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RFC2133 - Basic Socket Interface Extensions for IPv6

王朝other·作者佚名  2008-05-31
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Network Working Group R. Gilligan

Request for Comments: 2133 Freegate

Category: Informational S. Thomson

Bellcore

J. Bound

Digital

W. Stevens

Consultant

April 1997

Basic Socket Interface Extensions for IPv6

Status of this Memo

This memo provides information for the Internet community. This memo

does not specify an Internet standard of any kind. Distribution of

this memo is unlimited.

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 [5].

Table of Contents

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

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. Introduction

While IPv4 addresses are 32 bits long, IPv6 interfaces are identified

by 128-bit addresses. The socket interface make the size of an IP

address quite visible to an application; virtually all TCP/IP

applications for BSD-based systems have knowledge of the size of an

IP address. Those parts of the API that eXPose the addresses must be

changed to accommodate the larger IPv6 address size. IPv6 also

introduces new features (e.g., flow label and priority), some of

which must be made visible to applications via the API. This memo

defines a set of extensions to the socket interface to support the

larger address size and new features of IPv6.

2. Design Considerations

There are a number of important considerations in designing changes

to this well-worn API:

- 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.

- 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.

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.

The name-to-address translation functions in the socket interface are

gethostbyname() and gethostbyaddr(). These must be modified to

support IPv6 and the semantics defined must provide 100% backward

compatibility for all existing IPv4 applications, along with IPv6

support for new applications. Additionally, the POSIX 1003.g work in

progress [4] specifies a new hostname-to-address translation function

which is protocol independent. This function can also be used with

IPv6.

The address conversion functions -- inet_ntoa() and inet_addr() --

convert IPv4 addresses between binary and printable form. These

functions are quite specific to 32-bit IPv4 addresses. We have

designed two analogous functions that convert both IPv4 and IPv6

addresses, and carry an address type parameter so that they can be

extended to other protocol families as well.

Finally, a few miscellaneous features are needed to support IPv6.

New interfaces are needed to support the IPv6 flow label, priority,

and hop limit header fields. New socket options are needed to

control the sending and receiving of IPv6 multicast packets.

The socket interface will be enhanced in the future to provide access

to other IPv6 features. These extensions are described in [5].

2.2. Data Types

The data types of the structure elements given in this memo are

intended to be examples, not absolute requirements. Whenever

possible, POSIX 1003.1g data types are used: u_intN_t means an

unsigned integer of exactly N bits (e.g., u_int16_t) and u_intNm_t

means an unsigned integer of at least N bits (e.g., u_int32m_t). We

also assume the argument data types from 1003.1g when possible (e.g.,

the final argument to setsockopt() is a size_t value). Whenever

buffer sizes are specified, the POSIX 1003.1 size_t data type is used

(e.g., the two length arguments to getnameinfo()).

2.3. Headers

When function prototypes and structures are shown we show the headers

that must be #included to cause that item to be defined.

2.4. Structures

When structures are described the members shown are the ones that

must appear in an implementation. Additional, nonstandard members

may also be defined by an implementation.

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 PF_INET6 is used in the first argument to the socket() function

to indicate that an IPv6 socket is being created.

3.2. IPv6 Address Structure

A new data structure to hold a single IPv6 address is defined as

follows:

#include <netinet/in.h>

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 stored

in network byte order.

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

structure is defined to carry IPv6 addresses:

#include <netinet/in.h>

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 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 that contains two pieces of

information: the 24-bit IPv6 flow label and the 4-bit priority field.

The contents and interpretation of this member is unspecified at this

time.

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 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 than

the generic sockaddr structure. On many existing implementations the

sizeof(struct sockaddr_in) equals sizeof(struct sockaddr), with both

being 16 bytes. Any existing code that makes this assumption needs

to be examined carefully when converting to IPv6.

3.4. Socket Address Structure for 4.4BSD-Based Systems

The 4.4BSD release includes a small, but incompatible change to the

socket interface. The "sa_family" field of the sockaddr data

structure was changed from a 16-bit value to an 8-bit value, and the

space saved used to hold a length field, named "sa_len". The

sockaddr_in6 data structure given in the previous section cannot be

correctly cast into the newer sockaddr data structure. For this

reason, the following alternative IPv6 address data structure is

provided to be used on systems based on 4.4BSD:

#include <netinet/in.h>

#define SIN6_LEN

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 */

};

The only differences between this data structure and the 4.3BSD

variant are the inclusion of the length field, and the change of the

family field to a 8-bit data type. The definitions of all the other

fields are identical to the structure defined in the previous

section.

Systems that provide this version of the sockaddr_in6 data structure

must also declare SIN6_LEN as a result of including the

<netinet/in.h> header. This macro allows applications to determine

whether they are being built on a system that supports the 4.3BSD or

4.4BSD variants of the data structure.

3.5. The Socket Functions

Applications call the socket() function to create a socket descriptor

that represents a communication endpoint. The arguments to the

socket() function tell the system which protocol to use, and what

format address structure will be used in subsequent functions. For

example, to create an IPv4/TCP socket, applications make the call:

s = socket(PF_INET, SOCK_STREAM, 0);

To create an IPv4/UDP socket, applications make the call:

s = socket(PF_INET, SOCK_DGRAM, 0);

Applications may create IPv6/TCP and IPv6/UDP sockets by simply using

the constant PF_INET6 instead of PF_INET in the first argument. For

example, to create an IPv6/TCP socket, applications make the call:

s = socket(PF_INET6, SOCK_STREAM, 0);

To create an IPv6/UDP socket, applications make the call:

s = socket(PF_INET6, SOCK_DGRAM, 0);

Once the application has created a PF_INET6 socket, it must use the

sockaddr_in6 address structure when passing addresses in to the

system. The functions that the application uses to pass addresses

into the system are:

bind()

connect()

sendmsg()

sendto()

The system will use the sockaddr_in6 address structure to return

addresses to applications that are using PF_INET6 sockets. The

functions that return an address from the system to an application

are:

accept()

recvfrom()

recvmsg()

getpeername()

getsockname()

No changes to the syntax of the socket functions are needed to

support IPv6, since all of the "address carrying" functions use an

opaque address pointer, and carry an address length as a function

argument.

3.6. Compatibility with IPv4 Applications

In order to support the large base of applications using the original

API, system implementations must provide complete source and binary

compatibility with the original API. This means that systems must

continue to support PF_INET sockets and the sockaddr_in address

structure. Applications must be able to create IPv4/TCP and IPv4/UDP

sockets using the PF_INET constant in the socket() function, as

described in the previous section. Applications should be able to

hold a combination of IPv4/TCP, IPv4/UDP, IPv6/TCP and IPv6/UDP

sockets simultaneously within the same process.

Applications using the original API should continue to operate as

they did on systems supporting only IPv4. That is, they should

continue to interoperate with IPv4 nodes.

3.7. Compatibility with IPv4 Nodes

The API also provides a different type of compatibility: the ability

for IPv6 applications to interoperate with IPv4 applications. This

feature uses the IPv4-mapped IPv6 address format defined in the IPv6

addressing architecture specification [2]. This address format

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 are often generated automatically by the

gethostbyname() function when the specified host has only IPv4

addresses (as described in Section 6.1).

Applications may use PF_INET6 sockets to open TCP connections to IPv4

nodes, or send UDP packets to IPv4 nodes, by simply encoding the

destination's IPv4 address as an IPv4-mapped IPv6 address, and

passing that address, within a sockaddr_in6 structure, in the

connect() or sendto() call. When applications use PF_INET6 sockets

to accept TCP connections from IPv4 nodes, or receive UDP packets

from IPv4 nodes, the system returns the peer's address to the

application in the accept(), recvfrom(), or getpeername() call using

a sockaddr_in6 structure encoded this way.

Few applications will likely need to know which type of node they are

interoperating with. However, for those applications that do need to

know, the IN6_IS_ADDR_V4MAPPED() macro, defined in Section 6.6, is

provided.

3.8. IPv6 Wildcard Address

While the bind() function allows applications to select the source IP

address of UDP packets and TCP connections, applications often want

the system to select the source address for them. With IPv4, one

specifies the address as the symbolic constant INADDR_ANY (called the

"wildcard" address) in the bind() call, or simply omits the bind()

entirely.

Since the IPv6 address type is a structure (struct in6_addr), a

symbolic constant can be used to initialize an IPv6 address variable,

but cannot be used in an assignment. Therefore systems provide the

IPv6 wildcard address in two forms.

The first version is a global variable named "in6addr_any" that is an

in6_addr structure. The extern declaration for this variable is

defined in <netinet/in.h>:

extern const struct in6_addr in6addr_any;

Applications use in6addr_any similarly to the way they use INADDR_ANY

in IPv4. For example, to bind a socket to port number 23, but let

the system select the source address, an application could use the

following code:

struct sockaddr_in6 sin6;

. . .

sin6.sin6_family = AF_INET6;

sin6.sin6_flowinfo = 0;

sin6.sin6_port = htons(23);

sin6.sin6_addr = in6addr_any; /* structure assignment */

. . .

if (bind(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1)

. . .

The other version is a symbolic constant named IN6ADDR_ANY_INIT and

is defined in <netinet/in.h>. This constant can be used to

initialize an in6_addr structure:

struct in6_addr anyaddr = IN6ADDR_ANY_INIT;

Note that this constant can be used ONLY at declaration time. It can

not be used to assign a previously declared in6_addr structure. For

example, the following code will not work:

/* This is the WRONG way to assign an unspecified address */

struct sockaddr_in6 sin6;

. . .

sin6.sin6_addr = IN6ADDR_ANY_INIT; /* will NOT compile */

Be aware that the IPv4 INADDR_xxx constants are all defined in host

byte order but the IPv6 IN6ADDR_xxx constants and the IPv6

in6addr_xxx externals are defined in network byte order.

3.9. IPv6 Loopback Address

Applications may need to send UDP packets to, or originate TCP

connections to, services residing on the local node. In IPv4, they

can do this by using the constant IPv4 address INADDR_LOOPBACK in

their connect(), sendto(), or sendmsg() call.

IPv6 also provides a loopback address to contact local TCP and UDP

services. Like the unspecified address, the IPv6 loopback address is

provided in two forms -- a global variable and a symbolic constant.

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.

4. Interface Identification

This API uses an interface index (a small positive integer) to

identify the local interface on which a multicast group is joined

(Section 5.3). Additionally, the advanced API [5] uses these same

interface indexes to identify the interface on which a datagram is

received, or to specify the interface on which a datagram is to be

sent.

Interfaces are normally known by names such as "le0", "sl1", "ppp2",

and the like. On Berkeley-derived implementations, when an interface

is made known to the system, the kernel assigns a unique positive

integer value (called the interface index) to that interface. These

are small positive integers that start at 1. (Note that 0 is never

used for an interface index.) There may be gaps so that there is no

current interface for a particular positive interface index.

This API defines two functions that map between an interface name and

index, a third function that returns all the interface names and

indexes, and a fourth function to return the dynamic memory allocated

by the previous function. How these functions are implemented is

left up to the implementation. 4.4BSD implementations can implement

these functions using the existing sysctl() function with the

NET_RT_LIST 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 the specified interface does not exist, the return value is 0.

4.2. Index-to-Name

The second function maps an interface index into its corresponding

name.

#include <net/if.h>

char *if_indextoname(unsigned int ifindex, char *ifname);

The ifname argument must point to a buffer of at least IFNAMSIZ bytes

into which the interface name corresponding to the specified index is

returned. (IFNAMSIZ is also defined in <net/if.h> and its value

includes a terminating null byte at the end of the interface name.)

This pointer is also the return value of the function. If there is

no interface corresponding to the specified index, NULL is returned.

4.3. Return All Interface Names and Indexes

The final function returns an array of if_nameindex structures, one

structure per interface.

#include <net/if.h>

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 with

an if_index of 0 and an if_name of NULL. The function returns a NULL

pointer upon an error.

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 argument to this function must be a pointer that was returned by

if_nameindex().

5. Socket Options

A number of new socket options are defined for IPv6. All of these

new options are at the IPPROTO_IPV6 level. That is, the "level"

parameter in the getsockopt() and setsockopt() calls is IPPROTO_IPV6

when using these options. The constant name prefix IPV6_ is used in

all of the new socket options. This serves to clearly identify these

options as applying to IPv6.

The declaration for IPPROTO_IPV6, the new IPv6 socket options, and

related constants defined in this section are obtained by including

the header <netinet/in.h>.

5.1. Changing Socket Type

Unix allows open sockets to be passed between processes via the

exec() call and other means. It is a relatively common application

practice to pass open sockets across exec() calls. Thus it is

possible for an application using the original API to pass an open

PF_INET socket to an application that is expecting to receive a

PF_INET6 socket. Similarly, it is possible for an application using

the extended API to pass an open PF_INET6 socket to an application

using the original API, which would be equipped only to deal with

PF_INET sockets. Either of these cases could cause problems, because

the application that is passed the open socket might not know how to

decode the address structures returned in subsequent socket

functions.

To remedy this problem, a new setsockopt() option is defined that

allows an application to "convert" a PF_INET6 socket into a PF_INET

socket and vice versa.

An IPv6 application that is passed an open socket from an unknown

process may use the IPV6_ADDRFORM setsockopt() option to "convert"

the socket to PF_INET6. Once that has been done, the system will

return sockaddr_in6 address structures in subsequent socket

functions.

An IPv6 application that is about to pass an open PF_INET6 socket to

a program that is not be IPv6 capable can "downgrade" the socket to

PF_INET before calling exec(). After that, the system will return

sockaddr_in address structures to the application that was exec()'ed.

Be aware that you cannot downgrade an IPv6 socket to an IPv4 socket

unless all nonwildcard addresses already associated with the IPv6

socket are IPv4-mapped IPv6 addresses.

The IPV6_ADDRFORM option is valid at both the IPPROTO_IP and

IPPROTO_IPV6 levels. The only valid option values are PF_INET6 and

PF_INET. For example, to convert a PF_INET6 socket to PF_INET, a

program would call:

int addrform = PF_INET;

if (setsockopt(s, IPPROTO_IPV6, IPV6_ADDRFORM,

(char *) &addrform, sizeof(addrform)) == -1)

perror("setsockopt IPV6_ADDRFORM");

An application may use IPV6_ADDRFORM with getsockopt() to learn

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");

else

printf("This system is broken.\n");

5.2. 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;

size_t len = sizeof(hoplimit);

if (getsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS,

(char *) &hoplimit, &len) == -1)

perror("getsockopt IPV6_UNICAST_HOPS");

else

printf("Using %d for hop limit.\n", hoplimit);

5.3. Sending and Receiving Multicast Packets

IPv6 applications may send UDP multicast packets by simply specifying

an IPv6 multicast address in the address argument of the sendto()

function.

Three socket options at the IPPROTO_IPV6 layer control some of the

parameters for sending multicast packets. Setting these options is

not required: applications may send multicast packets without using

these options. The setsockopt() options for controlling the sending

of multicast packets are summarized below:

IPV6_MULTICAST_IF

Set the interface to use for outgoing multicast packets. The

argument is the index of the interface to use.

Argument type: unsigned int

IPV6_MULTICAST_HOPS

Set the hop limit to use for outgoing multicast packets.

(Note a separate option - IPV6_UNICAST_HOPS - is provided to

set the hop limit to use for outgoing unicast packets.) The

interpretation of the argument is the same as for the

IPV6_UNICAST_HOPS option:

x < -1: return an error of EINVAL

x == -1: use kernel default

0 <= x <= 255: use x

x >= 256: return an error of EINVAL

Argument type: int

IPV6_MULTICAST_LOOP

Controls whether outgoing multicast packets sent should be

delivered back to the local application. A toggle. If the

option is set to 1, multicast packets are looped back. If it

is set to 0, they are not.

Argument type: unsigned int

The reception of multicast packets is controlled by the two

setsockopt() options summarized below:

IPV6_ADD_MEMBERSHIP

Join a multicast group on a specified local interface. If

the interface index is specified as 0, the kernel chooses the

local interface. For example, some kernels look up the

multicast group in the normal IPv6 routing table and using

the resulting interface.

Argument type: struct ipv6_mreq

IPV6_DROP_MEMBERSHIP

Leave a multicast group on a specified interface.

Argument type: struct ipv6_mreq

The argument type of both of these options is the ipv6_mreq

structure, defined as:

#include <netinet/in.h>

struct ipv6_mreq {

struct in6_addr ipv6mr_multiaddr; /* IPv6 multicast addr */

unsigned int ipv6mr_interface; /* interface index */

};

Note that to receive multicast datagrams a process must join the

multicast group and bind the UDP port to which datagrams will be

sent. Some processes also bind the multicast group address to the

socket, in addition to the port, to prevent other datagrams destined

to that same port from being delivered to the socket.

6. Library Functions

New library functions are needed to perform a variety of operations

with IPv6 addresses. Functions are needed to lookup IPv6 addresses

in the Domain Name System (DNS). Both forward lookup (hostname-to-

address translation) and reverse lookup (address-to-hostname

translation) need to be supported. Functions are also needed to

convert IPv6 addresses between their binary and textual form.

6.1. Hostname-to-Address Translation

The commonly used function gethostbyname() remains unchanged as does

the hostent structure to which it returns a pointer. Existing

applications that call this function continue to receive only IPv4

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 a

hosts file or some other name resolution system, either of which may

impede renumbering. We also assume that the RES_USE_INET6 resolver

option is not set, which we describe in more detail shortly.)

Two new changes are made to support IPv6 addresses. First, the

following function is new:

#include <sys/socket.h>

#include <netdb.h>

struct hostent *gethostbyname2(const char *name, int af);

The af argument specifies the address family. The default operation

of this function is simple:

- If the af argument is AF_INET, then a query is made for A

records. If successful, IPv4 addresses are returned and the

h_length member of the hostent structure will be 4, else the

function returns a NULL pointer.

- If the af argument is AF_INET6, then a query is made for AAAA

records. If successful, IPv6 addresses are returned and the

h_length member of the hostent structure will be 16, else the

function returns a NULL pointer.

The second change, that provides additional functionality, is a new

resolver option RES_USE_INET6, which is defined as a result of

including the <resolv.h> header. (This option is provided starting

with the BIND 4.9.4 release.) There are three ways to set this

option.

- The first way is

res_init();

_res.options = RES_USE_INET6;

and then call either gethostbyname() or gethostbyname2(). This

option then affects only the process that is calling the

resolver.

- The second way to set this option is to set the environment

variable RES_OPTIONS, as in RES_OPTIONS=inet6. (This example is

for the Bourne and Korn shells.) This method affects any

processes that see this environment variable.

- The third way is to set this option in the resolver configuration

file (normally /etc/resolv.conf) and the option then affects all

applications on the host. This final method should not be done

until all applications on the host are capable of dealing with

IPv6 addresses.

There is no priority among these three methods. When the

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 calls

gethostbyname2(host, AF_INET) looking for A records.

- gethostbyname2(host, AF_INET) always returns IPv4-mapped IPv6

addresses with the h_length member of the hostent structure set

to 16.

An application must not enable the RES_USE_INET6 option until it is

prepared to deal with 16-byte addresses in the returned hostent

structure.

The following table summarizes the operation of the existing

gethostbyname() function, the new function gethostbyname2(), along

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 calls

gethostbyname() today is modified to use IPv6, it simply changes the

program to use IPv6 sockets and then enables the RES_USE_INET6

resolver option before calling gethostbyname(). This application

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. But

several vendors have defined a thread-safe gethostbyname_r() function

that requires four additional arguments. We expect these vendors to

also define a gethostbyname2_r() function.

6.2. Address To Hostname Translation

The existing gethostbyaddr() function already requires an address

family argument and can therefore work with IPv6 addresses:

#include <sys/socket.h>

#include <netdb.h>

struct hostent *gethostbyaddr(const char *src, int len, int af);

One possible source of confusion is the handling of IPv4-mapped IPv6

addresses and IPv4-compatible IPv6 addresses. This is addressed in

[6] and involves the following logic:

1. If af is AF_INET6, and if len equals 16, and if the IPv6 address

is an IPv4-mapped IPv6 address or an IPv4-compatible IPv6

address, then skip over the first 12 bytes of the IPv6 address,

set af to AF_INET, and set len to 4.

2. If af is AF_INET, 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.int

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 address

that is returned in the hostent structure (a copy of the first

argument to the function) is returned as an IPv4-mapped IPv6

address and the h_length member is set to 16.

All four steps listed are performed, in order. The same caveats

regarding a thread-safe version of gethostbyname() that were made at

the end of the previous section apply here as well.

6.3. Protocol-Independent Hostname and Service Name Translation

Hostname-to-address translation is done in a protocol-independent

fashion using the getaddrinfo() function that is taken from the

Institute of Electrical and Electronic Engineers (IEEE) POSIX 1003.1g

(Protocol Independent Interfaces) work in progress specification [4].

The official specification for this function will be the final POSIX

standard. We are providing this independent description of the

function because POSIX standards are not freely available (as are

IETF documents). Should there be any discrepancies between this

description and the POSIX description, the POSIX description takes

precedence.

#include <sys/socket.h>

#include <netdb.h>

int getaddrinfo(const char *hostname, const char *servname,

const struct addrinfo *hints,

struct addrinfo **res);

The addrinfo structure is defined as:

#include <sys/socket.h>

#include <netdb.h>

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 nonzero

error code. The following names are the nonzero error codes from

getaddrinfo(), and are defined in <netdb.h>:

EAI_ADDRFAMILY address family for hostname not supported

EAI_AGAIN temporary failure in name resolution

EAI_BADFLAGS invalid value for ai_flags

EAI_FAIL non-recoverable failure in name resolution

EAI_FAMILY ai_family not supported

EAI_MEMORY memory allocation failure

EAI_NODATA no address associated with hostname

EAI_NONAME hostname nor servname provided, or not known

EAI_SERVICE servname not supported for ai_socktype

EAI_SOCKTYPE ai_socktype not supported

EAI_SYSTEM system error returned in errno

The hostname and servname arguments are pointers to null-terminated

strings or NULL. One or both of these two arguments must be a non-

NULL pointer. In the normal client scenario, both the hostname and

servname are specified. In the normal server scenario, only the

servname is specified. A non-NULL hostname string can be either a

host name or a numeric host address string (i.e., a dotted-decimal

IPv4 address or an IPv6 hex address). A non-NULL servname string can

be either a service name or a decimal port number.

The caller can optionally pass an addrinfo structure, pointed to by

the third argument, to provide hints concerning the type of socket

that the caller supports. In this hints structure all members other

than ai_flags, ai_family, ai_socktype, and ai_protocol must be zero

or a NULL pointer. A value of PF_UNSPEC for ai_family means the

caller will accept any protocol family. A value of 0 for ai_socktype

means the caller will accept any socket type. A value of 0 for

ai_protocol means the caller will accept any protocol. For example,

if the caller handles only TCP and not UDP, then the ai_socktype

member of the hints structure should be set to SOCK_STREAM when

getaddrinfo() is called. If the caller handles only IPv4 and not

IPv6, then the ai_family member of the hints structure should be set

to PF_INET when getaddrinfo() is called. If the third argument to

getaddrinfo() is a NULL pointer, this is the same as if the caller

had filled in an addrinfo structure initialized to zero with

ai_family set to PF_UNSPEC.

Upon successful return a pointer to a linked list of one or more

addrinfo structures is returned through the final argument. The

caller can process each addrinfo structure in this list by following

the ai_next pointer, until a NULL pointer is encountered. In each

returned addrinfo structure the three members ai_family, ai_socktype,

and ai_protocol are the corresponding arguments for a call to the

socket() function. In each addrinfo structure the ai_addr member

points to a filled-in socket address structure whose length is

specified by the ai_addrlen member.

If the AI_PASSIVE bit is set in the ai_flags member of the hints

structure, then the caller plans to use the returned socket address

structure in a call to bind(). In this case, if the hostname

argument is a NULL pointer, then the IP address portion of the socket

address structure will be set to INADDR_ANY for an IPv4 address or

IN6ADDR_ANY_INIT for an IPv6 address.

If the AI_PASSIVE bit is not set in the ai_flags member of the hints

structure, then the returned socket address structure will be ready

for a call to connect() (for a connection-oriented protocol) or

either connect(), sendto(), or sendmsg() (for a connectionless

protocol). In this case, if the hostname argument is a NULL pointer,

then the IP address portion of the socket address structure will be

set to the loopback address.

If the AI_CANONNAME bit is set in the ai_flags member of the hints

structure, then upon successful return the ai_canonname member of the

first addrinfo structure in the linked list will point to a null-

terminated string containing the canonical name of the specified

hostname.

All of the information returned by getaddrinfo() is dynamically

allocated: the addrinfo structures, and the socket address structures

and canonical host name strings pointed to by the addrinfo

structures. To return this information to the system the function

freeaddrinfo() is called:

#include <sys/socket.h>

#include <netdb.h>

void freeaddrinfo(struct addrinfo *ai);

The addrinfo structure pointed to by the ai argument is freed, along

with any dynamic storage pointed to by the structure. This operation

is repeated until a NULL ai_next pointer is encountered.

To aid applications in printing error messages based on the EAI_xxx

codes returned by getaddrinfo(), the following function is defined.

#include <sys/socket.h>

#include <netdb.h>

char *gai_strerror(int ecode);

The argument is one of the EAI_xxx values defined earlier and the

eturn 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.

6.4. Socket Address Structure to Hostname and Service Name

The POSIX 1003.1g specification includes no function to perform the

reverse conversion from getaddrinfo(): to look up a hostname and

service name, given the binary address and port. Therefore, we

define the following function:

#include <sys/socket.h>

#include <netdb.h>

int getnameinfo(const struct sockaddr *sa, 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 the

caller in the DNS and system-specific database, and returns text

strings for both in buffers provided by the caller. The function

indicates successful completion by a zero return value; a non-zero

return value indicates failure.

The first argument, sa, points to either a sockaddr_in structure (for

IPv4) or a sockaddr_in6 structure (for IPv6) that holds the IP

address and port number. The salen argument gives the length of the

sockaddr_in or sockaddr_in6 structure.

The function returns the hostname associated with the IP address in

the buffer pointed to by the host argument. The caller provides the

size of this buffer via the hostlen argument. The service name

associated with the port number is returned in the buffer pointed to

by serv, and the servlen argument gives the length of this buffer.

The caller specifies not to return either string by providing a zero

value for the hostlen or servlen arguments. Otherwise, the caller

must provide buffers large enough to hold the hostname and the

service name, including the terminating null characters.

Unfortunately most systems do not provide constants that specify the

maximum size of either a fully-qualified domain name or a service

name. Therefore to aid the application in allocating buffers for

these two returned strings the following constants are defined in

<netdb.h>:

#define NI_MAXHOST 1025

#define NI_MAXSERV 32

The first value is actually defined as the constant MAXDNAME in

recent versions of BIND's <arpa/nameser.h> header (older versions of

BIND define this constant to be 256) and the second is a guess based

on the services listed in the current Assigned Numbers RFC.

The final argument is a flag that changes the default actions of this

function. By default the fully-qualified domain name (FQDN) for the

host is looked up in the DNS and returned. If the flag bit NI_NOFQDN

is set, only the hostname portion of the FQDN is returned for local

hosts.

If the flag bit NI_NUMERICHOST is set, or if the host's name cannot

be located in the DNS, the numeric form of the host's address is

returned instead of its name (e.g., by calling inet_ntop() instead of

gethostbyaddr()). If the flag bit NI_NAMEREQD is set, an error is

returned if the host's name cannot be located in the DNS.

If the flag bit NI_NUMERICSERV is set, the numeric form of the

service address is returned (e.g., its port number) instead of its

name. The two NI_NUMERICxxx flags are required to support the "-n"

flag that many commands provide.

A fifth flag bit, NI_DGRAM, specifies that the service is a datagram

service, and causes getservbyport() to be called with a second

argument of "udp" instead of its default of "tcp". This is required

for the few ports (512-514) that have different services for UDP and

TCP.

These NI_xxx flags are defined in <netdb.h> along with the AI_xxx

flags already defined for getaddrinfo().

6.5. Address Conversion Functions

The two functions inet_addr() and inet_ntoa() convert an IPv4 address

between binary and text form. IPv6 applications need similar

functions. The following two functions convert both IPv6 and IPv4

addresses:

#include <sys/socket.h>

#include <arpa/inet.h>

int inet_pton(int af, const char *src, void *dst);

const char *inet_ntop(int af, const void *src,

char *dst, size_t size);

The inet_pton() function converts an address in its standard text

presentation form into its numeric binary form. The af argument

specifies the family of the address. Currently the AF_INET and

AF_INET6 address families are supported. The src argument points to

the string being passed in. The dst argument points to a buffer into

which the function stores the numeric address. The address is

returned in network byte order. Inet_pton() returns 1 if the

conversion succeeds, 0 if the input is not a valid IPv4 dotted-

decimal string or a valid IPv6 address string, or -1 with errno set

to EAFNOSUPPORT if the af argument is unknown. The calling

application must ensure that the buffer referred to by dst is large

enough to hold the numeric address (e.g., 4 bytes for AF_INET or 16

bytes for AF_INET6).

If the af argument is AF_INET, the function accepts a string in the

standard IPv4 dotted-decimal form:

ddd.ddd.ddd.ddd

where ddd is a one to three digit decimal number between 0 and 255.

Note that many implementations of the existing inet_addr() and

inet_aton() functions accept nonstandard input: octal numbers,

hexadecimal numbers, and fewer than four numbers. inet_pton() does

not accept these formats.

If the af argument is AF_INET6, then the function accepts a string in

one of the standard IPv6 text forms defined in Section 2.2 of the

addressing architecture specification [2].

The inet_ntop() function converts a numeric address into a text

string suitable for presentation. The af argument specifies the

family of the address. This can be AF_INET or AF_INET6. The src

argument points to a buffer holding an IPv4 address if the af

argument is AF_INET, or an IPv6 address if the af argument is

AF_INET6. The dst argument points to a buffer where the function

will store the resulting text string. The size argument specifies

the size of this buffer. The application must specify a non-NULL dst

argument. For IPv6 addresses, the buffer must be at least 46-octets.

For IPv4 addresses, the buffer must be at least 16-octets. In order

to allow applications to easily declare buffers of the proper size to

store IPv4 and IPv6 addresses in string form, the following two

constants are defined in <netinet/in.h>:

#define INET_ADDRSTRLEN 16

#define INET6_ADDRSTRLEN 46

The inet_ntop() function returns a pointer to the buffer containing

the text string if the conversion succeeds, and NULL otherwise. Upon

failure, errno is set to EAFNOSUPPORT if the af argument is invalid

or ENOSPC if the size of the result buffer is inadequate.

6.6. 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.

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> IFNAMSIZ

<net/if.h> struct if_nameindex{};

<netdb.h> AI_CANONNAME

<netdb.h> AI_PASSIVE

<netdb.h> EAI_ADDRFAMILY

<netdb.h> EAI_AGAIN

<netdb.h> EAI_BADFLAGS

<netdb.h> EAI_FAIL

<netdb.h> EAI_FAMILY

<netdb.h> EAI_MEMORY

<netdb.h> EAI_NODATA

<netdb.h> EAI_NONAME

<netdb.h> EAI_SERVICE

<netdb.h> EAI_SOCKTYPE

<netdb.h> EAI_SYSTEM

<netdb.h> NI_DGRAM

<netdb.h> NI_MAXHOST

<netdb.h> NI_MAXSERV

<netdb.h> NI_NAMEREQD

<netdb.h> NI_NOFQDN

<netdb.h> NI_NUMERICHOST

<netdb.h> NI_NUMERICSERV

<netdb.h> struct addrinfo{};

<netinet/in.h> IN6ADDR_ANY_INIT

<netinet/in.h> IN6ADDR_LOOPBACK_INIT

<netinet/in.h> INET6_ADDRSTRLEN

<netinet/in.h> INET_ADDRSTRLEN

<netinet/in.h> IPPROTO_IPV6

<netinet/in.h> IPV6_ADDRFORM

<netinet/in.h> IPV6_ADD_MEMBERSHIP

<netinet/in.h> IPV6_DROP_MEMBERSHIP

<netinet/in.h> IPV6_MULTICAST_HOPS

<netinet/in.h> IPV6_MULTICAST_IF

<netinet/in.h> IPV6_MULTICAST_LOOP

<netinet/in.h> IPV6_UNICAST_HOPS

<netinet/in.h> SIN6_LEN

<netinet/in.h> extern const struct in6_addr in6addr_any;

<netinet/in.h> extern const struct in6_addr in6addr_loopback;

<netinet/in.h> struct in6_addr{};

<netinet/in.h> struct ipv6_mreq{};

<netinet/in.h> struct sockaddr_in6{};

<resolv.h> RES_USE_INET6

<sys/socket.h> AF_INET6

<sys/socket.h> PF_INET6

The following list summarizes the function and macro prototypes

discussed in this memo, sorted by header.

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

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

char *, size_t);

<net/if.h> char *if_indextoname(unsigned int, char *);

<net/if.h> unsigned int if_nametoindex(const char *);

<net/if.h> void if_freenameindex(struct if_nameindex *);

<net/if.h> struct if_nameindex *if_nameindex(void);

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

const struct addrinfo *,

struct addrinfo **);

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

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

<netdb.h> void freeaddrinfo(struct addrinfo *);

<netdb.h> char *gai_strerror(int);

<netdb.h> struct hostent *gethostbyname(const char *);

<netdb.h> struct hostent *gethostbyaddr(const char *, int, int);

<netdb.h> struct hostent *gethostbyname2(const char *, 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. A companion memo detailing the

extensions to the socket interfaces to support IPv6 security is being

written [3].

9. Acknowledgments

Thanks to the many people who made suggestions and provided feedback

to to the numerous revisions of this document, including: Werner

Almesberger, Ran Atkinson, Fred Baker, Dave Borman, Andrew Cherenson,

Alex Conta, Alan Cox, Steve Deering, Richard Draves, Francis Dupont,

Robert Elz, Marc Hasson, Tim Hartrick, Tom Herbert, Bob Hinden, Wan-

Yen Hsu, Christian Huitema, Koji Imada, Markus Jork, Ron Lee, Alan

Lloyd, Charles Lynn, Jack McCann, Dan McDonald, Dave Mitton, Thomas

Narten, Erik Nordmark, Josh Osborne, Craig Partridge, Jean-Luc

Richier, Erik Scoredos, Keith Sklower, Matt Thomas, Harvey Thompson,

Dean D. Throop, Karen Tracey, Glenn Trewitt, Paul Vixie, David

Waitzman, Carl Williams, and Kazuhiko Yamamoto,

The getaddrinfo() and getnameinfo() functions are taken from an

earlier Work in Progress 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 made many contributions to this document. Ramesh Govindan

made a number of contributions and co-authored an earlier version of

this memo.

10. References

[1] Deering, S., and R. Hinden, "Internet Protocol, Version 6 (IPv6)

Specification", RFC1883, December 1995.

[2] Hinden, R., and S. Deering, "IP Version 6 Addressing Architecture",

RFC1884, December 1995.

[3] McDonald, D., "A Simple IP Security API Extension to BSD Sockets",

Work in Progress.

[4] IEEE, "Protocol Independent Interfaces", IEEE Std 1003.1g, DRAFT

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 in

IPv6", Work in Progress.

11. Authors' Addresses

Robert E. Gilligan

Freegate Corporation

710 Lakeway Dr. STE 230

Sunnyvale, CA 94086

Phone: +1 408 524 4804

EMail: gilligan@freegate.net

Susan Thomson

Bell Communications Research

MRE 2P-343, 445 South Street

Morristown, NJ 07960

Phone: +1 201 829 4514

EMail: set@thumper.bellcore.com

Jim Bound

Digital Equipment Corporation

110 Spitbrook Road ZK3-3/U14

Nashua, NH 03062-2698

Phone: +1 603 881 0400

Email: bound@zk3.dec.com

W. Richard Stevens

1202 E. Paseo del Zorro

Tucson, AZ 85718-2826

Phone: +1 520 297 9416

EMail: rstevens@kohala.com

 
 
 
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