_PASSIVE bit is set in the ai_flags member of the hints
 structure, then the caller plans to use the returned socket address
 structure in a call to bind().  In this case, if the nodename
 argument is a NULL pointer, then the IP address portion of the socket
 address structure will be set to INADDR_ANY for an IPv4 address or
 IN6ADDR_ANY_INIT for an IPv6 address.
 If the AI_PASSIVE bit is not set in the ai_flags member of the hints
 structure, then the returned socket address structure will be ready
 for a call to connect() (for a connection-oriented protocol) or
 either connect(), sendto(), or sendmsg() (for a connectionless
 protocol).  In this case, if the nodename argument is a NULL pointer,
 then the IP address portion of the socket address structure will be
 set to the loopback address.
 If the AI_CANONNAME bit is set in the ai_flags member of the hints
 structure, then upon successful return the ai_canonname member of the
 first addrinfo structure in the linked list will point to a null-
 terminated string containing the canonical name of the specified
 nodename.
 If the AI_NUMERICHOST bit is set in the ai_flags member of the hints
 structure, then a non-NULL nodename string must be a numeric host
 address string.  Otherwise an error of EAI_NONAME is returned.  This
 flag prevents any type of name resolution service (e.g., the DNS)
 from being called.

Gilligan, et. al. Informational [Page 28] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 All of the information returned by getaddrinfo() is dynamically
 allocated: the addrinfo structures, and the socket address structures
 and canonical node name strings pointed to by the addrinfo
 structures.  To return this information to the system the function
 freeaddrinfo() is called:
    #include <sys/socket.h> #include <netdb.h>
    void freeaddrinfo(struct addrinfo *ai);
 The addrinfo structure pointed to by the ai argument is freed, along
 with any dynamic storage pointed to by the structure.  This operation
 is repeated until a NULL ai_next pointer is encountered.
 To aid applications in printing error messages based on the EAI_xxx
 codes returned by getaddrinfo(), the following function is defined.
    #include <sys/socket.h> #include <netdb.h>
    char *gai_strerror(int ecode);
 The argument is one of the EAI_xxx values defined earlier and the
 return value points to a string describing the error.  If the
 argument is not one of the EAI_xxx values, the function still returns
 a pointer to a string whose contents indicate an unknown error.

6.5 Socket Address Structure to Nodename and Service Name

 The POSIX 1003.1g specification includes no function to perform the
 reverse conversion from getaddrinfo(): to look up a nodename and
 service name, given the binary address and port.  Therefore, we
 define the following function:
    #include <sys/socket.h>
    #include <netdb.h>
    int getnameinfo(const struct sockaddr *sa, socklen_t salen,
                    char *host, size_t hostlen,
                    char *serv, size_t servlen,
                    int flags);
 This function looks up an IP address and port number provided by the
 caller in the DNS and system-specific database, and returns text
 strings for both in buffers provided by the caller.  The function
 indicates successful completion by a zero return value; a non-zero
 return value indicates failure.

Gilligan, et. al. Informational [Page 29] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 The first argument, sa, points to either a sockaddr_in structure (for
 IPv4) or a sockaddr_in6 structure (for IPv6) that holds the IP
 address and port number.  The salen argument gives the length of the
 sockaddr_in or sockaddr_in6 structure.
 The function returns the nodename associated with the IP address in
 the buffer pointed to by the host argument.  The caller provides the
 size of this buffer via the hostlen argument.  The service name
 associated with the port number is returned in the buffer pointed to
 by serv, and the servlen argument gives the length of this buffer.
 The caller specifies not to return either string by providing a zero
 value for the hostlen or servlen arguments.  Otherwise, the caller
 must provide buffers large enough to hold the nodename and the
 service name, including the terminating null characters.
 Unfortunately most systems do not provide constants that specify the
 maximum size of either a fully-qualified domain name or a service
 name.  Therefore to aid the application in allocating buffers for
 these two returned strings the following constants are defined in
 <netdb.h>:
    #define NI_MAXHOST  1025
    #define NI_MAXSERV    32
 The first value is actually defined as the constant MAXDNAME in recent
 versions of BIND's <arpa/nameser.h> header (older versions of BIND
 define this constant to be 256) and the second is a guess based on the
 services listed in the current Assigned Numbers RFC.
 The final argument is a flag that changes the default actions of this
 function.  By default the fully-qualified domain name (FQDN) for the
 host is looked up in the DNS and returned.  If the flag bit NI_NOFQDN
 is set, only the nodename portion of the FQDN is returned for local
 hosts.
 If the flag bit NI_NUMERICHOST is set, or if the host's name cannot be
 located in the DNS, the numeric form of the host's address is returned
 instead of its name (e.g., by calling inet_ntop() instead of
 getipnodebyaddr()).  If the flag bit NI_NAMEREQD is set, an error is
 returned if the host's name cannot be located in the DNS.
 If the flag bit NI_NUMERICSERV is set, the numeric form of the service
 address is returned (e.g., its port number) instead of its name.  The
 two NI_NUMERICxxx flags are required to support the "-n" flag that
 many commands provide.

Gilligan, et. al. Informational [Page 30] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 A fifth flag bit, NI_DGRAM, specifies that the service is a datagram
 service, and causes getservbyport() to be called with a second
 argument of "udp" instead of its default of "tcp".  This is required
 for the few ports (e.g. 512-514) that have different services for UDP
 and TCP.
 These NI_xxx flags are defined in <netdb.h> along with the AI_xxx
 flags already defined for getaddrinfo().

6.6 Address Conversion Functions

 The two functions inet_addr() and inet_ntoa() convert an IPv4 address
 between binary and text form.  IPv6 applications need similar
 functions.  The following two functions convert both IPv6 and IPv4
 addresses:
    #include <sys/socket.h>
    #include <arpa/inet.h>
    int inet_pton(int af, const char *src, void *dst);
    const char *inet_ntop(int af, const void *src,
                          char *dst, size_t size);
 The inet_pton() function converts an address in its standard text
 presentation form into its numeric binary form.  The af argument
 specifies the family of the address.  Currently the AF_INET and
 AF_INET6 address families are supported.  The src argument points to
 the string being passed in.  The dst argument points to a buffer into
 which the function stores the numeric address.  The address is
 returned in network byte order.  Inet_pton() returns 1 if the
 conversion succeeds, 0 if the input is not a valid IPv4 dotted-
 decimal string or a valid IPv6 address string, or -1 with errno set
 to EAFNOSUPPORT if the af argument is unknown.  The calling
 application must ensure that the buffer referred to by dst is large
 enough to hold the numeric address (e.g., 4 bytes for AF_INET or 16
 bytes for AF_INET6).
 If the af argument is AF_INET, the function accepts a string in the
 standard IPv4 dotted-decimal form:
    ddd.ddd.ddd.ddd
 where ddd is a one to three digit decimal number between 0 and 255.
 Note that many implementations of the existing inet_addr() and
 inet_aton() functions accept nonstandard input: octal numbers,
 hexadecimal numbers, and fewer than four numbers.  inet_pton() does
 not accept these formats.

Gilligan, et. al. Informational [Page 31] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 If the af argument is AF_INET6, then the function accepts a string in
 one of the standard IPv6 text forms defined in Section 2.2 of the
 addressing architecture specification [2].
 The inet_ntop() function converts a numeric address into a text
 string suitable for presentation.  The af argument specifies the
 family of the address.  This can be AF_INET or AF_INET6.  The src
 argument points to a buffer holding an IPv4 address if the af
 argument is AF_INET, or an IPv6 address if the af argument is
 AF_INET6, the address must be in network byte order.  The dst
 argument points to a buffer where the function will store the
 resulting text string.  The size argument specifies the size of this
 buffer.  The application must specify a non-NULL dst argument.  For
 IPv6 addresses, the buffer must be at least 46-octets.  For IPv4
 addresses, the buffer must be at least 16-octets.  In order to allow
 applications to easily declare buffers of the proper size to store
 IPv4 and IPv6 addresses in string form, the following two constants
 are defined in <netinet/in.h>:
    #define INET_ADDRSTRLEN    16
    #define INET6_ADDRSTRLEN   46
 The inet_ntop() function returns a pointer to the buffer containing
 the text string if the conversion succeeds, and NULL otherwise.  Upon
 failure, errno is set to EAFNOSUPPORT if the af argument is invalid or
 ENOSPC if the size of the result buffer is inadequate.

6.7 Address Testing Macros

 The following macros can be used to test for special IPv6 addresses.
    #include <netinet/in.h>
    int  IN6_IS_ADDR_UNSPECIFIED (const struct in6_addr *);
    int  IN6_IS_ADDR_LOOPBACK    (const struct in6_addr *);
    int  IN6_IS_ADDR_MULTICAST   (const struct in6_addr *);
    int  IN6_IS_ADDR_LINKLOCAL   (const struct in6_addr *);
    int  IN6_IS_ADDR_SITELOCAL   (const struct in6_addr *);
    int  IN6_IS_ADDR_V4MAPPED    (const struct in6_addr *);
    int  IN6_IS_ADDR_V4COMPAT    (const struct in6_addr *);
    int  IN6_IS_ADDR_MC_NODELOCAL(const struct in6_addr *);
    int  IN6_IS_ADDR_MC_LINKLOCAL(const struct in6_addr *);
    int  IN6_IS_ADDR_MC_SITELOCAL(const struct in6_addr *);
    int  IN6_IS_ADDR_MC_ORGLOCAL (const struct in6_addr *);
    int  IN6_IS_ADDR_MC_GLOBAL   (const struct in6_addr *);

Gilligan, et. al. Informational [Page 32] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 The first seven macros return true if the address is of the specified
 type, or false otherwise.  The last five test the scope of a
 multicast address and return true if the address is a multicast
 address of the specified scope or false if the address is either not
 a multicast address or not of the specified scope.  Note that
 IN6_IS_ADDR_LINKLOCAL and IN6_IS_ADDR_SITELOCAL return true only for
 the two local-use IPv6 unicast addresses.  These two macros do not
 return true for IPv6 multicast addresses of either link-local scope
 or site-local scope.

7. Summary of New Definitions

 The following list summarizes the constants, structure, and extern
 definitions discussed in this memo, sorted by header.
    <net/if.h>      IF_NAMESIZE
    <net/if.h>      struct if_nameindex{};
    <netdb.h>       AI_ADDRCONFIG
    <netdb.h>       AI_DEFAULT
    <netdb.h>       AI_ALL
    <netdb.h>       AI_CANONNAME
    <netdb.h>       AI_NUMERICHOST
    <netdb.h>       AI_PASSIVE
    <netdb.h>       AI_V4MAPPED
    <netdb.h>       EAI_ADDRFAMILY
    <netdb.h>       EAI_AGAIN
    <netdb.h>       EAI_BADFLAGS
    <netdb.h>       EAI_FAIL
    <netdb.h>       EAI_FAMILY
    <netdb.h>       EAI_MEMORY
    <netdb.h>       EAI_NODATA
    <netdb.h>       EAI_NONAME
    <netdb.h>       EAI_SERVICE
    <netdb.h>       EAI_SOCKTYPE
    <netdb.h>       EAI_SYSTEM
    <netdb.h>       NI_DGRAM
    <netdb.h>       NI_MAXHOST
    <netdb.h>       NI_MAXSERV
    <netdb.h>       NI_NAMEREQD
    <netdb.h>       NI_NOFQDN
    <netdb.h>       NI_NUMERICHOST
    <netdb.h>       NI_NUMERICSERV
    <netdb.h>       struct addrinfo{};
    <netinet/in.h>  IN6ADDR_ANY_INIT
    <netinet/in.h>  IN6ADDR_LOOPBACK_INIT
    <netinet/in.h>  INET6_ADDRSTRLEN

Gilligan, et. al. Informational [Page 33] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

    <netinet/in.h>  INET_ADDRSTRLEN
    <netinet/in.h>  IPPROTO_IPV6
    <netinet/in.h>  IPV6_JOIN_GROUP
    <netinet/in.h>  IPV6_LEAVE_GROUP
    <netinet/in.h>  IPV6_MULTICAST_HOPS
    <netinet/in.h>  IPV6_MULTICAST_IF
    <netinet/in.h>  IPV6_MULTICAST_LOOP
    <netinet/in.h>  IPV6_UNICAST_HOPS
    <netinet/in.h>  SIN6_LEN
    <netinet/in.h>  extern const struct in6_addr in6addr_any;
    <netinet/in.h>  extern const struct in6_addr in6addr_loopback;
    <netinet/in.h>  struct in6_addr{};
    <netinet/in.h>  struct ipv6_mreq{};
    <netinet/in.h>  struct sockaddr_in6{};
    <sys/socket.h>  AF_INET6
    <sys/socket.h>  PF_INET6
    <sys/socket.h>  struct sockaddr_storage;
 The following list summarizes the function and macro prototypes
 discussed in this memo, sorted by header.

<arpa/inet.h> int inet_pton(int, const char *, void *); <arpa/inet.h> const char *inet_ntop(int, const void *,

                                    char *, size_t);

<net/if.h> char *if_indextoname(unsigned int, char *); <net/if.h> unsigned int if_nametoindex(const char *); <net/if.h> void if_freenameindex(struct if_nameindex *); <net/if.h> struct if_nameindex *if_nameindex(void);

<netdb.h> int getaddrinfo(const char *, const char *,

                              const struct addrinfo *,
                              struct addrinfo **);

<netdb.h> int getnameinfo(const struct sockaddr *, socklen_t,

                              char *, size_t, char *, size_t, int);

<netdb.h> void freeaddrinfo(struct addrinfo *); <netdb.h> char *gai_strerror(int); <netdb.h> struct hostent *getipnodebyname(const char *, int, int,

                                     int *);

<netdb.h> struct hostent *getipnodebyaddr(const void *, size_t,

                                     int, int *);

<netdb.h> void freehostent(struct hostent *);

<netinet/in.h> int IN6_IS_ADDR_LINKLOCAL(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_LOOPBACK(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_MC_GLOBAL(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_MC_LINKLOCAL(const struct in6_addr *);

Gilligan, et. al. Informational [Page 34] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

<netinet/in.h> int IN6_IS_ADDR_MC_NODELOCAL(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_MC_ORGLOCAL(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_MC_SITELOCAL(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_MULTICAST(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_SITELOCAL(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_UNSPECIFIED(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_V4COMPAT(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_V4MAPPED(const struct in6_addr *);

8. Security Considerations

 IPv6 provides a number of new security mechanisms, many of which need
 to be accessible to applications.  Companion memos detailing the
 extensions to the socket interfaces to support IPv6 security are
 being written.

9. Year 2000 Considerations

 There are no issues for this memo concerning the Year 2000 issue
 regarding the use of dates.

Changes From RFC 2133

 Changes made in the March 1998 Edition (-01 draft):
    Changed all "hostname" to "nodename" for consistency with other
    IPv6 documents.
    Section 3.3: changed comment for sin6_flowinfo to be "traffic
    class & flow info" and updated corresponding text description to
    current definition of these two fields.
    Section 3.10 ("Portability Additions") is new.
    Section 6: a new paragraph was added reiterating that the existing
    gethostbyname() and gethostbyaddr() are not changed.
    Section 6.1: change gethostbyname3() to getnodebyname().  Add
    AI_DEFAULT to handle majority of applications.  Renamed
    AI_V6ADDRCONFIG to AI_ADDRCONFIG and define it for A records and
    IPv4 addresses too.  Defined exactly what getnodebyname() must
    return if the name argument is a numeric address string.
    Section 6.2: change gethostbyaddr() to getnodebyaddr().  Reword
    items 2 and 3 in the description of how to handle IPv4-mapped and
    IPv4- compatible addresses to "lookup a name" for a given address,
    instead of specifying what type of DNS query to issue.

Gilligan, et. al. Informational [Page 35] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

    Section 6.3: added two more requirements to getaddrinfo().
    Section 7: added the following constants to the list for
    <netdb.h>:  AI_ADDRCONFIG, AI_ALL, and AI_V4MAPPED.  Add union
    sockaddr_union and SA_LEN to the lists for <sys/socket.h>.
    Updated references.
 Changes made in the November 1997 Edition (-00 draft):
    The data types have been changed to conform with Draft 6.6 of the
    Posix 1003.1g standard.
    Section 3.2: data type of s6_addr changed to "uint8_t".
    Section 3.3: data type of sin6_family changed to "sa_family_t".
    data type of sin6_port changed to "in_port_t", data type of
    sin6_flowinfo changed to "uint32_t".
    Section 3.4: same as Section 3.3, plus data type of sin6_len
    changed to "uint8_t".
    Section 6.2: first argument of gethostbyaddr() changed from "const
    char *" to "const void *" and second argument changed from "int"
    to "size_t".
    Section 6.4: second argument of getnameinfo() changed from
    "size_t" to "socklen_t".
    The wording was changed when new structures were defined, to be
    more explicit as to which header must be included to define the
    structure:
    Section 3.2 (in6_addr{}), Section 3.3 (sockaddr_in6{}), Section
    3.4 (sockaddr_in6{}), Section 4.3 (if_nameindex{}), Section 5.3
    (ipv6_mreq{}), and Section 6.3 (addrinfo{}).
    Section 4: NET_RT_LIST changed to NET_RT_IFLIST.
    Section 5.1: The IPV6_ADDRFORM socket option was removed.
    Section 5.3: Added a note that an option value other than 0 or 1
    for IPV6_MULTICAST_LOOP returns an error.  Added a note that
    IPV6_MULTICAST_IF, IPV6_MULTICAST_HOPS, and IPV6_MULTICAST_LOOP
    can also be used with getsockopt(), but IPV6_ADD_MEMBERSHIP and
    IPV6_DROP_MEMBERSHIP cannot be used with getsockopt().

Gilligan, et. al. Informational [Page 36] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

    Section 6.1: Removed the description of gethostbyname2() and its
    associated RES_USE_INET6 option, replacing it with
    gethostbyname3().
    Section 6.2: Added requirement that gethostbyaddr() be thread
    safe.  Reworded step 4 to avoid using the RES_USE_INET6 option.
    Section 6.3: Added the requirement that getaddrinfo() and
    getnameinfo() be thread safe.  Added the AI_NUMERICHOST flag.
    Section 6.6: Added clarification about IN6_IS_ADDR_LINKLOCAL and
    IN6_IS_ADDR_SITELOCAL macros.
 Changes made to the draft -01 specification Sept 98
    Changed priority to traffic class in the spec.
    Added the need for scope identification in section 2.1.
    Added sin6_scope_id to struct sockaddr_in6 in sections 3.3 and
    3.4.
    Changed 3.10 to use generic storage structure to support holding
    IPv6 addresses and removed the SA_LEN macro.
    Distinguished between invalid input parameters and system failures
    for Interface Identification in Section 4.1 and 4.2.
    Added defaults for multicast operations in section 5.2 and changed
    the names from ADD to JOIN and DROP to LEAVE to be consistent with
    IPv6 multicast terminology.
    Changed getnodebyname to getipnodebyname, getnodebyaddr to
    getipnodebyaddr, and added MT safe error code to function
    parameters in section 6.
    Moved freehostent to its own sub-section after getipnodebyaddr now
    6.3 (so this bumps all remaining sections in section 6.
    Clarified the use of AI_ALL and AI_V4MAPPED that these are
    dependent on the AF parameter and must be used as a conjunction in
    section 6.1.
    Removed the restriction that literal addresses cannot be used with
    a flags argument in section 6.1.
    Added Year 2000 Section to the draft

Gilligan, et. al. Informational [Page 37] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

    Deleted Reference to the following because the attached is deleted
    from the ID directory and has expired.  But the logic from the
    aforementioned draft still applies, so that was kept in Section
    6.2 bullets after 3rd paragraph.
    [7]  P. Vixie, "Reverse Name Lookups of Encapsulated IPv4
         Addresses in IPv6", Internet-Draft, <draft-vixie-ipng-
         ipv4ptr-00.txt>, May 1996.
    Deleted the following reference as it is no longer referenced.
    And the draft has expired.
    [3]  D. McDonald, "A Simple IP Security API Extension to BSD
         Sockets", Internet-Draft, <draft-mcdonald-simple-ipsec-api-
         01.txt>, March 1997.
    Deleted the following reference as it is no longer referenced.
    [4]  C. Metz, "Network Security API for Sockets",
         Internet-Draft, <draft-metz-net-security-api-01.txt>, January
         1998.
    Update current references to current status.
    Added alignment notes for in6_addr and sin6_addr.
    Clarified further that AI_V4MAPPED must be used with a dotted IPv4
    literal address for getipnodebyname(), when address family is
    AF_INET6.
    Added text to clarify "::" and "::1" when used by
    getipnodebyaddr().

Acknowledgments

 Thanks to the many people who made suggestions and provided feedback
 to this document, including: Werner Almesberger, Ran Atkinson, Fred
 Baker, Dave Borman, Andrew Cherenson, Alex Conta, Alan Cox, Steve
 Deering, Richard Draves, Francis Dupont, Robert Elz, Marc Hasson, Tom
 Herbert, Bob Hinden, Wan-Yen Hsu, Christian Huitema, Koji Imada,
 Markus Jork, Ron Lee, Alan Lloyd, Charles Lynn, Dan McDonald, Dave
 Mitton, Thomas Narten, Josh Osborne, Craig Partridge, Jean-Luc
 Richier, Erik Scoredos, Keith Sklower, Matt Thomas, Harvey Thompson,
 Dean D. Throop, Karen Tracey, Glenn Trewitt, Paul Vixie, David
 Waitzman, Carl Williams, and Kazu Yamamoto,

Gilligan, et. al. Informational [Page 38] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

 The getaddrinfo() and getnameinfo() functions are taken from an
 earlier Internet Draft by Keith Sklower.  As noted in that draft,
 William Durst, Steven Wise, Michael Karels, and Eric Allman provided
 many useful discussions on the subject of protocol-independent name-
 to-address translation, and reviewed early versions of Keith
 Sklower's original proposal.  Eric Allman implemented the first
 prototype of getaddrinfo().  The observation that specifying the pair
 of name and service would suffice for connecting to a service
 independent of protocol details was made by Marshall Rose in a
 proposal to X/Open for a "Uniform Network Interface".
 Craig Metz, Jack McCann, Erik Nordmark, Tim Hartrick, and Mukesh
 Kacker made many contributions to this document.  Ramesh Govindan
 made a number of contributions and co-authored an earlier version of
 this memo.

References

 [1]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
      Specification", RFC 2460, December 1998.
 [2]  Hinden, R. and S. Deering, "IP Version 6 Addressing
      Architecture", RFC 2373, July 1998.
 [3]  IEEE, "Protocol Independent Interfaces", IEEE Std 1003.1g, DRAFT
      6.6, March 1997.
 [4]  Stevens, W. and M. Thomas, "Advanced Sockets API for IPv6", RFC
      2292, February 1998.

Gilligan, et. al. Informational [Page 39] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

Authors' Addresses

 Robert E. Gilligan
 FreeGate Corporation
 1208 E. Arques Ave.
 Sunnyvale, CA 94086
 Phone: +1 408 617 1004
 EMail: gilligan@freegate.com
 Susan Thomson
 Bell Communications Research
 MRE 2P-343, 445 South Street
 Morristown, NJ 07960
 Phone: +1 201 829 4514
 EMail: set@thumper.bellcore.com
 Jim Bound
 Compaq Computer Corporation
 110 Spitbrook Road ZK3-3/U14
 Nashua, NH 03062-2698
 Phone: +1 603 884 0400
 EMail: bound@zk3.dec.com
 W. Richard Stevens
 1202 E. Paseo del Zorro
 Tucson, AZ 85718-2826
 Phone: +1 520 297 9416
 EMail: rstevens@kohala.com

Gilligan, et. al. Informational [Page 40] RFC 2553 Basic Socket Interface Extensions for IPv6 March 1999

Full Copyright Statement

 Copyright (C) The Internet Society (1999).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Gilligan, et. al. Informational [Page 41]

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