As per Relevance of the word structure, we have this rfc below:
Network Working Group R.
Request for Comments: 2133
Category: Informational S.
J.
W.
April 1997
Basic Socket Interface Extensions for IPv
Status of this
This memo provides information for the Internet community. This
does not specify an Internet standard of any kind. Distribution
this memo is unlimited
The de facto standard application program interface (API) for TCP/
applications is the "sockets" interface. Although this API
developed for Unix in the early 1980s it has also been implemented
a wide variety of non-Unix systems. TCP/IP applications
using the sockets API have in the past enjoyed a high degree
portability and we would like the same portability with IPv
applications. But changes are required to the sockets API to
IPv6 and this memo describes these changes. These include a
socket address structure to carry IPv6 addresses, new
conversion functions, and some new socket options. These
are designed to provide access to the basic IPv6 features required
TCP and UDP applications, including multicasting, while introducing
minimum of change into the system and providing
compatibility for existing IPv4 applications. Additional
for advanced IPv6 features (raw sockets and access to the IPv
extension headers) are defined in another document [5].
Table of
1. Introduction ................................................ 2
2. Design Considerations ....................................... 3
2.1. What Needs to be Changed .................................. 3
2.2. Data Types ................................................ 5
2.3. Headers ................................................... 5
2.4. Structures ................................................ 5
3. Socket Interface ............................................ 5
3.1. IPv6 Address Family and Protocol Family ................... 5
3.2. IPv6 Address Structure .................................... 6
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3.3. Socket Address Structure for 4.3BSD-Based Systems ......... 6
3.4. Socket Address Structure for 4.4BSD-Based Systems ......... 7
3.5. The Socket Functions ...................................... 8
3.6. Compatibility with IPv4 Applications ...................... 9
3.7. Compatibility with IPv4 Nodes ............................. 9
3.8. IPv6 Wildcard Address ..................................... 10
3.9. IPv6 Loopback Address ..................................... 11
4. Interface Identification .................................... 12
4.1. Name-to-Index ............................................. 13
4.2. Index-to-Name ............................................. 13
4.3. Return All Interface Names and Indexes .................... 14
4.4. Free Memory ............................................... 14
5. Socket Options .............................................. 14
5.1. Changing Socket Type ...................................... 15
5.2. Unicast Hop Limit ......................................... 16
5.3. Sending and Receiving Multicast Packets ................... 17
6. Library Functions ........................................... 19
6.1. Hostname-to-Address Translation ........................... 19
6.2. Address To Hostname Translation ........................... 22
6.3. Protocol-Independent Hostname and Service Name Translation 22
6.4. Socket Address Structure to Hostname and Service Name ..... 25
6.5. Address Conversion Functions .............................. 27
6.6. Address Testing Macros .................................... 28
7. Summary of New Definitions .................................. 29
8. Security Considerations ..................................... 31
9. Acknowledgments ............................................. 31
10. References ................................................. 31
11. Authors' Addresses ......................................... 32
1.
While IPv4 addresses are 32 bits long, IPv6 interfaces are
by 128-bit addresses. The socket interface make the size of an
address quite visible to an application; virtually all TCP/
applications for BSD-based systems have knowledge of the size of
IP address. Those parts of the API that expose the addresses must
changed to accommodate the larger IPv6 address size. IPv6
introduces new features (e.g., flow label and priority), some
which must be made visible to applications via the API. This
defines a set of extensions to the socket interface to support
larger address size and new features of IPv6.
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2. Design
There are a number of important considerations in designing
to this well-worn API
- The API changes should provide both source and
compatibility for programs written to the original API. That is
existing program binaries should continue to operate when run
a system supporting the new API. In addition,
applications that are re-compiled and run on a system
the new API should continue to operate. Simply put, the
changes for IPv6 should not break existing programs
- The changes to the API should be as small as possible in order
simplify the task of converting existing IPv4 applications
IPv6.
- Where possible, applications should be able to use this API
interoperate with both IPv6 and IPv4 hosts. Applications
not need to know which type of host they are communicating with
- IPv6 addresses carried in data structures should be 64-
aligned. This is necessary in order to obtain
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
provide complete support for both IPv4 and IPv6. A subset of
API could probably be designed for operation on systems that
only IPv6. However, this is not addressed in this memo
2.1. What Needs to be
The socket interface API consists of a few distinct components
- Core socket functions
- Address data structures
- Name-to-address translation functions
- Address conversion functions
The core socket functions -- those functions that deal with
things as setting up and tearing down TCP connections, and
and receiving UDP packets -- were designed to be
independent. Where protocol addresses are passed as
arguments, they are carried via opaque pointers. A protocol-
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address data structure is defined for each protocol that the
functions support. Applications must cast pointers to
protocol-specific address structures into pointers to the
"sockaddr" address structure when using the socket functions.
functions need not change for IPv6, but a new IPv6-specific
data structure is needed
The "sockaddr_in" structure is the protocol-specific data
for IPv4. This data structure actually includes 8-octets of
space, and it is tempting to try to use this space to adapt
sockaddr_in structure to IPv6. Unfortunately, the sockaddr_
structure is not large enough to hold the 16-octet IPv6 address
well as the other information (address family and port number)
is needed. So a new address data structure must be defined for IPv6.
The name-to-address translation functions in the socket interface
gethostbyname() and gethostbyaddr(). These must be modified
support IPv6 and the semantics defined must provide 100%
compatibility for all existing IPv4 applications, along with IPv
support for new applications. Additionally, the POSIX 1003.g work
progress [4] specifies a new hostname-to-address translation
which is protocol independent. This function can also be used
IPv6.
The address conversion functions -- inet_ntoa() and inet_addr() --
convert IPv4 addresses between binary and printable form.
functions are quite specific to 32-bit IPv4 addresses. We
designed two analogous functions that convert both IPv4 and IPv
addresses, and carry an address type parameter so that they can
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 flow label, priority
and hop limit header fields. New socket options are needed
control the sending and receiving of IPv6 multicast packets
The socket interface will be enhanced in the future to provide
to other IPv6 features. These extensions are described in [5].
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2.2. Data
The data types of the structure elements given in this memo
intended to be examples, not absolute requirements.
possible, POSIX 1003.1g data types are used: u_intN_t means
unsigned integer of exactly N bits (e.g., u_int16_t) and u_intNm_
means an unsigned integer of at least N bits (e.g., u_int32m_t).
also assume the argument data types from 1003.1g when possible (e.g.,
the final argument to setsockopt() is a size_t value).
buffer sizes are specified, the POSIX 1003.1 size_t data type is
(e.g., the two length arguments to getnameinfo()).
2.3.
When function prototypes and structures are shown we show the
that must be #included to cause that item to be defined
2.4.
When structures are described the members shown are the ones
must appear in an implementation. Additional, nonstandard
may also be defined by an implementation
The ordering shown for the members of a structure is the
ordering, given alignment considerations of multibyte members, but
implementation may order the members differently
3. Socket
This section specifies the socket interface changes for IPv6.
3.1. IPv6 Address Family and Protocol
A new address family name, AF_INET6, is defined in .
The AF_INET6 definition distinguishes between the
sockaddr_in address data structure, and the new sockaddr_in6
structure
A new protocol family name, PF_INET6, is defined in .
Like most of the other protocol family names, this will usually
defined to have the same value as the corresponding address
name
#define PF_INET6 AF_INET
The PF_INET6 is used in the first argument to the socket()
to indicate that an IPv6 socket is being created
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3.2. IPv6 Address
A new data structure to hold a single IPv6 address is defined
follows
#include
struct in6_addr {
u_int8_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
in network byte order
3.3. Socket Address Structure for 4.3BSD-Based
In the socket interface, a different protocol-specific data
is defined to carry the addresses for each protocol suite.
protocol-specific data structure is designed so it can be cast into
protocol-independent data structure -- the "sockaddr" structure
Each has a "family" field that overlays the "sa_family" of
sockaddr data structure. This field identifies the type of the
structure
The sockaddr_in structure is the protocol-specific address
structure for IPv4. It is used to pass addresses
applications and the system in the socket functions. The
structure is defined to carry IPv6 addresses
#include
struct sockaddr_in6 {
u_int16m_t sin6_family; /* AF_INET6 */
u_int16m_t sin6_port; /* transport layer port # */
u_int32m_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */
};
This structure is designed to be compatible with the sockaddr
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
sockaddr data structure. The value of this field must be AF_INET6.
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The sin6_port field contains the 16-bit UDP or TCP port number.
field is used in the same way as the sin_port field of
sockaddr_in structure. The port number is stored in network
order
The sin6_flowinfo field is a 32-bit field that contains two pieces
information: the 24-bit IPv6 flow label and the 4-bit priority field
The contents and interpretation of this member is unspecified at
time
The sin6_addr field is a single in6_addr structure (defined in
previous section). This field holds one 128-bit IPv6 address.
address is stored in network byte order
The ordering of elements in this structure is specifically
so that the sin6_addr field will be aligned on a 64-bit boundary
This is done for optimum performance on 64-bit architectures
Notice that the sockaddr_in6 structure will normally be larger
the generic sockaddr structure. On many existing implementations
sizeof(struct sockaddr_in) equals sizeof(struct sockaddr), with
being 16 bytes. Any existing code that makes this assumption
to be examined carefully when converting to IPv6.
3.4. Socket Address Structure for 4.4BSD-Based
The 4.4BSD release includes a small, but incompatible change to
socket interface. The "sa_family" field of the sockaddr
structure was changed from a 16-bit value to an 8-bit value, and
space saved used to hold a length field, named "sa_len".
sockaddr_in6 data structure given in the previous section cannot
correctly cast into the newer sockaddr data structure. For
reason, the following alternative IPv6 address data structure
provided to be used on systems based on 4.4BSD
#include
#define SIN6_
struct sockaddr_in6 {
u_char sin6_len; /* length of this struct */
u_char sin6_family; /* AF_INET6 */
u_int16m_t sin6_port; /* transport layer port # */
u_int32m_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */
};
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The only differences between this data structure and the 4.3
variant are the inclusion of the length field, and the change of
family field to a 8-bit data type. The definitions of all the
fields are identical to the structure defined in the
section
Systems that provide this version of the sockaddr_in6 data
must also declare SIN6_LEN as a result of including
header. This macro allows applications to
whether they are being built on a system that supports the 4.3BSD
4.4BSD variants of the data structure
3.5. The Socket
Applications call the socket() function to create a socket
that represents a communication endpoint. The arguments to
socket() function tell the system which protocol to use, and
format address structure will be used in subsequent functions.
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
the constant PF_INET6 instead of PF_INET in the first argument.
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);
Once the application has created a PF_INET6 socket, it must use
sockaddr_in6 address structure when passing addresses in to
system. The functions that the application uses to pass
into the system are
bind()
connect()
sendmsg()
sendto()
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The system will use the sockaddr_in6 address structure to
addresses to applications that are using PF_INET6 sockets.
functions that return an address from the system to an
are
accept()
recvfrom()
recvmsg()
getpeername()
getsockname()
No changes to the syntax of the socket functions are needed
support IPv6, since all of the "address carrying" functions use
opaque address pointer, and carry an address length as a
argument
3.6. Compatibility with IPv4
In order to support the large base of applications using the
API, system implementations must provide complete source and
compatibility with the original API. This means that systems
continue to support PF_INET sockets and the sockaddr_in
structure. Applications must be able to create IPv4/TCP and IPv4/
sockets using the PF_INET constant in the socket() function,
described in the previous section. Applications should be able
hold a combination of IPv4/TCP, IPv4/UDP, IPv6/TCP and IPv6/
sockets simultaneously within the same process
Applications using the original API should continue to operate
they did on systems supporting only IPv4. That is, they
continue to interoperate with IPv4 nodes
3.7. Compatibility with IPv4
The API also provides a different type of compatibility: the
for IPv6 applications to interoperate with IPv4 applications.
feature uses the IPv4-mapped IPv6 address format defined in the IPv
addressing architecture specification [2]. This address
allows the IPv4 address of an IPv4 node to be represented as an IPv
address. The IPv4 address is encoded into the low-order 32 bits
the IPv6 address, and the high-order 96 bits hold the fixed
0:0:0:0:0:FFFF. IPv4-mapped addresses are written as follows
::FFFF:
These addresses are often generated automatically by
gethostbyname() function when the specified host has only IPv
addresses (as described in Section 6.1).
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Applications may use PF_INET6 sockets to open TCP connections to IPv
nodes, or send UDP packets to IPv4 nodes, by simply encoding
destination's IPv4 address as an IPv4-mapped IPv6 address,
passing that address, within a sockaddr_in6 structure, in
connect() or sendto() call. When applications use PF_INET6
to accept TCP connections from IPv4 nodes, or receive UDP
from IPv4 nodes, the system returns the peer's address to
application in the accept(), recvfrom(), or getpeername() call
a sockaddr_in6 structure encoded this way
Few applications will likely need to know which type of node they
interoperating with. However, for those applications that do need
know, the IN6_IS_ADDR_V4MAPPED() macro, defined in Section 6.6,
provided
3.8. IPv6 Wildcard
While the bind() function allows applications to select the source
address of UDP packets and TCP connections, applications often
the system to select the source address for them. With IPv4,
specifies the address as the symbolic constant INADDR_ANY (called
"wildcard" address) in the bind() call, or simply omits the bind()
entirely
Since the IPv6 address type is a structure (struct in6_addr),
symbolic constant can be used to initialize an IPv6 address variable
but cannot be used in an assignment. Therefore systems provide
IPv6 wildcard address in two forms
The first version is a global variable named "in6addr_any" that is
in6_addr structure. The extern declaration for this variable
defined in :
extern const struct in6_addr in6addr_any
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Applications use in6addr_any similarly to the way they use INADDR_
in IPv4. For example, to bind a socket to port number 23, but
the system select the source address, an application could use
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
is defined in . This constant can be used
initialize an in6_addr structure
struct in6_addr anyaddr = IN6ADDR_ANY_INIT
Note that this constant can be used ONLY at declaration time. It
not be used to assign a previously declared in6_addr structure.
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
byte order but the IPv6 IN6ADDR_xxx constants and the IPv
in6addr_xxx externals are defined in network byte order
3.9. IPv6 Loopback
Applications may need to send UDP packets to, or originate
connections to, services residing on the local node. In IPv4,
can do this by using the constant IPv4 address INADDR_LOOPBACK
their connect(), sendto(), or sendmsg() call
IPv6 also provides a loopback address to contact local TCP and
services. Like the unspecified address, the IPv6 loopback address
provided in two forms -- a global variable and a symbolic constant
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The global variable is an in6_addr structure
"in6addr_loopback." The extern declaration for this variable
defined in :
extern const struct in6_addr in6addr_loopback
Applications use in6addr_loopback as they would use INADDR_
in IPv4 applications (but beware of the byte ordering
mentioned at the end of the previous section). For example, to
a TCP connection to the local telnet server, an application could
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
in . It can be used at declaration time ONLY;
example
struct in6_addr loopbackaddr = IN6ADDR_LOOPBACK_INIT
Like IN6ADDR_ANY_INIT, this constant cannot be used in an
to a previously declared IPv6 address variable
4. Interface
This API uses an interface index (a small positive integer)
identify the local interface on which a multicast group is
(Section 5.3). Additionally, the advanced API [5] uses these
interface indexes to identify the interface on which a datagram
received, or to specify the interface on which a datagram is to
sent
Interfaces are normally known by names such as "le0", "sl1", "ppp2",
and the like. On Berkeley-derived implementations, when an
is made known to the system, the kernel assigns a unique
integer value (called the interface index) to that interface.
are small positive integers that start at 1. (Note that 0 is
used for an interface index.) There may be gaps so that there is
current interface for a particular positive interface index
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This API defines two functions that map between an interface name
index, a third function that returns all the interface names
indexes, and a fourth function to return the dynamic memory
by the previous function. How these functions are implemented
left up to the implementation. 4.4BSD implementations can
these functions using the existing sysctl() function with
NET_RT_LIST command. Other implementations may wish to use ioctl()
for this purpose
4.1. Name-to-
The first function maps an interface name into its
index
#include
unsigned int if_nametoindex(const char *ifname);
If the specified interface does not exist, the return value is 0.
4.2. Index-to-
The second function maps an interface index into its
name
#include
char *if_indextoname(unsigned int ifindex, char *ifname);
The ifname argument must point to a buffer of at least IFNAMSIZ
into which the interface name corresponding to the specified index
returned. (IFNAMSIZ is also defined in and its
includes a terminating null byte at the end of the interface name.)
This pointer is also the return value of the function. If there
no interface corresponding to the specified index, NULL is returned
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4.3. Return All Interface Names and
The final function returns an array of if_nameindex structures,
structure per interface
#include
struct if_nameindex {
unsigned int if_index; /* 1, 2, ... */
char *if_name; /* null terminated name: "le0", ... */
};
struct if_nameindex *if_nameindex(void);
The end of the array of structures is indicated by a structure
an if_index of 0 and an if_name of NULL. The function returns a
pointer upon an error
The memory used for this array of structures along with the
names pointed to by the if_name members is obtained dynamically
This memory is freed by the next function
4.4. Free
The following function frees the dynamic memory that was allocated
if_nameindex().
#include
void if_freenameindex(struct if_nameindex *ptr);
The argument to this function must be a pointer that was returned
if_nameindex().
5. Socket
A number of new socket options are defined for IPv6. All of
new options are at the IPPROTO_IPV6 level. That is, the "level
parameter in the getsockopt() and setsockopt() calls is IPPROTO_IPV
when using these options. The constant name prefix IPV6_ is used
all of the new socket options. This serves to clearly identify
options as applying to IPv6.
The declaration for IPPROTO_IPV6, the new IPv6 socket options,
related constants defined in this section are obtained by
the header .
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5.1. Changing Socket
Unix allows open sockets to be passed between processes via
exec() call and other means. It is a relatively common
practice to pass open sockets across exec() calls. Thus it
possible for an application using the original API to pass an
PF_INET socket to an application that is expecting to receive
PF_INET6 socket. Similarly, it is possible for an application
the extended API to pass an open PF_INET6 socket to an
using the original API, which would be equipped only to deal
PF_INET sockets. Either of these cases could cause problems,
the application that is passed the open socket might not know how
decode the address structures returned in subsequent
functions
To remedy this problem, a new setsockopt() option is defined
allows an application to "convert" a PF_INET6 socket into a PF_
socket and vice versa
An IPv6 application that is passed an open socket from an
process may use the IPV6_ADDRFORM setsockopt() option to "convert
the socket to PF_INET6. Once that has been done, the system
return sockaddr_in6 address structures in subsequent
functions
An IPv6 application that is about to pass an open PF_INET6 socket
a program that is not be IPv6 capable can "downgrade" the socket
PF_INET before calling exec(). After that, the system will
sockaddr_in address structures to the application that was exec()'ed
Be aware that you cannot downgrade an IPv6 socket to an IPv4
unless all nonwildcard addresses already associated with the IPv
socket are IPv4-mapped IPv6 addresses
The IPV6_ADDRFORM option is valid at both the IPPROTO_IP
IPPROTO_IPV6 levels. The only valid option values are PF_INET6
PF_INET. For example, to convert a PF_INET6 socket to PF_INET,
program would call
int addrform = PF_INET
if (setsockopt(s, IPPROTO_IPV6, IPV6_ADDRFORM
(char *) &addrform, sizeof(addrform)) == -1)
perror("setsockopt IPV6_ADDRFORM");
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An application may use IPV6_ADDRFORM with getsockopt() to
whether an open socket is a PF_INET of PF_INET6 socket. For example
int addrform
size_t len = sizeof(addrform);
if (getsockopt(s, IPPROTO_IPV6, IPV6_ADDRFORM
(char *) &addrform, &len) == -1)
perror("getsockopt IPV6_ADDRFORM");
else if (addrform == PF_INET
printf("This is an IPv4 socket.\n");
else if (addrform == PF_INET6)
printf("This is an IPv6 socket.\n");
printf("This system is broken.\n");
5.2. Unicast Hop
A new setsockopt() option controls the hop limit used in
unicast IPv6 packets. The name of this option is IPV6_UNICAST_HOPS
and it is used at the IPPROTO_IPV6 layer. The following
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(),
option value given is used as the hop limit for all
unicast packets sent via that socket. If the option is not set,
system selects a default value. The integer hop limit value (
x) is interpreted as follows
x < -1: return an error of
x == -1: use kernel
0 <= x <= 255: use
x >= 256: return an error of
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The IPV6_UNICAST_HOPS option may be used with getsockopt()
determine the hop limit value that the system will use for
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");
printf("Using %d for hop limit.\n", hoplimit);
5.3. Sending and Receiving Multicast
IPv6 applications may send UDP multicast packets by simply
an IPv6 multicast address in the address argument of the sendto()
function
Three socket options at the IPPROTO_IPV6 layer control some of
parameters for sending multicast packets. Setting these options
not required: applications may send multicast packets without
these options. The setsockopt() options for controlling the
of multicast packets are summarized below
IPV6_MULTICAST_
Set the interface to use for outgoing multicast packets.
argument is the index of the interface to use
Argument type: unsigned
IPV6_MULTICAST_
Set the hop limit to use for outgoing multicast packets
(Note a separate option - IPV6_UNICAST_HOPS - is provided
set the hop limit to use for outgoing unicast packets.)
interpretation of the argument is the same as for
IPV6_UNICAST_HOPS option
x < -1: return an error of
x == -1: use kernel
0 <= x <= 255: use
x >= 256: return an error of
Argument type:
Gilligan, et. al. Informational [Page 17]
RFC 2133 IPv6 Socket Interface Extensions April 1997
IPV6_MULTICAST_
Controls whether outgoing multicast packets sent should
delivered back to the local application. A toggle. If
option is set to 1, multicast packets are looped back. If
is set to 0, they are not
Argument type: unsigned
The reception of multicast packets is controlled by the
setsockopt() options summarized below
IPV6_ADD_
Join a multicast group on a specified local interface.
the interface index is specified as 0, the kernel chooses
local interface. For example, some kernels look up
multicast group in the normal IPv6 routing table and
the resulting interface
Argument type: struct ipv6_
IPV6_DROP_
Leave a multicast group on a specified interface
Argument type: struct ipv6_
The argument type of both of these options is the ipv6_
structure, defined as
#include
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
multicast group and bind the UDP port to which datagrams will
sent. Some processes also bind the multicast group address to
socket, in addition to the port, to prevent other datagrams
to that same port from being delivered to the socket
Gilligan, et. al. Informational [Page 18]
RFC 2133 IPv6 Socket Interface Extensions April 1997
6. Library
New library functions are needed to perform a variety of
with IPv6 addresses. Functions are needed to lookup IPv6
in the Domain Name System (DNS). Both forward lookup (hostname-to
address translation) and reverse lookup (address-to-
translation) need to be supported. Functions are also needed
convert IPv6 addresses between their binary and textual form
6.1. Hostname-to-Address
The commonly used function gethostbyname() remains unchanged as
the hostent structure to which it returns a pointer.
applications that call this function continue to receive only IPv
addresses that are the result of a query in the DNS for A records
(We assume the DNS is being used; some environments may be using
hosts file or some other name resolution system, either of which
impede renumbering. We also assume that the RES_USE_INET6
option is not set, which we describe in more detail shortly.)
Two new changes are made to support IPv6 addresses. First,
following function is new
#include
#include
struct hostent *gethostbyname2(const char *name, int af);
The af argument specifies the address family. The default
of this function is simple
- If the af argument is AF_INET, then a query is made for
records. If successful, IPv4 addresses are returned and
h_length member of the hostent structure will be 4, else
function returns a NULL pointer
- If the af argument is AF_INET6, then a query is made for
records. If successful, IPv6 addresses are returned and
h_length member of the hostent structure will be 16, else
function returns a NULL pointer
Gilligan, et. al. Informational [Page 19]
RFC 2133 IPv6 Socket Interface Extensions April 1997
The second change, that provides additional functionality, is a
resolver option RES_USE_INET6, which is defined as a result
including the header. (This option is provided
with the BIND 4.9.4 release.) There are three ways to set
option
- The first way
res_init();
_res.options |= RES_USE_INET6;
and then call either gethostbyname() or gethostbyname2().
option then affects only the process that is calling
resolver
- The second way to set this option is to set the
variable RES_OPTIONS, as in RES_OPTIONS=inet6. (This example
for the Bourne and Korn shells.) This method affects
processes that see this environment variable
- The third way is to set this option in the resolver
file (normally /etc/resolv.conf) and the option then affects
applications on the host. This final method should not be
until all applications on the host are capable of dealing
IPv6 addresses
There is no priority among these three methods. When
RES_USE_INET6 option is set, two changes occur
- gethostbyname(host) first calls gethostbyname2(host, AF_INET6)
looking for AAAA records, and if this fails it then
gethostbyname2(host, AF_INET) looking for A records
- gethostbyname2(host, AF_INET) always returns IPv4-mapped IPv
addresses with the h_length member of the hostent structure
to 16.
An application must not enable the RES_USE_INET6 option until it
prepared to deal with 16-byte addresses in the returned
structure
Gilligan, et. al. Informational [Page 20]
RFC 2133 IPv6 Socket Interface Extensions April 1997
The following table summarizes the operation of the
gethostbyname() function, the new function gethostbyname2(),
with the new resolver option RES_USE_INET6.
+------------------+---------------------------------------------------+
| | RES_USE_INET6 option |
| +-------------------------+-------------------------+
| | off | on |
+------------------+-------------------------+-------------------------+
| |Search for A records. |Search for AAAA records. |
| gethostbyname | If found, return IPv4 | If found, return IPv6 |
| (host) | addresses (h_length=4). | addresses (h_length=16).|
| | Else error. | Else search for A |
| | | records. If found, |
| |Provides backward | return IPv4-mapped IPv6 |
| | compatibility with all | addresses (h_length=16).|
| | existing IPv4 appls. | Else error. |
+------------------+-------------------------+-------------------------+
| |Search for A records. |Search for A records. |
| gethostbyname2 | If found, return IPv4 | If found, return |
| (host, AF_INET) | addresses (h_length=4). | IPv4-mapped IPv6 |
| | Else error. | addresses (h_length=16).|
| | | Else error. |
+------------------+-------------------------+-------------------------+
| |Search for AAAA records. |Search for AAAA records. |
| gethostbyname2 | If found, return IPv6 | If found, return IPv6 |
| (host, AF_INET6) | addresses (h_length=16).| addresses (h_length=16).|
| | Else error. | Else error. |
+------------------+-------------------------+-------------------------+
It is expected that when a typical naive application that
gethostbyname() today is modified to use IPv6, it simply changes
program to use IPv6 sockets and then enables the RES_USE_INET
resolver option before calling gethostbyname(). This
will then work with either IPv4 or IPv6 peers
Note that gethostbyname() and gethostbyname2() are not thread-safe
since both return a pointer to a static hostent structure.
several vendors have defined a thread-safe gethostbyname_r()
that requires four additional arguments. We expect these vendors
also define a gethostbyname2_r() function
Gilligan, et. al. Informational [Page 21]
RFC 2133 IPv6 Socket Interface Extensions April 1997
6.2. Address To Hostname
The existing gethostbyaddr() function already requires an
family argument and can therefore work with IPv6 addresses
#include
#include
struct hostent *gethostbyaddr(const char *src, int len, int af);
One possible source of confusion is the handling of IPv4-mapped IPv
addresses and IPv4-compatible IPv6 addresses. This is addressed
[6] and involves the following logic
1. If af is AF_INET6, and if len equals 16, and if the IPv6
is an IPv4-mapped IPv6 address or an IPv4-compatible IPv
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, then query for a PTR record in the in
addr.arpa domain
3. If af is AF_INET6, then query for a PTR record in the ip6.
domain
4. If the function is returning success, and if af equals AF_INET
and if the RES_USE_INET6 option was set, then the single
that is returned in the hostent structure (a copy of the
argument to the function) is returned as an IPv4-mapped IPv
address and the h_length member is set to 16.
All four steps listed are performed, in order. The same
regarding a thread-safe version of gethostbyname() that were made
the end of the previous section apply here as well
6.3. Protocol-Independent Hostname and Service Name
Hostname-to-address translation is done in a protocol-
fashion using the getaddrinfo() function that is taken from
Institute of Electrical and Electronic Engineers (IEEE) POSIX 1003.1
(Protocol Independent Interfaces) work in progress specification [4].
The official specification for this function will be the final
standard. We are providing this independent description of
function because POSIX standards are not freely available (as
IETF documents). Should there be any discrepancies between
description and the POSIX description, the POSIX description
precedence
Gilligan, et. al. Informational [Page 22]
RFC 2133 IPv6 Socket Interface Extensions April 1997
#include
#include
int getaddrinfo(const char *hostname, const char *servname
const struct addrinfo *hints
struct addrinfo **res);
The addrinfo structure is defined as
#include
#include
struct addrinfo {
int ai_flags; /* AI_PASSIVE, AI_CANONNAME */
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 hostname */
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
error code. The following names are the nonzero error codes
getaddrinfo(), and are defined in :
EAI_ADDRFAMILY address family for hostname not
EAI_AGAIN temporary failure in name
EAI_BADFLAGS invalid value for ai_
EAI_FAIL non-recoverable failure in name
EAI_FAMILY ai_family not
EAI_MEMORY memory allocation
EAI_NODATA no address associated with
EAI_NONAME hostname nor servname provided, or not
EAI_SERVICE servname not supported for ai_
EAI_SOCKTYPE ai_socktype not
EAI_SYSTEM system error returned in
The hostname and servname arguments are pointers to null-
strings or NULL. One or both of these two arguments must be a non
NULL pointer. In the normal client scenario, both the hostname
servname are specified. In the normal server scenario, only
servname is specified. A non-NULL hostname string can be either
host name or a numeric host address string (i.e., a dotted-
IPv4 address or an IPv6 hex address). A non-NULL servname string
be either a service name or a decimal port number
Gilligan, et. al. Informational [Page 23]
RFC 2133 IPv6 Socket Interface Extensions April 1997
The caller can optionally pass an addrinfo structure, pointed to
the third argument, to provide hints concerning the type of
that the caller supports. In this hints structure all members
than ai_flags, ai_family, ai_socktype, and ai_protocol must be
or a NULL pointer. A value of PF_UNSPEC for ai_family means
caller will accept any protocol family. A value of 0 for ai_
means the caller will accept any socket type. A value of 0
ai_protocol means the caller will accept any protocol. For example
if the caller handles only TCP and not UDP, then the ai_
member of the hints structure should be set to SOCK_STREAM
getaddrinfo() is called. If the caller handles only IPv4 and
IPv6, then the ai_family member of the hints structure should be
to PF_INET when getaddrinfo() is called. If the third argument
getaddrinfo() is a NULL pointer, this is the same as if the
had filled in an addrinfo structure initialized to zero
ai_family set to PF_UNSPEC
Upon successful return a pointer to a linked list of one or
addrinfo structures is returned through the final argument.
caller can process each addrinfo structure in this list by
the ai_next pointer, until a NULL pointer is encountered. In
returned addrinfo structure the three members ai_family, ai_socktype
and ai_protocol are the corresponding arguments for a call to
socket() function. In each addrinfo structure the ai_addr
points to a filled-in socket address structure whose length
specified by the ai_addrlen member
If the AI_PASSIVE bit is set in the ai_flags member of the
structure, then the caller plans to use the returned socket
structure in a call to bind(). In this case, if the
argument is a NULL pointer, then the IP address portion of the
address structure will be set to INADDR_ANY for an IPv4 address
IN6ADDR_ANY_INIT for an IPv6 address
If the AI_PASSIVE bit is not set in the ai_flags member of the
structure, then the returned socket address structure will be
for a call to connect() (for a connection-oriented protocol)
either connect(), sendto(), or sendmsg() (for a
protocol). In this case, if the hostname argument is a NULL pointer
then the IP address portion of the socket address structure will
set to the loopback address
If the AI_CANONNAME bit is set in the ai_flags member of the
structure, then upon successful return the ai_canonname member of
first addrinfo structure in the linked list will point to a null
terminated string containing the canonical name of the
hostname
Gilligan, et. al. Informational [Page 24]
RFC 2133 IPv6 Socket Interface Extensions April 1997
All of the information returned by getaddrinfo() is
allocated: the addrinfo structures, and the socket address
and canonical host name strings pointed to by the
structures. To return this information to the system the
freeaddrinfo() is called
#include
#include
void freeaddrinfo(struct addrinfo *ai);
The addrinfo structure pointed to by the ai argument is freed,
with any dynamic storage pointed to by the structure. This
is repeated until a NULL ai_next pointer is encountered
To aid applications in printing error messages based on the EAI_
codes returned by getaddrinfo(), the following function is defined
#include
#include
char *gai_strerror(int ecode);
The argument is one of the EAI_xxx values defined earlier and
eturn value points to a string describing the error. If the
is not one of the EAI_xxx values, the function still returns
pointer to a string whose contents indicate an unknown error
6.4. Socket Address Structure to Hostname and Service
The POSIX 1003.1g specification includes no function to perform
reverse conversion from getaddrinfo(): to look up a hostname
service name, given the binary address and port. Therefore,
define the following function
#include
#include
int getnameinfo(const struct sockaddr *sa, size_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
caller in the DNS and system-specific database, and returns
strings for both in buffers provided by the caller. The
indicates successful completion by a zero return value; a non-
return value indicates failure
Gilligan, et. al. Informational [Page 25]
RFC 2133 IPv6 Socket Interface Extensions April 1997
The first argument, sa, points to either a sockaddr_in structure (
IPv4) or a sockaddr_in6 structure (for IPv6) that holds the
address and port number. The salen argument gives the length of
sockaddr_in or sockaddr_in6 structure
The function returns the hostname associated with the IP address
the buffer pointed to by the host argument. The caller provides
size of this buffer via the hostlen argument. The service
associated with the port number is returned in the buffer pointed
by serv, and the servlen argument gives the length of this buffer
The caller specifies not to return either string by providing a
value for the hostlen or servlen arguments. Otherwise, the
must provide buffers large enough to hold the hostname and
service name, including the terminating null characters
Unfortunately most systems do not provide constants that specify
maximum size of either a fully-qualified domain name or a
name. Therefore to aid the application in allocating buffers
these two returned strings the following constants are defined
:
#define NI_MAXHOST 1025
#define NI_MAXSERV 32
The first value is actually defined as the constant MAXDNAME
recent versions of BIND's header (older versions
BIND define this constant to be 256) and the second is a guess
on the services listed in the current Assigned Numbers RFC
The final argument is a flag that changes the default actions of
function. By default the fully-qualified domain name (FQDN) for
host is looked up in the DNS and returned. If the flag bit NI_
is set, only the hostname portion of the FQDN is returned for
hosts
If the flag bit NI_NUMERICHOST is set, or if the host's name
be located in the DNS, the numeric form of the host's address
returned instead of its name (e.g., by calling inet_ntop() instead
gethostbyaddr()). If the flag bit NI_NAMEREQD is set, an error
returned if the host's name cannot be located in the DNS
If the flag bit NI_NUMERICSERV is set, the numeric form of
service address is returned (e.g., its port number) instead of
name. The two NI_NUMERICxxx flags are required to support the "-n
flag that many commands provide
Gilligan, et. al. Informational [Page 26]
RFC 2133 IPv6 Socket Interface Extensions April 1997
A fifth flag bit, NI_DGRAM, specifies that the service is a
service, and causes getservbyport() to be called with a
argument of "udp" instead of its default of "tcp". This is
for the few ports (512-514) that have different services for UDP
TCP
These NI_xxx flags are defined in along with the AI_
flags already defined for getaddrinfo().
6.5. Address Conversion
The two functions inet_addr() and inet_ntoa() convert an IPv4
between binary and text form. IPv6 applications need
functions. The following two functions convert both IPv6 and IPv
addresses
#include
#include
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
presentation form into its numeric binary form. The af
specifies the family of the address. Currently the AF_INET
AF_INET6 address families are supported. The src argument points
the string being passed in. The dst argument points to a buffer
which the function stores the numeric address. The address
returned in network byte order. Inet_pton() returns 1 if
conversion succeeds, 0 if the input is not a valid IPv4 dotted
decimal string or a valid IPv6 address string, or -1 with errno
to EAFNOSUPPORT if the af argument is unknown. The
application must ensure that the buffer referred to by dst is
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
standard IPv4 dotted-decimal form
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()
inet_aton() functions accept nonstandard input: octal numbers
hexadecimal numbers, and fewer than four numbers. inet_pton()
not accept these formats
Gilligan, et. al. Informational [Page 27]
RFC 2133 IPv6 Socket Interface Extensions April 1997
If the af argument is AF_INET6, then the function accepts a string
one of the standard IPv6 text forms defined in Section 2.2 of
addressing architecture specification [2].
The inet_ntop() function converts a numeric address into a
string suitable for presentation. The af argument specifies
family of the address. This can be AF_INET or AF_INET6. The
argument points to a buffer holding an IPv4 address if the
argument is AF_INET, or an IPv6 address if the af argument
AF_INET6. The dst argument points to a buffer where the
will store the resulting text string. The size argument
the size of this buffer. The application must specify a non-NULL
argument. For IPv6 addresses, the buffer must be at least 46-octets
For IPv4 addresses, the buffer must be at least 16-octets. In
to allow applications to easily declare buffers of the proper size
store IPv4 and IPv6 addresses in string form, the following
constants are defined in :
#define INET_ADDRSTRLEN 16
#define INET6_ADDRSTRLEN 46
The inet_ntop() function returns a pointer to the buffer
the text string if the conversion succeeds, and NULL otherwise.
failure, errno is set to EAFNOSUPPORT if the af argument is
or ENOSPC if the size of the result buffer is inadequate
6.6. Address Testing
The following macros can be used to test for special IPv6 addresses
#include
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 28]
RFC 2133 IPv6 Socket Interface Extensions April 1997
The first seven macros return true if the address is of the
type, or false otherwise. The last five test the scope of
multicast address and return true if the address is a
address of the specified scope or false if the address is either
a multicast address or not of the specified scope
7. Summary of New
The following list summarizes the constants, structure, and
definitions discussed in this memo, sorted by header
struct if_nameindex{};
AI_
AI_
EAI_
EAI_
EAI_
EAI_
EAI_
EAI_
EAI_
EAI_
EAI_
EAI_
EAI_
NI_
NI_
NI_
NI_
NI_
NI_
NI_
struct addrinfo{};
IN6ADDR_ANY_
IN6ADDR_LOOPBACK_
INET6_
INET_
IPPROTO_IPV
IPV6_
IPV6_ADD_
IPV6_DROP_
IPV6_MULTICAST_
IPV6_MULTICAST_
IPV6_MULTICAST_
IPV6_UNICAST_
Gilligan, et. al. Informational [Page 29]
RFC 2133 IPv6 Socket Interface Extensions April 1997
SIN6_
extern const struct in6_addr in6addr_any
extern const struct in6_addr in6addr_loopback
struct in6_addr{};
struct ipv6_mreq{};
struct sockaddr_in6{};
RES_USE_INET
AF_INET
PF_INET
The following list summarizes the function and macro
discussed in this memo, sorted by header
int inet_pton(int, const char *, void *);
const char *inet_ntop(int, const void *,
char *, size_t);
char *if_indextoname(unsigned int, char *);
unsigned int if_nametoindex(const char *);
void if_freenameindex(struct if_nameindex *);
struct if_nameindex *if_nameindex(void);
int getaddrinfo(const char *, const char *,
const struct addrinfo *,
struct addrinfo **);
int getnameinfo(const struct sockaddr *, size_t
char *, size_t, char *, size_t, int);
void freeaddrinfo(struct addrinfo *);
char *gai_strerror(int);
struct hostent *gethostbyname(const char *);
struct hostent *gethostbyaddr(const char *, int, int);
struct hostent *gethostbyname2(const char *, int);
int IN6_IS_ADDR_LINKLOCAL(const struct in6_addr *);
int IN6_IS_ADDR_LOOPBACK(const struct in6_addr *);
int IN6_IS_ADDR_MC_GLOBAL(const struct in6_addr *);
int IN6_IS_ADDR_MC_LINKLOCAL(const struct in6_addr *);
int IN6_IS_ADDR_MC_NODELOCAL(const struct in6_addr *);
int IN6_IS_ADDR_MC_ORGLOCAL(const struct in6_addr *);
int IN6_IS_ADDR_MC_SITELOCAL(const struct in6_addr *);
int IN6_IS_ADDR_MULTICAST(const struct in6_addr *);
int IN6_IS_ADDR_SITELOCAL(const struct in6_addr *);
int IN6_IS_ADDR_UNSPECIFIED(const struct in6_addr *);
int IN6_IS_ADDR_V4COMPAT(const struct in6_addr *);
int IN6_IS_ADDR_V4MAPPED(const struct in6_addr *);
Gilligan, et. al. Informational [Page 30]
RFC 2133 IPv6 Socket Interface Extensions April 1997
8. Security
IPv6 provides a number of new security mechanisms, many of which
to be accessible to applications. A companion memo detailing
extensions to the socket interfaces to support IPv6 security is
written [3].
9.
Thanks to the many people who made suggestions and provided
to to the numerous revisions of this document, including:
Almesberger, Ran Atkinson, Fred Baker, Dave Borman, Andrew Cherenson
Alex Conta, Alan Cox, Steve Deering, Richard Draves, Francis Dupont
Robert Elz, Marc Hasson, Tim Hartrick, Tom Herbert, Bob Hinden, Wan
Yen Hsu, Christian Huitema, Koji Imada, Markus Jork, Ron Lee,
Lloyd, Charles Lynn, Jack McCann, Dan McDonald, Dave Mitton,
Narten, Erik Nordmark, Josh Osborne, Craig Partridge, Jean-
Richier, Erik Scoredos, Keith Sklower, Matt Thomas, Harvey Thompson
Dean D. Throop, Karen Tracey, Glenn Trewitt, Paul Vixie,
Waitzman, Carl Williams, and Kazuhiko Yamamoto
The getaddrinfo() and getnameinfo() functions are taken from
earlier Work in Progress by Keith Sklower. As noted in
document, William Durst, Steven Wise, Michael Karels, and Eric
provided many useful discussions on the subject of protocol
independent name-to-address translation, and reviewed early
of Keith Sklower's original proposal. Eric Allman implemented
first prototype of getaddrinfo(). The observation that
the pair of name and service would suffice for connecting to
service independent of protocol details was made by Marshall Rose
a proposal to X/Open for a "Uniform Network Interface".
Craig Metz made many contributions to this document. Ramesh
made a number of contributions and co-authored an earlier version
this memo
10.
[1] Deering, S., and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 1883, December 1995.
[2] Hinden, R., and S. Deering, "IP Version 6 Addressing Architecture",
RFC 1884, December 1995.
[3] McDonald, D., "A Simple IP Security API Extension to BSD Sockets",
Work in Progress
Gilligan, et. al. Informational [Page 31]
RFC 2133 IPv6 Socket Interface Extensions April 1997
[4] IEEE, "Protocol Independent Interfaces", IEEE Std 1003.1g,
6.3, November 1995.
[5] Stevens, W., and M. Thomas, "Advanced Sockets API for IPv6",
Work in Progress
[6] Vixie, P., "Reverse Name Lookups of Encapsulated IPv4 Addresses
IPv6", Work in Progress
11. Authors'
Robert E.
Freegate
710 Lakeway Dr. STE 230
Sunnyvale, CA 94086
Phone: +1 408 524 4804
EMail: gilligan@freegate.
Susan
Bell Communications
MRE 2P-343, 445 South
Morristown, NJ 07960
Phone: +1 201 829 4514
EMail: set@thumper.bellcore.
Jim
Digital Equipment
110 Spitbrook Road ZK3-3/U14
Nashua, NH 03062-2698
Phone: +1 603 881 0400
Email: bound@zk3.dec.
W. Richard
1202 E. Paseo del
Tucson, AZ 85718-2826
Phone: +1 520 297 9416
EMail: rstevens@kohala.
Gilligan, et. al. Informational [Page 32]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
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