draft-ietf-ipngwg-rfc2553bis-09.txt   rfc3493.txt 
IPNG Working Group R.E. Gilligan Network Working Group R. Gilligan
INTERNET-DRAFT: draft-ietf-ipngwg-rfc2553bis-09.txt Cache Flow Request for Comments: 3493 Intransa, Inc.
Obsoletes RFC 2553 S. Thomson Obsoletes: 2553 S. Thomson
Cisco Category: Informational Cisco
J. Bound J. Bound
J. McCann J. McCann
Hewlett-Packard Hewlett-Packard
W. R. Stevens W. Stevens
December 2002 February 2003
Basic Socket Interface Extensions for IPv6 Basic Socket Interface Extensions for IPv6
<draft-ietf-ipngwg-rfc2553bis-09.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This memo provides information for the Internet community. It does
all provisions of Section 10 of RFC2026. not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
This document is a submission by the Internet Protocol IPv6 Working
Group of the Internet Engineering Task Force (IETF). Comments should
be submitted to the ipng@sunroof.eng.sun.com mailing list.
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The list of current Internet-Drafts can be accessed at Copyright Notice
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at Copyright (C) The Internet Society (2003). All Rights Reserved.
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Abstract Abstract
The de facto standard application program interface (API) for TCP/IP The de facto standard Application Program Interface (API) for TCP/IP
applications is the "sockets" interface. Although this API was applications is the "sockets" interface. Although this API was
developed for Unix in the early 1980s it has also been implemented on developed for Unix in the early 1980s it has also been implemented on
a wide variety of non-Unix systems. TCP/IP applications written a wide variety of non-Unix systems. TCP/IP applications written
using the sockets API have in the past enjoyed a high degree of using the sockets API have in the past enjoyed a high degree of
portability and we would like the same portability with IPv6 portability and we would like the same portability with IPv6
applications. But changes are required to the sockets API to support applications. But changes are required to the sockets API to support
IPv6 and this memo describes these changes. These include a new IPv6 and this memo describes these changes. These include a new
socket address structure to carry IPv6 addresses, new address socket address structure to carry IPv6 addresses, new address
conversion functions, and some new socket options. These extensions conversion functions, and some new socket options. These extensions
are designed to provide access to the basic IPv6 features required by are designed to provide access to the basic IPv6 features required by
TCP and UDP applications, including multicasting, while introducing a TCP and UDP applications, including multicasting, while introducing a
minimum of change into the system and providing complete minimum of change into the system and providing complete
compatibility for existing IPv4 applications. Additional extensions compatibility for existing IPv4 applications. Additional extensions
for advanced IPv6 features (raw sockets and access to the IPv6 for advanced IPv6 features (raw sockets and access to the IPv6
extension headers) are defined in another document [4]. extension headers) are defined in another document.
Table of Contents: Table of Contents
1. Introduction................................................3
2. Design Considerations.......................................4
2.1 What Needs to be Changed...............................4
2.2 Data Types.............................................6
2.3 Headers................................................6
2.4 Structures.............................................6
3. Socket Interface............................................6
3.1 IPv6 Address Family and Protocol Family................6
3.2 IPv6 Address Structure.................................7
3.3 Socket Address Structure for 4.3BSD-Based Systems......7
3.4 Socket Address Structure for 4.4BSD-Based Systems......9
3.5 The Socket Functions...................................9
3.6 Compatibility with IPv4 Applications..................10
3.7 Compatibility with IPv4 Nodes.........................11
3.8 IPv6 Wildcard Address.................................11
3.9 IPv6 Loopback Address.................................13
3.10 Portability Additions.................................14
4. Interface Identification...................................16
4.1 Name-to-Index.........................................17
4.2 Index-to-Name.........................................17
4.3 Return All Interface Names and Indexes................18
4.4 Free Memory...........................................18
5. Socket Options.............................................18
5.1 Unicast Hop Limit.....................................19
5.2 Sending and Receiving Multicast Packets...............19
5.3 IPV6_V6ONLY option for AF_INET6 Sockets...............22
6. Library Functions..........................................22
6.1 Protocol-Independent Nodename and
Service Name Translation..............................23
6.2 Socket Address Structure to Node Name
and Service Name......................................28
6.3 Address Conversion Functions..........................31
6.4 Address Testing Macros................................33
7. Summary of New Definitions.................................33
8. Security Considerations....................................35
9. Changes from RFC 2553......................................35
10. Acknowledgments............................................36
11. References.................................................37
12. Authors' Addresses.........................................38
13. Full Copyright Statement...................................39
1. Introduction.................................................3
2. Design Considerations........................................3
2.1 What Needs to be Changed....................................4
2.2 Data Types..................................................5
2.3 Headers.....................................................5
2.4 Structures..................................................5
3. Socket Interface.............................................5
3.1 IPv6 Address Family and Protocol Family.....................6
3.2 IPv6 Address Structure......................................6
3.3 Socket Address Structure for 4.3BSD-Based Systems...........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
3.10 Portability Additions.....................................11
4. Interface Identification....................................13
4.1 Name-to-Index..............................................14
4.2 Index-to-Name..............................................14
4.3 Return All Interface Names and Indexes.....................14
4.4 Free Memory................................................15
5. Socket Options..............................................15
5.1 Unicast Hop Limit..........................................15
5.2 Sending and Receiving Multicast Packets....................16
5.3 IPV6_V6ONLY option for AF_INET6 Sockets....................18
6. Library Functions...........................................18
6.1 Protocol-Independent Nodename and Service Name Translation.19
6.2 Socket Address Structure to Node Name and Service Name.....23
6.3 Address Conversion Functions...............................25
6.4 Address Testing Macros.....................................26
7. Summary of New Definitions..................................27
8. Security Considerations.....................................29
Changes from RFC 2553..........................................29
Acknowledgments................................................29
References.....................................................30
Authors' Addresses.............................................31
1. Introduction 1. Introduction
While IPv4 addresses are 32 bits long, IPv6 addresses are 128 bits long. While IPv4 addresses are 32 bits long, IPv6 addresses are 128 bits
The socket interface makes the size of an IP address quite visible to an long. The socket interface makes the size of an IP address quite
application; virtually all TCP/IP applications for BSD-based systems visible to an application; virtually all TCP/IP applications for
have knowledge of the size of an IP address. Those parts of the API BSD-based systems have knowledge of the size of an IP address. Those
that expose the addresses must be changed to accommodate the larger IPv6 parts of the API that expose the addresses must be changed to
address size. IPv6 also introduces new features (e.g., traffic class accommodate the larger IPv6 address size. IPv6 also introduces new
and flowlabel), some of which must be made visible to applications via features, some of which must be made visible to applications via the
the API. This memo defines a set of extensions to the socket interface API. This memo defines a set of extensions to the socket interface
to support the larger address size and new features of IPv6. It defines to support the larger address size and new features of IPv6. It
"basic" extensions that are of use to a broad range of applications. A defines "basic" extensions that are of use to a broad range of
companion document, the "advanced" API [4], covers extensions that are applications. A companion document, the "advanced" API [4], covers
of use to more specialized applications, examples of which include extensions that are of use to more specialized applications, examples
routing daemons, and the "ping" and "traceroute" utilities. of which include routing daemons, and the "ping" and "traceroute"
utilities.
The development of this API was started in 1994 in the IETF IPng working The development of this API was started in 1994 in the IETF IPng
group. The API has evolved over the years, published first in RFC 2133, working group. The API has evolved over the years, published first
then again in RFC 2553, and reaching its final form in this document. in RFC 2133, then again in RFC 2553, and reaching its final form in
this document.
As the API matured and stabilized, it was incorporated into the Open As the API matured and stabilized, it was incorporated into the Open
Group's Networking Services (XNS) specification, issue 5.2, which was Group's Networking Services (XNS) specification, issue 5.2, which was
subsequently incorporated into a joint Open Group/IEEE/ISO standard [3]. subsequently incorporated into a joint Open Group/IEEE/ISO standard
[3].
Effort has been made to ensure that this document and [3] contain the Effort has been made to ensure that this document and [3] contain the
same information with regard to the API definitions. However, the same information with regard to the API definitions. However, the
reader should note that this document is for informational purposes reader should note that this document is for informational purposes
only, and that the official standard specification of the sockets API is only, and that the official standard specification of the sockets API
[3]. is [3].
It is expected that any future standardization work on this API would be It is expected that any future standardization work on this API would
done by the Open Group Base Working Group [6]. be done by the Open Group Base Working Group [6].
It should also be noted that this document describes only those portions It should also be noted that this document describes only those
of the API needed for IPv4 and IPv6 communications. Other potential portions of the API needed for IPv4 and IPv6 communications. Other
uses of the API, for example the use of getaddrinfo() and getnameinfo() potential uses of the API, for example the use of getaddrinfo() and
with the AF_UNIX address family, are beyond the scope of this document. getnameinfo() with the AF_UNIX address family, are beyond the scope
of this document.
2. Design Considerations 2. Design Considerations
There are a number of important considerations in designing changes to There are a number of important considerations in designing changes
this well-worn API: to this well-worn API:
- The API changes should provide both source and binary - The API changes should provide both source and binary
compatibility for programs written to the original API. That compatibility for programs written to the original API. That is,
is, existing program binaries should continue to operate when existing program binaries should continue to operate when run on a
run on a system supporting the new API. In addition, existing system supporting the new API. In addition, existing applications
applications that are re-compiled and run on a system supporting that are re-compiled and run on a system supporting the new API
the new API should continue to operate. Simply put, the API should continue to operate. Simply put, the API changes for IPv6
changes for IPv6 should not break existing programs. An additional should not break existing programs. An additional mechanism for
mechanism for implementations to verify this is to verify the new implementations to verify this is to verify the new symbols are
symbols are protected by Feature Test Macros as described in [3]. protected by Feature Test Macros as described in [3]. (Such
(Such Feature Test Macros are not defined by this RFC.) Feature Test Macros are not defined by this RFC.)
- The changes to the API should be as small as possible in order - The changes to the API should be as small as possible in order to
to simplify the task of converting existing IPv4 applications to simplify the task of converting existing IPv4 applications to
IPv6. IPv6.
- Where possible, applications should be able to use this - Where possible, applications should be able to use this API to
API to interoperate with both IPv6 and IPv4 hosts. Applications interoperate with both IPv6 and IPv4 hosts. Applications should
should not need to know which type of host they are not need to know which type of host they are communicating with.
communicating with.
- IPv6 addresses carried in data structures should be 64-bit - IPv6 addresses carried in data structures should be 64-bit
aligned. This is necessary in order to obtain optimum aligned. This is necessary in order to obtain optimum performance
performance on 64-bit machine architectures. on 64-bit machine architectures.
Because of the importance of providing IPv4 compatibility in the API, Because of the importance of providing IPv4 compatibility in the API,
these extensions are explicitly designed to operate on machines that these extensions are explicitly designed to operate on machines that
provide complete support for both IPv4 and IPv6. A subset of this API provide complete support for both IPv4 and IPv6. A subset of this
could probably be designed for operation on systems that support only API could probably be designed for operation on systems that support
IPv6. However, this is not addressed in this memo. only IPv6. However, this is not addressed in this memo.
2.1 What Needs to be Changed 2.1 What Needs to be Changed
The socket interface API consists of a few distinct components: The socket interface API consists of a few distinct components:
- Core socket functions. - Core socket functions.
- Address data structures. - Address data structures.
- Name-to-address translation functions. - Name-to-address translation functions.
- Address conversion functions. - Address conversion functions.
The core socket functions -- those functions that deal with such things The core socket functions -- those functions that deal with such
as setting up and tearing down TCP connections, and sending and things as setting up and tearing down TCP connections, and sending
receiving UDP packets -- were designed to be transport independent. and receiving UDP packets -- were designed to be transport
Where protocol addresses are passed as function arguments, they are independent. Where protocol addresses are passed as function
carried via opaque pointers. A protocol-specific address data structure arguments, they are carried via opaque pointers. A protocol-specific
is defined for each protocol that the socket functions support. address data structure is defined for each protocol that the socket
Applications must cast pointers to these protocol-specific address functions support. Applications must cast pointers to these
structures into pointers to the generic "sockaddr" address structure protocol-specific address structures into pointers to the generic
when using the socket functions. These functions need not change for "sockaddr" address structure when using the socket functions. These
IPv6, but a new IPv6-specific address data structure is needed. 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 The "sockaddr_in" structure is the protocol-specific data structure
IPv4. This data structure actually includes 8-octets of unused space, for IPv4. This data structure actually includes 8-octets of unused
and it is tempting to try to use this space to adapt the sockaddr_in space, and it is tempting to try to use this space to adapt the
structure to IPv6. Unfortunately, the sockaddr_in structure is not sockaddr_in structure to IPv6. Unfortunately, the sockaddr_in
large enough to hold the 16-octet IPv6 address as well as the other structure is not large enough to hold the 16-octet IPv6 address as
information (address family and port number) that is needed. So a new well as the other information (address family and port number) that
address data structure must be defined for IPv6. is needed. So a new address data structure must be defined for IPv6.
IPv6 addresses are scoped [2] so they could be link-local, site, IPv6 addresses are scoped [2] so they could be link-local, site,
organization, global, or other scopes at this time undefined. To organization, global, or other scopes at this time undefined. To
support applications that want to be able to identify a set of support applications that want to be able to identify a set of
interfaces for a specific scope, the IPv6 sockaddr_in structure must interfaces for a specific scope, the IPv6 sockaddr_in structure must
support a field that can be used by an implementation to identify a set support a field that can be used by an implementation to identify a
of interfaces identifying the scope for an IPv6 address. set of interfaces identifying the scope for an IPv6 address.
The IPv4 name-to-address translation functions in the socket interface The IPv4 name-to-address translation functions in the socket
are gethostbyname() and gethostbyaddr(). These are left as is, and new interface are gethostbyname() and gethostbyaddr(). These are left as
functions are defined which support both IPv4 and IPv6. is, and new functions are defined which support both IPv4 and IPv6.
The IPv4 address conversion functions -- inet_ntoa() and inet_addr() -- The IPv4 address conversion functions -- inet_ntoa() and inet_addr()
convert IPv4 addresses between binary and printable form. These -- convert IPv4 addresses between binary and printable form. These
functions are quite specific to 32-bit IPv4 addresses. We have designed functions are quite specific to 32-bit IPv4 addresses. We have
two analogous functions that convert both IPv4 and IPv6 addresses, and designed two analogous functions that convert both IPv4 and IPv6
carry an address type parameter so that they can be extended to other addresses, and carry an address type parameter so that they can be
protocol families as well. extended to other protocol families as well.
Finally, a few miscellaneous features are needed to support IPv6. New Finally, a few miscellaneous features are needed to support IPv6. A
interfaces are needed to support the IPv6 traffic class, flow label, and new interface is needed to support the IPv6 hop limit header field.
hop limit header fields. New socket options are needed to control the New socket options are needed to control the sending and receiving of
sending and receiving of IPv6 multicast packets. IPv6 multicast packets.
The socket interface will be enhanced in the future to provide access to The socket interface will be enhanced in the future to provide access
other IPv6 features. These extensions are described in [4]. to other IPv6 features. Some of these extensions are described in
[4].
2.2 Data Types 2.2 Data Types
The data types of the structure elements given in this memo are intended The data types of the structure elements given in this memo are
to track the relevant standards. uintN_t means an unsigned integer of intended to track the relevant standards. uintN_t means an unsigned
exactly N bits (e.g., uint16_t). The sa_family_t and in_port_t types integer of exactly N bits (e.g., uint16_t). The sa_family_t and
are defined in [3]. in_port_t types are defined in [3].
2.3 Headers 2.3 Headers
When function prototypes and structures are shown we show the headers When function prototypes and structures are shown we show the headers
that must be #included to cause that item to be defined. that must be #included to cause that item to be defined.
2.4 Structures 2.4 Structures
When structures are described the members shown are the ones that must When structures are described the members shown are the ones that
appear in an implementation. Additional, nonstandard members may also must appear in an implementation. Additional, nonstandard members
be defined by an implementation. As an additional precaution may also be defined by an implementation. As an additional
nonstandard members could be verified by Feature Test Macros as precaution nonstandard members could be verified by Feature Test
described in [3]. (Such Feature Test Macros are not defined by this Macros as described in [3]. (Such Feature Test Macros are not
RFC.) defined by this RFC.)
The ordering shown for the members of a structure is the recommended The ordering shown for the members of a structure is the recommended
ordering, given alignment considerations of multibyte members, but an ordering, given alignment considerations of multibyte members, but an
implementation may order the members differently. implementation may order the members differently.
3. Socket Interface 3. Socket Interface
This section specifies the socket interface changes for IPv6. This section specifies the socket interface changes for IPv6.
3.1 IPv6 Address Family and Protocol Family 3.1 IPv6 Address Family and Protocol Family
A new address family name, AF_INET6, is defined in <sys/socket.h>. The A new address family name, AF_INET6, is defined in <sys/socket.h>.
AF_INET6 definition distinguishes between the original sockaddr_in The AF_INET6 definition distinguishes between the original
address data structure, and the new sockaddr_in6 data structure. 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>. 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 Like most of the other protocol family names, this will usually be
defined to have the same value as the corresponding address family name: defined to have the same value as the corresponding address family
name:
#define PF_INET6 AF_INET6 #define PF_INET6 AF_INET6
The AF_INET6 is used in the first argument to the socket() function to The AF_INET6 is used in the first argument to the socket() function
indicate that an IPv6 socket is being created. to indicate that an IPv6 socket is being created.
3.2 IPv6 Address Structure 3.2 IPv6 Address Structure
A new in6_addr structure holds a single IPv6 address and is defined as a A new in6_addr structure holds a single IPv6 address and is defined
result of including <netinet/in.h>: as a result of including <netinet/in.h>:
struct in6_addr { struct in6_addr {
uint8_t s6_addr[16]; /* IPv6 address */ uint8_t s6_addr[16]; /* IPv6 address */
}; };
This data structure contains an array of sixteen 8-bit elements, which This data structure contains an array of sixteen 8-bit elements,
make up one 128-bit IPv6 address. The IPv6 address is stored in network which make up one 128-bit IPv6 address. The IPv6 address is stored
byte order. in network byte order.
The structure in6_addr above is usually implemented with an embedded The structure in6_addr above is usually implemented with an embedded
union with extra fields that force the desired alignment level in a union with extra fields that force the desired alignment level in a
manner similar to BSD implementations of "struct in_addr". Those manner similar to BSD implementations of "struct in_addr". Those
additional implementation details are omitted here for simplicity. additional implementation details are omitted here for simplicity.
An example is as follows: An example is as follows:
struct in6_addr { struct in6_addr {
union { union {
uint8_t _S6_u8[16]; uint8_t _S6_u8[16];
uint32_t _S6_u32[4]; uint32_t _S6_u32[4];
uint64_t _S6_u64[2]; uint64_t _S6_u64[2];
} _S6_un; } _S6_un;
}; };
#define s6_addr _S6_un._S6_u8 #define s6_addr _S6_un._S6_u8
3.3 Socket Address Structure for 4.3BSD-Based Systems 3.3 Socket Address Structure for 4.3BSD-Based Systems
In the socket interface, a different protocol-specific data structure is In the socket interface, a different protocol-specific data structure
defined to carry the addresses for each protocol suite. Each protocol- is defined to carry the addresses for each protocol suite. Each
specific data structure is designed so it can be cast into a protocol- protocol-specific data structure is designed so it can be cast into a
independent data structure -- the "sockaddr" structure. Each has a protocol-independent data structure -- the "sockaddr" structure.
"family" field that overlays the "sa_family" of the sockaddr data Each has a "family" field that overlays the "sa_family" of the
structure. This field identifies the type of the data structure. sockaddr data structure. This field identifies the type of the data
structure.
The sockaddr_in structure is the protocol-specific address data The sockaddr_in structure is the protocol-specific address data
structure for IPv4. It is used to pass addresses between applications structure for IPv4. It is used to pass addresses between
and the system in the socket functions. The following sockaddr_in6 applications and the system in the socket functions. The following
structure holds IPv6 addresses and is defined as a result of including sockaddr_in6 structure holds IPv6 addresses and is defined as a
the <netinet/in.h> header: result of including the <netinet/in.h> header:
struct sockaddr_in6 { struct sockaddr_in6 {
sa_family_t sin6_family; /* AF_INET6 */ sa_family_t sin6_family; /* AF_INET6 */
in_port_t sin6_port; /* transport layer port # */ in_port_t sin6_port; /* transport layer port # */
uint32_t sin6_flowinfo; /* IPv6 traffic class & flow info */ uint32_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */ struct in6_addr sin6_addr; /* IPv6 address */
uint32_t sin6_scope_id; /* set of interfaces for a scope */ uint32_t sin6_scope_id; /* set of interfaces for a scope */
}; };
This structure is designed to be compatible with the sockaddr data This structure is designed to be compatible with the sockaddr data
structure used in the 4.3BSD release. structure used in the 4.3BSD release.
The sin6_family field identifies this as a sockaddr_in6 structure. This The sin6_family field identifies this as a sockaddr_in6 structure.
field overlays the sa_family field when the buffer is cast to a sockaddr This field overlays the sa_family field when the buffer is cast to a
data structure. The value of this field must be AF_INET6. 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 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 field is used in the same way as the sin_port field of the
structure. The port number is stored in network byte order. sockaddr_in structure. The port number is stored in network byte
order.
The sin6_flowinfo field is a 32-bit field intended to contain flow- The sin6_flowinfo field is a 32-bit field intended to contain flow-
related information. The exact way this field is mapped to or from a related information. The exact way this field is mapped to or from a
packet is not currently specified. Until such time as its use is packet is not currently specified. Until such time as its use is
specified, applications should set this field to zero when constructing specified, applications should set this field to zero when
a sockaddr_in6, and ignore this field in a sockaddr_in6 structure constructing a sockaddr_in6, and ignore this field in a sockaddr_in6
constructed by the system. structure constructed by the system.
The sin6_addr field is a single in6_addr structure (defined in the The sin6_addr field is a single in6_addr structure (defined in the
previous section). This field holds one 128-bit IPv6 address. The previous section). This field holds one 128-bit IPv6 address. The
address is stored in network byte order. address is stored in network byte order.
The ordering of elements in this structure is specifically designed so The ordering of elements in this structure is specifically designed
that when sin6_addr field is aligned on a 64-bit boundary, the start of so that when sin6_addr field is aligned on a 64-bit boundary, the
the structure will also be aligned on a 64-bit boundary. This is done start of the structure will also be aligned on a 64-bit boundary.
for optimum performance on 64-bit architectures. This is done for optimum performance on 64-bit architectures.
The sin6_scope_id field is a 32-bit integer that identifies a set of The sin6_scope_id field is a 32-bit integer that identifies a set of
interfaces as appropriate for the scope [2] of the address carried in interfaces as appropriate for the scope [2] of the address carried in
the sin6_addr field. The mapping of sin6_scope_id to an interface or the sin6_addr field. The mapping of sin6_scope_id to an interface or
set of interfaces is left to implementation and future specifications on set of interfaces is left to implementation and future specifications
the subject of scoped addresses. on the subject of scoped addresses.
Notice that the sockaddr_in6 structure will normally be larger than the Notice that the sockaddr_in6 structure will normally be larger than
generic sockaddr structure. On many existing implementations the the generic sockaddr structure. On many existing implementations the
sizeof(struct sockaddr_in) equals sizeof(struct sockaddr), with both sizeof(struct sockaddr_in) equals sizeof(struct sockaddr), with both
being 16 bytes. Any existing code that makes this assumption needs to being 16 bytes. Any existing code that makes this assumption needs
be examined carefully when converting to IPv6. to be examined carefully when converting to IPv6.
3.4 Socket Address Structure for 4.4BSD-Based Systems 3.4 Socket Address Structure for 4.4BSD-Based Systems
The 4.4BSD release includes a small, but incompatible change to the The 4.4BSD release includes a small, but incompatible change to the
socket interface. The "sa_family" field of the sockaddr data structure socket interface. The "sa_family" field of the sockaddr data
was changed from a 16-bit value to an 8-bit value, and the space saved structure was changed from a 16-bit value to an 8-bit value, and the
used to hold a length field, named "sa_len". The sockaddr_in6 data space saved used to hold a length field, named "sa_len". The
structure given in the previous section cannot be correctly cast into sockaddr_in6 data structure given in the previous section cannot be
the newer sockaddr data structure. For this reason, the following correctly cast into the newer sockaddr data structure. For this
alternative IPv6 address data structure is provided to be used on reason, the following alternative IPv6 address data structure is
systems based on 4.4BSD. It is defined as a result of including the provided to be used on systems based on 4.4BSD. It is defined as a
<netinet/in.h> header. result of including the <netinet/in.h> header.
struct sockaddr_in6 { struct sockaddr_in6 {
uint8_t sin6_len; /* length of this struct */ uint8_t sin6_len; /* length of this struct */
sa_family_t sin6_family; /* AF_INET6 */ sa_family_t sin6_family; /* AF_INET6 */
in_port_t sin6_port; /* transport layer port # */ in_port_t sin6_port; /* transport layer port # */
uint32_t sin6_flowinfo; /* IPv6 flow information */ uint32_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */ struct in6_addr sin6_addr; /* IPv6 address */
uint32_t sin6_scope_id; /* set of interfaces for a scope */ uint32_t sin6_scope_id; /* set of interfaces for a scope */
}; };
The only differences between this data structure and the 4.3BSD variant The only differences between this data structure and the 4.3BSD
are the inclusion of the length field, and the change of the family variant are the inclusion of the length field, and the change of the
field to a 8-bit data type. The definitions of all the other fields are family field to a 8-bit data type. The definitions of all the other
identical to the structure defined in the previous section. fields are identical to the structure defined in the previous
section.
Systems that provide this version of the sockaddr_in6 data structure 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> must also declare SIN6_LEN as a result of including the
header. This macro allows applications to determine whether they are <netinet/in.h> header. This macro allows applications to determine
being built on a system that supports the 4.3BSD or 4.4BSD variants of whether they are being built on a system that supports the 4.3BSD or
the data structure. 4.4BSD variants of the data structure.
3.5 The Socket Functions 3.5 The Socket Functions
Applications call the socket() function to create a socket descriptor Applications call the socket() function to create a socket descriptor
that represents a communication endpoint. The arguments to the socket() that represents a communication endpoint. The arguments to the
function tell the system which protocol to use, and what format address socket() function tell the system which protocol to use, and what
structure will be used in subsequent functions. For example, to create format address structure will be used in subsequent functions. For
an IPv4/TCP socket, applications make the call: example, to create an IPv4/TCP socket, applications make the call:
s = socket(AF_INET, SOCK_STREAM, 0); s = socket(AF_INET, SOCK_STREAM, 0);
To create an IPv4/UDP socket, applications make the call: To create an IPv4/UDP socket, applications make the call:
s = socket(AF_INET, SOCK_DGRAM, 0); s = socket(AF_INET, SOCK_DGRAM, 0);
Applications may create IPv6/TCP and IPv6/UDP sockets (which may also Applications may create IPv6/TCP and IPv6/UDP sockets (which may also
handle IPv4 communication as described in section 3.7) by simply using handle IPv4 communication as described in section 3.7) by simply
the constant AF_INET6 instead of AF_INET in the first argument. For using the constant AF_INET6 instead of AF_INET in the first argument.
example, to create an IPv6/TCP socket, applications make the call: For example, to create an IPv6/TCP socket, applications make the
call:
s = socket(AF_INET6, SOCK_STREAM, 0); s = socket(AF_INET6, SOCK_STREAM, 0);
To create an IPv6/UDP socket, applications make the call: To create an IPv6/UDP socket, applications make the call:
s = socket(AF_INET6, SOCK_DGRAM, 0); s = socket(AF_INET6, SOCK_DGRAM, 0);
Once the application has created a AF_INET6 socket, it must use the Once the application has created a AF_INET6 socket, it must use the
sockaddr_in6 address structure when passing addresses in to the system. sockaddr_in6 address structure when passing addresses in to the
The functions that the application uses to pass addresses into the system. The functions that the application uses to pass addresses
system are: into the system are:
bind() bind()
connect() connect()
sendmsg() sendmsg()
sendto() sendto()
The system will use the sockaddr_in6 address structure to return The system will use the sockaddr_in6 address structure to return
addresses to applications that are using AF_INET6 sockets. The addresses to applications that are using AF_INET6 sockets. The
functions that return an address from the system to an application are: functions that return an address from the system to an application
are:
accept() accept()
recvfrom() recvfrom()
recvmsg() recvmsg()
getpeername() getpeername()
getsockname() getsockname()
No changes to the syntax of the socket functions are needed to support No changes to the syntax of the socket functions are needed to
IPv6, since all of the "address carrying" functions use an opaque support IPv6, since all of the "address carrying" functions use an
address pointer, and carry an address length as a function argument. opaque address pointer, and carry an address length as a function
argument.
3.6 Compatibility with IPv4 Applications 3.6 Compatibility with IPv4 Applications
In order to support the large base of applications using the original In order to support the large base of applications using the original
API, system implementations must provide complete source and binary API, system implementations must provide complete source and binary
compatibility with the original API. This means that systems must compatibility with the original API. This means that systems must
continue to support AF_INET sockets and the sockaddr_in address continue to support AF_INET sockets and the sockaddr_in address
structure. Applications must be able to create IPv4/TCP and IPv4/UDP structure. Applications must be able to create IPv4/TCP and IPv4/UDP
sockets using the AF_INET constant in the socket() function, as sockets using the AF_INET constant in the socket() function, as
described in the previous section. Applications should be able to hold described in the previous section. Applications should be able to
a combination of IPv4/TCP, IPv4/UDP, IPv6/TCP and IPv6/UDP sockets hold a combination of IPv4/TCP, IPv4/UDP, IPv6/TCP and IPv6/UDP
simultaneously within the same process. sockets simultaneously within the same process.
Applications using the original API should continue to operate as they Applications using the original API should continue to operate as
did on systems supporting only IPv4. That is, they should continue to they did on systems supporting only IPv4. That is, they should
interoperate with IPv4 nodes. continue to interoperate with IPv4 nodes.
3.7 Compatibility with IPv4 Nodes 3.7 Compatibility with IPv4 Nodes
The API also provides a different type of compatibility: the ability for The API also provides a different type of compatibility: the ability
IPv6 applications to interoperate with IPv4 applications. This feature for IPv6 applications to interoperate with IPv4 applications. This
uses the IPv4-mapped IPv6 address format defined in the IPv6 addressing feature uses the IPv4-mapped IPv6 address format defined in the IPv6
architecture specification [2]. This address format allows the IPv4 addressing architecture specification [2]. This address format
address of an IPv4 node to be represented as an IPv6 address. The IPv4 allows the IPv4 address of an IPv4 node to be represented as an IPv6
address is encoded into the low-order 32 bits of the IPv6 address, and address. The IPv4 address is encoded into the low-order 32 bits of
the high-order 96 bits hold the fixed prefix 0:0:0:0:0:FFFF. IPv4- the IPv6 address, and the high-order 96 bits hold the fixed prefix
mapped addresses are written as follows: 0:0:0:0:0:FFFF. IPv4-mapped addresses are written as follows:
::FFFF:<IPv4-address> ::FFFF:<IPv4-address>
These addresses can be generated automatically by the getaddrinfo() These addresses can be generated automatically by the getaddrinfo()
function, as described in Section 6.1. function, as described in Section 6.1.
Applications may use AF_INET6 sockets to open TCP connections to IPv4 Applications may use AF_INET6 sockets to open TCP connections to IPv4
nodes, or send UDP packets to IPv4 nodes, by simply encoding the nodes, or send UDP packets to IPv4 nodes, by simply encoding the
destination's IPv4 address as an IPv4-mapped IPv6 address, and passing destination's IPv4 address as an IPv4-mapped IPv6 address, and
that address, within a sockaddr_in6 structure, in the connect() or passing that address, within a sockaddr_in6 structure, in the
sendto() call. When applications use AF_INET6 sockets to accept TCP connect() or sendto() call. When applications use AF_INET6 sockets
connections from IPv4 nodes, or receive UDP packets from IPv4 nodes, the to accept TCP connections from IPv4 nodes, or receive UDP packets
system returns the peer's address to the application in the accept(), from IPv4 nodes, the system returns the peer's address to the
recvfrom(), or getpeername() call using a sockaddr_in6 structure encoded application in the accept(), recvfrom(), or getpeername() call using
this way. a sockaddr_in6 structure encoded this way.
Few applications will likely need to know which type of node they are Few applications will likely need to know which type of node they are
interoperating with. However, for those applications that do need to interoperating with. However, for those applications that do need to
know, the IN6_IS_ADDR_V4MAPPED() macro, defined in Section 6.7, is know, the IN6_IS_ADDR_V4MAPPED() macro, defined in Section 6.4, is
provided. provided.
3.8 IPv6 Wildcard Address 3.8 IPv6 Wildcard Address
While the bind() function allows applications to select the source IP While the bind() function allows applications to select the source IP
address of UDP packets and TCP connections, applications often want the address of UDP packets and TCP connections, applications often want
system to select the source address for them. With IPv4, one specifies the system to select the source address for them. With IPv4, one
the address as the symbolic constant INADDR_ANY (called the "wildcard" specifies the address as the symbolic constant INADDR_ANY (called the
address) in the bind() call, or simply omits the bind() entirely. "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 Since the IPv6 address type is a structure (struct in6_addr), a
constant can be used to initialize an IPv6 address variable, but cannot symbolic constant can be used to initialize an IPv6 address variable,
be used in an assignment. Therefore systems provide the IPv6 wildcard but cannot be used in an assignment. Therefore systems provide the
address in two forms. IPv6 wildcard address in two forms.
The first version is a global variable named "in6addr_any" that is an The first version is a global variable named "in6addr_any" that is an
in6_addr structure. The extern declaration for this variable is defined in6_addr structure. The extern declaration for this variable is
in <netinet/in.h>: defined in <netinet/in.h>:
extern const struct in6_addr in6addr_any; extern const struct in6_addr in6addr_any;
Applications use in6addr_any similarly to the way they use INADDR_ANY in Applications use in6addr_any similarly to the way they use INADDR_ANY
IPv4. For example, to bind a socket to port number 23, but let the in IPv4. For example, to bind a socket to port number 23, but let
system select the source address, an application could use the following the system select the source address, an application could use the
code: following code:
struct sockaddr_in6 sin6; struct sockaddr_in6 sin6;
. . . . . .
sin6.sin6_family = AF_INET6; sin6.sin6_family = AF_INET6;
sin6.sin6_flowinfo = 0; sin6.sin6_flowinfo = 0;
sin6.sin6_port = htons(23); sin6.sin6_port = htons(23);
sin6.sin6_addr = in6addr_any; /* structure assignment */ sin6.sin6_addr = in6addr_any; /* structure assignment */
. . . . . .
if (bind(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1) if (bind(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1)
. . . . . .
The other version is a symbolic constant named IN6ADDR_ANY_INIT and is The other version is a symbolic constant named IN6ADDR_ANY_INIT and
defined in <netinet/in.h>. This constant can be used to initialize an is defined in <netinet/in.h>. This constant can be used to
in6_addr structure: initialize an in6_addr structure:
struct in6_addr anyaddr = IN6ADDR_ANY_INIT; struct in6_addr anyaddr = IN6ADDR_ANY_INIT;
Note that this constant can be used ONLY at declaration time. It can 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 not be used to assign a previously declared in6_addr structure. For
example, the following code will not work: example, the following code will not work:
/* This is the WRONG way to assign an unspecified address */ /* This is the WRONG way to assign an unspecified address */
struct sockaddr_in6 sin6; struct sockaddr_in6 sin6;
. . . . . .
sin6.sin6_addr = IN6ADDR_ANY_INIT; /* will NOT compile */ sin6.sin6_addr = IN6ADDR_ANY_INIT; /* will NOT compile */
Be aware that the IPv4 INADDR_xxx constants are all defined in host byte Be aware that the IPv4 INADDR_xxx constants are all defined in host
order but the IPv6 IN6ADDR_xxx constants and the IPv6 in6addr_xxx byte order but the IPv6 IN6ADDR_xxx constants and the IPv6
externals are defined in network byte order. in6addr_xxx externals are defined in network byte order.
3.9 IPv6 Loopback Address 3.9 IPv6 Loopback Address
Applications may need to send UDP packets to, or originate TCP Applications may need to send UDP packets to, or originate TCP
connections to, services residing on the local node. In IPv4, they can connections to, services residing on the local node. In IPv4, they
do this by using the constant IPv4 address INADDR_LOOPBACK in their can do this by using the constant IPv4 address INADDR_LOOPBACK in
connect(), sendto(), or sendmsg() call. their connect(), sendto(), or sendmsg() call.
IPv6 also provides a loopback address to contact local TCP and UDP IPv6 also provides a loopback address to contact local TCP and UDP
services. Like the unspecified address, the IPv6 loopback address is services. Like the unspecified address, the IPv6 loopback address is
provided in two forms -- a global variable and a symbolic constant. provided in two forms -- a global variable and a symbolic constant.
The global variable is an in6_addr structure named "in6addr_loopback." The global variable is an in6_addr structure named
The extern declaration for this variable is defined in <netinet/in.h>: "in6addr_loopback." The extern declaration for this variable is
defined in <netinet/in.h>:
extern const struct in6_addr in6addr_loopback; extern const struct in6_addr in6addr_loopback;
Applications use in6addr_loopback as they would use INADDR_LOOPBACK in Applications use in6addr_loopback as they would use INADDR_LOOPBACK
IPv4 applications (but beware of the byte ordering difference mentioned in IPv4 applications (but beware of the byte ordering difference
at the end of the previous section). For example, to open a TCP mentioned at the end of the previous section). For example, to open
connection to the local telnet server, an application could use the a TCP connection to the local telnet server, an application could use
following code: the following code:
struct sockaddr_in6 sin6; struct sockaddr_in6 sin6;
. . . . . .
sin6.sin6_family = AF_INET6; sin6.sin6_family = AF_INET6;
sin6.sin6_flowinfo = 0; sin6.sin6_flowinfo = 0;
sin6.sin6_port = htons(23); sin6.sin6_port = htons(23);
sin6.sin6_addr = in6addr_loopback; /* structure assignment */ sin6.sin6_addr = in6addr_loopback; /* structure assignment */
. . . . . .
if (connect(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1) if (connect(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1)
. . . . . .
The symbolic constant is named IN6ADDR_LOOPBACK_INIT and is defined in The symbolic constant is named IN6ADDR_LOOPBACK_INIT and is defined
<netinet/in.h>. It can be used at declaration time ONLY; for example: in <netinet/in.h>. It can be used at declaration time ONLY; for
example:
struct in6_addr loopbackaddr = IN6ADDR_LOOPBACK_INIT; struct in6_addr loopbackaddr = IN6ADDR_LOOPBACK_INIT;
Like IN6ADDR_ANY_INIT, this constant cannot be used in an assignment to Like IN6ADDR_ANY_INIT, this constant cannot be used in an assignment
a previously declared IPv6 address variable. to a previously declared IPv6 address variable.
3.10 Portability Additions 3.10 Portability Additions
One simple addition to the sockets API that can help application writers One simple addition to the sockets API that can help application
is the "struct sockaddr_storage". This data structure can simplify writers is the "struct sockaddr_storage". This data structure can
writing code that is portable across multiple address families and simplify writing code that is portable across multiple address
platforms. This data structure is designed with the following goals. families and platforms. This data structure is designed with the
following goals.
- Large enough to accommodate all supported protocol-specific address - Large enough to accommodate all supported protocol-specific address
structures. structures.
- Aligned at an appropriate boundary so that pointers to it can be cast - Aligned at an appropriate boundary so that pointers to it can be
as pointers to protocol specific address structures and used to cast as pointers to protocol specific address structures and used
access the fields of those structures without alignment problems. to access the fields of those structures without alignment
problems.
The sockaddr_storage structure contains field ss_family which is of type The sockaddr_storage structure contains field ss_family which is of
sa_family_t. When a sockaddr_storage structure is cast to a sockaddr type sa_family_t. When a sockaddr_storage structure is cast to a
structure, the ss_family field of the sockaddr_storage structure maps sockaddr structure, the ss_family field of the sockaddr_storage
onto the sa_family field of the sockaddr structure. When a structure maps onto the sa_family field of the sockaddr structure.
sockaddr_storage structure is cast as a protocol specific address When a sockaddr_storage structure is cast as a protocol specific
structure, the ss_family field maps onto a field of that structure that address structure, the ss_family field maps onto a field of that
is of type sa_family_t and that identifies the protocol's address structure that is of type sa_family_t and that identifies the
family. protocol's address family.
An example implementation design of such a data structure would be as An example implementation design of such a data structure would be as
follows. follows.
/* /*
* Desired design of maximum size and alignment * Desired design of maximum size and alignment
*/ */
#define _SS_MAXSIZE 128 /* Implementation specific max size */ #define _SS_MAXSIZE 128 /* Implementation specific max size */
#define _SS_ALIGNSIZE (sizeof (int64_t)) #define _SS_ALIGNSIZE (sizeof (int64_t))
/* Implementation specific desired alignment */ /* Implementation specific desired alignment */
/* /*
* Definitions used for sockaddr_storage structure paddings design. * Definitions used for sockaddr_storage structure paddings design.
*/ */
#define _SS_PAD1SIZE (_SS_ALIGNSIZE - sizeof (sa_family_t)) #define _SS_PAD1SIZE (_SS_ALIGNSIZE - sizeof (sa_family_t))
#define _SS_PAD2SIZE (_SS_MAXSIZE - (sizeof (sa_family_t) + #define _SS_PAD2SIZE (_SS_MAXSIZE - (sizeof (sa_family_t) +
_SS_PAD1SIZE + _SS_ALIGNSIZE)) _SS_PAD1SIZE + _SS_ALIGNSIZE))
struct sockaddr_storage { struct sockaddr_storage {
sa_family_t ss_family; /* address family */ sa_family_t ss_family; /* address family */
/* Following fields are implementation specific */ /* Following fields are implementation specific */
char __ss_pad1[_SS_PAD1SIZE]; char __ss_pad1[_SS_PAD1SIZE];
skipping to change at page 12, line 51 skipping to change at page 15, line 35
/* specific pad up to alignment field that */ /* specific pad up to alignment field that */
/* follows explicit in the data structure */ /* follows explicit in the data structure */
int64_t __ss_align; /* field to force desired structure */ int64_t __ss_align; /* field to force desired structure */
/* storage alignment */ /* storage alignment */
char __ss_pad2[_SS_PAD2SIZE]; char __ss_pad2[_SS_PAD2SIZE];
/* 112 byte pad to achieve desired size, */ /* 112 byte pad to achieve desired size, */
/* _SS_MAXSIZE value minus size of ss_family */ /* _SS_MAXSIZE value minus size of ss_family */
/* __ss_pad1, __ss_align fields is 112 */ /* __ss_pad1, __ss_align fields is 112 */
}; };
The above example implementation illustrates a data structure which will The above example implementation illustrates a data structure which
align on a 64-bit boundary. An implementation-specific field will align on a 64-bit boundary. An implementation-specific field
"__ss_align" along with "__ss_pad1" is used to force a 64-bit alignment "__ss_align" along with "__ss_pad1" is used to force a 64-bit
which covers proper alignment good enough for the needs of sockaddr_in6 alignment which covers proper alignment good enough for the needs of
(IPv6), sockaddr_in (IPv4) address data structures. The size of padding sockaddr_in6 (IPv6), sockaddr_in (IPv4) address data structures. The
field __ss_pad1 depends on the chosen alignment boundary. The size of size of padding field __ss_pad1 depends on the chosen alignment
padding field __ss_pad2 depends on the value of overall size chosen for boundary. The size of padding field __ss_pad2 depends on the value
the total size of the structure. This size and alignment are represented of overall size chosen for the total size of the structure. This
in the above example by implementation specific (not required) constants size and alignment are represented in the above example by
_SS_MAXSIZE (chosen value 128) and _SS_ALIGNSIZE (with chosen value 8). implementation specific (not required) constants _SS_MAXSIZE (chosen
Constants _SS_PAD1SIZE (derived value 6) and _SS_PAD2SIZE (derived value value 128) and _SS_ALIGNSIZE (with chosen value 8). Constants
112) are also for illustration and not required. The derived values _SS_PAD1SIZE (derived value 6) and _SS_PAD2SIZE (derived value 112)
assume sa_family_t is 2 bytes. The implementation specific definitions are also for illustration and not required. The derived values
and structure field names above start with an underscore to denote assume sa_family_t is 2 bytes. The implementation specific
implementation private namespace. Portable code is not expected to definitions and structure field names above start with an underscore
access or reference those fields or constants. to denote implementation private namespace. Portable code is not
expected to access or reference those fields or constants.
On implementations where the sockaddr data structure includes a "sa_len" On implementations where the sockaddr data structure includes a
field this data structure would look like this: "sa_len" field this data structure would look like this:
/* /*
* Definitions used for sockaddr_storage structure paddings design. * Definitions used for sockaddr_storage structure paddings design.
*/ */
#define _SS_PAD1SIZE (_SS_ALIGNSIZE - #define _SS_PAD1SIZE (_SS_ALIGNSIZE -
(sizeof (uint8_t) + sizeof (sa_family_t)) (sizeof (uint8_t) + sizeof (sa_family_t))
#define _SS_PAD2SIZE (_SS_MAXSIZE - #define _SS_PAD2SIZE (_SS_MAXSIZE -
(sizeof (uint8_t) + sizeof (sa_family_t) + (sizeof (uint8_t) + sizeof (sa_family_t) +
_SS_PAD1SIZE + _SS_ALIGNSIZE)) _SS_PAD1SIZE + _SS_ALIGNSIZE))
struct sockaddr_storage { struct sockaddr_storage {
skipping to change at page 13, line 39 skipping to change at page 16, line 34
int64_t __ss_align; /* field to force desired structure */ int64_t __ss_align; /* field to force desired structure */
/* storage alignment */ /* storage alignment */
char __ss_pad2[_SS_PAD2SIZE]; char __ss_pad2[_SS_PAD2SIZE];
/* 112 byte pad to achieve desired size, */ /* 112 byte pad to achieve desired size, */
/* _SS_MAXSIZE value minus size of ss_len, */ /* _SS_MAXSIZE value minus size of ss_len, */
/* __ss_family, __ss_pad1, __ss_align fields is 112 */ /* __ss_family, __ss_pad1, __ss_align fields is 112 */
}; };
4. Interface Identification 4. Interface Identification
This API uses an interface index (a small positive integer) to identify This API uses an interface index (a small positive integer) to
the local interface on which a multicast group is joined (Section 5.3). identify the local interface on which a multicast group is joined
Additionally, the advanced API [4] uses these same interface indexes to (Section 5.2). Additionally, the advanced API [4] uses these same
identify the interface on which a datagram is received, or to specify interface indexes to identify the interface on which a datagram is
the interface on which a datagram is to be sent. 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 Interfaces are normally known by names such as "le0", "sl1", "ppp2",
the like. On Berkeley-derived implementations, when an interface is and the like. On Berkeley-derived implementations, when an interface
made known to the system, the kernel assigns a unique positive integer is made known to the system, the kernel assigns a unique positive
value (called the interface index) to that interface. These are small integer value (called the interface index) to that interface. These
positive integers that start at 1. (Note that 0 is never used for an are small positive integers that start at 1. (Note that 0 is never
interface index.) There may be gaps so that there is no current used for an interface index.) There may be gaps so that there is no
interface for a particular positive interface index. current interface for a particular positive interface index.
This API defines two functions that map between an interface name and This API defines two functions that map between an interface name and
index, a third function that returns all the interface names and index, a third function that returns all the interface names and
indexes, and a fourth function to return the dynamic memory allocated by indexes, and a fourth function to return the dynamic memory allocated
the previous function. How these functions are implemented is left up by the previous function. How these functions are implemented is
to the implementation. 4.4BSD implementations can implement these left up to the implementation. 4.4BSD implementations can implement
functions using the existing sysctl() function with the NET_RT_IFLIST these functions using the existing sysctl() function with the
command. Other implementations may wish to use ioctl() for this NET_RT_IFLIST command. Other implementations may wish to use ioctl()
purpose. for this purpose.
4.1 Name-to-Index 4.1 Name-to-Index
The first function maps an interface name into its corresponding index. The first function maps an interface name into its corresponding
index.
#include <net/if.h> #include <net/if.h>
unsigned int if_nametoindex(const char *ifname); unsigned int if_nametoindex(const char *ifname);
If ifname is the name of an interface, the if_nametoindex() function If ifname is the name of an interface, the if_nametoindex() function
shall return the interface index corresponding to name ifname; shall return the interface index corresponding to name ifname;
otherwise, it shall return zero. No errors are defined. otherwise, it shall return zero. No errors are defined.
4.2 Index-to-Name 4.2 Index-to-Name
The second function maps an interface index into its corresponding name. The second function maps an interface index into its corresponding
name.
#include <net/if.h> #include <net/if.h>
char *if_indextoname(unsigned int ifindex, char *ifname); char *if_indextoname(unsigned int ifindex, char *ifname);
When this function is called, the ifname argument shall point to a When this function is called, the ifname argument shall point to a
buffer of at least IF_NAMESIZE bytes. The function shall place in this buffer of at least IF_NAMESIZE bytes. The function shall place in
buffer the name of the interface with index ifindex. (IF_NAMESIZE is this buffer the name of the interface with index ifindex.
also defined in <net/if.h> and its value includes a terminating null (IF_NAMESIZE is also defined in <net/if.h> and its value includes a
byte at the end of the interface name.) If ifindex is an interface terminating null byte at the end of the interface name.) If ifindex
index, then the function shall return the value supplied in ifname, is an interface index, then the function shall return the value
which points to a buffer now containing the interface name. Otherwise, supplied in ifname, which points to a buffer now containing the
the function shall return a NULL pointer and set errno to indicate the interface name. Otherwise, the function shall return a NULL pointer
error. If there is no interface corresponding to the specified index, and set errno to indicate the error. If there is no interface
errno is set to ENXIO. If there was a system error (such as running out corresponding to the specified index, errno is set to ENXIO. If
of memory), errno would be set to the proper value (e.g., ENOMEM). there was a system error (such as running out of memory), errno would
be set to the proper value (e.g., ENOMEM).
4.3 Return All Interface Names and Indexes 4.3 Return All Interface Names and Indexes
The if_nameindex structure holds the information about a single The if_nameindex structure holds the information about a single
interface and is defined as a result of including the <net/if.h> header. interface and is defined as a result of including the <net/if.h>
header.
struct if_nameindex { struct if_nameindex {
unsigned int if_index; /* 1, 2, ... */ unsigned int if_index; /* 1, 2, ... */
char *if_name; /* null terminated name: "le0", ... */ char *if_name; /* null terminated name: "le0", ... */
}; };
The final function returns an array of if_nameindex structures, one The final function returns an array of if_nameindex structures, one
structure per interface. structure per interface.
#include <net/if.h> #include <net/if.h>
struct if_nameindex *if_nameindex(void); struct if_nameindex *if_nameindex(void);
The end of the array of structures is indicated by a structure with an The end of the array of structures is indicated by a structure with
if_index of 0 and an if_name of NULL. The function returns a NULL an if_index of 0 and an if_name of NULL. The function returns a NULL
pointer upon an error, and would set errno to the appropriate value. pointer upon an error, and would set errno to the appropriate value.
The memory used for this array of structures along with the interface The memory used for this array of structures along with the interface
names pointed to by the if_name members is obtained dynamically. This names pointed to by the if_name members is obtained dynamically.
memory is freed by the next function. This memory is freed by the next function.
4.4 Free Memory 4.4 Free Memory
The following function frees the dynamic memory that was allocated by The following function frees the dynamic memory that was allocated by
if_nameindex(). if_nameindex().
#include <net/if.h> #include <net/if.h>
void if_freenameindex(struct if_nameindex *ptr); void if_freenameindex(struct if_nameindex *ptr);
The ptr argument shall be a pointer that was returned by if_nameindex(). The ptr argument shall be a pointer that was returned by
After if_freenameindex() has been called, the application shall not use if_nameindex(). After if_freenameindex() has been called, the
the array of which ptr is the address. application shall not use the array of which ptr is the address.
5. Socket Options 5. Socket Options
A number of new socket options are defined for IPv6. All of these new A number of new socket options are defined for IPv6. All of these
options are at the IPPROTO_IPV6 level. That is, the "level" parameter new options are at the IPPROTO_IPV6 level. That is, the "level"
in the getsockopt() and setsockopt() calls is IPPROTO_IPV6 when using parameter in the getsockopt() and setsockopt() calls is IPPROTO_IPV6
these options. The constant name prefix IPV6_ is used in all of the new when using these options. The constant name prefix IPV6_ is used in
socket options. This serves to clearly identify these options as all of the new socket options. This serves to clearly identify these
applying to IPv6. options as applying to IPv6.
The declaration for IPPROTO_IPV6, the new IPv6 socket options, and The declaration for IPPROTO_IPV6, the new IPv6 socket options, and
related constants defined in this section are obtained by including the related constants defined in this section are obtained by including
header <netinet/in.h>. the header <netinet/in.h>.
5.1 Unicast Hop Limit 5.1 Unicast Hop Limit
A new setsockopt() option controls the hop limit used in outgoing A new setsockopt() option controls the hop limit used in outgoing
unicast IPv6 packets. The name of this option is IPV6_UNICAST_HOPS, and unicast IPv6 packets. The name of this option is IPV6_UNICAST_HOPS,
it is used at the IPPROTO_IPV6 layer. The following example illustrates and it is used at the IPPROTO_IPV6 layer. The following example
how it is used: illustrates how it is used:
int hoplimit = 10; int hoplimit = 10;
if (setsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS, if (setsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS,
(char *) &hoplimit, sizeof(hoplimit)) == -1) (char *) &hoplimit, sizeof(hoplimit)) == -1)
perror("setsockopt IPV6_UNICAST_HOPS"); perror("setsockopt IPV6_UNICAST_HOPS");
When the IPV6_UNICAST_HOPS option is set with setsockopt(), the option When the IPV6_UNICAST_HOPS option is set with setsockopt(), the
value given is used as the hop limit for all subsequent unicast packets option value given is used as the hop limit for all subsequent
sent via that socket. If the option is not set, the system selects a unicast packets sent via that socket. If the option is not set, the
default value. The integer hop limit value (called x) is interpreted as system selects a default value. The integer hop limit value (called
follows: x) is interpreted as follows:
x < -1: return an error of EINVAL x < -1: return an error of EINVAL
x == -1: use kernel default x == -1: use kernel default
0 <= x <= 255: use x 0 <= x <= 255: use x
x >= 256: return an error of EINVAL x >= 256: return an error of EINVAL
The IPV6_UNICAST_HOPS option may be used with getsockopt() to determine The IPV6_UNICAST_HOPS option may be used with getsockopt() to
the hop limit value that the system will use for subsequent unicast determine the hop limit value that the system will use for subsequent
packets sent via that socket. For example: unicast packets sent via that socket. For example:
int hoplimit; int hoplimit;
socklen_t len = sizeof(hoplimit); socklen_t len = sizeof(hoplimit);
if (getsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS, if (getsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS,
(char *) &hoplimit, &len) == -1) (char *) &hoplimit, &len) == -1)
perror("getsockopt IPV6_UNICAST_HOPS"); perror("getsockopt IPV6_UNICAST_HOPS");
else else
printf("Using %d for hop limit.\n", hoplimit); printf("Using %d for hop limit.\n", hoplimit);
5.2 Sending and Receiving Multicast Packets 5.2 Sending and Receiving Multicast Packets
IPv6 applications may send multicast packets by simply specifying an IPv6 applications may send multicast packets by simply specifying an
IPv6 multicast address as the destination address, for example in the IPv6 multicast address as the destination address, for example in the
destination address argument of the sendto() function. destination address argument of the sendto() function.
Three socket options at the IPPROTO_IPV6 layer control some of the Three socket options at the IPPROTO_IPV6 layer control some of the
parameters for sending multicast packets. Setting these options is not parameters for sending multicast packets. Setting these options is
required: applications may send multicast packets without using these not required: applications may send multicast packets without using
options. The setsockopt() options for controlling the sending of these options. The setsockopt() options for controlling the sending
multicast packets are summarized below. These three options can also be of multicast packets are summarized below. These three options can
used with getsockopt(). also be used with getsockopt().
IPV6_MULTICAST_IF IPV6_MULTICAST_IF
Set the interface to use for outgoing multicast packets. Set the interface to use for outgoing multicast packets. The
The argument is the index of the interface to use. argument is the index of the interface to use. If the
If the interface index is specified as zero, the system interface index is specified as zero, the system selects the
selects the interface (for example, by looking up the interface (for example, by looking up the address in a routing
address in a routing table and using the resulting interface). table and using the resulting interface).
Argument type: unsigned int Argument type: unsigned int
IPV6_MULTICAST_HOPS IPV6_MULTICAST_HOPS
Set the hop limit to use for outgoing multicast packets. Set the hop limit to use for outgoing multicast packets. (Note
(Note a separate option - IPV6_UNICAST_HOPS - is a separate option - IPV6_UNICAST_HOPS - is provided to set the
provided to set the hop limit to use for outgoing hop limit to use for outgoing unicast packets.)
unicast packets.)
The interpretation of the argument is the same The interpretation of the argument is the same as for the
as for the IPV6_UNICAST_HOPS option: IPV6_UNICAST_HOPS option:
x < -1: return an error of EINVAL x < -1: return an error of EINVAL
x == -1: use kernel default x == -1: use kernel default
0 <= x <= 255: use x 0 <= x <= 255: use x
x >= 256: return an error of EINVAL x >= 256: return an error of EINVAL
If IPV6_MULTICAST_HOPS is not set, the default is 1
(same as IPv4 today)
Argument type: int If IPV6_MULTICAST_HOPS is not set, the default is 1
(same as IPv4 today)
IPV6_MULTICAST_LOOP Argument type: int
If a multicast datagram is sent to a group to which the sending host IPV6_MULTICAST_LOOP
itself belongs (on the outgoing interface), a copy of the datagram is
looped back by the IP layer for local delivery if this option is set to
1. If this option is set to 0 a copy is not looped back. Other option
values return an error of EINVAL.
If IPV6_MULTICAST_LOOP is not set, the default is 1 (loopback; same as If a multicast datagram is sent to a group to which the sending
IPv4 today). host itself belongs (on the outgoing interface), a copy of the
datagram is looped back by the IP layer for local delivery if
this option is set to 1. If this option is set to 0 a copy is
not looped back. Other option values return an error of
EINVAL.
Argument type: unsigned int If IPV6_MULTICAST_LOOP is not set, the default is 1 (loopback;
same as IPv4 today).
The reception of multicast packets is controlled by the two setsockopt() Argument type: unsigned int
options summarized below. An error of EOPNOTSUPP is returned if these
two options are used with getsockopt().
IPV6_JOIN_GROUP The reception of multicast packets is controlled by the two
setsockopt() options summarized below. An error of EOPNOTSUPP is
returned if these two options are used with getsockopt().
Join a multicast group on a specified local interface. IPV6_JOIN_GROUP
If the interface index is specified as 0,
the kernel chooses the local interface.
For example, some kernels look up the multicast group
in the normal IPv6 routing table and use the resulting interface.
Argument type: struct ipv6_mreq Join a multicast group on a specified local interface.
If the interface index is specified as 0,
the kernel chooses the local interface.
For example, some kernels look up the multicast group
in the normal IPv6 routing table and use the resulting
interface.
IPV6_LEAVE_GROUP Argument type: struct ipv6_mreq
Leave a multicast group on a specified interface. IPV6_LEAVE_GROUP
If the interface index is specified as 0, the system
may choose a multicast group membership to drop by
matching the multicast address only.
Argument type: struct ipv6_mreq Leave a multicast group on a specified interface.
If the interface index is specified as 0, the system
may choose a multicast group membership to drop by
matching the multicast address only.
The argument type of both of these options is the ipv6_mreq structure, Argument type: struct ipv6_mreq
defined as a result of including the <netinet/in.h> header;
The argument type of both of these options is the ipv6_mreq
structure, defined as a result of including the <netinet/in.h>
header;
struct ipv6_mreq { struct ipv6_mreq {
struct in6_addr ipv6mr_multiaddr; /* IPv6 multicast addr */ struct in6_addr ipv6mr_multiaddr; /* IPv6 multicast addr */
unsigned int ipv6mr_interface; /* interface index */ unsigned int ipv6mr_interface; /* interface index */
}; };
Note that to receive multicast datagrams a process must join the Note that to receive multicast datagrams a process must join the
multicast group to which datagrams will be sent. UDP applications must multicast group to which datagrams will be sent. UDP applications
also bind the UDP port to which datagrams will be sent. Some processes must also bind the UDP port to which datagrams will be sent. Some
also bind the multicast group address to the socket, in addition to the processes also bind the multicast group address to the socket, in
port, to prevent other datagrams destined to that same port from being addition to the port, to prevent other datagrams destined to that
delivered to the socket. same port from being delivered to the socket.
5.3 IPV6_V6ONLY option for AF_INET6 Sockets 5.3 IPV6_V6ONLY option for AF_INET6 Sockets
This socket option restricts AF_INET6 sockets to IPv6 communications This socket option restricts AF_INET6 sockets to IPv6 communications
only. As stated in section <3.7 Compatibility with IPv4 Nodes>, only. As stated in section <3.7 Compatibility with IPv4 Nodes>,
AF_INET6 sockets may be used for both IPv4 and IPv6 communications. Some AF_INET6 sockets may be used for both IPv4 and IPv6 communications.
applications may want to restrict their use of an AF_INET6 socket to Some applications may want to restrict their use of an AF_INET6
IPv6 communications only. For these applications the IPV6_V6ONLY socket socket to IPv6 communications only. For these applications the
option is defined. When this option is turned on, the socket can be IPV6_V6ONLY socket option is defined. When this option is turned on,
used to send and receive IPv6 packets only. This is an IPPROTO_IPV6 the socket can be used to send and receive IPv6 packets only. This
level option. This option takes an int value. This is a boolean is an IPPROTO_IPV6 level option. This option takes an int value.
option. By default this option is turned off. This is a boolean option. By default this option is turned off.
Here is an example of setting this option: Here is an example of setting this option:
int on = 1; int on = 1;
if (setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY, if (setsockopt(s, IPPROTO_IPV6, IPV6_V6ONLY,
(char *)&on, sizeof(on)) == -1) (char *)&on, sizeof(on)) == -1)
perror("setsockopt IPV6_V6ONLY"); perror("setsockopt IPV6_V6ONLY");
else else
printf("IPV6_V6ONLY set\n"); printf("IPV6_V6ONLY set\n");
Note - This option has no effect on the use of IPv4 Mapped addresses Note - This option has no effect on the use of IPv4 Mapped addresses
which enter a node as a valid IPv6 addresses for IPv6 communications as which enter a node as a valid IPv6 addresses for IPv6 communications
defined by Stateless IP/ICMP Translation Algorithm (SIIT) [5]. as defined by Stateless IP/ICMP Translation Algorithm (SIIT) [5].
An example use of this option is to allow two versions of the same An example use of this option is to allow two versions of the same
server process to run on the same port, one providing service over IPv6, server process to run on the same port, one providing service over
the other providing the same service over IPv4. IPv6, the other providing the same service over IPv4.
6. Library Functions 6. Library Functions
New library functions are needed to perform a variety of operations with New library functions are needed to perform a variety of operations
IPv6 addresses. Functions are needed to lookup IPv6 addresses in the with IPv6 addresses. Functions are needed to lookup IPv6 addresses
Domain Name System (DNS). Both forward lookup (nodename-to-address in the Domain Name System (DNS). Both forward lookup (nodename-to-
translation) and reverse lookup (address-to-nodename translation) need address translation) and reverse lookup (address-to-nodename
to be supported. Functions are also needed to convert IPv6 addresses translation) need to be supported. Functions are also needed to
between their binary and textual form. convert IPv6 addresses between their binary and textual form.
We note that the two existing functions, gethostbyname() and We note that the two existing functions, gethostbyname() and
gethostbyaddr(), are left as-is. New functions are defined to handle gethostbyaddr(), are left as-is. New functions are defined to handle
both IPv4 and IPv6 addresses. both IPv4 and IPv6 addresses.
The commonly used function gethostbyname() is inadequate for many The commonly used function gethostbyname() is inadequate for many
applications, first because it provides no way for the caller to specify applications, first because it provides no way for the caller to
anything about the types of addresses desired (IPv4 only, IPv6 only, specify anything about the types of addresses desired (IPv4 only,
IPv4-mapped IPv6 are OK, etc.), and second because many implementations IPv6 only, IPv4-mapped IPv6 are OK, etc.), and second because many
of this function are not thread safe. RFC 2133 defined a function named implementations of this function are not thread safe. RFC 2133
gethostbyname2() but this function was also inadequate, first because defined a function named gethostbyname2() but this function was also
its use required setting a global option (RES_USE_INET6) when IPv6 inadequate, first because its use required setting a global option
addresses were required, and second because a flag argument is needed to (RES_USE_INET6) when IPv6 addresses were required, and second because
provide the caller with additional control over the types of addresses a flag argument is needed to provide the caller with additional
required. The gethostbyname2() function was deprecated in RFC 2553 and control over the types of addresses required. The gethostbyname2()
is no longer part of the basic API. function was deprecated in RFC 2553 and is no longer part of the
basic API.
6.1 Protocol-Independent Nodename and Service Name Translation 6.1 Protocol-Independent Nodename and Service Name Translation
Nodename-to-address translation is done in a protocol-independent Nodename-to-address translation is done in a protocol-independent
fashion using the getaddrinfo() function. fashion using the getaddrinfo() function.
#include <sys/socket.h> #include <sys/socket.h>
#include <netdb.h> #include <netdb.h>
int getaddrinfo(const char *nodename, const char *servname, int getaddrinfo(const char *nodename, const char *servname,
const struct addrinfo *hints, struct addrinfo **res); const struct addrinfo *hints, struct addrinfo **res);
void freeaddrinfo(struct addrinfo *ai); void freeaddrinfo(struct addrinfo *ai);
struct addrinfo { struct addrinfo {
int ai_flags; /* AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST, .. */ int ai_flags; /* AI_PASSIVE, AI_CANONNAME,
int ai_family; /* AF_xxx */ AI_NUMERICHOST, .. */
int ai_socktype; /* SOCK_xxx */ int ai_family; /* AF_xxx */
int ai_protocol; /* 0 or IPPROTO_xxx for IPv4 and IPv6 */ int ai_socktype; /* SOCK_xxx */
socklen_t ai_addrlen; /* length of ai_addr */ int ai_protocol; /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
char *ai_canonname; /* canonical name for nodename */ socklen_t ai_addrlen; /* length of ai_addr */
struct sockaddr *ai_addr; /* binary address */ char *ai_canonname; /* canonical name for nodename */
struct addrinfo *ai_next; /* next structure in linked list */ struct sockaddr *ai_addr; /* binary address */
}; struct addrinfo *ai_next; /* next structure in linked list */
};
The getaddrinfo() function translates the name of a service location The getaddrinfo() function translates the name of a service location
(for example, a host name) and/or a service name and returns a set of (for example, a host name) and/or a service name and returns a set of
socket addresses and associated information to be used in creating a socket addresses and associated information to be used in creating a
socket with which to address the specified service. socket with which to address the specified service.
The nodename and servname arguments are either null pointers or The nodename and servname arguments are either null pointers or
pointers to null-terminated strings. One or both of these two pointers to null-terminated strings. One or both of these two
arguments must be a non-null pointer. arguments must be a non-null pointer.
The format of a valid name depends on the address family or families. The format of a valid name depends on the address family or families.
If a specific family is not given and the name could be interpreted If a specific family is not given and the name could be interpreted
as valid within multiple supported families, the implementation will as valid within multiple supported families, the implementation will
attempt to resolve the name in all supported families and, in absence attempt to resolve the name in all supported families and, in absence
of errors, one or more results shall be returned. of errors, one or more results shall be returned.
If the nodename argument is not null, it can be a descriptive name or If the nodename argument is not null, it can be a descriptive name or
can be an address string. If the specified address family is AF_INET, can be an address string. If the specified address family is
AF_INET6, or AF_UNSPEC, valid descriptive names include host names. AF_INET, AF_INET6, or AF_UNSPEC, valid descriptive names include host
If the specified address family is AF_INET or AF_UNSPEC, address names. If the specified address family is AF_INET or AF_UNSPEC,
strings using Internet standard dot notation as specified in address strings using Internet standard dot notation as specified in
inet_addr() are valid. If the specified address family is AF_INET6 inet_addr() are valid. If the specified address family is AF_INET6
or AF_UNSPEC, standard IPv6 text forms described in inet_pton() are or AF_UNSPEC, standard IPv6 text forms described in inet_pton() are
valid. valid.
If nodename is not null, the requested service location is named by If nodename is not null, the requested service location is named by
nodename; otherwise, the requested service location is local to the nodename; otherwise, the requested service location is local to the
caller. caller.
If servname is null, the call shall return network-level addresses If servname is null, the call shall return network-level addresses
for the specified nodename. If servname is not null, it is a null- for the specified nodename. If servname is not null, it is a null-
terminated character string identifying the requested service. This terminated character string identifying the requested service. This
can be either a descriptive name or a numeric representation suitable can be either a descriptive name or a numeric representation suitable
for use with the address family or families. If the specified address for use with the address family or families. If the specified
family is AF_INET, AF_INET6 or AF_UNSPEC, the service can be address family is AF_INET, AF_INET6 or AF_UNSPEC, the service can be
specified as a string specifying a decimal port number. specified as a string specifying a decimal port number.
If the argument hints is not null, it refers to a structure If the argument hints is not null, it refers to a structure
containing input values that may direct the operation by providing containing input values that may direct the operation by providing
options and by limiting the returned information to a specific socket options and by limiting the returned information to a specific socket
type, address family and/or protocol. In this hints structure every type, address family and/or protocol. In this hints structure every
member other than ai_flags, ai_family, ai_socktype and ai_protocol member other than ai_flags, ai_family, ai_socktype and ai_protocol
shall be set to zero or a null pointer. A value of AF_UNSPEC for shall be set to zero or a null pointer. A value of AF_UNSPEC for
ai_family means that the caller shall accept any address family. A ai_family means that the caller shall accept any address family. A
value of zero for ai_socktype means that the caller shall accept any value of zero for ai_socktype means that the caller shall accept any
socket type. A value of zero for ai_protocol means that the caller socket type. A value of zero for ai_protocol means that the caller
shall accept any protocol. If hints is a null pointer, the behavior shall accept any protocol. If hints is a null pointer, the behavior
shall be as if it referred to a structure containing the value zero shall be as if it referred to a structure containing the value zero
for the ai_flags, ai_socktype and ai_protocol fields, and AF_UNSPEC for the ai_flags, ai_socktype and ai_protocol fields, and AF_UNSPEC
for the ai_family field. for the ai_family field.
Note: Note:
1. If the caller handles only TCP and not UDP, for example, then the 1. If the caller handles only TCP and not UDP, for example, then the
ai_protocol member of the hints structure should be set to ai_protocol member of the hints structure should be set to
IPPROTO_TCP when getaddrinfo() is called. IPPROTO_TCP when getaddrinfo() is called.
2. If the caller handles only IPv4 and not IPv6, then the ai_family 2. If the caller handles only IPv4 and not IPv6, then the ai_family
member of the hints structure should be set to AF_INET when member of the hints structure should be set to AF_INET when
getaddrinfo() is called. getaddrinfo() is called.
The ai_flags field to which hints parameter points shall be set to The ai_flags field to which hints parameter points shall be set to
zero or be the bitwise-inclusive OR of one or more of the values zero or be the bitwise-inclusive OR of one or more of the values
AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST, AI_NUMERICSERV, AI_PASSIVE, AI_CANONNAME, AI_NUMERICHOST, AI_NUMERICSERV,
AI_V4MAPPED, AI_ALL, and AI_ADDRCONFIG. AI_V4MAPPED, AI_ALL, and AI_ADDRCONFIG.
If the AI_PASSIVE flag is specified, the returned address information If the AI_PASSIVE flag is specified, the returned address information
shall be suitable for use in binding a socket for accepting incoming shall be suitable for use in binding a socket for accepting incoming
connections for the specified service (i.e. a call to bind()). In connections for the specified service (i.e., a call to bind()). In
this case, if the nodename argument is null, then the IP address this case, if the nodename argument is null, then the IP address
portion of the socket address structure shall be set to INADDR_ANY portion of the socket address structure shall be set to INADDR_ANY
for an IPv4 address or IN6ADDR_ANY_INIT for an IPv6 address. If the for an IPv4 address or IN6ADDR_ANY_INIT for an IPv6 address. If the
AI_PASSIVE flag is not specified, the returned address information AI_PASSIVE flag is not specified, the returned address information
shall be suitable for a call to connect() (for a connection-mode shall be suitable for a call to connect() (for a connection-mode
protocol) or for a call to connect(), sendto() or sendmsg() (for a protocol) or for a call to connect(), sendto() or sendmsg() (for a
connectionless protocol). In this case, if the nodename argument is connectionless protocol). In this case, if the nodename argument is
null, then the IP address portion of the socket address structure null, then the IP address portion of the socket address structure
shall be set to the loopback address. This flag is ignored if the shall be set to the loopback address. This flag is ignored if the
nodename argument is not null. nodename argument is not null.
If the AI_CANONNAME flag is specified and the nodename argument is If the AI_CANONNAME flag is specified and the nodename argument is
not null, the function shall attempt to determine the canonical name not null, the function shall attempt to determine the canonical name
corresponding to nodename (for example, if nodename is an alias or corresponding to nodename (for example, if nodename is an alias or
shorthand notation for a complete name). shorthand notation for a complete name).
If the AI_NUMERICHOST flag is specified, then a non-null nodename If the AI_NUMERICHOST flag is specified, then a non-null nodename
string supplied shall be a numeric host address string. Otherwise, an string supplied shall be a numeric host address string. Otherwise,
[EAI_NONAME] error is returned. This flag shall prevent any type of an [EAI_NONAME] error is returned. This flag shall prevent any type
name resolution service (for example, the DNS) from being invoked. of name resolution service (for example, the DNS) from being invoked.
If the AI_NUMERICSERV flag is specified, then a non-null servname If the AI_NUMERICSERV flag is specified, then a non-null servname
string supplied shall be a numeric port string. Otherwise, an string supplied shall be a numeric port string. Otherwise, an
[EAI_NONAME] error shall be returned. This flag shall prevent any
[EAI_NONAME] error shall be returned. This flag shall prevent any
type of name resolution service (for example, NIS+) from being type of name resolution service (for example, NIS+) from being
invoked. invoked.
If the AI_V4MAPPED flag is specified along with an ai_family of If the AI_V4MAPPED flag is specified along with an ai_family of
AF_INET6, then getaddrinfo() shall return IPv4-mapped IPv6 addresses AF_INET6, then getaddrinfo() shall return IPv4-mapped IPv6 addresses
on finding no matching IPv6 addresses (ai_addrlen shall be 16). on finding no matching IPv6 addresses (ai_addrlen shall be 16).
For example, when using the DNS, if no AAAA records are found For example, when using the DNS, if no AAAA records are found then
then a query is made for A records and any found are returned as a query is made for A records and any found are returned as IPv4-
IPv4-mapped IPv6 addresses. mapped IPv6 addresses.
The AI_V4MAPPED flag shall be ignored unless ai_family equals The AI_V4MAPPED flag shall be ignored unless ai_family equals
AF_INET6. AF_INET6.
If the AI_ALL flag is used with the AI_V4MAPPED flag, then If the AI_ALL flag is used with the AI_V4MAPPED flag, then
getaddrinfo() shall return all matching IPv6 and IPv4 addresses. getaddrinfo() shall return all matching IPv6 and IPv4 addresses.
For example, when using the DNS, queries are made for both AAAA For example, when using the DNS, queries are made for both AAAA
records and A records, and getaddrinfo() returns the combined records and A records, and getaddrinfo() returns the combined
results of both queries. Any IPv4 addresses found are returned results of both queries. Any IPv4 addresses found are returned as
as IPv4-mapped IPv6 addresses. IPv4-mapped IPv6 addresses.
The AI_ALL flag without the AI_V4MAPPED flag is ignored. The AI_ALL flag without the AI_V4MAPPED flag is ignored.
Note: Note:
When ai_family is not specified (AF_UNSPEC), AI_V4MAPPED and When ai_family is not specified (AF_UNSPEC), AI_V4MAPPED and
AI_ALL flags will only be used if AF_INET6 is supported. AI_ALL flags will only be used if AF_INET6 is supported.
If the AI_ADDRCONFIG flag is specified, IPv4 addresses shall be If the AI_ADDRCONFIG flag is specified, IPv4 addresses shall be
returned only if an IPv4 address is configured on the local system, returned only if an IPv4 address is configured on the local system,
and IPv6 addresses shall be returned only if an IPv6 address is and IPv6 addresses shall be returned only if an IPv6 address is
configured on the local system. The loopback address is not configured on the local system. The loopback address is not
considered for this case as valid as a configured address. considered for this case as valid as a configured address.
For example, when using the DNS, a query for AAAA records For example, when using the DNS, a query for AAAA records should
should occur only if the node has at least one IPv6 address occur only if the node has at least one IPv6 address configured
configured (other than IPv6 loopback) and a query for A records (other than IPv6 loopback) and a query for A records should occur
should occur only if the node has at least one IPv4 address only if the node has at least one IPv4 address configured (other
configured (other than the IPv4 loopback). than the IPv4 loopback).
The ai_socktype field to which argument hints points specifies the The ai_socktype field to which argument hints points specifies the
socket type for the service, as defined for socket(). If a specific socket type for the service, as defined for socket(). If a specific
socket type is not given (for example, a value of zero) and the socket type is not given (for example, a value of zero) and the
service name could be interpreted as valid with multiple supported service name could be interpreted as valid with multiple supported
socket types, the implementation shall attempt to resolve the service socket types, the implementation shall attempt to resolve the service
name for all supported socket types and, in the absence of errors, name for all supported socket types and, in the absence of errors,
all possible results shall be returned. A non-zero socket type value all possible results shall be returned. A non-zero socket type value
shall limit the returned information to values with the specified shall limit the returned information to values with the specified
socket type. socket type.
If the ai_family field to which hints points has the value AF_UNSPEC, If the ai_family field to which hints points has the value AF_UNSPEC,
addresses shall be returned for use with any address family that can addresses shall be returned for use with any address family that can
be used with the specified nodename and/or servname. Otherwise, be used with the specified nodename and/or servname. Otherwise,
addresses shall be returned for use only with the specified address addresses shall be returned for use only with the specified address
family. If ai_family is not AF_UNSPEC and ai_protocol is not zero, family. If ai_family is not AF_UNSPEC and ai_protocol is not zero,
then addresses are returned for use only with the specified address then addresses are returned for use only with the specified address
family and protocol; the value of ai_protocol shall be interpreted as family and protocol; the value of ai_protocol shall be interpreted as
in a call to the socket() function with the corresponding values of in a call to the socket() function with the corresponding values of
ai_family and ai_protocol . ai_family and ai_protocol.
The freeaddrinfo() function frees one or more addrinfo structures The freeaddrinfo() function frees one or more addrinfo structures
returned by getaddrinfo(), along with any additional storage returned by getaddrinfo(), along with any additional storage
associated with those structures (for example, storage pointed to by associated with those structures (for example, storage pointed to by
the ai_canonname and ai_addr fields; an application must not the ai_canonname and ai_addr fields; an application must not
reference this storage after the associated addrinfo structure has reference this storage after the associated addrinfo structure has
been freed). If the ai_next field of the structure is not null, the been freed). If the ai_next field of the structure is not null, the
entire list of structures is freed. The freeaddrinfo() function must entire list of structures is freed. The freeaddrinfo() function must
support the freeing of arbitrary sublists of an addrinfo list support the freeing of arbitrary sublists of an addrinfo list
originally returned by getaddrinfo(). originally returned by getaddrinfo().
Functions getaddrinfo() and freeaddrinfo() must be thread-safe. Functions getaddrinfo() and freeaddrinfo() must be thread-safe.
A zero return value for getaddrinfo() indicates successful A zero return value for getaddrinfo() indicates successful
completion; a non-zero return value indicates failure. The possible completion; a non-zero return value indicates failure. The possible
values for the failures are listed below under Error Return Values. values for the failures are listed below under Error Return Values.
Upon successful return of getaddrinfo(), the location to which res Upon successful return of getaddrinfo(), the location to which res
points shall refer to a linked list of addrinfo structures, each of points shall refer to a linked list of addrinfo structures, each of
which shall specify a socket address and information for use in which shall specify a socket address and information for use in
creating a socket with which to use that socket address. The list creating a socket with which to use that socket address. The list
shall include at least one addrinfo structure. The ai_next field of shall include at least one addrinfo structure. The ai_next field of
each structure contains a pointer to the next structure on the list, each structure contains a pointer to the next structure on the list,
or a null pointer if it is the last structure on the list. Each or a null pointer if it is the last structure on the list. Each
structure on the list shall include values for use with a call to the structure on the list shall include values for use with a call to the
socket() function, and a socket address for use with the connect() socket() function, and a socket address for use with the connect()
function or, if the AI_PASSIVE flag was specified, for use with the function or, if the AI_PASSIVE flag was specified, for use with the
bind() function. The fields ai_family, ai_socktype, and ai_protocol bind() function. The fields ai_family, ai_socktype, and ai_protocol
shall be usable as the arguments to the socket() function to create a shall be usable as the arguments to the socket() function to create a
socket suitable for use with the returned address. The fields ai_addr socket suitable for use with the returned address. The fields
and ai_addrlen are usable as the arguments to the connect() or bind() ai_addr and ai_addrlen are usable as the arguments to the connect()
functions with such a socket, according to the AI_PASSIVE flag. or bind() functions with such a socket, according to the AI_PASSIVE
flag.
If nodename is not null, and if requested by the AI_CANONNAME flag, If nodename is not null, and if requested by the AI_CANONNAME flag,
the ai_canonname field of the first returned addrinfo structure shall the ai_canonname field of the first returned addrinfo structure shall
point to a null-terminated string containing the canonical name point to a null-terminated string containing the canonical name
corresponding to the input nodename; if the canonical name is not corresponding to the input nodename; if the canonical name is not
available, then ai_canonname shall refer to the nodename argument or available, then ai_canonname shall refer to the nodename argument or
a string with the same contents. The contents of the ai_flags field a string with the same contents. The contents of the ai_flags field
of the returned structures are undefined. of the returned structures are undefined.
All fields in socket address structures returned by getaddrinfo() All fields in socket address structures returned by getaddrinfo()
that are not filled in through an explicit argument (for example, that are not filled in through an explicit argument (for example,
sin6_flowinfo) shall be set to zero. sin6_flowinfo) shall be set to zero.
Note: This makes it easier to compare socket address structures. Note: This makes it easier to compare socket address structures.
Error Return Values: Error Return Values:
The getaddrinfo() function shall fail and return the corresponding The getaddrinfo() function shall fail and return the corresponding
value if: value if:
[EAI_AGAIN] The name could not be resolved at this time. Future [EAI_AGAIN] The name could not be resolved at this time. Future
attempts may succeed. attempts may succeed.
[EAI_BADFLAGS] The flags parameter had an invalid value. [EAI_BADFLAGS] The flags parameter had an invalid value.
[EAI_FAIL] A non-recoverable error occurred when attempting to [EAI_FAIL] A non-recoverable error occurred when attempting to
resolve the name. resolve the name.
[EAI_FAMILY] The address family was not recognized. [EAI_FAMILY] The address family was not recognized.
[EAI_MEMORY] There was a memory allocation failure when trying to [EAI_MEMORY] There was a memory allocation failure when trying to
allocate storage for the return value. allocate storage for the return value.
[EAI_NONAME] The name does not resolve for the supplied parameters. [EAI_NONAME] The name does not resolve for the supplied
Neither nodename nor servname were supplied. At least one parameters. Neither nodename nor servname were
of these must be supplied. supplied. At least one of these must be supplied.
[EAI_SERVICE] The service passed was not recognized for the specified [EAI_SERVICE] The service passed was not recognized for the
socket type. specified socket type.
[EAI_SOCKTYPE] The intended socket type was not recognized. [EAI_SOCKTYPE] The intended socket type was not recognized.
[EAI_SYSTEM] A system error occurred; the error code can be found in [EAI_SYSTEM] A system error occurred; the error code can be found
errno. in errno.
The gai_strerror() function provides a descriptive text string The gai_strerror() function provides a descriptive text string
corresponding to an EAI_xxx error value. corresponding to an EAI_xxx error value.
#include <netdb.h> #include <netdb.h>
const char *gai_strerror(int ecode); const char *gai_strerror(int ecode);
The argument is one of the EAI_xxx values defined for the getaddrinfo() The argument is one of the EAI_xxx values defined for the
and getnameinfo() functions. The return value points to a string getaddrinfo() and getnameinfo() functions. The return value points
describing the error. If the argument is not one of the EAI_xxx values, to a string describing the error. If the argument is not one of the
the function still returns a pointer to a string whose contents indicate EAI_xxx values, the function still returns a pointer to a string
an unknown error. whose contents indicate an unknown error.
6.2 Socket Address Structure to Node Name and Service Name 6.2 Socket Address Structure to Node Name and Service Name
The getnameinfo() function is used to translate the contents of a socket The getnameinfo() function is used to translate the contents of a
address structure to a node name and/or service name. socket address structure to a node name and/or service name.
#include <sys/socket.h> #include <sys/socket.h>
#include <netdb.h> #include <netdb.h>
int getnameinfo(const struct sockaddr *sa, socklen_t salen, int getnameinfo(const struct sockaddr *sa, socklen_t salen,
char *node, socklen_t nodelen, char *node, socklen_t nodelen,
char *service, socklen_t servicelen, char *service, socklen_t servicelen,
int flags); int flags);
The getnameinfo() function shall translate a socket address to a node The getnameinfo() function shall translate a socket address to a node
name and service location, all of which are defined as in getaddrinfo(). name and service location, all of which are defined as in
getaddrinfo().
The sa argument points to a socket address structure to be translated. The sa argument points to a socket address structure to be
translated.
The salen argument holds the size of the socket address structure The salen argument holds the size of the socket address structure
pointed to by sa. pointed to by sa.
If the socket address structure contains an IPv4-mapped IPv6 address or If the socket address structure contains an IPv4-mapped IPv6 address
an IPv4-compatible IPv6 address, the implementation shall extract the or an IPv4-compatible IPv6 address, the implementation shall extract
embedded IPv4 address and lookup the node name for that IPv4 address. the embedded IPv4 address and lookup the node name for that IPv4
address.
Note: The IPv6 unspecified address ("::") and the IPv6 Note: The IPv6 unspecified address ("::") and the IPv6 loopback
loopback address ("::1") are not IPv4-compatible addresses. address ("::1") are not IPv4-compatible addresses. If the address
If the address is the IPv6 unspecified address ("::"), a is the IPv6 unspecified address ("::"), a lookup is not performed,
lookup is not performed, and the [EAI_NONAME] error is returned. and the [EAI_NONAME] error is returned.
If the node argument is non-NULL and the nodelen argument is nonzero, If the node argument is non-NULL and the nodelen argument is nonzero,
then the node argument points to a buffer able to contain up to nodelen then the node argument points to a buffer able to contain up to
characters that receives the node name as a null-terminated string. If nodelen characters that receives the node name as a null-terminated
the node argument is NULL or the nodelen argument is zero, the node name string. If the node argument is NULL or the nodelen argument is
shall not be returned. If the node's name cannot be located, the numeric zero, the node name shall not be returned. If the node's name cannot
form of the node's address is returned instead of its name. be located, the numeric form of the node's address is returned
instead of its name.
If the service argument is non-NULL and the servicelen argument is non- If the service argument is non-NULL and the servicelen argument is
zero, then the service argument points to a buffer able to contain up to non-zero, then the service argument points to a buffer able to
servicelen bytes that receives the service name as a null-terminated contain up to servicelen bytes that receives the service name as a
string. If the service argument is NULL or the servicelen argument is null-terminated string. If the service argument is NULL or the
zero, the service name shall not be returned. If the service's name servicelen argument is zero, the service name shall not be returned.
cannot be located, the numeric form of the service address (for example, If the service's name cannot be located, the numeric form of the
its port number) shall be returned instead of its name. service address (for example, its port number) shall be returned
instead of its name.
The arguments node and service cannot both be NULL. The arguments node and service cannot both be NULL.
The flags argument is a flag that changes the default actions of the The flags argument is a flag that changes the default actions of the
function. By default the fully-qualified domain name (FQDN) for the host function. By default the fully-qualified domain name (FQDN) for the
shall be returned, but: host shall be returned, but:
- If the flag bit NI_NOFQDN is set, only the node name portion of the - If the flag bit NI_NOFQDN is set, only the node name portion of
FQDN shall be returned for local hosts. the FQDN shall be returned for local hosts.
- If the flag bit NI_NUMERICHOST is set, the numeric form of the - If the flag bit NI_NUMERICHOST is set, the numeric form of the
host's address shall be returned instead of its name, under all host's address shall be returned instead of its name, under all
circumstances. circumstances.
- If the flag bit NI_NAMEREQD is set, an error shall be returned if the - If the flag bit NI_NAMEREQD is set, an error shall be returned if
host's name cannot be located. the host's name cannot be located.
- If the flag bit NI_NUMERICSERV is set, the numeric form of the - If the flag bit NI_NUMERICSERV is set, the numeric form of the
service address shall be returned (for example, its port number) service address shall be returned (for example, its port number)
instead of its name, under all circumstances. instead of its name, under all circumstances.
- If the flag bit NI_NUMERICSCOPE is set, the numeric form of the - If the flag bit NI_DGRAM is set, this indicates that the service
scope identifier shall be returned (for example, interface index) is a datagram service (SOCK_DGRAM). The default behavior shall
instead of its name. This flag is ignored if the sa argument is assume that the service is a stream service (SOCK_STREAM).
not an IPv6 address.
- If the flag bit NI_DGRAM is set, this indicates that the service is Note:
a datagram service (SOCK_DGRAM). The default behavior shall assume that
the service is a stream service (SOCK_STREAM).
Note: 1. The NI_NUMERICxxx flags are required to support the "-n" flags
that many commands provide.
1. The three NI_NUMERICxxx flags are required to support the "-n" 2. The NI_DGRAM flag is required for the few AF_INET and AF_INET6
flags that many commands provide. port numbers (for example, [512,514]) that represent different
2. The NI_DGRAM flag is required for the few AF_INET and AF_INET6 port services for UDP and TCP.
numbers (for example, [512,514]) that represent different services
for UDP and TCP.
The getnameinfo() function shall be thread safe. The getnameinfo() function shall be thread safe.
A zero return value for getnameinfo() indicates successful completion; a A zero return value for getnameinfo() indicates successful
non-zero return value indicates failure. completion; a non-zero return value indicates failure.
Upon successful completion, getnameinfo() shall return the node and Upon successful completion, getnameinfo() shall return the node and
service names, if requested, in the buffers provided. The returned names service names, if requested, in the buffers provided. The returned
are always null-terminated strings. names are always null-terminated strings.
Error Return Values: Error Return Values:
The getnameinfo() function shall fail and return the corresponding value The getnameinfo() function shall fail and return the corresponding
if: value if:
[EAI_AGAIN] The name could not be resolved at this time. [EAI_AGAIN] The name could not be resolved at this time.
Future attempts may succeed. Future attempts may succeed.
[EAI_BADFLAGS] The flags had an invalid value. [EAI_BADFLAGS] The flags had an invalid value.
[EAI_FAIL] A non-recoverable error occurred. [EAI_FAIL] A non-recoverable error occurred.
[EAI_FAMILY] The address family was not recognized or the address [EAI_FAMILY] The address family was not recognized or the address
length was invalid for the specified family. length was invalid for the specified family.
[EAI_MEMORY] There was a memory allocation failure. [EAI_MEMORY] There was a memory allocation failure.
[EAI_NONAME] The name does not resolve for the supplied parameters. [EAI_NONAME] The name does not resolve for the supplied parameters.
NI_NAMEREQD is set and the host's name cannot be located, or NI_NAMEREQD is set and the host's name cannot be
both nodename and servname were null. located, or both nodename and servname were null.
[EAI_OVERFLOW] An argument buffer overflowed. [EAI_OVERFLOW] An argument buffer overflowed.
[EAI_SYSTEM] A system error occurred. The error code can be found in [EAI_SYSTEM] A system error occurred. The error code can be found
errno. in errno.
6.3 Address Conversion Functions 6.3 Address Conversion Functions
The two IPv4 functions inet_addr() and inet_ntoa() convert an IPv4 The two IPv4 functions inet_addr() and inet_ntoa() convert an IPv4
address between binary and text form. IPv6 applications need similar address between binary and text form. IPv6 applications need similar
functions. The following two functions convert both IPv6 and IPv4 functions. The following two functions convert both IPv6 and IPv4
addresses: addresses:
#include <arpa/inet.h> #include <arpa/inet.h>
int inet_pton(int af, const char *src, void *dst); int inet_pton(int af, const char *src, void *dst);
const char *inet_ntop(int af, const void *src, const char *inet_ntop(int af, const void *src,
char *dst, socklen_t size); char *dst, socklen_t size);
The inet_pton() function shall convert an address in its standard text The inet_pton() function shall convert an address in its standard
presentation form into its numeric binary form. The af argument shall text presentation form into its numeric binary form. The af argument
specify the family of the address. The AF_INET and AF_INET6 address shall specify the family of the address. The AF_INET and AF_INET6
families shall be supported. The src argument points to the string address families shall be supported. The src argument points to the
being passed in. The dst argument points to a buffer into which the string being passed in. The dst argument points to a buffer into
function stores the numeric address; this shall be large enough to hold which the function stores the numeric address; this shall be large
the numeric address (32 bits for AF_INET, 128 bits for AF_INET6). The enough to hold the numeric address (32 bits for AF_INET, 128 bits for
inet_pton() function shall return 1 if the conversion succeeds, with the AF_INET6). The inet_pton() function shall return 1 if the conversion
address pointed to by dst in network byte order. It shall return 0 if succeeds, with the address pointed to by dst in network byte order.
the input is not a valid IPv4 dotted-decimal string or a valid IPv6 It shall return 0 if the input is not a valid IPv4 dotted-decimal
address string, or -1 with errno set to EAFNOSUPPORT if the af argument string or a valid IPv6 address string, or -1 with errno set to
is unknown. EAFNOSUPPORT if the af argument is unknown.
If the af argument of inet_pton() is AF_INET, the src string shall be in If the af argument of inet_pton() is AF_INET, the src string shall be
the standard IPv4 dotted-decimal form: in the standard IPv4 dotted-decimal form:
ddd.ddd.ddd.ddd ddd.ddd.ddd.ddd
where "ddd" is a one to three digit decimal number between 0 and 255. where "ddd" is a one to three digit decimal number between 0 and 255.
The inet_pton() function does not accept other formats (such as the The inet_pton() function does not accept other formats (such as the
octal numbers, hexadecimal numbers, and fewer than four numbers that octal numbers, hexadecimal numbers, and fewer than four numbers that
inet_addr() accepts). inet_addr() accepts).
If the af argument of inet_pton() is AF_INET6, the src string shall be If the af argument of inet_pton() is AF_INET6, the src string shall
in one of the standard IPv6 text forms defined in Section 2.2 of the be in one of the standard IPv6 text forms defined in Section 2.2 of
addressing architecture specification [2]. the addressing architecture specification [2].
The inet_ntop() function shall convert a numeric address into a text The inet_ntop() function shall convert a numeric address into a text
string suitable for presentation. The af argument shall specify the string suitable for presentation. The af argument shall specify the
family of the address. This can be AF_INET or AF_INET6. The src 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 argument points to a buffer holding an IPv4 address if the af
is AF_INET, or an IPv6 address if the af argument is AF_INET6; the argument is AF_INET, or an IPv6 address if the af argument is
address must be in network byte order. The dst argument points to a AF_INET6; the address must be in network byte order. The dst
buffer where the function stores the resulting text string; it shall not argument points to a buffer where the function stores the resulting
be NULL. The size argument specifies the size of this buffer, which text string; it shall not be NULL. The size argument specifies the
shall be large enough to hold the text string (INET_ADDRSTRLEN size of this buffer, which shall be large enough to hold the text
characters for IPv4, INET6_ADDRSTRLEN characters for IPv6). string (INET_ADDRSTRLEN characters for IPv4, INET6_ADDRSTRLEN
characters for IPv6).
In order to allow applications to easily declare buffers of the proper In order to allow applications to easily declare buffers of the
size to store IPv4 and IPv6 addresses in string form, the following two proper size to store IPv4 and IPv6 addresses in string form, the
constants are defined in <netinet/in.h>: following two constants are defined in <netinet/in.h>:
#define INET_ADDRSTRLEN 16 #define INET_ADDRSTRLEN 16
#define INET6_ADDRSTRLEN 46 #define INET6_ADDRSTRLEN 46
The inet_ntop() function shall return a pointer to the buffer containing The inet_ntop() function shall return a pointer to the buffer
the text string if the conversion succeeds, and NULL otherwise. Upon containing the text string if the conversion succeeds, and NULL
failure, errno is set to EAFNOSUPPORT if the af argument is invalid or otherwise. Upon failure, errno is set to EAFNOSUPPORT if the af
ENOSPC if the size of the result buffer is inadequate. argument is invalid or ENOSPC if the size of the result buffer is
inadequate.
6.4 Address Testing Macros 6.4 Address Testing Macros
The following macros can be used to test for special IPv6 addresses. The following macros can be used to test for special IPv6 addresses.
#include <netinet/in.h> #include <netinet/in.h>
int IN6_IS_ADDR_UNSPECIFIED (const struct in6_addr *); int IN6_IS_ADDR_UNSPECIFIED (const struct in6_addr *);
int IN6_IS_ADDR_LOOPBACK (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_MULTICAST (const struct in6_addr *);
int IN6_IS_ADDR_LINKLOCAL (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_SITELOCAL (const struct in6_addr *);
int IN6_IS_ADDR_V4MAPPED (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_V4COMPAT (const struct in6_addr *);
int IN6_IS_ADDR_MC_NODELOCAL(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_LINKLOCAL(const struct in6_addr *);
int IN6_IS_ADDR_MC_SITELOCAL(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_ORGLOCAL (const struct in6_addr *);
int IN6_IS_ADDR_MC_GLOBAL (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 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 type, or false otherwise. The last five test the scope of a
address and return true if the address is a multicast address of the multicast address and return true if the address is a multicast
specified scope or false if the address is either not a multicast address of the specified scope or false if the address is either not
address or not of the specified scope. a multicast address or not of the specified scope.
Note that IN6_IS_ADDR_LINKLOCAL and IN6_IS_ADDR_SITELOCAL return true Note that IN6_IS_ADDR_LINKLOCAL and IN6_IS_ADDR_SITELOCAL return true
only for the two types of local-use IPv6 unicast addresses (Link-Local only for the two types of local-use IPv6 unicast addresses (Link-
and Site-Local) defined in [2], and that by this definition, the Local and Site-Local) defined in [2], and that by this definition,
IN6_IS_ADDR_LINKLOCAL macro returns false for the IPv6 loopback address the IN6_IS_ADDR_LINKLOCAL macro returns false for the IPv6 loopback
(::1). These two macros do not return true for IPv6 multicast addresses address (::1). These two macros do not return true for IPv6
of either link-local scope or site-local scope. multicast addresses of either link-local scope or site-local scope.
7. Summary of New Definitions 7. Summary of New Definitions
The following list summarizes the constants, structure, and extern The following list summarizes the constants, structure, and extern
definitions discussed in this memo, sorted by header. definitions discussed in this memo, sorted by header.
<net/if.h> IF_NAMESIZE <net/if.h> IF_NAMESIZE
<net/if.h> struct if_nameindex{}; <net/if.h> struct if_nameindex{};
<netdb.h> AI_ADDRCONFIG <netdb.h> AI_ADDRCONFIG
<netdb.h> AI_ALL <netdb.h> AI_ALL
<netdb.h> AI_CANONNAME <netdb.h> AI_CANONNAME
<netdb.h> AI_NUMERICHOST <netdb.h> AI_NUMERICHOST
<netdb.h> AI_NUMERICSERV <netdb.h> AI_NUMERICSERV
<netdb.h> AI_PASSIVE <netdb.h> AI_PASSIVE
<netdb.h> AI_V4MAPPED <netdb.h> AI_V4MAPPED
<netdb.h> EAI_AGAIN <netdb.h> EAI_AGAIN
<netdb.h> EAI_BADFLAGS <netdb.h> EAI_BADFLAGS
<netdb.h> EAI_FAIL <netdb.h> EAI_FAIL
<netdb.h> EAI_FAMILY <netdb.h> EAI_FAMILY
<netdb.h> EAI_MEMORY <netdb.h> EAI_MEMORY
<netdb.h> EAI_NONAME <netdb.h> EAI_NONAME
<netdb.h> EAI_OVERFLOW <netdb.h> EAI_OVERFLOW
<netdb.h> EAI_SERVICE <netdb.h> EAI_SERVICE
<netdb.h> EAI_SOCKTYPE <netdb.h> EAI_SOCKTYPE
<netdb.h> EAI_SYSTEM <netdb.h> EAI_SYSTEM
<netdb.h> NI_DGRAM <netdb.h> NI_DGRAM
<netdb.h> NI_NAMEREQD <netdb.h> NI_NAMEREQD
<netdb.h> NI_NOFQDN <netdb.h> NI_NOFQDN
<netdb.h> NI_NUMERICHOST <netdb.h> NI_NUMERICHOST
<netdb.h> NI_NUMERICSERV <netdb.h> NI_NUMERICSERV
<netdb.h> struct addrinfo{}; <netdb.h> struct addrinfo{};
<netinet/in.h> IN6ADDR_ANY_INIT <netinet/in.h> IN6ADDR_ANY_INIT
<netinet/in.h> IN6ADDR_LOOPBACK_INIT <netinet/in.h> IN6ADDR_LOOPBACK_INIT
<netinet/in.h> INET6_ADDRSTRLEN <netinet/in.h> INET6_ADDRSTRLEN
<netinet/in.h> INET_ADDRSTRLEN <netinet/in.h> INET_ADDRSTRLEN
<netinet/in.h> IPPROTO_IPV6 <netinet/in.h> IPPROTO_IPV6
<netinet/in.h> IPV6_JOIN_GROUP <netinet/in.h> IPV6_JOIN_GROUP
<netinet/in.h> IPV6_LEAVE_GROUP <netinet/in.h> IPV6_LEAVE_GROUP
<netinet/in.h> IPV6_MULTICAST_HOPS <netinet/in.h> IPV6_MULTICAST_HOPS
<netinet/in.h> IPV6_MULTICAST_IF <netinet/in.h> IPV6_MULTICAST_IF
<netinet/in.h> IPV6_MULTICAST_LOOP <netinet/in.h> IPV6_MULTICAST_LOOP
<netinet/in.h> IPV6_UNICAST_HOPS <netinet/in.h> IPV6_UNICAST_HOPS
<netinet/in.h> IPV6_V6ONLY <netinet/in.h> IPV6_V6ONLY
<netinet/in.h> SIN6_LEN <netinet/in.h> SIN6_LEN
<netinet/in.h> extern const struct in6_addr in6addr_any; <netinet/in.h> extern const struct in6_addr in6addr_any;
<netinet/in.h> extern const struct in6_addr in6addr_loopback; <netinet/in.h> extern const struct in6_addr in6addr_loopback;
<netinet/in.h> struct in6_addr{}; <netinet/in.h> struct in6_addr{};
<netinet/in.h> struct ipv6_mreq{}; <netinet/in.h> struct ipv6_mreq{};
<netinet/in.h> struct sockaddr_in6{}; <netinet/in.h> struct sockaddr_in6{};
<sys/socket.h> AF_INET6 <sys/socket.h> AF_INET6
<sys/socket.h> PF_INET6 <sys/socket.h> PF_INET6
<sys/socket.h> struct sockaddr_storage; <sys/socket.h> struct sockaddr_storage;
The following list summarizes the function and macro prototypes The following list summarizes the function and macro prototypes
discussed in this memo, sorted by header. discussed in this memo, sorted by header.
<arpa/inet.h> int inet_pton(int, const char *, void *); <arpa/inet.h> int inet_pton(int, const char *, void *);
<arpa/inet.h> const char *inet_ntop(int, const void *, <arpa/inet.h> const char *inet_ntop(int, const void *,
char *, socklen_t); char *, socklen_t);
<net/if.h> char *if_indextoname(unsigned int, char *); <net/if.h> char *if_indextoname(unsigned int, char *);
<net/if.h> unsigned int if_nametoindex(const char *); <net/if.h> unsigned int if_nametoindex(const char *);
<net/if.h> void if_freenameindex(struct if_nameindex *); <net/if.h> void if_freenameindex(struct if_nameindex *);
<net/if.h> struct if_nameindex *if_nameindex(void); <net/if.h> struct if_nameindex *if_nameindex(void);
<netdb.h> int getaddrinfo(const char *, const char *, <netdb.h> int getaddrinfo(const char *, const char *,
const struct addrinfo *, const struct addrinfo *,
struct addrinfo **); struct addrinfo **);
<netdb.h> int getnameinfo(const struct sockaddr *, socklen_t, <netdb.h> int getnameinfo(const struct sockaddr *, socklen_t,
char *, socklen_t, char *, socklen_t, int); char *, socklen_t, char *, socklen_t, int);
<netdb.h> void freeaddrinfo(struct addrinfo *); <netdb.h> void freeaddrinfo(struct addrinfo *);
<netdb.h> const char *gai_strerror(int); <netdb.h> const char *gai_strerror(int);
<netinet/in.h> int IN6_IS_ADDR_LINKLOCAL(const struct in6_addr *); <netinet/in.h> int IN6_IS_ADDR_LINKLOCAL(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_LOOPBACK(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_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_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_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_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_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_MULTICAST(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_SITELOCAL(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_UNSPECIFIED(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_V4COMPAT(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 *); <netinet/in.h> int IN6_IS_ADDR_V4MAPPED(const struct in6_addr *);
8. Security Considerations 8. Security Considerations
IPv6 provides a number of new security mechanisms, many of which need to IPv6 provides a number of new security mechanisms, many of which need
be accessible to applications. Companion memos detailing the extensions to be accessible to applications. Companion memos detailing the
to the socket interfaces to support IPv6 security are being written. extensions to the socket interfaces to support IPv6 security are
being written.
Changes from RFC 2553
1. Add brief description of the history of this API and its
relation to the Open Group/IEEE/ISO standards.
2. Alignments with [3]. 9. Changes from RFC 2553
3. Removed all references to getipnodebyname() and 1. Add brief description of the history of this API and its relation
getipnodebyaddr(), which are deprecated in favor to the Open Group/IEEE/ISO standards.
of getaddrinfo() and getnameinfo().
4. Added IPV6_V6ONLY IP level socket option to permit nodes 2. Alignments with [3].
to not process IPv4 packets as IPv4 Mapped addresses
in implementations.
5. Added SIIT to references and added new contributors. 3. Removed all references to getipnodebyname() and getipnodebyaddr(),
which are deprecated in favor of getaddrinfo() and getnameinfo().
Acknowledgments 4. Added IPV6_V6ONLY IP level socket option to permit nodes to not
process IPv4 packets as IPv4 Mapped addresses in implementations.
This specification's evolution and completeness were significantly 5. Added SIIT to references and added new contributors.
influenced by the efforts of Richard Stevens, who has passed on.
Richard's wisdom and talent made the specification what it is today.
The co-authors will long think of Richard with great respect.
Thanks to the many people who made suggestions and provided feedback to 6. In previous versions of this specification, the sin6_flowinfo
this document, including: field was associated with the IPv6 traffic class and flow label,
but its usage was not completely specified. The complete
definition of the sin6_flowinfo field, including its association
with the traffic class or flow label, is now deferred to a future
specification.
Werner Almesberger, Ran Atkinson, Fred Baker, Dave Borman, Andrew 10. Acknowledgments
Cherenson, Alex Conta, Alan Cox, Steve Deering, Richard Draves, Francis
Dupont, Robert Elz, Brian Haberman, Jun-ichiro itojun Hagino, Marc
Hasson, Tom Herbert, Bob Hinden, Wan-Yen Hsu, Christian Huitema, Koji
Imada, Markus Jork, Ron Lee, Alan Lloyd, Charles Lynn, Dan McDonald,
Dave Mitton, Finnbarr Murphy, Thomas Narten, Josh Osborne, Craig
Partridge, Jean-Luc Richier, Bill Sommerfield, Erik Scoredos, Keith
Sklower, JINMEI Tatuya, Dave Thaler, Matt Thomas, Harvey Thompson, Dean
D. Throop, Karen Tracey, Glenn Trewitt, Paul Vixie, David Waitzman, Carl
Williams, Kazu Yamamoto, Vlad Yasevich, Stig Venaas, and Brian Zill.
The getaddrinfo() and getnameinfo() functions are taken from an earlier This specification's evolution and completeness were significantly
Internet Draft by Keith Sklower. As noted in that draft, William Durst, influenced by the efforts of Richard Stevens, who has passed on.
Steven Wise, Michael Karels, and Eric Allman provided many useful Richard's wisdom and talent made the specification what it is today.
discussions on the subject of protocol-independent name-to-address The co-authors will long think of Richard with great respect.
translation, and reviewed early versions of Keith Sklower's original
proposal. Eric Allman implemented the first prototype of getaddrinfo().
The observation that specifying the pair of name and service would
suffice for connecting to a service independent of protocol details was
made by Marshall Rose in a proposal to X/Open for a "Uniform Network
Interface".
Craig Metz, Jack McCann, Erik Nordmark, Tim Hartrick, and Mukesh Kacker Thanks to the many people who made suggestions and provided feedback
made many contributions to this document. Ramesh Govindan made a number to this document, including:
of contributions and co-authored an earlier version of this memo.
References Werner Almesberger, Ran Atkinson, Fred Baker, Dave Borman, Andrew
Cherenson, Alex Conta, Alan Cox, Steve Deering, Richard Draves,
Francis Dupont, Robert Elz, Brian Haberman, Jun-ichiro itojun Hagino,
Marc Hasson, Tom Herbert, Bob Hinden, Wan-Yen Hsu, Christian Huitema,
Koji Imada, Markus Jork, Ron Lee, Alan Lloyd, Charles Lynn, Dan
McDonald, Dave Mitton, Finnbarr Murphy, Thomas Narten, Josh Osborne,
Craig Partridge, Jean-Luc Richier, Bill Sommerfield, Erik Scoredos,
Keith Sklower, JINMEI Tatuya, Dave Thaler, Matt Thomas, Harvey
Thompson, Dean D. Throop, Karen Tracey, Glenn Trewitt, Paul Vixie,
David Waitzman, Carl Williams, Kazu Yamamoto, Vlad Yasevich, Stig
Venaas, and Brian Zill.
[1] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) The getaddrinfo() and getnameinfo() functions are taken from an
Specification", RFC 2460 Draft Standard. earlier document by Keith Sklower. As noted in that document,
William Durst, Steven Wise, Michael Karels, and Eric Allman provided
many useful discussions on the subject of protocol-independent name-
to-address translation, and reviewed early versions of Keith
Sklower's original proposal. Eric Allman implemented the first
prototype of getaddrinfo(). The observation that specifying the pair
of name and service would suffice for connecting to a service
independent of protocol details was made by Marshall Rose in a
proposal to X/Open for a "Uniform Network Interface".
[2] R. Hinden, S. Deering, "IP Version 6 Addressing Architecture", Craig Metz, Jack McCann, Erik Nordmark, Tim Hartrick, and Mukesh
RFC 2373, July 1998 Draft Standard. Kacker made many contributions to this document. Ramesh Govindan
made a number of contributions and co-authored an earlier version of
this memo.
[3] IEEE Std. 1003.1-2001 Standard for Information Technology -- 11. References
Portable Operating System Interface (POSIX)
Open Group Technical Standard: Base Specifications, Issue 6 [1] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
December 2001 Specification", RFC 2460, December 1998.
ISO 9945 (pending final approval by ISO) [2] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
http://www.opengroup.org/austin [3] IEEE Std. 1003.1-2001 Standard for Information Technology --
Portable Operating System Interface (POSIX). Open Group
Technical Standard: Base Specifications, Issue 6, December 2001.
ISO/IEC 9945:2002. http://www.opengroup.org/austin
[4] W. Stevens, M. Thomas, "Advanced Sockets API for IPv6", [4] Stevens, W. and M. Thomas, "Advanced Sockets API for IPv6", RFC
RFC 2292, February 1998. 2292, February 1998.
[5] E. Nordmark "Stateless IP/ICMP Translation Algorithm (SIIT)" [5] Nordmark, E., "Stateless IP/ICMP Translation Algorithm (SIIT)",
RFC 2765, February 2000. RFC 2765, February 2000.
[6] The Open Group Base Working Group [6] The Open Group Base Working Group
http://www.opengroup.org/platform/base.html http://www.opengroup.org/platform/base.html
Authors' Addresses 12. Authors' Addresses
Bob Gilligan Bob Gilligan
Cacheflow, Inc. Intransa, Inc.
650 Almanor Ave. 2870 Zanker Rd.
Sunnyvale, CA 94086 San Jose, CA 95134
Telephone: 408-220-2084 (voice)
408-220-2250 (fax)
Email: gilligan@cacheflow.com
Susan Thomson Phone: 408-678-8647
Cisco Systems EMail: gilligan@intransa.com
499 Thornall Street, 8th floor
Edison, NJ 08837
Telephone: 732-635-3086
Email: sethomso@cisco.com
Jim Bound Susan Thomson
Hewlett-Packard Company Cisco Systems
110 Spitbrook Road ZKO3-3/W20 499 Thornall Street, 8th floor
Nashua, NH 03062 Edison, NJ 08837
Telephone: 603-884-0062
Email: Jim.Bound@hp.com
Jack McCann Phone: 732-635-3086
Hewlett-Packard Company EMail: sethomso@cisco.com
110 Spitbrook Road ZKO3-3/W20
Nashua, NH 03062 Jim Bound
Telephone: 603-884-2608 Hewlett-Packard Company
Email: Jack.McCann@hp.com 110 Spitbrook Road ZKO3-3/W20
Nashua, NH 03062
Phone: 603-884-0062
EMail: Jim.Bound@hp.com
Jack McCann
Hewlett-Packard Company
110 Spitbrook Road ZKO3-3/W20
Nashua, NH 03062
Phone: 603-884-2608
EMail: Jack.McCann@hp.com
13. Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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