draft-ietf-ipngwg-bsd-api-06.txt   rfc2133.txt 
Internet Engineering Task Force R. E. Gilligan (Freegate) Network Working Group R. Gilligan
INTERNET-DRAFT S. Thomson (Bellcore) Request for Comments: 2133 Freegate
J. Bound (Digital) Category: Informational S. Thomson
W. R. Stevens (Consultant) Bellcore
November 23, 1996 J. Bound
Digital
W. Stevens
Consultant
April 1997
Basic Socket Interface Extensions for IPv6 Basic Socket Interface Extensions for IPv6
<draft-ietf-ipngwg-bsd-api-06.txt>
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract 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 [5]. extension headers) are defined in another document [5].
Status of this Memo
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute
working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six
months. This Internet Draft expires on May 23, 1997. Internet
Drafts may be updated, replaced, or obsoleted by other documents at
any time. It is not appropriate to use Internet Drafts as reference
material or to cite them other than as a "working draft" or "work in
progress."
To learn the current status of any Internet-Draft, please check the
1id-abstracts.txt listing contained in the Internet-Drafts Shadow
Directories on ds.internic.net, nic.nordu.net, ftp.isi.edu, or
munnari.oz.au.
Distribution of this memo is unlimited.
Table of Contents Table of Contents
1. Introduction ..................................................... 3 1. Introduction ................................................ 2
2. Design Considerations ....................................... 3
2. Design Considerations ............................................ 3 2.1. What Needs to be Changed .................................. 3
2.1. What Needs to be Changed ....................................... 3 2.2. Data Types ................................................ 5
2.2. Data Types ..................................................... 5 2.3. Headers ................................................... 5
2.4. Structures ................................................ 5
3. Socket Interface ................................................. 5 3. Socket Interface ............................................ 5
3.1. IPv6 Address Family and Protocol Family ........................ 5 3.1. IPv6 Address Family and Protocol Family ................... 5
3.2. IPv6 Address Structure ......................................... 5 3.2. IPv6 Address Structure .................................... 6
3.3. Socket Address Structure for 4.3BSD-Based Systems .............. 6 3.3. Socket Address Structure for 4.3BSD-Based Systems ......... 6
3.4. Socket Address Structure for 4.4BSD-Based Systems .............. 7 3.4. Socket Address Structure for 4.4BSD-Based Systems ......... 7
3.5. The Socket Functions ........................................... 8 3.5. The Socket Functions ...................................... 8
3.6. Compatibility with IPv4 Applications ........................... 9 3.6. Compatibility with IPv4 Applications ...................... 9
3.7. Compatibility with IPv4 Nodes .................................. 9 3.7. Compatibility with IPv4 Nodes ............................. 9
3.8. Flow Information ............................................... 10 3.8. IPv6 Wildcard Address ..................................... 10
3.9. IPv6 Wildcard Address .......................................... 12 3.9. IPv6 Loopback Address ..................................... 11
3.10. IPv6 Loopback Address ......................................... 13 4. Interface Identification .................................... 12
4.1. Name-to-Index ............................................. 13
4. Interface Identification ......................................... 14 4.2. Index-to-Name ............................................. 13
4.1. Name-to-Index .................................................. 15 4.3. Return All Interface Names and Indexes .................... 14
4.2. Index-to-Name .................................................. 15 4.4. Free Memory ............................................... 14
4.3. Return All Interface Names and Indexes ......................... 15 5. Socket Options .............................................. 14
5.1. Changing Socket Type ...................................... 15
5. Socket Options ................................................... 16 5.2. Unicast Hop Limit ......................................... 16
5.1. Changing Socket Type ........................................... 16 5.3. Sending and Receiving Multicast Packets ................... 17
5.2. Unicast Hop Limit .............................................. 17 6. Library Functions ........................................... 19
5.3. Sending and Receiving Multicast Packets ........................ 18 6.1. Hostname-to-Address Translation ........................... 19
6.2. Address To Hostname Translation ........................... 22
6. Library Functions ................................................ 20 6.3. Protocol-Independent Hostname and Service Name Translation 22
6.1. Hostname-to-Address Translation ................................ 20 6.4. Socket Address Structure to Hostname and Service Name ..... 25
6.2. Address To Hostname Translation ................................ 22 6.5. Address Conversion Functions .............................. 27
6.3. Protocol-Independent Hostname and Service Name Translation ..... 23 6.6. Address Testing Macros .................................... 28
6.4. Socket Address Structure to Hostname and Service Name .......... 26 7. Summary of New Definitions .................................. 29
6.5. Address Conversion Functions ................................... 27 8. Security Considerations ..................................... 31
6.6. IPv4-Mapped Addresses .......................................... 28 9. Acknowledgments ............................................. 31
10. References ................................................. 31
7. Security Considerations .......................................... 29 11. Authors' Addresses ......................................... 32
8. Change History ................................................... 29
9. Acknowledgments .................................................. 33
10. References ...................................................... 33
11. Authors' Addresses .............................................. 34
1. Introduction 1. Introduction
While IPv4 addresses are 32 bits long, IPv6 nodes are identified by While IPv4 addresses are 32 bits long, IPv6 interfaces are identified
128-bit addresses. The socket interface make the size of an IP by 128-bit addresses. The socket interface make the size of an IP
address quite visible to an application; virtually all TCP/IP address quite visible to an application; virtually all TCP/IP
applications for BSD-based systems have knowledge of the size of an applications for BSD-based systems have knowledge of the size of an
IP address. Those parts of the API that expose the addresses must be IP address. Those parts of the API that expose the addresses must be
changed to accommodate the larger IPv6 address size. IPv6 also changed to accommodate the larger IPv6 address size. IPv6 also
introduces new features (e.g., flow label and priority), some of introduces new features (e.g., flow label and priority), some of
which must be made visible to applications via the API. This memo which must be made visible to applications via the API. This memo
defines a set of extensions to the socket interface to support the defines a set of extensions to the socket interface to support the
larger address size and new features of IPv6. larger address size and new features of IPv6.
2. Design Considerations 2. Design Considerations
There are a number of important considerations in designing changes There are a number of important considerations in designing changes
to 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 is, compatibility for programs written to the original API. That is,
existing program binaries should continue to operate when run on existing program binaries should continue to operate when run on
a system supporting the new API. In addition, existing a system supporting the new API. In addition, existing
applications that are re-compiled and run on a system supporting applications that are re-compiled and run on a system supporting
the new API should continue to operate. Simply put, the API the new API should continue to operate. Simply put, the API
changes for IPv6 should not break existing programs. changes for IPv6 should not break existing programs.
- The changes to the API should be as small as possible in order to - The changes to the API should be as small as possible in order 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 API to - Where possible, applications should be able to use this API to
interoperate with both IPv6 and IPv4 hosts. Applications should interoperate with both IPv6 and IPv4 hosts. Applications should
not need to know which type of host they are communicating with. not need to know which type of host they are 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 on 64-bit machine architectures. performance 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 provide complete support for both IPv4 and IPv6. A subset of this
API could probably be designed for operation on systems that support API could probably be designed for operation on systems that support
only 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
skipping to change at page 4, line 14 skipping to change at page 3, line 48
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 The core socket functions -- those functions that deal with such
things as setting up and tearing down TCP connections, and sending things as setting up and tearing down TCP connections, and sending
and receiving UDP packets -- were designed to be transport and receiving UDP packets -- were designed to be transport
independent. Where protocol addresses are passed as function independent. Where protocol addresses are passed as function
arguments, they are carried via opaque pointers. A protocol-specific arguments, they are carried via opaque pointers. A protocol-specific
address data structure is defined for each protocol that the socket address data structure is defined for each protocol that the socket
functions support. Applications must cast pointers to these functions support. Applications must cast pointers to these
protocol-specific address structures into pointers to the generic protocol-specific address structures into pointers to the generic
"sockaddr" address structure when using the socket functions. These "sockaddr" address structure when using the socket functions. These
functions need not change for IPv6, but a new IPv6-specific address functions need not change for IPv6, but a new IPv6-specific address
data structure is needed. data structure is needed.
The "sockaddr_in" structure is the protocol-specific data structure The "sockaddr_in" structure is the protocol-specific data structure
for IPv4. This data structure actually includes 8-octets of unused for IPv4. This data structure actually includes 8-octets of unused
space, and it is tempting to try to use this space to adapt the space, and it is tempting to try to use this space to adapt the
sockaddr_in structure to IPv6. Unfortunately, the sockaddr_in sockaddr_in structure to IPv6. Unfortunately, the sockaddr_in
structure is not large enough to hold the 16-octet IPv6 address as structure is not large enough to hold the 16-octet IPv6 address as
well as the other information (address family and port number) that well as the other information (address family and port number) that
is needed. So a new address data structure must be defined for IPv6. is needed. So a new address data structure must be defined for IPv6.
The name-to-address translation functions in the socket interface are The name-to-address translation functions in the socket interface are
gethostbyname() and gethostbyaddr(). These must be modified to gethostbyname() and gethostbyaddr(). These must be modified to
support IPv6 and the semantics defined must provide 100% backward support IPv6 and the semantics defined must provide 100% backward
compatibility for all existing IPv4 applications, along with IPv6 compatibility for all existing IPv4 applications, along with IPv6
support for new applications. Additionally, the POSIX 1003.g draft support for new applications. Additionally, the POSIX 1003.g work in
[4] specifies a new hostname-to-address translation function which is progress [4] specifies a new hostname-to-address translation function
protocol independent. This function can also be used with IPv6. which is protocol independent. This function can also be used with
IPv6.
The address conversion functions -- inet_ntoa() and inet_addr() -- The 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 functions are quite specific to 32-bit IPv4 addresses. We have
designed two analogous functions that convert both IPv4 and IPv6 designed two analogous functions that convert both IPv4 and IPv6
addresses, and carry an address type parameter so that they can be addresses, and carry an address type parameter so that they can be
extended to other protocol families as well. extended to other protocol families as well.
Finally, a few miscellaneous features are needed to support IPv6. Finally, a few miscellaneous features are needed to support IPv6.
New interfaces are needed to support the IPv6 flow label, priority, New interfaces are needed to support the IPv6 flow label, priority,
and hop limit header fields. New socket options are needed to and hop limit header fields. New socket options are needed to
control the sending and receiving of IPv6 multicast packets. control the sending and receiving of IPv6 multicast packets.
The socket interface may be enhanced in the future to provide access The socket interface will be enhanced in the future to provide access
to other IPv6 features. These extensions are described in [5]. to other IPv6 features. These extensions are described in [5].
2.2. Data Types 2.2. Data Types
The data types of the structure elements given in this memo are The data types of the structure elements given in this memo are
intended to be examples, not absolute requirements. Whenever intended to be examples, not absolute requirements. Whenever
possible, POSIX 1003.1g data types are used: u_intN_t means an possible, POSIX 1003.1g data types are used: u_intN_t means an
unsigned integer of exactly N bits (e.g., u_int16_t) and u_intNm_t unsigned integer of exactly N bits (e.g., u_int16_t) and u_intNm_t
means an unsigned integer of at least N bits (e.g., u_int32m_t). We means an unsigned integer of at least N bits (e.g., u_int32m_t). We
also assume the argument data types from 1003.1g when possible (e.g., also assume the argument data types from 1003.1g when possible (e.g.,
the final argument to setsockopt() is a size_t value). Whenever the final argument to setsockopt() is a size_t value). Whenever
buffer sizes are specified, the POSIX 1003.1 size_t data type is used buffer sizes are specified, the POSIX 1003.1 size_t data type is used
(e.g., the two length arguments to getnameinfo()). (e.g., the two length arguments to getnameinfo()).
2.3. Headers
When function prototypes and structures are shown we show the headers
that must be #included to cause that item to be defined.
2.4. Structures
When structures are described the members shown are the ones that
must appear in an implementation. Additional, nonstandard members
may also be defined by an implementation.
The ordering shown for the members of a structure is the recommended
ordering, given alignment considerations of multibyte members, but an
implementation may order the members differently.
3. Socket Interface 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>. A new address family name, AF_INET6, is defined in <sys/socket.h>.
The AF_INET6 definition distinguishes between the original The AF_INET6 definition distinguishes between the original
sockaddr_in address data structure, and the new sockaddr_in6 data sockaddr_in address data structure, and the new sockaddr_in6 data
structure. structure.
skipping to change at page 5, line 45 skipping to change at page 6, line 8
name: name:
#define PF_INET6 AF_INET6 #define PF_INET6 AF_INET6
The PF_INET6 is used in the first argument to the socket() function The PF_INET6 is used in the first argument to the socket() function
to 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 data structure to hold a single IPv6 address is defined as A new data structure to hold a single IPv6 address is defined as
follows: follows:
#include <netinet/in.h>
struct in6_addr { struct in6_addr {
u_char s6_addr[16]; /* IPv6 address */ u_int8_t s6_addr[16]; /* IPv6 address */
} }
This data structure contains an array of sixteen 8-bit elements, This data structure contains an array of sixteen 8-bit elements,
which make up one 128-bit IPv6 address. The IPv6 address is stored which make up one 128-bit IPv6 address. The IPv6 address is stored
in network byte order. in network byte order.
Applications obtain the declaration for this structure by including
the header <netinet/in.h>.
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 In the socket interface, a different protocol-specific data structure
is defined to carry the addresses for each protocol suite. Each is defined to carry the addresses for each protocol suite. Each
protocol-specific data structure is designed so it can be cast into a protocol-specific data structure is designed so it can be cast into a
protocol-independent data structure -- the "sockaddr" structure. protocol-independent data structure -- the "sockaddr" structure.
Each has a "family" field that overlays the "sa_family" of the Each has a "family" field that overlays the "sa_family" of the
sockaddr data structure. This field identifies the type of the data sockaddr data structure. This field identifies the type of the data
structure. 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 structure for IPv4. It is used to pass addresses between
applications and the system in the socket functions. The following applications and the system in the socket functions. The following
structure is defined to carry IPv6 addresses: structure is defined to carry IPv6 addresses:
#include <netinet/in.h>
struct sockaddr_in6 { struct sockaddr_in6 {
u_int16m_t sin6_family; /* AF_INET6 */ u_int16m_t sin6_family; /* AF_INET6 */
u_int16m_t sin6_port; /* transport layer port # */ u_int16m_t sin6_port; /* transport layer port # */
u_int32m_t sin6_flowinfo; /* IPv6 flow information */ u_int32m_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */ struct in6_addr sin6_addr; /* IPv6 address */
}; };
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.
skipping to change at page 7, line 5 skipping to change at page 7, line 12
This field overlays the sa_family field when the buffer is cast to a This field overlays the sa_family field when the buffer is cast to a
sockaddr data structure. The value of this field must be AF_INET6. 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 field is used in the same way as the sin_port field of the
sockaddr_in structure. The port number is stored in network byte sockaddr_in structure. The port number is stored in network byte
order. order.
The sin6_flowinfo field is a 32-bit field that contains two pieces of The sin6_flowinfo field is a 32-bit field that contains two pieces of
information: the 24-bit IPv6 flow label and the 4-bit priority field. information: the 24-bit IPv6 flow label and the 4-bit priority field.
The IPv6 flow label is represented as the low-order 24 bits of the The contents and interpretation of this member is unspecified at this
32-bit field. The priority is represented in the next 4 bits above time.
this. The high-order 4 bits of this field are reserved. The
sin6_flowinfo field is stored in network byte order. The use of the
flow label and priority fields are explained in Section 3.8.
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 The ordering of elements in this structure is specifically designed
so that the sin6_addr field will be aligned on a 64-bit boundary. so that the sin6_addr field will be aligned on a 64-bit boundary.
This is done for optimum performance on 64-bit architectures. This is done for optimum performance on 64-bit architectures.
Applications obtain the declaration of the sockaddr_in6 structure by Notice that the sockaddr_in6 structure will normally be larger than
including the header <netinet/in.h>. the generic sockaddr structure. On many existing implementations the
sizeof(struct sockaddr_in) equals sizeof(struct sockaddr), with both
being 16 bytes. Any existing code that makes this assumption needs
to be examined carefully when converting to IPv6.
3.4. Socket Address Structure for 4.4BSD-Based Systems 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 socket interface. The "sa_family" field of the sockaddr data
structure was changed from a 16-bit value to an 8-bit value, and the structure was changed from a 16-bit value to an 8-bit value, and the
space saved used to hold a length field, named "sa_len". The space saved used to hold a length field, named "sa_len". The
sockaddr_in6 data structure given in the previous section cannot be sockaddr_in6 data structure given in the previous section cannot be
correctly cast into the newer sockaddr data structure. For this correctly cast into the newer sockaddr data structure. For this
reason, the following alternative IPv6 address data structure is reason, the following alternative IPv6 address data structure is
provided to be used on systems based on 4.4BSD: provided to be used on systems based on 4.4BSD:
#include <netinet/in.h>
#define SIN6_LEN #define SIN6_LEN
struct sockaddr_in6 { struct sockaddr_in6 {
u_char sin6_len; /* length of this struct */ u_char sin6_len; /* length of this struct */
u_char sin6_family; /* AF_INET6 */ u_char sin6_family; /* AF_INET6 */
u_int16m_t sin6_port; /* Transport layer port # */ u_int16m_t sin6_port; /* transport layer port # */
u_int32m_t sin6_flowinfo; /* IPv6 flow information */ u_int32m_t sin6_flowinfo; /* IPv6 flow information */
struct in6_addr sin6_addr; /* IPv6 address */ struct in6_addr sin6_addr; /* IPv6 address */
}; };
The only differences between this data structure and the 4.3BSD The only differences between this data structure and the 4.3BSD
variant are the inclusion of the length field, and the change of the variant are the inclusion of the length field, and the change of the
family field to a 8-bit data type. The definitions of all the other family field to a 8-bit data type. The definitions of all the other
fields are identical to the structure defined in the previous fields are identical to the structure defined in the previous
section. 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 must also declare SIN6_LEN as a result of including the
<netinet/in.h> header. This macro allows applications to determine <netinet/in.h> header. This macro allows applications to determine
whether they are being built on a system that supports the 4.3BSD or whether they are being built on a system that supports the 4.3BSD or
4.4BSD variants of the data structure. 4.4BSD variants of the data structure.
Note that the size of the sockaddr_in6 structure is larger than the
size of the sockaddr structure. Applications that use the
sockaddr_in6 structure need to be aware that they cannot use
sizeof(sockaddr) to allocate a buffer to hold a sockaddr_in6
structure. They should use sizeof(sockaddr_in6) instead.
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 that represents a communication endpoint. The arguments to the
socket() function tell the system which protocol to use, and what socket() function tell the system which protocol to use, and what
format address structure will be used in subsequent functions. For format address structure will be used in subsequent functions. For
example, to create an IPv4/TCP socket, applications make the call: example, to create an IPv4/TCP socket, applications make the call:
s = socket(PF_INET, SOCK_STREAM, 0); s = socket(PF_INET, SOCK_STREAM, 0);
skipping to change at page 9, line 6 skipping to change at page 9, line 10
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 PF_INET6 sockets. The addresses to applications that are using PF_INET6 sockets. The
functions that return an address from the system to an application functions that return an address from the system to an application
are: are:
accept() accept()
recvfrom() recvfrom()
recvmsg() recvmsg()
getpeername() getpeername()
getsockname() getsockname()
No changes to the syntax of the socket functions are needed to No changes to the syntax of the socket functions are needed to
support IPv6, since the all of the "address carrying" functions use support IPv6, since all of the "address carrying" functions use an
an opaque address pointer, and carry an address length as a function opaque address pointer, and carry an address length as a function
argument. 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 PF_INET sockets and the sockaddr_in address continue to support PF_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 PF_INET constant in the socket() function, as sockets using the PF_INET constant in the socket() function, as
skipping to change at page 10, line 17 skipping to change at page 10, line 17
destination's IPv4 address as an IPv4-mapped IPv6 address, and destination's IPv4 address as an IPv4-mapped IPv6 address, and
passing that address, within a sockaddr_in6 structure, in the passing that address, within a sockaddr_in6 structure, in the
connect() or sendto() call. When applications use PF_INET6 sockets connect() or sendto() call. When applications use PF_INET6 sockets
to accept TCP connections from IPv4 nodes, or receive UDP packets to accept TCP connections from IPv4 nodes, or receive UDP packets
from IPv4 nodes, the system returns the peer's address to the from IPv4 nodes, the system returns the peer's address to the
application in the accept(), recvfrom(), or getpeername() call using application in the accept(), recvfrom(), or getpeername() call using
a sockaddr_in6 structure encoded 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 inet6_isipv4mapped() function, defined in Section 6.6, is know, the IN6_IS_ADDR_V4MAPPED() macro, defined in Section 6.6, is
provided. provided.
3.8. Flow Information 3.8. IPv6 Wildcard Address
The IPv6 header has a 24-bit field to hold a "flow label", and a 4-
bit field to hold a "priority" value. Applications must have control
over what values for these fields are used in packets that they
originate, and must have access to the field values of packets that
they receive.
The sin6_flowinfo field of the sockaddr_in6 structure encodes two
pieces of information: IPv6 flow label and IPv6 priority.
Applications use this field to set the flow label and priority in
IPv6 headers of packets they generate, and to retrieve the flow label
and priority from the packets they receive. The header fields of an
actively opened TCP connection are set by assigning in the
sin6_flowinfo field of the destination address sockaddr_in6 structure
passed in the connect() function. The same technique can be used
with the sockaddr_in6 structure passed to the sendto() or sendmsg()
function to set the flow label and priority fields of UDP packets.
Similarly, the flow label and priority values of received UDP packets
and accepted TCP connections are reflected in the sin6_flowinfo field
of the sockaddr_in6 structure returned to the application by the
recvfrom(), recvmsg(), and accept() functions. An application may
specify the flow label and priority to use in transmitted packets of
a passively accepted TCP connection, by setting the sin6_flowinfo
field of the address passed to the bind() function.
Implementations provide two bitmask constant declarations to help
applications select out the flow label and priority fields. These
constants are:
IPV6_FLOWINFO_FLOWLABEL
IPV6_FLOWINFO_PRIORITY
These constants can be applied to the sin6_flowinfo field of
addresses returned to the application, for example:
int recv_flow; /* host byte ordered, 0-0x00ffffff */
int recv_prio; /* host byte ordered, 0-15 */
struct sockaddr_in6 sin6;
. . .
recvfrom(s, buf, buflen, flags, (struct sockaddr *) &sin6, &fromlen);
. . .
recv_flow = ntohl(sin6.sin6_flowinfo & IPV6_FLOWINFO_FLOWLABEL);
recv_prio = ntohl(sin6.sin6_flowinfo & IPV6_FLOWINFO_PRIORITY) >> 24;
printf("flow = %d, prio = %d\n", recv_flow, recv_prio);
Recall that sin6_flowinfo is network byte ordered, as are the two
IPV6_FLOWINFO_xxx constants.
On the sending side, applications are responsible for selecting the
flow label value and specifying a priority. The headers provide
constant declarations for the 16 IPv6 priority values defined in the
IPv6 specification [1]. These constants are:
IPV6_PRIORITY_UNCHARACTERIZED
IPV6_PRIORITY_FILLER
IPV6_PRIORITY_UNATTENDED
IPV6_PRIORITY_RESERVED1
IPV6_PRIORITY_BULK
IPV6_PRIORITY_RESERVED2
IPV6_PRIORITY_INTERACTIVE
IPV6_PRIORITY_CONTROL
IPV6_PRIORITY_8
IPV6_PRIORITY_9
IPV6_PRIORITY_10
IPV6_PRIORITY_11
IPV6_PRIORITY_12
IPV6_PRIORITY_13
IPV6_PRIORITY_14
IPV6_PRIORITY_15
Most applications will use these constants (e.g.,
IPV6_PRIORITY_INTERACTIVE can be built into Telnet clients and
servers). Since these constants are defined in network byte order an
example is:
int send_flow; /* host byte ordered, 0-0x00ffffff */
struct sockaddr_in6 sin6;
send_flow = /* undefined at this time; perhaps a system call */
sin6.sin6_flowinfo = htonl(send_flow) & IPV6_FLOWINFO_FLOWLABEL |
IPV6_PRIORITY_INTERACTIVE;
. . .
connect( ... )
Some applications may specify the priority as a value between 0 and
15 (perhaps a command-line argument) and the following example shows
the required byte ordering and shifting:
int send_flow; /* host byte ordered, 0-0x00ffffff */
int send_prio; /* host byte ordered, 0-15 */
struct sockaddr_in6 sin6;
send_flow = /* undefined at this time; perhaps a system call */
send_prio = 12; /* or some other host byte ordered value, 0-15 */
sin6.sin6_flowinfo = htonl(send_flow) & IPV6_FLOWINFO_FLOWLABEL |
htonl(send_prio << 24) & IPV6_FLOWINFO_PRIORITY;
. . .
sendto( ... )
The declarations for these constants are obtained by including the
header <netinet/in.h>.
3.9. 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 address of UDP packets and TCP connections, applications often want
the system select the source address for them. With IPv4, one the system to select the source address for them. With IPv4, one
specifies the address as the symbolic constant INADDR_ANY (called the specifies the address as the symbolic constant INADDR_ANY (called the
"wildcard" address) in the bind() call, or simply omits the bind() "wildcard" address) in the bind() call, or simply omits the bind()
entirely. entirely.
Since the IPv6 address type is a structure (struct in6_addr), a Since the IPv6 address type is a structure (struct in6_addr), a
symbolic constant can be used to initialize an IPv6 address variable, symbolic constant can be used to initialize an IPv6 address variable,
but cannot be used in an assignment. Therefore systems provide the but cannot be used in an assignment. Therefore systems provide the
IPv6 wildcard 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: in6_addr structure. The extern declaration for this variable is
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 Applications use in6addr_any similarly to the way they use INADDR_ANY
in IPv4. For example, to bind a socket to port number 23, but let in IPv4. For example, to bind a socket to port number 23, but let
the system select the source address, an application could use the the system select the source address, an application could use the
following 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. The other version is a symbolic constant named IN6ADDR_ANY_INIT and
This constant can be used to initialize an in6_addr structure: is defined in <netinet/in.h>. This constant can be used to
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 type. 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 */
The extern declaration for in6addr_any and the declaration for
IN6ADDR_ANY_INIT are obtained by including the header <netinet/in.h>.
Be aware that the IPv4 INADDR_xxx constants are all defined in host Be aware that the IPv4 INADDR_xxx constants are all defined in host
byte order but the IPv6 IN6ADDR_xxx constants and the IPv6 byte order but the IPv6 IN6ADDR_xxx constants and the IPv6
in6addr_xxx externals are defined in network byte order. in6addr_xxx externals are defined in network byte order.
3.10. 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 connections to, services residing on the local node. In IPv4, they
can do this by using the constant IPv4 address INADDR_LOOPBACK in can do this by using the constant IPv4 address INADDR_LOOPBACK in
their 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 The global variable is an in6_addr structure named
"in6addr_loopback." The extern declaration for this variable is: "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 Applications use in6addr_loopback as they would use INADDR_LOOPBACK
in IPv4 applications (but beware of the byte ordering difference in IPv4 applications (but beware of the byte ordering difference
mentioned at the end of the previous section). For example, to open mentioned at the end of the previous section). For example, to open
a TCP connection to the local telnet server, an application could use a TCP connection to the local telnet server, an application could use
the 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. It can be used The symbolic constant is named IN6ADDR_LOOPBACK_INIT and is defined
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 Like IN6ADDR_ANY_INIT, this constant cannot be used in an assignment
to a previously declared IPv6 address variable. to a previously declared IPv6 address variable.
The extern declaration for in6addr_loopback and the declaration for
IN6ADDR_LOOPBACK_INIT are obtained by including the header
<netinet/in.h>.
4. Interface Identification 4. Interface Identification
This API uses an interface index (a small positive integer) to This API uses an interface index (a small positive integer) to
identify the local interface on which a multicast group is joined identify the local interface on which a multicast group is joined
(Section 5.3). Additionally, the advanced API [5] uses these same (Section 5.3). Additionally, the advanced API [5] uses these same
interface indexes to identify the interface on which a datagram is interface indexes to identify the interface on which a datagram is
received, or to specify the interface on which a datagram is to be received, or to specify the interface on which a datagram is to be
sent. sent.
Interfaces are normally known by names such as "le0", "sl1", "ppp2", Interfaces are normally known by names such as "le0", "sl1", "ppp2",
and the like. On Berkeley-derived implementations, when an interface and the like. On Berkeley-derived implementations, when an interface
is made known to the system, the kernel assigns a unique positive is made known to the system, the kernel assigns a unique positive
integer value (called the interface index) to that interface. These integer value (called the interface index) to that interface. These
are small positive integers that start at 1. (Note that 0 is never are small positive integers that start at 1. (Note that 0 is never
used for an interface index.) There may be gaps so that there is no used for an interface index.) There may be gaps so that there is no
current 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, and a third function that returns all the interface names and index, a third function that returns all the interface names and
indexes. How these three functions are implemented is left up to the indexes, and a fourth function to return the dynamic memory allocated
implementation. 4.4BSD implementations can implement all three by the previous function. How these functions are implemented is
functions using the existing sysctl() function with the NET_RT_LIST left up to the implementation. 4.4BSD implementations can implement
command. Other implementations may wish to use ioctl() for this these functions using the existing sysctl() function with the
purpose. The function prototypes for these three functions, the NET_RT_LIST command. Other implementations may wish to use ioctl()
constant IF_MAXNAME, and the if_nameindex structure are defined as a for this purpose.
result of including the <sys/socket.h> header.
4.1. Name-to-Index 4.1. Name-to-Index
The first function maps an interface names into its corresponding The first function maps an interface name into its corresponding
index. index.
#include <net/if.h>
unsigned int if_nametoindex(const char *ifname); unsigned int if_nametoindex(const char *ifname);
If the specified interface does not exist, the return value is 0. If the specified interface does not exist, the return value is 0.
4.2. Index-to-Name 4.2. Index-to-Name
The second function maps an interface index into its corresponding The second function maps an interface index into its corresponding
name. name.
#include <net/if.h>
char *if_indextoname(unsigned int ifindex, char *ifname); char *if_indextoname(unsigned int ifindex, char *ifname);
The ifname argument must point to a buffer of at least IF_MAXNAME The ifname argument must point to a buffer of at least IFNAMSIZ bytes
bytes into which the interface name corresponding to the specified into which the interface name corresponding to the specified index is
index is returned. This pointer is also the return value of the returned. (IFNAMSIZ is also defined in <net/if.h> and its value
function. If there is no interface corresponding to the specified includes a terminating null byte at the end of the interface name.)
index, NULL is returned and the buffer pointed to by ifname is not This pointer is also the return value of the function. If there is
modified. no interface corresponding to the specified index, NULL is returned.
4.3. Return All Interface Names and Indexes 4.3. Return All Interface Names and Indexes
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>
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", ... */
}; };
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 The end of the array of structures is indicated by a structure with
an if_index of 0 and an if_name of NULL. The memory used for this an if_index of 0 and an if_name of NULL. The function returns a NULL
array of structures along with the interface names pointed to by the pointer upon an error.
if_name members is obtained using one call to malloc() and can be
returned by calling free() with an argument that is the pointer The memory used for this array of structures along with the interface
returned by if_nameindex(). names pointed to by the if_name members is obtained dynamically.
This memory is freed by the next function.
4.4. Free Memory
The following function frees the dynamic memory that was allocated by
if_nameindex().
#include <net/if.h>
void if_freenameindex(struct if_nameindex *ptr);
The argument to this function must be a pointer that was returned by
if_nameindex().
5. Socket Options 5. Socket Options
A number of new socket options are defined for IPv6. All of these A number of new socket options are defined for IPv6. All of these
new options are at the IPPROTO_IPV6 level. That is, the "level" new options are at the IPPROTO_IPV6 level. That is, the "level"
parameter in the getsockopt() and setsockopt() calls is IPPROTO_IPV6 parameter in the getsockopt() and setsockopt() calls is IPPROTO_IPV6
when using these options. The constant name prefix IPV6_ is used in when using these options. The constant name prefix IPV6_ is used in
all of the new socket options. This serves to clearly identify these all of the new socket options. This serves to clearly identify these
options as applying to IPv6. options as applying to IPv6.
skipping to change at page 18, line 15 skipping to change at page 16, line 37
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 When the IPV6_UNICAST_HOPS option is set with setsockopt(), the
option value given is used as the hop limit for all subsequent option value given is used as the hop limit for all subsequent
unicast packets sent via that socket. If the option is not set, the unicast packets sent via that socket. If the option is not set, the
system selects a default value. system selects a default value. The integer hop limit value (called
x) is interpreted as follows:
x < -1: return an error of EINVAL
x == -1: use kernel default
0 <= x <= 255: use x
x >= 256: return an error of EINVAL
The IPV6_UNICAST_HOPS option may be used with getsockopt() to The IPV6_UNICAST_HOPS option may be used with getsockopt() to
determine the hop limit value that the system will use for subsequent determine the hop limit value that the system will use for subsequent
unicast packets sent via that socket. For example: unicast packets sent via that socket. For example:
int hoplimit; int hoplimit;
size_t len = sizeof(hoplimit); size_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)
skipping to change at page 19, line 14 skipping to change at page 17, line 39
IPV6_MULTICAST_IF IPV6_MULTICAST_IF
Set the interface to use for outgoing multicast packets. The Set the interface to use for outgoing multicast packets. The
argument is the index of the interface to use. argument is the index of the interface to use.
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 a separate option - IPV6_UNICAST_HOPS - is provided to (Note a separate option - IPV6_UNICAST_HOPS - is provided to
set the hop limit to use for outgoing unicast packets.) set the hop limit to use for outgoing unicast packets.) The
interpretation of the argument is the same as for the
IPV6_UNICAST_HOPS option:
Argument type: unsigned int x < -1: return an error of EINVAL
x == -1: use kernel default
0 <= x <= 255: use x
x >= 256: return an error of EINVAL
Argument type: int
IPV6_MULTICAST_LOOP IPV6_MULTICAST_LOOP
Controls whether outgoing multicast packets sent should be Controls whether outgoing multicast packets sent should be
delivered back to the local application. A toggle. If the delivered back to the local application. A toggle. If the
option is set to 1, multicast packets are looped back. If it option is set to 1, multicast packets are looped back. If it
is set to 0, they are not. is set to 0, they are not.
Argument type: unsigned int Argument type: unsigned int
The reception of multicast packets is controlled by the two The reception of multicast packets is controlled by the two
setsockopt() options summarized below: setsockopt() options summarized below:
IPV6_ADD_MEMBERSHIP IPV6_ADD_MEMBERSHIP
Join a multicast group on a specified local interface. If Join a multicast group on a specified local interface. If
the interface index is specified as 0, the kernel chooses the the interface index is specified as 0, the kernel chooses the
local interface by looking up the multicast group in the local interface. For example, some kernels look up the
normal IPv6 routing table and using the resulting interface. multicast group in the normal IPv6 routing table and using
the resulting interface.
Argument type: struct ipv6_mreq Argument type: struct ipv6_mreq
IPV6_DROP_MEMBERSHIP IPV6_DROP_MEMBERSHIP
Leave a multicast group on a specified interface. Leave a multicast group on a specified interface.
Argument type: struct ipv6_mreq Argument type: struct ipv6_mreq
The argument type of both of these options is the ipv6_mreq The argument type of both of these options is the ipv6_mreq
structure, defined as follows: structure, defined as:
#include <netinet/in.h>
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 and bind the UDP port to which datagrams will be multicast group and bind the UDP port to which datagrams will be
sent. Some processes also bind the multicast group address to the sent. Some processes also bind the multicast group address to the
socket, in addition to the port, to prevent other datagrams destined socket, in addition to the port, to prevent other datagrams destined
skipping to change at page 20, line 33 skipping to change at page 19, line 22
convert IPv6 addresses between their binary and textual form. convert IPv6 addresses between their binary and textual form.
6.1. Hostname-to-Address Translation 6.1. Hostname-to-Address Translation
The commonly used function gethostbyname() remains unchanged as does The commonly used function gethostbyname() remains unchanged as does
the hostent structure to which it returns a pointer. Existing the hostent structure to which it returns a pointer. Existing
applications that call this function continue to receive only IPv4 applications that call this function continue to receive only IPv4
addresses that are the result of a query in the DNS for A records. addresses that are the result of a query in the DNS for A records.
(We assume the DNS is being used; some environments may be using a (We assume the DNS is being used; some environments may be using a
hosts file or some other name resolution system, either of which may hosts file or some other name resolution system, either of which may
impede renumbering.) impede renumbering. We also assume that the RES_USE_INET6 resolver
option is not set, which we describe in more detail shortly.)
Two new changes are made to support IPv6 addresses. First the Two new changes are made to support IPv6 addresses. First, the
following function is new: following function is new:
#include <sys/socket.h>
#include <netdb.h>
struct hostent *gethostbyname2(const char *name, int af); struct hostent *gethostbyname2(const char *name, int af);
The af argument specifies the address family. The default operation The af argument specifies the address family. The default operation
of this function is simple: of this function is simple:
- If the af argument is AF_INET, then a query is made for A - If the af argument is AF_INET, then a query is made for A
records. If successful, IPv4 addresses are returned and the records. If successful, IPv4 addresses are returned and the
h_length member of the hostent structure will be 4, else the h_length member of the hostent structure will be 4, else the
function returns a NULL pointer. function returns a NULL pointer.
skipping to change at page 21, line 24 skipping to change at page 20, line 21
- The first way is - The first way is
res_init(); res_init();
_res.options |= RES_USE_INET6; _res.options |= RES_USE_INET6;
and then call either gethostbyname() or gethostbyname2(). This and then call either gethostbyname() or gethostbyname2(). This
option then affects only the process that is calling the option then affects only the process that is calling the
resolver. resolver.
- The second way to set this option is to set the environment - The second way to set this option is to set the environment
variable RES_OPTIONS, as in RES_OPTIONS=inet6. This method variable RES_OPTIONS, as in RES_OPTIONS=inet6. (This example is
affects any processes that see this environment variable. for the Bourne and Korn shells.) This method affects any
processes that see this environment variable.
- The third way is to set this option in the resolver configuration - The third way is to set this option in the resolver configuration
file (normally /etc/resolv.conf) and the option then affects all file (normally /etc/resolv.conf) and the option then affects all
applications on the host. This final method should not be done applications on the host. This final method should not be done
until all applications on the host are capable of dealing with until all applications on the host are capable of dealing with
IPv6 addresses. IPv6 addresses.
When the RES_USE_INET6 option is set, two changes occur: There is no priority among these three methods. When the
RES_USE_INET6 option is set, two changes occur:
- gethostbyname(host) first calls gethostbyname2(host, AF_INET6) - gethostbyname(host) first calls gethostbyname2(host, AF_INET6)
looking for AAAA records, and if this fails it then calls looking for AAAA records, and if this fails it then calls
gethostbyname2(host, AF_INET) looking for A records. gethostbyname2(host, AF_INET) looking for A records.
- gethostbyname2(host, AF_INET) always returns IPv4-mapped IPv6 - gethostbyname2(host, AF_INET) always returns IPv4-mapped IPv6
addresses with the h_length member of the hostent structure set addresses with the h_length member of the hostent structure set
to 16. to 16.
An application must not enable the RES_USE_INET6 option until it is An application must not enable the RES_USE_INET6 option until it is
prepared to deal with 16-byte addresses in the returned hostent prepared to deal with 16-byte addresses in the returned hostent
structure. structure.
The following table summarizes the operation of the existing The following table summarizes the operation of the existing
gethostbyname() function, the new function gethostbyname2(), along gethostbyname() function, the new function gethostbyname2(), along
with the new resolver option RES_USE_INET6. with the new resolver option RES_USE_INET6.
+------------------+---------------------------------------------------+ +------------------+---------------------------------------------------+
| | RES_USE_INET6 option | | | RES_USE_INET6 option |
| +-------------------------+-------------------------+ | +-------------------------+-------------------------+
| | off | on | | | off | on |
+------------------+-------------------------+-------------------------+ +------------------+-------------------------+-------------------------+
| |Search for A records. |Search for AAAA records. | | |Search for A records. |Search for AAAA records. |
| gethostbyname | If found, return IPv4 | If found, return IPv6 | | gethostbyname | If found, return IPv4 | If found, return IPv6 |
| (host) | addresses (h_length=4). | addresses (h_length=16).| | (host) | addresses (h_length=4). | addresses (h_length=16).|
| | Else error. | Else search for A | | | Else error. | Else search for A |
| | | records. If found, | | | | records. If found, |
| |Provides backward | return IPv4-mapped IPv6 | | |Provides backward | return IPv4-mapped IPv6 |
| | compatibility with all | addresses (h_length=16).| | | compatibility with all | addresses (h_length=16).|
| | existing IPv4 appls. | Else error. | | | existing IPv4 appls. | Else error. |
+------------------+-------------------------+-------------------------+ +------------------+-------------------------+-------------------------+
| |Search for A records. |Search for A records. | | |Search for A records. |Search for A records. |
| gethostbyname2 | If found, return IPv4 | If found, return | | gethostbyname2 | If found, return IPv4 | If found, return |
| (host, AF_INET) | addresses (h_length=4). | IPv4-mapped IPv6 | | (host, AF_INET) | addresses (h_length=4). | IPv4-mapped IPv6 |
| | Else error. | addresses (h_length=16).| | | Else error. | addresses (h_length=16).|
| | | Else error. | | | | Else error. |
+------------------+-------------------------+-------------------------+ +------------------+-------------------------+-------------------------+
| |Search for AAAA records. |Search for AAAA records. | | |Search for AAAA records. |Search for AAAA records. |
| gethostbyname2 | If found, return IPv6 | If found, return IPv6 | | gethostbyname2 | If found, return IPv6 | If found, return IPv6 |
| (host, AF_INET6) | addresses (h_length=16).| addresses (h_length=16).| | (host, AF_INET6) | addresses (h_length=16).| addresses (h_length=16).|
| | Else error. | Else error. | | | Else error. | Else error. |
+------------------+-------------------------+-------------------------+ +------------------+-------------------------+-------------------------+
------------------+-------------------------+-------------------------+
It is expected that when a typical naive application that calls It is expected that when a typical naive application that calls
gethostbyname() today is modified to use IPv6, it simply changes the gethostbyname() today is modified to use IPv6, it simply changes the
program to use IPv6 sockets and then enables the RES_USE_INET6 program to use IPv6 sockets and then enables the RES_USE_INET6
resolver option before calling gethostbyname(). This application resolver option before calling gethostbyname(). This application
will then work with either IPv4 or IPv6 peers. will then work with either IPv4 or IPv6 peers.
Note that gethostbyname() and gethostbyname2() are not thread-safe, Note that gethostbyname() and gethostbyname2() are not thread-safe,
since both return a pointer to a static hostent structure. But since both return a pointer to a static hostent structure. But
several vendors have defined a thread-safe gethostbyname_r() function several vendors have defined a thread-safe gethostbyname_r() function
that requires four additional arguments. We expect these vendors to that requires four additional arguments. We expect these vendors to
also define a gethostbyname2_r() function. also define a gethostbyname2_r() function.
6.2. Address To Hostname Translation 6.2. Address To Hostname Translation
The existing gethostbyaddr() function already requires an address The existing gethostbyaddr() function already requires an address
family argument and can therefore work with IPv6 addresses: family argument and can therefore work with IPv6 addresses:
#include <sys/socket.h>
#include <netdb.h>
struct hostent *gethostbyaddr(const char *src, int len, int af); struct hostent *gethostbyaddr(const char *src, int len, int af);
One possible source of confusion is the handling of IPv4-mapped IPv6 One possible source of confusion is the handling of IPv4-mapped IPv6
addresses and IPv4-compatible IPv6 addresses. Current thinking addresses and IPv4-compatible IPv6 addresses. This is addressed in
involves the following logic: [6] and involves the following logic:
- If af is AF_INET6, and if len equals 16, and if the IPv6 address 1. If af is AF_INET6, and if len equals 16, and if the IPv6 address
is an IPv4-mapped IPv6 address or an IPv4-compatible IPv6 is an IPv4-mapped IPv6 address or an IPv4-compatible IPv6
address, then skip over the first 12 bytes of the IPv6 address, address, then skip over the first 12 bytes of the IPv6 address,
set af to AF_INET, and set len to 4. set af to AF_INET, and set len to 4.
- If af is AF_INET, then query for a PTR record in the in-addr.arpa 2. If af is AF_INET, then query for a PTR record in the in-
domain. addr.arpa domain.
- If af is AF_INET6, then query for a PTR record in the ip6.int 3. If af is AF_INET6, then query for a PTR record in the ip6.int
domain. domain.
- If the function is returning success, and if af equals AF_INET, 4. If the function is returning success, and if af equals AF_INET,
and if the RES_USE_INET6 option was set, then the single address and if the RES_USE_INET6 option was set, then the single address
that is returned in the hostent structure (a copy of the first that is returned in the hostent structure (a copy of the first
argument to the function) is returned as an IPv4-mapped IPv6 argument to the function) is returned as an IPv4-mapped IPv6
address and the h_length member is set to 16. address and the h_length member is set to 16.
The same caveats regarding a thread-safe version of gethostbyname() All four steps listed are performed, in order. The same caveats
that were made at the end of the previous section apply here as well. regarding a thread-safe version of gethostbyname() that were made at
the end of the previous section apply here as well.
6.3. Protocol-Independent Hostname and Service Name Translation 6.3. Protocol-Independent Hostname and Service Name Translation
Hostname-to-address translation is done in a protocol-independent Hostname-to-address translation is done in a protocol-independent
fashion using the getaddrinfo() function that is taken from the fashion using the getaddrinfo() function that is taken from the
Institute of Electrical and Electronic Engineers (IEEE) POSIX 1003.1g Institute of Electrical and Electronic Engineers (IEEE) POSIX 1003.1g
(Protocol Independent Interfaces) draft specification [4]. (Protocol Independent Interfaces) work in progress specification [4].
The official specification for this function will be the final POSIX The official specification for this function will be the final POSIX
standard. We are providing this independent description of the standard. We are providing this independent description of the
function because POSIX standards are not freely available (as are function because POSIX standards are not freely available (as are
IETF documents). Should there be any discrepancies between this IETF documents). Should there be any discrepancies between this
description and the POSIX description, the POSIX description takes description and the POSIX description, the POSIX description takes
precedence. precedence.
#include <sys/socket.h> #include <sys/socket.h>
#include <netdb.h> #include <netdb.h>
int getaddrinfo(const char *hostname, const char *servname, int getaddrinfo(const char *hostname, const char *servname,
const struct addrinfo *hints, const struct addrinfo *hints,
struct addrinfo **res); struct addrinfo **res);
The addrinfo structure is defined as: The addrinfo structure is defined as:
#include <sys/socket.h>
#include <netdb.h>
struct addrinfo { struct addrinfo {
int ai_flags; /* AI_PASSIVE, AI_CANONNAME */ int ai_flags; /* AI_PASSIVE, AI_CANONNAME */
int ai_family; /* PF_xxx */ int ai_family; /* PF_xxx */
int ai_socktype; /* SOCK_xxx */ int ai_socktype; /* SOCK_xxx */
int ai_protocol; /* 0 or IPPROTO_xxx for IPv4 and IPv6 */ int ai_protocol; /* 0 or IPPROTO_xxx for IPv4 and IPv6 */
size_t ai_addrlen; /* length of ai_addr */ size_t ai_addrlen; /* length of ai_addr */
char *ai_canonname; /* canonical name for hostname */ char *ai_canonname; /* canonical name for hostname */
struct sockaddr *ai_addr; /* binary address */ struct sockaddr *ai_addr; /* binary address */
struct addrinfo *ai_next; /* next structure in linked list */ struct addrinfo *ai_next; /* next structure in linked list */
}; };
The return value from the function is 0 upon success or a nonzero The return value from the function is 0 upon success or a nonzero
error code. The following names are the nonzero error codes from error code. The following names are the nonzero error codes from
getaddrinfo(): getaddrinfo(), and are defined in <netdb.h>:
EAI_ADDRFAMILY address family for hostname not supported EAI_ADDRFAMILY address family for hostname not supported
EAI_AGAIN temporary failure in name resolution EAI_AGAIN temporary failure in name resolution
EAI_BADFLAGS invalid value for ai_flags EAI_BADFLAGS invalid value for ai_flags
EAI_FAIL non-recoverable failure in name resolution EAI_FAIL non-recoverable failure in name resolution
EAI_FAMILY ai_family not supported EAI_FAMILY ai_family not supported
EAI_MEMORY memory allocation failure EAI_MEMORY memory allocation failure
EAI_NODATA no address associated with hostname EAI_NODATA no address associated with hostname
EAI_NONAME hostname nor servname provided, or not known EAI_NONAME hostname nor servname provided, or not known
EAI_SERVICE servname not supported for ai_socktype EAI_SERVICE servname not supported for ai_socktype
skipping to change at page 25, line 25 skipping to change at page 24, line 37
and ai_protocol are the corresponding arguments for a call to the and ai_protocol are the corresponding arguments for a call to the
socket() function. In each addrinfo structure the ai_addr member socket() function. In each addrinfo structure the ai_addr member
points to a filled-in socket address structure whose length is points to a filled-in socket address structure whose length is
specified by the ai_addrlen member. specified by the ai_addrlen member.
If the AI_PASSIVE bit is set in the ai_flags member of the hints If the AI_PASSIVE bit is set in the ai_flags member of the hints
structure, then the caller plans to use the returned socket address structure, then the caller plans to use the returned socket address
structure in a call to bind(). In this case, if the hostname structure in a call to bind(). In this case, if the hostname
argument is a NULL pointer, then the IP address portion of the socket argument is a NULL pointer, then the IP address portion of the socket
address structure will be set to INADDR_ANY for an IPv4 address or address structure will be set to INADDR_ANY for an IPv4 address or
IN6ADDR_ANY_INIT for an IPv6 address. Notice that if the AI_PASSIVE IN6ADDR_ANY_INIT for an IPv6 address.
bit is set and the hostname argument is a NULL pointer then the
caller must also specify a nonzero ai_family, otherwise getaddrinfo()
is unable to allocate and initialize a socket address structure of
the correct type.
If the AI_PASSIVE bit is not set in the ai_flags member of the hints If the AI_PASSIVE bit is not set in the ai_flags member of the hints
structure, then the returned socket address structure will be ready structure, then the returned socket address structure will be ready
for a call to connect() (for a connection-oriented protocol) or for a call to connect() (for a connection-oriented protocol) or
either connect(), sendto(), or sendmsg() (for a connectionless either connect(), sendto(), or sendmsg() (for a connectionless
protocol). In this case, if the hostname argument is a NULL pointer, protocol). In this case, if the hostname argument is a NULL pointer,
then the IP address portion of the socket address structure will be then the IP address portion of the socket address structure will be
set to the loopback address. set to the loopback address.
If the AI_CANONNAME bit is set in the ai_flags member of the hints If the AI_CANONNAME bit is set in the ai_flags member of the hints
skipping to change at page 26, line 14 skipping to change at page 25, line 20
#include <sys/socket.h> #include <sys/socket.h>
#include <netdb.h> #include <netdb.h>
void freeaddrinfo(struct addrinfo *ai); void freeaddrinfo(struct addrinfo *ai);
The addrinfo structure pointed to by the ai argument is freed, along The addrinfo structure pointed to by the ai argument is freed, along
with any dynamic storage pointed to by the structure. This operation with any dynamic storage pointed to by the structure. This operation
is repeated until a NULL ai_next pointer is encountered. is repeated until a NULL ai_next pointer is encountered.
To aid applications in printing error messages based on the EAI_xxx
codes returned by getaddrinfo(), the following function is defined.
#include <sys/socket.h>
#include <netdb.h>
char *gai_strerror(int ecode);
The argument is one of the EAI_xxx values defined earlier and the
eturn value points to a string describing the error. If the argument
is not one of the EAI_xxx values, the function still returns a
pointer to a string whose contents indicate an unknown error.
6.4. Socket Address Structure to Hostname and Service Name 6.4. Socket Address Structure to Hostname and Service Name
The POSIX 1003.1g specification includes no function to perform the The POSIX 1003.1g specification includes no function to perform the
reverse conversion from getaddrinfo(): to look up a hostname and reverse conversion from getaddrinfo(): to look up a hostname and
service name, given the binary address and port. Therefore, we service name, given the binary address and port. Therefore, we
define the following function: define the following function:
#include <sys/socket.h> #include <sys/socket.h>
#include <netdb.h> #include <netdb.h>
int getnameinfo(const struct sockaddr *sa, size_t salen, int getnameinfo(const struct sockaddr *sa, size_t salen,
char *host, size_t hostlen, char *host, size_t hostlen,
char *serv, size_t servlen); char *serv, size_t servlen,
int flags);
This function looks up an IP address and port number provided by the This function looks up an IP address and port number provided by the
caller in the DNS and system-specific database, and returns text caller in the DNS and system-specific database, and returns text
strings for both in buffers provided by the caller. The first strings for both in buffers provided by the caller. The function
argument, sa, points to either a sockaddr_in structure (for IPv4) or
a sockaddr_in6 structure (for IPv6) that holds the IP address and
port number. The salen argument gives the length of the sockaddr_in
or sockaddr_in6 structure. The function returns the hostname
associated with the IP address in the buffer pointed to by the host
argument. The caller provides the size of this buffer via the
hostlen argument. The service name associated with the port number
is returned in the buffer pointed to by serv, and the servlen
argument gives the length of this buffer. The caller specifies not
to return either string by providing a zero value for the hostlen or
servlen arguments. Otherwise, the caller must provide buffers large
enough to hold the fully qualified domain hostname, and the full
service name, including the terminating null character. The function
indicates successful completion by a zero return value; a non-zero indicates successful completion by a zero return value; a non-zero
return value indicates failure. return value indicates failure.
Note that this function does not know the protocol of the socket The first argument, sa, points to either a sockaddr_in structure (for
address structure. Normally this is not a problem because the same IPv4) or a sockaddr_in6 structure (for IPv6) that holds the IP
port is assigned to a given service for both TCP and UDP. But there address and port number. The salen argument gives the length of the
exist historical artifacts that violate this rule (e.g., ports 512, sockaddr_in or sockaddr_in6 structure.
513, and 514).
The function returns the hostname associated with the IP address in
the buffer pointed to by the host argument. The caller provides the
size of this buffer via the hostlen argument. The service name
associated with the port number is returned in the buffer pointed to
by serv, and the servlen argument gives the length of this buffer.
The caller specifies not to return either string by providing a zero
value for the hostlen or servlen arguments. Otherwise, the caller
must provide buffers large enough to hold the hostname and the
service name, including the terminating null characters.
Unfortunately most systems do not provide constants that specify the
maximum size of either a fully-qualified domain name or a service
name. Therefore to aid the application in allocating buffers for
these two returned strings the following constants are defined in
<netdb.h>:
#define NI_MAXHOST 1025
#define NI_MAXSERV 32
The first value is actually defined as the constant MAXDNAME in
recent versions of BIND's <arpa/nameser.h> header (older versions of
BIND define this constant to be 256) and the second is a guess based
on the services listed in the current Assigned Numbers RFC.
The final argument is a flag that changes the default actions of this
function. By default the fully-qualified domain name (FQDN) for the
host is looked up in the DNS and returned. If the flag bit NI_NOFQDN
is set, only the hostname portion of the FQDN is returned for local
hosts.
If the flag bit NI_NUMERICHOST is set, or if the host's name cannot
be located in the DNS, the numeric form of the host's address is
returned instead of its name (e.g., by calling inet_ntop() instead of
gethostbyaddr()). If the flag bit NI_NAMEREQD is set, an error is
returned if the host's name cannot be located in the DNS.
If the flag bit NI_NUMERICSERV is set, the numeric form of the
service address is returned (e.g., its port number) instead of its
name. The two NI_NUMERICxxx flags are required to support the "-n"
flag that many commands provide.
A fifth flag bit, NI_DGRAM, specifies that the service is a datagram
service, and causes getservbyport() to be called with a second
argument of "udp" instead of its default of "tcp". This is required
for the few ports (512-514) that have different services for UDP and
TCP.
These NI_xxx flags are defined in <netdb.h> along with the AI_xxx
flags already defined for getaddrinfo().
6.5. Address Conversion Functions 6.5. Address Conversion Functions
The two functions inet_addr() and inet_ntoa() convert an IPv4 address The two functions inet_addr() and inet_ntoa() convert an IPv4 address
between binary and text form. IPv6 applications need similar 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:
int inet_pton(int af, const char *src, void *dst); #include <sys/socket.h>
#include <arpa/inet.h>
and 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, size_t size); char *dst, size_t size);
The inet_pton() function converts an address in its standard text The inet_pton() function converts an address in its standard text
presentation form into its numeric binary form. The af argument presentation form into its numeric binary form. The af argument
specifies the family of the address. Currently the AF_INET and specifies the family of the address. Currently the AF_INET and
AF_INET6 address families are supported. The src argument points to AF_INET6 address families are supported. The src argument points to
the string being passed in. The dst argument points to a buffer into the string being passed in. The dst argument points to a buffer into
which the function stores the numeric address. The address is which the function stores the numeric address. The address is
returned in network byte order. Inet_pton() returns 1 if the returned in network byte order. Inet_pton() returns 1 if the
conversion succeeds, 0 if the input is not a valid IPv4 dotted- conversion succeeds, 0 if the input is not a valid IPv4 dotted-
decimal string or a valid IPv6 address string, or -1 with errno set decimal string or a valid IPv6 address string, or -1 with errno set
to EAFNOSUPPORT if the af argument is unknown. The function does not to EAFNOSUPPORT if the af argument is unknown. The calling
modify the buffer pointed to by dst if the conversion fails. The application must ensure that the buffer referred to by dst is large
calling application must ensure that the buffer referred to by dst is enough to hold the numeric address (e.g., 4 bytes for AF_INET or 16
large enough to hold the numeric address (e.g., 4 bytes for AF_INET bytes for AF_INET6).
or 16 bytes for AF_INET6).
If the af argument is AF_INET, the function accepts a string in the If the af argument is AF_INET, the function accepts a string in the
standard IPv4 dotted-decimal form: 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.
Note that many implementations of the existing inet_addr() and
inet_aton() functions accept nonstandard input: octal numbers,
hexadecimal numbers, and fewer than four numbers. inet_pton() does
not accept these formats.
If the af argument is AF_INET6, then the function accepts a string in If the af argument is AF_INET6, then the function accepts a string in
one of the standard IPv6 text forms defined in Section 2.2 of the one of the standard IPv6 text forms defined in Section 2.2 of the
addressing architecture specification [2]. addressing architecture specification [2].
The inet_ntop() function converts a numeric address into a text The inet_ntop() function converts a numeric address into a text
string suitable for presentation. The af argument specifies the string suitable for presentation. The af argument specifies 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 points to a buffer holding an IPv4 address if the af
argument is AF_INET, or an IPv6 address if the af argument is argument is AF_INET, or an IPv6 address if the af argument is
AF_INET6. The dst argument points to a buffer where the function AF_INET6. The dst argument points to a buffer where the function
will store the resulting text string. The size argument specifies will store the resulting text string. The size argument specifies
the size of this buffer. The application must specify a non-NULL dst the size of this buffer. The application must specify a non-NULL dst
argument. For IPv6 addresses, the buffer must be at least 46-octets. argument. For IPv6 addresses, the buffer must be at least 46-octets.
For IPv4 addresses, the buffer must be at least 16-octets. In order For IPv4 addresses, the buffer must be at least 16-octets. In order
to allow applications to easily declare buffers of the proper size to to allow applications to easily declare buffers of the proper size to
store IPv4 and IPv6 addresses in string form, implementations should store IPv4 and IPv6 addresses in string form, the following two
provide the following constants, made available to applications that constants are defined in <netinet/in.h>:
include <netinet/in.h>:
#define INET_ADDRSTRLEN 16 #define INET_ADDRSTRLEN 16
#define INET6_ADDRSTRLEN 46 #define INET6_ADDRSTRLEN 46
The inet_ntop() function returns a pointer to the buffer containing The inet_ntop() function returns a pointer to the buffer containing
the text string if the conversion succeeds, and NULL otherwise. Upon the text string if the conversion succeeds, and NULL otherwise. Upon
failure, errno is set to EAFNOSUPPORT if the af argument is invalid failure, errno is set to EAFNOSUPPORT if the af argument is invalid
or ENOSPC if the size of the result buffer is inadequate. The or ENOSPC if the size of the result buffer is inadequate.
function does not modify the storage pointed to by dst if the
conversion fails.
Applications obtain the prototype declarations for inet_ntop() and
inet_pton() by including the header <arpa/inet.h>.
6.6. IPv4-Mapped Addresses
The IPv4-mapped IPv6 address format represents IPv4 addresses as IPv6
addresses. Most applications should be able to manipulate IPv6
addresses as opaque 16-octet quantities, without needing to know
whether they represent IPv4 addresses. However, a few applications
may need to determine whether an IPv6 address is an IPv4-mapped
address or not. The following function is provided for those
applications:
int inet6_isipv4mapped(const struct in6_addr *addr);
The "addr" argument to this function points to a buffer holding an
IPv6 address in network byte order. The function returns non-zero if
that address is an IPv4-mapped address, and returns 0 otherwise.
This function could be used by server applications to determine
whether the peer is an IPv4 node or an IPv6 node. After accepting a
TCP connection via accept(), or receiving a UDP packet via
recvfrom(), the application can apply the inet6_isipv4mapped()
function to the returned address.
Applications obtain the prototype for this function by including the
header <arpa/inet.h>.
7. Security Considerations
IPv6 provides a number of new security mechanisms, many of which need
to be accessible to applications. A companion memo detailing the
extensions to the socket interfaces to support IPv6 security is being
written [3].
8. Change History
Changes from the April 1996 Edition (-05 draft)
- Rewrote Abstract.
- Added Table of Contents.
- New Section 2.2 (Data Types).
- Removed the example from Section 3.4 (Socket Address Structure
for 4.4BSD-Based Systems) implying that the process must set the
sin6_len field. This field need not be set by the process before
passing a socket address structure to the kernel: bind(),
connect(), sendto(), and sendmsg().
- The examples in Section 3.8 (Flow Information) on setting and
fetching the flow label and priority have been expanded, since
the byte ordering and shifting required to set and fetch these
fields can be confusing. It is also explicitly stated that the
two IPV6_FLOWLABEL_xxx constants and the 16 IPV6_PRIORITY_xxx
constants are all network byte ordered.
- Warning placed at the end of Section 3.9 concerning the byte
ordering of the IPv4 INADDR_xxx constants versus the IPv6
IN6ADDR_xxx constants and in6addr_xxx externals.
- Added a new Section 4 (Interface Identification). This provides
functions to map between an interface name and an interface
index.
- In Section 5.1 (Changing Socket Type) the qualifier was added
that you cannot downgrade an IPv6 socket to an IPv4 socket unless
all nonwildcard addresses already associated with the IPv6 socket
are IPv4-mapped IPv6 addresses.
- In Section 5.3 (Sending and Receiving Multicast Packets) the
method of specifying the local interface was changed from using a
local IPv6 address to using the interface index. This changes
the argument type for IPV6_MULTICAST_IF and the second member of
the ipv6_mreq structure.
- In Section 5.3 (Sending and Receiving Multicast Packets) the
IPV6_ADD_MEMBERSHIP socket option description was corrected. A
note was also added at the end of this section concerning joining
the group versus binding the group address to the socket.
- The old Sections 5.1, 5.2, and 5.3 are gone, and new Sections
6.1, 6.2, 6.3, 6.4, and 6.5 are provided. The new sections
describe the BIND 4.9.4 implementation of the name-to-address
functions (which support IPv6), a POSIX-free description of the
getaddrinfo() function, a description of the new getnameinfo()
function, and the inet_ntop() and inet_pton() functions. The old
Section 5.4 (Embedded IPv4 addresses) is now Section 6.6 (IPv4-
Mapped Addresses).
- Renamed inet6_isipv4addr() to inet6_isipv4mapped() so the name
better describes the function.
- Section 8 (Open Issues) was removed.
Changes from the January 1996 Edition (-04 draft)
- Re-arranged the ipv6_hostent_addr structure, placing the IPv6
address element first.
Changes from the November 1995 Edition (-03 draft)
- Added the symbolic constants IN6ADDR_ANY_INIT and
IN6ADDR_LOOPBACK_INIT for applications to use for
initializations.
- Eliminated restrictions on the value of ipv6addr_any. Systems
may now choose any value, including all-zeros.
- Added a mechanism for returning time to live with the address in
the name-to-address translation functions.
- Added a mechanism for applications to specify the interface in
the setsockopt() options to join and leave a multicast group.
Changes from the July 1995 Edition
- Changed u_long and u_short types in structures to u_int32_t and
u_int16_t for consistency and clarity.
- Added implementation-provided constants for IPv4 and IPv6 text
address buffer length.
- Defined a set of constants for subfields of sin6_flowid and for
priority values.
- Defined constants for getting and setting the source route flag.
- Define where ansi prototypes for hostname2addr(),
addr2hostname(), addr2ascii(), ascii2addr(), and
ipv6_isipv4addr() reside.
- Clarified the include file requirements. Say that the structure
definitions are defined as a result of including the header
<netinet/in.h>, not that the structures are necessarily defined
there.
- Removed underscore chars from is_ipv4_addr() function name for
BSD compatibility.
- Added inet6_ prefix to is_ipv4_addr() function name to avoid name
space conflicts.
- Changes setsockopt option naming convention to use IPV6_ prefix
instead of IP_ so that there is clearly no ambiguity with IPv4
options. Also, use level IPPROTO_IPV6 for these options.
- Made hostname2addr() and addr2hostname() functions thread-safe.
- Added support for sendmsg() and recvmsg() in source routing
section.
- Changed in_addr6 to in6_addr for consistency.
- Re-structured document into sub-sections.
- Deleted the implementation experience section. It was too wordy.
- Added argument types to multicast socket options.
- Added constant for largest source route array buffer.
- Added the freehostent() function.
- Added receiving interface determination and sending interface 6.6. Address Testing Macros
selection options.
- Added definitions of ipv6addr_any and ipv6addr_loopback. The following macros can be used to test for special IPv6 addresses.
- Added text making the lookup of IPv4 addresses by hostname2addr() #include <netinet/in.h>
optional.
Changes from the June 1995 Edition int IN6_IS_ADDR_UNSPECIFIED (const struct in6_addr *);
int IN6_IS_ADDR_LOOPBACK (const struct in6_addr *);
int IN6_IS_ADDR_MULTICAST (const struct in6_addr *);
int IN6_IS_ADDR_LINKLOCAL (const struct in6_addr *);
int IN6_IS_ADDR_SITELOCAL (const struct in6_addr *);
int IN6_IS_ADDR_V4MAPPED (const struct in6_addr *);
int IN6_IS_ADDR_V4COMPAT (const struct in6_addr *);
- Added capability for application to select loose or strict source int IN6_IS_ADDR_MC_NODELOCAL(const struct in6_addr *);
routing. int IN6_IS_ADDR_MC_LINKLOCAL(const struct in6_addr *);
int IN6_IS_ADDR_MC_SITELOCAL(const struct in6_addr *);
int IN6_IS_ADDR_MC_ORGLOCAL (const struct in6_addr *);
int IN6_IS_ADDR_MC_GLOBAL (const struct in6_addr *);
Changes from the March 1995 Edition The first seven macros return true if the address is of the specified
type, or false otherwise. The last five test the scope of a
multicast address and return true if the address is a multicast
address of the specified scope or false if the address is either not
a multicast address or not of the specified scope.
- Changed the definition of the ipv6_addr structure to be an array 7. Summary of New Definitions
of sixteen chars instead of four longs. This change is necessary
to support machines that implement the socket interface, but do
not have a 32-bit addressable word. Virtually all machines that
provide the socket interface do support an 8-bit addressable data
type.
- Added a more detailed explanation that the data types defined in The following list summarizes the constants, structure, and extern
this documented are not intended to be hard and fast definitions discussed in this memo, sorted by header.
requirements. Systems may use other data types if they wish.
- Added a note flagging the fact that the sockaddr_in6 structure is <net/if.h> IFNAMSIZ
not the same size as the sockaddr structure. <net/if.h> struct if_nameindex{};
- Changed the sin6_flowlabel field to sin6_flowinfo to accommodate <netdb.h> AI_CANONNAME
the addition of the priority field to the IPv6 header. <netdb.h> AI_PASSIVE
<netdb.h> EAI_ADDRFAMILY
<netdb.h> EAI_AGAIN
<netdb.h> EAI_BADFLAGS
<netdb.h> EAI_FAIL
<netdb.h> EAI_FAMILY
<netdb.h> EAI_MEMORY
<netdb.h> EAI_NODATA
<netdb.h> EAI_NONAME
<netdb.h> EAI_SERVICE
<netdb.h> EAI_SOCKTYPE
<netdb.h> EAI_SYSTEM
<netdb.h> NI_DGRAM
<netdb.h> NI_MAXHOST
<netdb.h> NI_MAXSERV
<netdb.h> NI_NAMEREQD
<netdb.h> NI_NOFQDN
<netdb.h> NI_NUMERICHOST
<netdb.h> NI_NUMERICSERV
<netdb.h> struct addrinfo{};
Changes from the October 1994 Edition <netinet/in.h> IN6ADDR_ANY_INIT
<netinet/in.h> IN6ADDR_LOOPBACK_INIT
<netinet/in.h> INET6_ADDRSTRLEN
<netinet/in.h> INET_ADDRSTRLEN
<netinet/in.h> IPPROTO_IPV6
<netinet/in.h> IPV6_ADDRFORM
<netinet/in.h> IPV6_ADD_MEMBERSHIP
<netinet/in.h> IPV6_DROP_MEMBERSHIP
<netinet/in.h> IPV6_MULTICAST_HOPS
<netinet/in.h> IPV6_MULTICAST_IF
<netinet/in.h> IPV6_MULTICAST_LOOP
<netinet/in.h> IPV6_UNICAST_HOPS
<netinet/in.h> SIN6_LEN
<netinet/in.h> extern const struct in6_addr in6addr_any;
<netinet/in.h> extern const struct in6_addr in6addr_loopback;
<netinet/in.h> struct in6_addr{};
<netinet/in.h> struct ipv6_mreq{};
<netinet/in.h> struct sockaddr_in6{};
- Added variant of sockaddr_in6 for 4.4BSD-based systems (sa_len <resolv.h> RES_USE_INET6
compatibility).
- Removed references to SIT transition specification, and added <sys/socket.h> AF_INET6
reference to addressing architecture document, for definition of <sys/socket.h> PF_INET6
IPv4-mapped addresses.
- Added a solution to the problem of the application not providing The following list summarizes the function and macro prototypes
enough buffer space to hold a received source route. discussed in this memo, sorted by header.
- Moved discussion of IPv4 applications interoperating with IPv6 <arpa/inet.h> int inet_pton(int, const char *, void *);
nodes to open issues section. <arpa/inet.h> const char *inet_ntop(int, const void *,
char *, size_t);
- Added length parameter to addr2ascii() function to be consistent <net/if.h> char *if_indextoname(unsigned int, char *);
with addr2hostname(). <net/if.h> unsigned int if_nametoindex(const char *);
<net/if.h> void if_freenameindex(struct if_nameindex *);
<net/if.h> struct if_nameindex *if_nameindex(void);
- Changed IP_MULTICAST_TTL to IP_MULTICAST_HOPS to match IPv6 <netdb.h> int getaddrinfo(const char *, const char *,
terminology, and added IP_UNICAST_HOPS option to match const struct addrinfo *,
IP_MULTICAST_HOPS. struct addrinfo **);
<netdb.h> int getnameinfo(const struct sockaddr *, size_t,
char *, size_t, char *, size_t, int);
<netdb.h> void freeaddrinfo(struct addrinfo *);
<netdb.h> char *gai_strerror(int);
<netdb.h> struct hostent *gethostbyname(const char *);
<netdb.h> struct hostent *gethostbyaddr(const char *, int, int);
<netdb.h> struct hostent *gethostbyname2(const char *, int);
- Removed specification of numeric values for AF_INET6, <netinet/in.h> int IN6_IS_ADDR_LINKLOCAL(const struct in6_addr *);
IP_ADDRFORM, and IP_RCVSRCRT, since they need not be the same on <netinet/in.h> int IN6_IS_ADDR_LOOPBACK(const struct in6_addr *);
different implementations. <netinet/in.h> int IN6_IS_ADDR_MC_GLOBAL(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_MC_LINKLOCAL(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_MC_NODELOCAL(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_MC_ORGLOCAL(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_MC_SITELOCAL(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_MULTICAST(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_SITELOCAL(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_UNSPECIFIED(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_V4COMPAT(const struct in6_addr *);
<netinet/in.h> int IN6_IS_ADDR_V4MAPPED(const struct in6_addr *);
8. Security Considerations
- Added a definition for the in_addr6 IPv6 address data structure. IPv6 provides a number of new security mechanisms, many of which need
Added this so that applications could use sizeof(struct in_addr6) to be accessible to applications. A companion memo detailing the
to get the size of an IPv6 address, and so that a structured type extensions to the socket interfaces to support IPv6 security is being
could be used in the is_ipv4_addr(). written [3].
9. Acknowledgments 9. Acknowledgments
Thanks to the many people who made suggestions and provided feedback Thanks to the many people who made suggestions and provided feedback
to to the numerous revisions of this document, including: Werner to to the numerous revisions of this document, including: Werner
Almesberger, Ran Atkinson, Fred Baker, Dave Borman, Andrew Cherenson, Almesberger, Ran Atkinson, Fred Baker, Dave Borman, Andrew Cherenson,
Alex Conta, Alan Cox, Steve Deering, Francis Dupont, Robert Elz, Marc Alex Conta, Alan Cox, Steve Deering, Richard Draves, Francis Dupont,
Hasson, Tom Herbert, Christian Huitema, Wan-Yen Hsu, Alan Lloyd, Robert Elz, Marc Hasson, Tim Hartrick, Tom Herbert, Bob Hinden, Wan-
Charles Lynn, Dan McDonald, Craig Metz, Erik Nordmark, Josh Osborne, Yen Hsu, Christian Huitema, Koji Imada, Markus Jork, Ron Lee, Alan
Craig Partridge, Matt Thomas, Dean D. Throop, Glenn Trewitt, Paul Lloyd, Charles Lynn, Jack McCann, Dan McDonald, Dave Mitton, Thomas
Vixie, David Waitzman, and Carl Williams. Narten, Erik Nordmark, Josh Osborne, Craig Partridge, Jean-Luc
Richier, Erik Scoredos, Keith Sklower, Matt Thomas, Harvey Thompson,
Dean D. Throop, Karen Tracey, Glenn Trewitt, Paul Vixie, David
Waitzman, Carl Williams, and Kazuhiko Yamamoto,
The getaddrinfo() and getnameinfo() functions are taken from an The getaddrinfo() and getnameinfo() functions are taken from an
earlier Internet Draft by Keith Sklower. As noted in that draft, earlier Work in Progress by Keith Sklower. As noted in that
William Durst, Steven Wise, Michael Karels, and Eric Allman provided document, William Durst, Steven Wise, Michael Karels, and Eric Allman
many useful discussions on the subject of protocol-independent name- provided many useful discussions on the subject of protocol-
to-address translation, and reviewed early versions of Keith independent name-to-address translation, and reviewed early versions
Sklower's original proposal. Eric Allman implemented the first of Keith Sklower's original proposal. Eric Allman implemented the
prototype of getaddrinfo(). The observation that specifying the pair first prototype of getaddrinfo(). The observation that specifying
of name and service would suffice for connecting to a service the pair of name and service would suffice for connecting to a
independent of protocol details was made by Marshall Rose in a service independent of protocol details was made by Marshall Rose in
proposal to X/Open for a "Uniform Network Interface". a proposal to X/Open for a "Uniform Network Interface".
Ramesh Govindan made a number of contributions and co-authored an Craig Metz made many contributions to this document. Ramesh Govindan
earlier version of this memo. made a number of contributions and co-authored an earlier version of
this memo.
10. References 10. References
[1] S. Deering, R. Hinden, "Internet Protocol, Version 6 (IPv6) [1] Deering, S., and R. Hinden, "Internet Protocol, Version 6 (IPv6)
Specification", RFC 1883, December 1995. Specification", RFC 1883, December 1995.
[2] R. Hinden, S. Deering, "IP Version 6 Addressing Architecture", [2] Hinden, R., and S. Deering, "IP Version 6 Addressing Architecture",
RFC 1884, December 1995. RFC 1884, December 1995.
[3] D. McDonald, "A Simple IP Security API Extension to BSD Sockets", [3] McDonald, D., "A Simple IP Security API Extension to BSD Sockets",
Internet-Draft, <draft-mcdonald-simple-ipsec-api-00.txt>, Work in Progress.
November 1996.
[4] IEEE, "Protocol Independent Interfaces", IEEE Std 1003.1g, DRAFT [4] IEEE, "Protocol Independent Interfaces", IEEE Std 1003.1g, DRAFT
6.3, November 1995. 6.3, November 1995.
[5] W. R. Stevens, M. Thomas, "Advanced Sockets API for IPv6", [5] Stevens, W., and M. Thomas, "Advanced Sockets API for IPv6",
Internet-Draft, <draft-stevens-advanced-api-00.txt>, October Work in Progress.
1996.
[6] Vixie, P., "Reverse Name Lookups of Encapsulated IPv4 Addresses in
IPv6", Work in Progress.
11. Authors' Addresses 11. Authors' Addresses
Robert E. Gilligan Robert E. Gilligan
Freegate Corporation Freegate Corporation
710 Lakeway Dr. STE 230 710 Lakeway Dr. STE 230
Sunnyvale, CA 94086 Sunnyvale, CA 94086
Phone: +1 408 524 4804 Phone: +1 408 524 4804
Email: gilligan@freegate.net EMail: gilligan@freegate.net
Susan Thomson Susan Thomson
Bell Communications Research Bell Communications Research
MRE 2P-343, 445 South Street MRE 2P-343, 445 South Street
Morristown, NJ 07960 Morristown, NJ 07960
Telephone: +1 201 829 4514
Email: set@thumper.bellcore.com Phone: +1 201 829 4514
EMail: set@thumper.bellcore.com
Jim Bound Jim Bound
Digital Equipment Corporation Digital Equipment Corporation
110 Spitbrook Road ZK3-3/U14 110 Spitbrook Road ZK3-3/U14
Nashua, NH 03062-2698 Nashua, NH 03062-2698
Phone: +1 603 881 0400 Phone: +1 603 881 0400
Email: bound@zk3.dec.com Email: bound@zk3.dec.com
W. Richard Stevens W. Richard Stevens
1202 E. Paseo del Zorro 1202 E. Paseo del Zorro
Tucson, AZ 85718-2826 Tucson, AZ 85718-2826
Phone: +1 520 297 9416 Phone: +1 520 297 9416
Email: rstevens@kohala.com EMail: rstevens@kohala.com
 End of changes. 114 change blocks. 
621 lines changed or deleted 506 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/