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+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.
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                      [Page 1]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                      [Page 2]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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.
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                      [Page 3]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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.
+
+
+
+
+
+
+Gilligan, et al.             Informational                      [Page 4]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   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].
+
+
+
+
+
+Gilligan, et al.             Informational                      [Page 5]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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.
+
+
+
+
+
+
+Gilligan, et al.             Informational                      [Page 6]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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:
+
+   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:
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                      [Page 7]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+struct sockaddr_in6 {
+    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 */
+};
+
+   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.
+
+   The sin6_flowinfo field is a 32-bit field intended to contain flow-
+   related information.  The exact way this field is mapped to or from a
+   packet is not currently specified.  Until such time as its use is
+   specified, applications should set this field to zero when
+   constructing a sockaddr_in6, and ignore this field in a sockaddr_in6
+   structure constructed by the system.
+
+   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 [2] of the address carried in
+   the sin6_addr field.  The mapping of sin6_scope_id to an interface or
+   set of interfaces is left to implementation and future specifications
+   on the subject of scoped addresses.
+
+   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.
+
+
+
+
+Gilligan, et al.             Informational                      [Page 8]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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.
+
+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(AF_INET, SOCK_STREAM, 0);
+
+   To create an IPv4/UDP socket, applications make the call:
+
+      s = socket(AF_INET, SOCK_DGRAM, 0);
+
+
+
+
+
+Gilligan, et al.             Informational                      [Page 9]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   Applications may create IPv6/TCP and IPv6/UDP sockets (which may also
+   handle IPv4 communication as described in section 3.7) by simply
+   using the constant AF_INET6 instead of AF_INET in the first argument.
+   For example, to create an IPv6/TCP socket, applications make the
+   call:
+
+      s = socket(AF_INET6, SOCK_STREAM, 0);
+
+   To create an IPv6/UDP socket, applications make the call:
+
+      s = socket(AF_INET6, SOCK_DGRAM, 0);
+
+   Once the application has created a AF_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 AF_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 AF_INET sockets and the sockaddr_in address
+   structure.  Applications must be able to create IPv4/TCP and IPv4/UDP
+   sockets using the AF_INET constant in the socket() function, as
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 10]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   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
+   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 getaddrinfo()
+   function, as described in Section 6.1.
+
+   Applications may use AF_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 AF_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 6.4, 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.
+
+
+
+
+Gilligan, et al.             Informational                     [Page 11]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   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;
+
+   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.
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 12]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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.
+
+   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.
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 13]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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 that is portable across multiple address
+   families and platforms.  This data structure is designed with the
+   following goals.
+
+   - Large enough to accommodate all supported protocol-specific address
+      structures.
+
+   - Aligned at an appropriate boundary so that pointers to it can be
+      cast as pointers to protocol specific address structures and used
+      to access the fields of those structures without alignment
+      problems.
+
+   The sockaddr_storage structure contains field ss_family which is of
+   type sa_family_t.  When a sockaddr_storage structure is cast to a
+   sockaddr structure, the ss_family field of the sockaddr_storage
+   structure maps onto the sa_family field of the sockaddr structure.
+   When a sockaddr_storage structure is cast as a protocol specific
+   address structure, the ss_family field maps onto a field of that
+   structure that is of type sa_family_t and that identifies the
+   protocol's address family.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 14]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   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 */
+};
+
+   The above example implementation illustrates a data structure which
+   will align on a 64-bit boundary.  An implementation-specific field
+   "__ss_align" along with "__ss_pad1" is used to force a 64-bit
+   alignment which covers proper alignment good enough for the needs of
+   sockaddr_in6 (IPv6), sockaddr_in (IPv4) address data structures.  The
+   size of padding field __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_ALIGNSIZE (with chosen value 8).  Constants
+   _SS_PAD1SIZE (derived value 6) and _SS_PAD2SIZE (derived value 112)
+   are also for illustration and not required.  The derived values
+   assume sa_family_t is 2 bytes.  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.
+
+
+
+
+Gilligan, et al.             Informational                     [Page 15]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   On implementations where the 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 (uint8_t) + sizeof (sa_family_t) +
+                             _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 */
+};
+
+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 5.2).  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
+
+
+
+Gilligan, et al.             Informational                     [Page 16]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   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);
+
+   If ifname is the name of an interface, the if_nametoindex() function
+   shall return the interface index corresponding to name ifname;
+   otherwise, it shall return zero.  No errors are defined.
+
+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);
+
+   When this function is called, the ifname argument shall point to a
+   buffer of at least IF_NAMESIZE bytes.  The function shall place in
+   this buffer the name of the interface with index ifindex.
+   (IF_NAMESIZE is also defined in <net/if.h> and its value includes a
+   terminating null byte at the end of the interface name.)  If ifindex
+   is an interface index, then the function shall return the value
+   supplied in ifname, which points to a buffer now containing the
+   interface name.  Otherwise, the function shall return a NULL pointer
+   and set errno to indicate the error.  If there is no interface
+   corresponding to the specified index, errno is set to ENXIO.  If
+   there was a system error (such as running out of memory), errno would
+   be set to the proper value (e.g., ENOMEM).
+
+
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 17]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+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.
+
+      #include <net/if.h>
+
+      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.
+
+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 ptr argument shall be a pointer that was returned by
+   if_nameindex().  After if_freenameindex() has been called, the
+   application shall not use the array of which ptr is the address.
+
+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.
+
+
+
+
+Gilligan, et al.             Informational                     [Page 18]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   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:
+
+      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;
+      socklen_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 multicast packets by simply specifying an
+   IPv6 multicast address as the destination address, for example in the
+   destination address argument of the sendto() function.
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 19]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   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.  If the
+         interface index is specified as zero, the system selects the
+         interface (for example, by looking up the address in a routing
+         table and using the resulting interface).
+
+         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:
+
+            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.
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 20]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+         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 use the resulting
+         interface.
+
+         Argument type: struct ipv6_mreq
+
+      IPV6_LEAVE_GROUP
+
+         Leave a multicast group on a specified interface.
+         If the interface index is specified as 0, the system
+         may choose a multicast group membership to drop by
+         matching the multicast address only.
+
+         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;
+
+   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 to which datagrams will be sent.  UDP applications
+   must also 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.
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 21]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+5.3 IPV6_V6ONLY option for AF_INET6 Sockets
+
+   This socket option restricts AF_INET6 sockets to IPv6 communications
+   only.  As stated in section <3.7 Compatibility with IPv4 Nodes>,
+   AF_INET6 sockets may be used for both IPv4 and IPv6 communications.
+   Some applications may want to restrict their use of an AF_INET6
+   socket to IPv6 communications only.  For these applications the
+   IPV6_V6ONLY socket option is defined.  When this option is turned on,
+   the socket can be used to send and receive IPv6 packets only.  This
+   is an IPPROTO_IPV6 level option.  This option takes an int value.
+   This is a boolean option.  By default this option is turned off.
+
+   Here is an example of setting this option:
+
+      int on = 1;
+
+      if (setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY,
+                     (char *)&on, sizeof(on)) == -1)
+          perror("setsockopt IPV6_V6ONLY");
+      else
+          printf("IPV6_V6ONLY set\n");
+
+   Note - This option has no effect on the use of IPv4 Mapped addresses
+   which enter a node as a valid IPv6 addresses for IPv6 communications
+   as defined by Stateless IP/ICMP Translation Algorithm (SIIT) [5].
+
+   An example use of this option is to allow two versions of the same
+   server process to run on the same port, one providing service over
+   IPv6, the other providing the same service over IPv4.
+
+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.
+
+   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
+
+
+
+Gilligan, et al.             Informational                     [Page 22]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   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 gethostbyname2()
+   function was deprecated in RFC 2553 and is no longer part of the
+   basic API.
+
+6.1 Protocol-Independent Nodename and Service Name Translation
+
+   Nodename-to-address translation is done in a protocol-independent
+   fashion using the getaddrinfo() function.
+
+#include <sys/socket.h>
+#include <netdb.h>
+
+
+int getaddrinfo(const char *nodename, const char *servname,
+                const struct addrinfo *hints, struct addrinfo **res);
+
+void freeaddrinfo(struct addrinfo *ai);
+
+struct addrinfo {
+  int     ai_flags;     /* AI_PASSIVE, AI_CANONNAME,
+                           AI_NUMERICHOST, .. */
+  int     ai_family;    /* AF_xxx */
+  int     ai_socktype;  /* SOCK_xxx */
+  int     ai_protocol;  /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
+  socklen_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 getaddrinfo() function translates the name of a service location
+   (for example, a host name) and/or a service name and returns a set of
+   socket addresses and associated information to be used in creating a
+   socket with which to address the specified service.
+
+   The nodename and servname arguments are either null pointers or
+   pointers to null-terminated strings.  One or both of these two
+   arguments must be a non-null pointer.
+
+   The format of a valid name depends on the address family or families.
+   If a specific family is not given and the name could be interpreted
+   as valid within multiple supported families, the implementation will
+   attempt to resolve the name in all supported families and, in absence
+   of errors, one or more results shall be returned.
+
+
+
+Gilligan, et al.             Informational                     [Page 23]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   If the nodename argument is not null, it can be a descriptive name or
+   can be an address string.  If the specified address family is
+   AF_INET, AF_INET6, or AF_UNSPEC, valid descriptive names include host
+   names. If the specified address family is AF_INET or AF_UNSPEC,
+   address strings using Internet standard dot notation as specified in
+   inet_addr() are valid.  If the specified address family is AF_INET6
+   or AF_UNSPEC, standard IPv6 text forms described in inet_pton() are
+   valid.
+
+   If nodename is not null, the requested service location is named by
+   nodename; otherwise, the requested service location is local to the
+   caller.
+
+   If servname is null, the call shall return network-level addresses
+   for the specified nodename.  If servname is not null, it is a null-
+   terminated character string identifying the requested service.  This
+   can be either a descriptive name or a numeric representation suitable
+   for use with the address family or families.  If the specified
+   address family is AF_INET, AF_INET6 or AF_UNSPEC, the service can be
+   specified as a string specifying a decimal port number.
+
+   If the argument hints is not null, it refers to a structure
+   containing input values that may direct the operation by providing
+   options and by limiting the returned information to a specific socket
+   type, address family and/or protocol.  In this hints structure every
+   member other than ai_flags, ai_family, ai_socktype and ai_protocol
+   shall be set to zero or a null pointer.  A value of AF_UNSPEC for
+   ai_family means that the caller shall accept any address family.  A
+   value of zero for ai_socktype means that the caller shall accept any
+   socket type.  A value of zero for ai_protocol means that the caller
+   shall accept any protocol.  If hints is a null pointer, the behavior
+   shall be as if it referred to a structure containing the value zero
+   for the ai_flags, ai_socktype and ai_protocol fields, and AF_UNSPEC
+   for the ai_family field.
+
+   Note:
+
+   1. If the caller handles only TCP and not UDP, for example, then the
+      ai_protocol member of the hints structure should be set to
+      IPPROTO_TCP when getaddrinfo() is called.
+
+   2. If the caller handles only IPv4 and not IPv6, then the ai_family
+      member of the hints structure should be set to AF_INET when
+      getaddrinfo() is called.
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 24]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   The ai_flags field to which hints parameter points shall be set to
+   zero or be the bitwise-inclusive OR of one or more of the values
+   AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST, AI_NUMERICSERV,
+   AI_V4MAPPED, AI_ALL, and AI_ADDRCONFIG.
+
+   If the AI_PASSIVE flag is specified, the returned address information
+   shall be suitable for use in binding a socket for accepting incoming
+   connections for the specified service (i.e., a call to bind()).  In
+   this case, if the nodename argument is null, then the IP address
+   portion of the socket address structure shall be set to INADDR_ANY
+   for an IPv4 address or IN6ADDR_ANY_INIT for an IPv6 address.  If the
+   AI_PASSIVE flag is not specified, the returned address information
+   shall be suitable for a call to connect() (for a connection-mode
+   protocol) or for a call to connect(), sendto() or sendmsg() (for a
+   connectionless protocol).  In this case, if the nodename argument is
+   null, then the IP address portion of the socket address structure
+   shall be set to the loopback address.  This flag is ignored if the
+   nodename argument is not null.
+
+   If the AI_CANONNAME flag is specified and the nodename argument is
+   not null, the function shall attempt to determine the canonical name
+   corresponding to nodename (for example, if nodename is an alias or
+   shorthand notation for a complete name).
+
+   If the AI_NUMERICHOST flag is specified, then a non-null nodename
+   string supplied shall be a numeric host address string.  Otherwise,
+   an [EAI_NONAME] error is returned.  This flag shall prevent any type
+   of name resolution service (for example, the DNS) from being invoked.
+
+   If the AI_NUMERICSERV flag is specified, then a non-null servname
+   string supplied shall be a numeric port string.  Otherwise, an
+   [EAI_NONAME] error shall be returned.  This flag shall prevent any
+   type of name resolution service (for example, NIS+) from being
+   invoked.
+
+   If the AI_V4MAPPED flag is specified along with an ai_family of
+   AF_INET6, then getaddrinfo() shall return IPv4-mapped IPv6 addresses
+   on finding no matching IPv6 addresses (ai_addrlen shall be 16).
+
+      For example, when using the DNS, if no AAAA records are found then
+      a query is made for A records and any found are returned as IPv4-
+      mapped IPv6 addresses.
+
+   The AI_V4MAPPED flag shall be ignored unless ai_family equals
+   AF_INET6.
+
+   If the AI_ALL flag is used with the AI_V4MAPPED flag, then
+   getaddrinfo() shall return all matching IPv6 and IPv4 addresses.
+
+
+
+Gilligan, et al.             Informational                     [Page 25]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+      For example, when using the DNS, queries are made for both AAAA
+      records and A records, and getaddrinfo() returns the combined
+      results of both queries.  Any IPv4 addresses found are returned as
+      IPv4-mapped IPv6 addresses.
+
+   The AI_ALL flag without the AI_V4MAPPED flag is ignored.
+
+      Note:
+
+      When ai_family is not specified (AF_UNSPEC), AI_V4MAPPED and
+      AI_ALL flags will only be used if AF_INET6 is supported.
+
+   If the AI_ADDRCONFIG flag is specified, IPv4 addresses shall be
+   returned only if an IPv4 address is configured on the local system,
+   and IPv6 addresses shall be returned only if an IPv6 address is
+   configured on the local system.  The loopback address is not
+   considered for this case as valid as a configured address.
+
+      For example, when using the DNS, a query for AAAA records should
+      occur only if the node has at least one IPv6 address configured
+      (other than IPv6 loopback) and a query for A records should occur
+      only if the node has at least one IPv4 address configured (other
+      than the IPv4 loopback).
+
+   The ai_socktype field to which argument hints points specifies the
+   socket type for the service, as defined for socket().  If a specific
+   socket type is not given (for example, a value of zero) and the
+   service name could be interpreted as valid with multiple supported
+   socket types, the implementation shall attempt to resolve the service
+   name for all supported socket types and, in the absence of errors,
+   all possible results shall be returned.  A non-zero socket type value
+   shall limit the returned information to values with the specified
+   socket type.
+
+   If the ai_family field to which hints points has the value AF_UNSPEC,
+   addresses shall be returned for use with any address family that can
+   be used with the specified nodename and/or servname.  Otherwise,
+   addresses shall be returned for use only with the specified address
+   family.  If ai_family is not AF_UNSPEC and ai_protocol is not zero,
+   then addresses are returned for use only with the specified address
+   family and protocol; the value of ai_protocol shall be interpreted as
+   in a call to the socket() function with the corresponding values of
+   ai_family and ai_protocol.
+
+   The freeaddrinfo() function frees one or more addrinfo structures
+   returned by getaddrinfo(), along with any additional storage
+   associated with those structures (for example, storage pointed to by
+   the ai_canonname and ai_addr fields; an application must not
+
+
+
+Gilligan, et al.             Informational                     [Page 26]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   reference this storage after the associated addrinfo structure has
+   been freed).  If the ai_next field of the structure is not null, the
+   entire list of structures is freed.  The freeaddrinfo() function must
+   support the freeing of arbitrary sublists of an addrinfo list
+   originally returned by getaddrinfo().
+
+   Functions getaddrinfo() and freeaddrinfo() must be thread-safe.
+
+   A zero return value for getaddrinfo() indicates successful
+   completion; a non-zero return value indicates failure.  The possible
+   values for the failures are listed below under Error Return Values.
+
+   Upon successful return of getaddrinfo(), the location to which res
+   points shall refer to a linked list of addrinfo structures, each of
+   which shall specify a socket address and information for use in
+   creating a socket with which to use that socket address.  The list
+   shall include at least one addrinfo structure.  The ai_next field of
+   each structure contains a pointer to the next structure on the list,
+   or a null pointer if it is the last structure on the list.  Each
+   structure on the list shall include values for use with a call to the
+   socket() function, and a socket address for use with the connect()
+   function or, if the AI_PASSIVE flag was specified, for use with the
+   bind() function.  The fields ai_family, ai_socktype, and ai_protocol
+   shall be usable as the arguments to the socket() function to create a
+   socket suitable for use with the returned address.  The fields
+   ai_addr and ai_addrlen are usable as the arguments to the connect()
+   or bind() functions with such a socket, according to the AI_PASSIVE
+   flag.
+
+   If nodename is not null, and if requested by the AI_CANONNAME flag,
+   the ai_canonname field of the first returned addrinfo structure shall
+   point to a null-terminated string containing the canonical name
+   corresponding to the input nodename; if the canonical name is not
+   available, then ai_canonname shall refer to the nodename argument or
+   a string with the same contents.  The contents of the ai_flags field
+   of the returned structures are undefined.
+
+   All fields in socket address structures returned by getaddrinfo()
+   that are not filled in through an explicit argument (for example,
+   sin6_flowinfo) shall be set to zero.
+
+   Note: This makes it easier to compare socket address structures.
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 27]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   Error Return Values:
+
+   The getaddrinfo() function shall fail and return the corresponding
+   value if:
+
+   [EAI_AGAIN]     The name could not be resolved at this time.  Future
+                   attempts may succeed.
+
+   [EAI_BADFLAGS]  The flags parameter had an invalid value.
+
+   [EAI_FAIL]      A non-recoverable error occurred when attempting to
+                   resolve the name.
+
+   [EAI_FAMILY]    The address family was not recognized.
+
+   [EAI_MEMORY]    There was a memory allocation failure when trying to
+                   allocate storage for the return value.
+
+   [EAI_NONAME]    The name does not resolve for the supplied
+                   parameters.  Neither nodename nor servname were
+                   supplied.  At least one of these must be supplied.
+
+   [EAI_SERVICE]   The service passed was not recognized for the
+                   specified socket type.
+
+   [EAI_SOCKTYPE]  The intended socket type was not recognized.
+
+   [EAI_SYSTEM]    A system error occurred; the error code can be found
+                   in errno.
+
+   The gai_strerror() function provides a descriptive text string
+   corresponding to an EAI_xxx error value.
+
+      #include <netdb.h>
+
+      const char *gai_strerror(int ecode);
+
+   The argument is one of the EAI_xxx values defined for the
+   getaddrinfo() and getnameinfo() functions.  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.
+
+6.2 Socket Address Structure to Node Name and Service Name
+
+   The getnameinfo() function is used to translate the contents of a
+   socket address structure to a node name and/or service name.
+
+
+
+
+Gilligan, et al.             Informational                     [Page 28]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   #include <sys/socket.h>
+   #include <netdb.h>
+
+   int getnameinfo(const struct sockaddr *sa, socklen_t salen,
+                       char *node, socklen_t nodelen,
+                       char *service, socklen_t servicelen,
+                         int flags);
+
+   The getnameinfo() function shall translate a socket address to a node
+   name and service location, all of which are defined as in
+   getaddrinfo().
+
+   The sa argument points to a socket address structure to be
+   translated.
+
+   The salen argument holds the size of the socket address structure
+   pointed to by sa.
+
+   If the socket address structure contains an IPv4-mapped IPv6 address
+   or an IPv4-compatible IPv6 address, the implementation shall extract
+   the embedded IPv4 address and lookup the node name for that IPv4
+   address.
+
+      Note: The IPv6 unspecified address ("::") and the IPv6 loopback
+      address ("::1") are not IPv4-compatible addresses.  If the address
+      is the IPv6 unspecified address ("::"), a lookup is not performed,
+      and the [EAI_NONAME] error is returned.
+
+   If the node argument is non-NULL and the nodelen argument is nonzero,
+   then the node argument points to a buffer able to contain up to
+   nodelen characters that receives the node name as a null-terminated
+   string.  If the node argument is NULL or the nodelen argument is
+   zero, the node name shall not be returned.  If the node's name cannot
+   be located, the numeric form of the node's address is returned
+   instead of its name.
+
+   If the service argument is non-NULL and the servicelen argument is
+   non-zero, then the service argument points to a buffer able to
+   contain up to servicelen bytes that receives the service name as a
+   null-terminated string.  If the service argument is NULL or the
+   servicelen argument is zero, the service name shall not be returned.
+   If the service's name cannot be located, the numeric form of the
+   service address (for example, its port number) shall be returned
+   instead of its name.
+
+   The arguments node and service cannot both be NULL.
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 29]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   The flags argument is a flag that changes the default actions of the
+   function.  By default the fully-qualified domain name (FQDN) for the
+   host shall be returned, but:
+
+   -  If the flag bit NI_NOFQDN is set, only the node name portion of
+      the FQDN shall be returned for local hosts.
+
+   -  If the flag bit NI_NUMERICHOST is set, the numeric form of the
+      host's address shall be returned instead of its name, under all
+      circumstances.
+
+   -  If the flag bit NI_NAMEREQD is set, an error shall be returned if
+      the host's name cannot be located.
+
+   -  If the flag bit NI_NUMERICSERV is set, the numeric form of the
+      service address shall be returned (for example, its port number)
+      instead of its name, under all circumstances.
+
+   -  If the flag bit NI_DGRAM is set, this indicates that the service
+      is a datagram service (SOCK_DGRAM).  The default behavior shall
+      assume that the service is a stream service (SOCK_STREAM).
+
+   Note:
+
+   1. The NI_NUMERICxxx flags are required to support the "-n" flags
+      that many commands provide.
+
+   2. The NI_DGRAM flag is required for the few AF_INET and AF_INET6
+      port numbers (for example, [512,514]) that represent different
+      services for UDP and TCP.
+
+   The getnameinfo() function shall be thread safe.
+
+   A zero return value for getnameinfo() indicates successful
+   completion; a non-zero return value indicates failure.
+
+   Upon successful completion, getnameinfo() shall return the node and
+   service names, if requested, in the buffers provided.  The returned
+   names are always null-terminated strings.
+
+
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 30]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   Error Return Values:
+
+   The getnameinfo() function shall fail and return the corresponding
+   value if:
+
+   [EAI_AGAIN]    The name could not be resolved at this time.
+                  Future attempts may succeed.
+
+   [EAI_BADFLAGS] The flags had an invalid value.
+
+   [EAI_FAIL]     A non-recoverable error occurred.
+
+   [EAI_FAMILY]   The address family was not recognized or the address
+                  length was invalid for the specified family.
+
+   [EAI_MEMORY]   There was a memory allocation failure.
+
+   [EAI_NONAME]   The name does not resolve for the supplied parameters.
+                  NI_NAMEREQD is set and the host's name cannot be
+                  located, or both nodename and servname were null.
+
+   [EAI_OVERFLOW] An argument buffer overflowed.
+
+   [EAI_SYSTEM]   A system error occurred.  The error code can be found
+                  in errno.
+
+6.3 Address Conversion Functions
+
+   The two IPv4 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 <arpa/inet.h>
+
+   int inet_pton(int af, const char *src, void *dst);
+
+   const char *inet_ntop(int af, const void *src,
+                            char *dst, socklen_t size);
+
+   The inet_pton() function shall convert an address in its standard
+   text presentation form into its numeric binary form.  The af argument
+   shall specify the family of the address.  The AF_INET and AF_INET6
+   address families shall be 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; this shall be large
+   enough to hold the numeric address (32 bits for AF_INET, 128 bits for
+   AF_INET6).  The inet_pton() function shall return 1 if the conversion
+
+
+
+Gilligan, et al.             Informational                     [Page 31]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   succeeds, with the address pointed to by dst in network byte order.
+   It shall return 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.
+
+   If the af argument of inet_pton() is AF_INET, the src string shall be
+   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.
+   The inet_pton() function does not accept other formats (such as the
+   octal numbers, hexadecimal numbers, and fewer than four numbers that
+   inet_addr() accepts).
+
+   If the af argument of inet_pton() is AF_INET6, the src string shall
+   be in one of the standard IPv6 text forms defined in Section 2.2 of
+   the addressing architecture specification [2].
+
+   The inet_ntop() function shall convert a numeric address into a text
+   string suitable for presentation.  The af argument shall specify 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 stores the resulting
+   text string; it shall not be NULL.  The size argument specifies the
+   size of this buffer, which shall be large enough to hold the text
+   string (INET_ADDRSTRLEN characters for IPv4, INET6_ADDRSTRLEN
+   characters for IPv6).
+
+   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 shall return 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.
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 32]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+6.4 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 *);
+
+   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 types of local-use IPv6 unicast addresses (Link-
+   Local and Site-Local) defined in [2], and that by this definition,
+   the IN6_IS_ADDR_LINKLOCAL macro returns false for the IPv6 loopback
+   address (::1).  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_ALL
+<netdb.h>       AI_CANONNAME
+<netdb.h>       AI_NUMERICHOST
+<netdb.h>       AI_NUMERICSERV
+<netdb.h>       AI_PASSIVE
+<netdb.h>       AI_V4MAPPED
+
+
+
+Gilligan, et al.             Informational                     [Page 33]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+<netdb.h>       EAI_AGAIN
+<netdb.h>       EAI_BADFLAGS
+<netdb.h>       EAI_FAIL
+<netdb.h>       EAI_FAMILY
+<netdb.h>       EAI_MEMORY
+<netdb.h>       EAI_NONAME
+<netdb.h>       EAI_OVERFLOW
+<netdb.h>       EAI_SERVICE
+<netdb.h>       EAI_SOCKTYPE
+<netdb.h>       EAI_SYSTEM
+<netdb.h>       NI_DGRAM
+<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
+<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>  IPV6_V6ONLY
+<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 *, socklen_t);
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 34]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+<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 *, socklen_t, char *, socklen_t, int);
+<netdb.h>       void freeaddrinfo(struct addrinfo *);
+<netdb.h>       const char *gai_strerror(int);
+
+<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 *);
+<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. Changes from RFC 2553
+
+   1. Add brief description of the history of this API and its relation
+      to the Open Group/IEEE/ISO standards.
+
+   2. Alignments with [3].
+
+   3. Removed all references to getipnodebyname() and getipnodebyaddr(),
+      which are deprecated in favor of getaddrinfo() and getnameinfo().
+
+   4. Added IPV6_V6ONLY IP level socket option to permit nodes to not
+      process IPv4 packets as IPv4 Mapped addresses in implementations.
+
+   5. Added SIIT to references and added new contributors.
+
+
+
+
+Gilligan, et al.             Informational                     [Page 35]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+   6. In previous versions of this specification, the sin6_flowinfo
+      field was associated with the IPv6 traffic class and flow label,
+      but its usage was not completely specified.  The complete
+      definition of the sin6_flowinfo field, including its association
+      with the traffic class or flow label, is now deferred to a future
+      specification.
+
+10. Acknowledgments
+
+   This specification's evolution and completeness were significantly
+   influenced by the efforts of Richard Stevens, who has passed on.
+   Richard's wisdom and talent made the specification what it is today.
+   The co-authors will long think of Richard with great respect.
+
+   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, Brian Haberman, Jun-ichiro itojun Hagino,
+   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, Finnbarr Murphy, Thomas Narten, Josh Osborne,
+   Craig Partridge, Jean-Luc Richier, Bill Sommerfield, Erik Scoredos,
+   Keith Sklower, JINMEI Tatuya, Dave Thaler, Matt Thomas, Harvey
+   Thompson, Dean D. Throop, Karen Tracey, Glenn Trewitt, Paul Vixie,
+   David Waitzman, Carl Williams, Kazu Yamamoto, Vlad Yasevich, Stig
+   Venaas, and Brian Zill.
+
+   The getaddrinfo() and getnameinfo() functions are taken from an
+   earlier document by Keith Sklower.  As noted in that document,
+   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.
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 36]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+11. 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 Std. 1003.1-2001 Standard for Information Technology --
+        Portable Operating System Interface (POSIX). Open Group
+        Technical Standard: Base Specifications, Issue 6, December 2001.
+        ISO/IEC 9945:2002.  http://www.opengroup.org/austin
+
+   [4]  Stevens, W. and M. Thomas, "Advanced Sockets API for IPv6", RFC
+        2292, February 1998.
+
+   [5]  Nordmark, E., "Stateless IP/ICMP Translation Algorithm (SIIT)",
+        RFC 2765, February 2000.
+
+   [6]  The Open Group Base Working Group
+        http://www.opengroup.org/platform/base.html
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 37]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+12. Authors' Addresses
+
+   Bob Gilligan
+   Intransa, Inc.
+   2870 Zanker Rd.
+   San Jose, CA 95134
+
+   Phone: 408-678-8647
+   EMail: gilligan@intransa.com
+
+
+   Susan Thomson
+   Cisco Systems
+   499 Thornall Street, 8th floor
+   Edison, NJ 08837
+
+   Phone: 732-635-3086
+   EMail:  sethomso@cisco.com
+
+
+   Jim Bound
+   Hewlett-Packard Company
+   110 Spitbrook Road ZKO3-3/W20
+   Nashua, NH 03062
+
+   Phone: 603-884-0062
+   EMail: Jim.Bound@hp.com
+
+
+   Jack McCann
+   Hewlett-Packard Company
+   110 Spitbrook Road ZKO3-3/W20
+   Nashua, NH 03062
+
+   Phone: 603-884-2608
+   EMail: Jack.McCann@hp.com
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 38]
+
+RFC 3493       Basic Socket Interface Extensions for IPv6  February 2003
+
+
+13. Full Copyright Statement
+
+   Copyright (C) The Internet Society (2003).  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.
+
+Acknowledgement
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+Gilligan, et al.             Informational                     [Page 39]
+