draft-ietf-ipngwg-bsd-api-02.txt   draft-ietf-ipngwg-bsd-api-03.txt 
Internet Engineering Task Force R. E. Gilligan (Sun) Internet Engineering Task Force R. E. Gilligan (Sun)
INTERNET-DRAFT S. Thomson (Bellcore) INTERNET-DRAFT S. Thomson (Bellcore)
J. Bound (Digital) J. Bound (Digital)
July 7, 1995 November 21, 1995
IPv6 Program Interfaces for BSD Systems IPv6 Program Interfaces for BSD Systems
<draft-ietf-ipngwg-bsd-api-02.txt> <draft-ietf-ipngwg-bsd-api-03.txt>
Abstract Abstract
In order to implement the version 6 Internet Protocol (IPv6) [1] in an In order to implement the version 6 Internet Protocol (IPv6) [1] in an
operating system based on Berkeley Unix (4.x BSD), changes must be made operating system based on Berkeley Unix (4.x BSD), changes must be made
to the application program interface (API). TCP/IP applications written to the application program interface (API). TCP/IP applications written
for BSD-based operating systems have in the past enjoyed a high degree for BSD-based operating systems have in the past enjoyed a high degree
of portability because most of the systems derived from BSD provide the of portability because most of the systems derived from BSD provide the
same API, known informally as "the socket interface". We would like the same API, known informally as "the socket interface". We would like the
same portability with IPv6. This memo presents a set of extensions to same portability with IPv6. This memo presents a set of extensions to
the BSD socket API to support IPv6. The changes include a new data the BSD socket API to support IPv6. The changes include a new data
structure to carry IPv6 addresses, new name to address translation structure to carry IPv6 addresses, new name to address translation
library functions, new address conversion functions, and some new library functions, new address conversion functions, and some new
setsockopt() options. The extensions are designed to provide access to setsockopt() options. The extensions are designed to provide access to
IPv6 features, while introducing a minimum of change into the system and IPv6 features, while introducing a minimum of change into the system and
providing complete compatibility for existing IPv4 applications. providing complete compatibility for existing IPv4 applications.
Status of this Memo Status of this Memo
This document is an Internet Draft. Internet Drafts are working This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas, and documents of the Internet Engineering Task Force (IETF), its Areas,
its Working Groups. Note that other groups may also distribute working and its Working Groups. Note that other groups may also distribute
documents as Internet Drafts. working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts are draft documents valid for a maximum of six months.
This Internet Draft expires on January 6, 1996. Internet Drafts may This Internet Draft expires on May 21, 1996. Internet Drafts may be
be updated, replaced, or obsoleted by other documents at any time. It updated, replaced, or obsoleted by other documents at any time. It is
is not appropriate to use Internet Drafts as reference material or to not appropriate to use Internet Drafts as reference material or to cite
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To learn the current status of any Internet-Draft, please check the To learn the current status of any Internet-Draft, please check the
1id-abstracts.txt listing contained in the Internet-Drafts Shadow 1id-abstracts.txt listing contained in the Internet-Drafts Shadow
Directories on ds.internic.net, nic.nordu.net, ftp.isi.edu, or Directories on ds.internic.net, nic.nordu.net, ftp.isi.edu, or
munnari.oz.au. munnari.oz.au.
Distribution of this memo is unlimited. Distribution of this memo is unlimited.
1. Introduction. 1. Introduction.
While IPv4 addresses are 32-bits long, IPv6 nodes are identified by While IPv4 addresses are 32-bits long, IPv6 nodes are identified by
128-bit addresses. The socket interface API make the size of an IP 128-bit addresses. The socket interface make the size of an IP address
address quite visible to an application; virtually all TCP/IP quite visible to an application; virtually all TCP/IP applications for
applications for BSD-based systems have knowledge of the size of an IP BSD-based systems have knowledge of the size of an IP address. Those
address. Those parts of the API that expose the addresses need to be parts of the API that expose the addresses need to be extended to
extended to accommodate the larger IPv6 address size. This paper accommodate the larger IPv6 address size. IPv6 also introduces new
defines a set of extensions to the socket interface API to support IPv6. features, some of which must be made visible to applications via the
This specification is preliminary. The API extensions are expected to API. This paper defines a set of extensions to the socket interface to
support the larger address size and new features of IPv6.
This specification is preliminary. These API extensions are expected to
evolve as we gain more implementation experience. evolve as we gain more implementation experience.
2. Design Considerations 2. Design Considerations
There are a number of important considerations in designing changes to There are a number of important considerations in designing changes to
this well-worn API: this well-worn API:
- The extended API should provide both source and binary - The extended API should provide both source and binary
compatibility for programs written to the original API. That compatibility for programs written to the original API. That
is, existing program binaries should continue to operate when is, existing program binaries should continue to operate when
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- Where possible, applications should be able to use the extended - Where possible, applications should be able to use the extended
API to interoperate with both IPv6 and IPv4 hosts. Applications API to interoperate with both IPv6 and IPv4 hosts. Applications
should not need to know which type of host they are should not need to know which type of host they are
communicating with. communicating with.
- IPv6 addresses carried in data structures should be 64-bit - IPv6 addresses carried in data structures should be 64-bit
aligned. This is necessary in order to obtain optimum aligned. This is necessary in order to obtain optimum
performance 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,
our extensions are explicitly designed to operate on machines that these extensions are explicitly designed to operate on machines that
provide complete support for both IPv4 and IPv6. A subset of this API provide complete support for both IPv4 and IPv6. A subset of this API
could probably be designed for operation on systems that support only could probably be designed for operation on systems that support only
IPv6. However, this is not addressed in this document. IPv6. However, this is not addressed in this document.
2.1. Overview of Changes 2.1. What Needs to be Changed
The socket interface API consists of a few distinct components: The socket interface API consists of a few distinct components:
- Core socket functions. - Core socket functions.
- Address data structures. - Address data structures.
- Name-to-address translation functions. - Name-to-address translation functions.
- Address conversion functions. - Address conversion functions.
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family argument and can be extended to support both address families family argument and can be extended to support both address families
without introducing compatibility problems. However, we have chosen to without introducing compatibility problems. However, we have chosen to
introduce a new function to maintain symmetry with the replacement to introduce a new function to maintain symmetry with the replacement to
gethostbyname(). The new functions both carry an address family gethostbyname(). The new functions both carry an address family
parameter, so they can be extended to operate with other protocol parameter, so they can be extended to operate with other protocol
families in addition to IPv4 and IPv6. families in addition to IPv4 and 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 designed functions are quite specific to 32-bit IPv4 addresses. We have designed
two analogous functions which convert both IPv4 and IPv6 addresses, and two analogous functions which convert both IPv4 and IPv6 addresses, and
carry an address type parameter so that they can be extended to other carry an address type parameter so that they can be extended to other
protocol families as well. protocol families as well.
Finally, a few miscellaneous features are needed to support IPv6. A new Finally, a few miscellaneous features are needed to support IPv6. A new
interface is needed in order to support the IPv6 flow label and priority interface is needed in order to support the IPv6 flow label and priority
header fields. New interfaces are needed in order to receive IPv6 header fields. New interfaces are needed in order to receive IPv6
multicast packets and control the sending of multicast packets. And an multicast packets and control the sending of multicast packets. And an
interface is necessary in order to pass IPv6 source route information interface is necessary in order to pass IPv6 source route information
between the application and the system. between the application and the system.
3. Implementation Experience 3. Socket Interface
A few issues exposed in experimenting with prototype implementations of
IPv6 helped to guide the design of this API:
First, we discovered that, by providing a way to represent the addresses
of IPv4 nodes as IPv6 addresses, we could greatly simplify the
applications' task of providing IPv4 compatibility. New applications
could interoperate with IPv4 nodes by using the new API and expressing
the addresses of IPv4 nodes they interoperate with as IPv6 addresses.
For example, a client application could open a TCP connection to an IPv4
server by giving the IPv6 representation of the server's IPv4 address in
the connect() call. Most applications do not even need to know whether
the peer is an IPv4 or IPv6 node. Such applications can simply treat
IPv6 addresses as opaque values; They need not understand the
"structure" by which IPv4 addresses are encoded within IPv6 addresses.
Yet the structure can be decoded by those applications that do need to
know whether the peer is IPv6 or IPv4. This should prove to be a
significant simplification since most applications will need to
interoperate with both IPv4 and IPv6 nodes for some time to come.
Second, we learned that existing applications written to the IPv4 API
could be made to interoperate with IPv6 nodes to a limited degree. This
technique does not work for all applications, but does for certain
applications, such as those that do not "look at" the peer address that
is provided by the API. (e.g. the source address provided by the
recvfrom() function when a UDP packet is received, or the client address
returned by the accept() function.)
Third, we learned that the common application practice of passing open
socket descriptors between processes across an exec() call can cause
problems. It is possible, for example, for an application using the
extended API to pass an open socket to an older application using the
original API. The old application could be confused if the socket
functions return IPv6 address structures to it. The solution designed
was to provide a mechanism by which applications could have explicit
control over what form of addresses are returned.
4. Interface Specification
This section specifies the interface changes for IPv6. This section specifies the socket interface changes for IPv6.
The data types of the structure elements given in the following section The data types of the structure elements given in the following section
are intended to be examples, not absolute requirements. System are intended to be examples, not absolute requirements. System
implementations may use other types if they are appropriate. In some implementations may use other types if they are appropriate. In some
cases, such as when a field of a data structure holds a protocol value, cases, such as when a field of a data structure holds a protocol value,
the structure field must be of some minimum size. These size the structure field must be of some minimum size. These size
requirements are noted in the text. For example, since the UDP and TCP requirements are noted in the text. For example, since the UDP and TCP
port values are 16-bit quantities, the sin6_port field must be at least port values are 16-bit quantities, the sin6_port field must be at least
a 16-bit data types. We specify the sin6_port field as a u_short type, a 16-bit data types. The sin6_port field is specified as a u_int16_t
but an implementation may use any data type that is at least 16-bits type, but an implementation may use any data type that is at least
long. 16-bits long.
4.1. New Address Family 3.1. New Address Family
A new address family macro, named AF_INET6, is defined in A new address family macro, named AF_INET6, is defined in
<sys/socket.h>. The AF_INET6 definition is used to distinguish between <sys/socket.h>. The AF_INET6 definition is used to distinguish between
the original sockaddr_in address data structure, and the new the original sockaddr_in address data structure, and the new
sockaddr_in6 data structure. sockaddr_in6 data structure.
A new protocol family macro, named PF_INET6, is defined in A new protocol family macro, named PF_INET6, is defined in
<sys/socket.h>. Like most of the other protocol family macros, this <sys/socket.h>. Like most of the other protocol family macros, this
will usually be defined to have the same value as the corresponding will usually be defined to have the same value as the corresponding
address family macro: address family macro:
#define PF_INET6 AF_INET6 #define PF_INET6 AF_INET6
The PF_INET6 is used in the first argument to the socket() function to The PF_INET6 is used in the first argument to the socket() function to
indicate that an IPv6 socket is being created. indicate that an IPv6 socket is being created.
4.2. IPv6 Address Data Structure 3.2. IPv6 Address Data Structure
A new data structure to hold a single IPv6 address is defined in A new data structure to hold a single IPv6 address is defined as
<netinet/in.h>: follows:
struct in_addr6 { struct in6_addr {
u_char s6_addr[16]; /* IPv6 address */ u_char s6_addr[16]; /* IPv6 address */
} }
This data structure contains an array of sixteen 8-bit elements, which This data structure contains an array of sixteen 8-bit elements, which
make up one 128-bit IPv6 address. make up one 128-bit IPv6 address. The IPv6 address is stored in network
byte order.
The IPv6 address is stored in network byte order. Applications obtain the declaration for this structure by including
the system header file <netinet/in.h>.
4.3. Socket Address Structure for 4.3 BSD-Based Systems 3.3. Socket Address Structure for 4.3 BSD-Based Systems
In the socket interface, a different protocol-specific data structure In the socket interface, a different protocol-specific data structure is
is defined to carry the addresses for each of the protocol suite. defined to carry the addresses for each of the protocol suite. Each
Each protocol-specific data structure is designed so it can be cast protocol-specific data structure is designed so it can be cast into a
into a protocol-independent data structure -- the "sockaddr" protocol-independent data structure -- the "sockaddr" structure. Each
structure. Each has a "family" field which overlays the "sa_family" has a "family" field which overlays the "sa_family" of the sockaddr data
of the sockaddr data structure. This field can be used to identify structure. This field can be used to identify the type of the data
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 applications structure for IPv4. It is used to pass addresses between applications
and the system in the socket functions. We have defined the following and the system in the socket functions. The following structure is
structure in <netinet/in.h> to carry IPv6 addresses: defined to carry IPv6 addresses:
struct sockaddr_in6 { struct sockaddr_in6 {
u_short sin6_family; /* AF_INET6 */ u_int16_t sin6_family; /* AF_INET6 */
u_short sin6_port; /* Transport layer port # */ u_int16_t sin6_port; /* Transport layer port # */
u_long sin6_flowinfo; /* IPv6 flow information */ u_int32_t sin6_flowinfo; /* IPv6 flow information */
struct in_addr6 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 4.3 BSD release. structure used in the 4.3 BSD release.
The sin6_family field is used to identify this as a sockaddr_in6 The sin6_family field is used to identify this as a sockaddr_in6
structure. This field is designed to overlay the sa_family field when structure. This field is designed to overlay the sa_family field when
the buffer is cast to a sockaddr data structure. The value of this the buffer is cast to a sockaddr data structure. The value of this
field must be AF_INET6. field must be AF_INET6.
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the buffer is cast to a sockaddr data structure. The value of this the buffer is cast to a sockaddr data structure. The value of this
field must be AF_INET6. field must be AF_INET6.
The sin6_port field is used to store the 16-bit UDP or TCP port The sin6_port field is used to store the 16-bit UDP or TCP port
number. This field is used in the same way as the sin_port field of number. This field is used in the same way as the sin_port field of
the sockaddr_in structure. The port number is stored in network byte the sockaddr_in structure. The port number is stored in network byte
order. order.
The sin6_flowinfo field is a 32-bit field that is used to store three The sin6_flowinfo field is a 32-bit field that is used to store three
pieces of information: the 24-bit IPv6 flow label, the 4-bit priority pieces of information: the 24-bit IPv6 flow label, the 4-bit priority
field, and a 1-bit loose/strict source routing flag. The IPv6 flow field, and a 1-bit loose/strict source routing flag. The IPv6 flow
label is represented as the low-order 24-bits of the 32-bit field. The label is represented as the low-order 24-bits of the 32-bit field. The
priority is represented in the next 4-bits above this, and the priority is represented in the next 4-bits above this, and the
loose/strict flag is the 1 bit above this. The high-order 3 bits of loose/strict flag is the 1 bit above this. The high-order 3 bits of
this field are reserved. The sin6_flowinfo field is stored in network 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 byte order. The use of the flow label and priority fields are explained
in sec 4.9. The use of the loose/strict flag is discussed in section in sec 4.9. The use of the loose/strict flag is discussed in section
4.10. 4.10.
The sin6_addr field is a single in_addr6 structure (defined in the The sin6_addr field is a single in6_addr structure (defined in the
previous section). This field holds one 128-bit IPv6 address. The previous section). This field holds one 128-bit IPv6 address. The
address is stored in network byte order. address is stored in network byte order.
The ordering of elements in this structure is specifically designed so The ordering of elements in this structure is specifically designed so
that the sin6_addr field will be aligned on a 64-bit boundary. This is that the sin6_addr field will be aligned on a 64-bit boundary. This is
done for optimum performance on 64-bit architectures. done for optimum performance on 64-bit architectures.
4.4. Socket Address Structure for 4.4 BSD-Based Systems Applications obtain the declaration of the sockaddr_in6 structure by
including the system header file <netinet/in.h>.
3.4. Socket Address Structure for 4.4 BSD-Based Systems
The 4.4 BSD release includes a small, but incompatible change to the The 4.4 BSD release includes a small, but incompatible change to the
socket interface. The "sa_family" field of the sockaddr data structure socket interface. The "sa_family" field of the sockaddr data structure
was changed from a 16-bit value to an 8-bit value, and the space saved was changed from a 16-bit value to an 8-bit value, and the space saved
used to hold a length field, named "sa_len". The sockaddr_in6 data used to hold a length field, named "sa_len". The sockaddr_in6 data
structure given in the previous section can not be correctly cast into structure given in the previous section can not be correctly cast into
the newer sockaddr data structure. For this reason, we have defined the the newer sockaddr data structure. For this reason, following
following alternative IPv6 address data structure to be used on systems alternative IPv6 address data structure is provided to be used on
based on 4.4 BSD: systems based on 4.4 BSD:
#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_short sin6_port; /* Transport layer port # */ u_int16_t sin6_port; /* Transport layer port # */
u_long sin6_flowinfo; /* IPv6 flow information */ u_int32_t sin6_flowinfo; /* IPv6 flow information */
struct in_addr6 sin6_addr; /* IPv6 address */ struct in6_addr sin6_addr; /* IPv6 address */
}; };
This structure is defined in the <netinet/in.h> header file. The only The only differences between this data structure and the 4.3 BSD variant
differences between this data structure and the 4.3 BSD variant are the are the inclusion of the length field, and the change of the family
inclusion of the length field, and the change of the family field to a field to a 8-bit data type. The definitions of all the other fields are
8-bit data type. The definitions of all the other fields are identical identical to the 4.3 BSD variant defined in the previous section.
to the 4.3 BSD variant defined in the previous section.
Systems that provide this version of the sockaddr_in6 data structure Systems that provide this version of the sockaddr_in6 data structure
must include the SIN6_LEN macro definition in <netinet/in.h>. This must also declare the SIN6_LEN as a result of including the
macro allows applications to determine whether they are being built on a
system that supports the 4.3 BSD or 4.4 BSD variants of the data <netinet/in.h> header file. This macro allows applications to determine
structure. Applications can be written to run on both systems by simply whether they are being built on a system that supports the 4.3 BSD or
making their assignments and use of the sin6_len field conditional on 4.4 BSD variants of the data structure. Applications can be written to
the SIN6_LEN field. For example, to fill in an IPv6 address structure run on both systems by simply making their assignments and use of the
in an application, one might write: sin6_len field conditional on the SIN6_LEN field. For example, to fill
in an IPv6 address structure in an application, one might write:
struct sockaddr_in6 sin6; struct sockaddr_in6 sin6;
bzero((char *) &sin6, sizeof(struct sockaddr_in6)); bzero((char *) &sin6, sizeof(struct sockaddr_in6));
#ifdef SIN6_LEN #ifdef SIN6_LEN
sin6.sin6_len = sizeof(struct sockaddr_in6); sin6.sin6_len = sizeof(struct sockaddr_in6);
#endif #endif
sin6.sin6_family = AF_INET6; sin6.sin6_family = AF_INET6;
sin6.sin6_port = htons(23); sin6.sin6_port = htons(23);
Note that the size of the sockaddr_in6 structure is larger than the size Note that the size of the sockaddr_in6 structure is larger than the size
of the sockaddr structure. Applications that use the sockaddr_in6 of the sockaddr structure. Applications that use the sockaddr_in6
structure need to be aware that they can not use sizeof(sockaddr) to structure need to be aware that they can not use sizeof(sockaddr) to
allocate a buffer to hold a sockaddr_in6 structure. They should use allocate a buffer to hold a sockaddr_in6 structure. They should use
sizeof(sockaddr_in6) instead. sizeof(sockaddr_in6) instead.
4.5. The Socket Functions 3.5. The Socket Functions
Applications use the socket() function to create a socket descriptor Applications use the socket() function to create a socket descriptor
that represents a communication endpoint. The arguments to the socket() that represents a communication endpoint. The arguments to the socket()
function tell the system which protocol to use, and what format address function tell the system which protocol to use, and what format address
structure will be used in subsequent functions. For example, to create structure will be used in subsequent functions. For example, to create
an IPv4/TCP socket, applications make the call: an IPv4/TCP socket, applications make the call:
s = socket (PF_INET, SOCK_STREAM, 0); s = socket (PF_INET, SOCK_STREAM, 0);
To create an IPv4/UDP socket, applications make the call: To create an IPv4/UDP socket, applications make the call:
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accept() accept()
recvfrom() recvfrom()
recvmsg() recvmsg()
getpeername() getpeername()
getsockname() getsockname()
No changes to the syntax of the socket functions are needed to support No changes to the syntax of the socket functions are needed to support
IPv6, since the all of the "address carrying" functions use an opaque IPv6, since the all of the "address carrying" functions use an opaque
address pointer, and carry an address length as a function argument. address pointer, and carry an address length as a function argument.
4.6. 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 addresses continue to support PF_INET sockets and the sockaddr_in addresses
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
described in the previous section. Applications should be able to hold described in the previous section. Applications should be able to hold
a combination of IPv4/TCP, IPv4/UDP, IPv6/TCP and IPv6/UDP sockets a combination of IPv4/TCP, IPv4/UDP, IPv6/TCP and IPv6/UDP sockets
simultaneously within the same process. simultaneously within the same process.
Applications using the original API should continue to operate as they Applications using the original API should continue to operate as they
did on systems supporting only IPv4. That is, they should continue to did on systems supporting only IPv4. That is, they should continue to
interoperate with IPv4 nodes. It is not clear, though, how, or even if, interoperate with IPv4 nodes. It is not clear, though, how, or even if,
those IPv4 applications should interoperate with IPv6 nodes. The open those IPv4 applications should interoperate with IPv6 nodes. The open
issues section (section 7) discusses some of the alternatives. issues section (section 9) discusses some of the alternatives.
4.7. Compatibility with IPv4 Nodes 3.7. Compatibility with IPv4 Nodes
The API also provides a different type of compatibility: the ability for The API also provides a different type of compatibility: the ability for
applications using the extended API to interoperate with IPv4 nodes. applications using the extended API to interoperate with IPv4 nodes.
This feature uses the IPv4-mapped IPv6 address format defined in the This feature uses the IPv4-mapped IPv6 address format defined in the
IPv6 addressing architecture specification [3]. This address format IPv6 addressing architecture specification [3]. This address format
allows the IPv4 address of an IPv4 node to be represented as an IPv6 allows the IPv4 address of an IPv4 node to be represented as an IPv6
address. The IPv4 address is encoded into the low-order 32-bits of the address. The IPv4 address is encoded into the low-order 32-bits of the
IPv6 address, and the high-order 96-bits hold the fixed prefix IPv6 address, and the high-order 96-bits hold the fixed prefix
0:0:0:0:0:FFFF. IPv4-mapped addresses are written as follows: 0:0:0:0:0:FFFF. IPv4-mapped addresses are written as follows:
::FFFF:<IPv4-address> ::FFFF:<IPv4-address>
Applications may use PF_INET6 sockets to open TCP connections to IPv4 Applications may use PF_INET6 sockets to open TCP connections to IPv4
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::FFFF:<IPv4-address> ::FFFF:<IPv4-address>
Applications may use PF_INET6 sockets to open TCP connections to IPv4 Applications may use PF_INET6 sockets to open TCP connections to IPv4
nodes, or send UDP packets to IPv4 nodes, by simply encoding the nodes, or send UDP packets to IPv4 nodes, by simply encoding the
destination's IPv4 address as an IPv4-mapped IPv6 address, and passing destination's IPv4 address as an IPv4-mapped IPv6 address, and passing
that address, within a sockaddr_in6 structure, in the connect() or that address, within a sockaddr_in6 structure, in the connect() or
sendto() call. When applications use PF_INET6 sockets to accept TCP sendto() call. When applications use PF_INET6 sockets to accept TCP
connections from IPv4 nodes, or receive UDP packets from IPv4 nodes, the connections from IPv4 nodes, or receive UDP packets from IPv4 nodes, the
system returns the peer's address to the application in the accept(), system returns the peer's address to the application in the accept(),
recvfrom(), or getpeername() call using a sockaddr_in6 structure encoded recvfrom(), or getpeername() call using a sockaddr_in6 structure encoded
this way. this way.
We expect that few applications will need to know which type of node Few applications will likely need to know which type of node they are
they are interoperating with. However, for those applications that do interoperating with. However, for those applications that do need to
need to know, the following function is provided: know, the inet6_isipv4addr() function, defined in section 6.3, is
provided.
int is_ipv4_addr (const struct in_addr6 *ap); 3.8. Flow Information
The "ap" argument to this function points to a buffer holding an IPv6 The IPv6 header has a 24-bit field to hold a "flow label", and a 4-bit
address in network byte order. The function returns true (non-zero) field to hold a "priority" value. Applications have control over what
if that address is an IPv4-mapped address, and returns 0 otherwise. values for these fields are used in packets that they originate, and
When an application using the extended API accepts a TCP connection, have access to the field values of packets that they receive.
or receives a UDP packet, it may determine whether the peer is an IPv4
node by applying the is_ipv4_addr() function to the address returned
by accept() or recvfrom().
4.8. Sockets Passed Across exec() The sin6_flowinfo field of the sockaddr_in6 structure encodes three
pieces of information: IPv6 flow label, IPv6 priority, and a
strict/loose source routing flag which is discussed in section 4.2.
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 in 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. And 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
Unix allows open sockets to be passed across an exec() call. It is a address passed in the bind() function.
relatively common application practice to pass open sockets across
exec() calls. Because of this, it is possible for an application
using the original API to pass an open PF_INET socket to an
application that is expecting to receive a PF_INET6 socket.
Similarly, it is possible for an application using the extended API to
pass an open PF_INET6 socket to an application using the original API,
which would be equipped only to deal with PF_INET sockets. Either of
these cases could cause problems, because the application which is
passed the open socket might not know how to decode the address
structures returned in subsequent socket functions.
To remedy this problem, we have defined a new setsockopt() option that Implementations provide two bitmask constant declarations to help
allows an application to "transform" a PF_INET6 socket into a PF_INET applications select out the flow label and priority fields. These
socket and vice-versa. 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:
struct sockaddr_in6 sin6;
. . .
recvfrom(s, buf, buflen, flags, (struct sockaddr *) &sin6, &fromlen);
. . .
received_flowlabel = sin6.sin6_flowinfo & IPV6_FLOWINFO_FLOWLABEL;
received_priority = sin6.sin6_flowinfo & IPV6_FLOWINFO_PRIORITY;
On the sending side, applications are responsible for selecting the flow
label value. The system provides constant declarations for the 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
Applications can use these constants along with the flow label they
selected to assign the sin6_flowinfo field, for example:
struct sockaddr_in6 sin6;
. . .
send_flowlabel = . . . ;
. . .
sin6.sin6_flowinfo = IPV6_PRIORITY_UNATTENDED |
(IPV6_FLOWINFO_FLOWLABEL & send_flowlabel);
The macro declarations for these constants are obtained by including
the header file <netinet/in.h>.
3.9. Binding to System-Selected Address
While the bind() function allows applications to select the source IP
address of UDP packets and TCP connections, applications often wish to
let the system to select the source address for them. In IPv4, this
is done by specifying the IPv4 address represented by the symbolic
constant INADDR_ANY in the bind() call, or by simply by skipping the
bind() entirely.
A symbolic constant can not be used for IPv6 because the address is
not a scalar type. Instead, the system provides a global variable
holding the distinguished IPv6 address that can be used in the bind()
call to instruct the system to select the source IPv6 address. The
global variable is an in6_addr type structure named "ipv6addr_any."
The extern declaration for this is:
extern struct in6_addr ipv6addr_any;
Applications use ipv6addr_any similarly to the way they use INADDR_ANY
in IPv4. For example, to bind a socket to port number 23, but let the
system select the source address, an application could use the
following code:
struct sockaddr_in6 sin6;
. . .
sin6.sin6_family = AF_INET6;
sin6.sin6_flowinfo = 0;
sin6.sin6_port = htons(23);
sin6.sin6_addr = ipv6addr_any;
. . .
if (bind(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1)
. . .
Note that the value of ipv6addr_any can not be the all-zeros IPv6
address, since that can be used as a valid IPv6 source address in some
cases.
3.10. Communicating with Local Services
Applications may need to send UDP packets to, or originate TCP
connections to, services residing on the local node. In IPv4, they can
do this by using the constant IPv4 address INADDR_LOOPBACK in their
connect(), sendto(), or sendmsg() call.
For IPv6, the system provides a global variable holding a distinguished
IPv6 address that can be used to contact local TCP and UDP services.
This variable is an in6_addr type structure named "ipv6addr_loopback."
The extern declaration for this variable is:
extern struct in6_addr ipv6addr_loopback;
Applications use ipv6addr_loopback as they would use INADDR_LOOPBACK
in IPv4 applications. For example, to open a TCP connection to the
local telnet server, an application could use the following code:
struct sockaddr_in6 sin6;
. . .
sin6.sin6_family = AF_INET6;
sin6.sin6_flowinfo = 0;
sin6.sin6_port = htons(23);
sin6.sin6_addr = ipv6addr_loopback;
. . .
if (connect(s, (struct sockaddr *) &sin6, sizeof(sin6)) == -1)
. . .
4. Socket Options
A number of new socket options are defined for IPv6. All of these new
options are at the IPPROTO_IPV6 level. That is, the "level" parameter
in the getsockopt() and setsockopt() call is IPPROTO_IPV6 when using
these options. The constant name prefix IPV6_ is used in all of the new
socket options. This serves to clearly identify these options as
applying to IPv6.
The macro declaration for IPPROTO_IPV6, the new IPv6 socket options, and
related constants defined in this section are obtained by including the
header file <netinet/in.h>
4.1 Changing Socket Type
Unix allows open sockets to be passed between processes via the exec()
call and other means. It is a relatively common application practice to
pass open sockets across exec() calls. Thus it is possible for an
application using the original API to pass an open PF_INET socket to an
application that is expecting to receive a PF_INET6 socket. Similarly,
it is possible for an application using the extended API to pass an open
PF_INET6 socket to an application using the original API, which would be
equipped only to deal with PF_INET sockets. Either of these cases could
cause problems, because the application which is passed the open socket
might not know how to decode the address structures returned in
subsequent socket functions.
To remedy this problem, a new setsockopt() option is defined that allows
an application to "transform" a PF_INET6 socket into a PF_INET socket
and vice-versa.
An IPv6 application that is passed an open socket from an unknown An IPv6 application that is passed an open socket from an unknown
process may use the IP_ADDRFORM setsockopt() option to "convert" the process may use the IPV6_ADDRFORM setsockopt() option to "convert" the
socket to PF_INET6. Once that has been done, the system will return socket to PF_INET6. Once that has been done, the system will return
sockaddr_in6 address structures in subsequent socket functions. sockaddr_in6 address structures in subsequent socket functions.
Similarly, an IPv6 application that is about to pass an open PF_INET6 Similarly, an IPv6 application that is about to pass an open PF_INET6
socket to a program that may not be IPv6 capable may "downgrade" the socket to a program that may not be IPv6 capable may "downgrade" the
socket to PF_INET before calling exec(). After that, the system will socket to PF_INET before calling exec(). After that, the system will
return sockaddr_in address structures to the application that was return sockaddr_in address structures to the application that was
exec()'ed. exec()'ed.
The macro definition for IP_ADDRFORM is in <netinet/in.h>. The IPV6_ADDRFORM option is at the IPPROTO_IP level. The only valid
The IP_ADDRFORM option is at the IPPROTO_IP level. The only valid
option values are PF_INET6 and PF_INET. For example, to convert a option values are PF_INET6 and PF_INET. For example, to convert a
PF_INET6 socket to PF_INET, a program would call: PF_INET6 socket to PF_INET, a program would call:
int addrform = PF_INET; int addrform = PF_INET;
if (setsockopt(s, IPPROTO_IP, IP_ADDRFORM, (char *) &addrform, if (setsockopt(s, IPPROTO_IPV6, IPV6_ADDRFORM, (char *) &addrform,
sizeof(addrform)) == -1) sizeof(addrform)) == -1)
perror("setsockopt IP_ADDRFORM"); perror("setsockopt IPV6_ADDRFORM");
An application may use IP_ADDRFORM in the getsckopt() function to learn An application may use IPV6_ADDRFORM in the getsockopt() function to
whether an open socket is a PF_INET of PF_INET6 socket. For example: learn whether an open socket is a PF_INET of PF_INET6 socket. For
example:
int addrform; int addrform;
int len = sizeof(int); int len = sizeof(int);
if (getsockopt(s, IPPROTO_IP, IP_ADDRFORM, (char *) &addrform, if (getsockopt(s, IPPROTO_IPV6, IPV6_ADDRFORM, (char *) &addrform,
&len) == -1) &len) == -1)
perror("getsockopt IP_ADDRFORM"); perror("getsockopt IPV6_ADDRFORM");
if (addrform == PF_INET) if (addrform == PF_INET)
printf("This is an IPv4 socket.\n"); printf("This is an IPv4 socket.\n");
else if (addrform == PF_INET6) else if (addrform == PF_INET6)
printf("This is an IPv6 socket.\n"); printf("This is an IPv6 socket.\n");
else else
printf("This system is broken.\n"); printf("This system is broken.\n");
4.9. Flow Information 4.2. Handling IPv6 Source Routes
The IPv6 header has a 24-bit field to hold a "flow label", and a 4-bit
field to hold a "priority". Applications have control over what values
for these fields are used in packets that they originate, and have
access to the field values of packets that they receive.
The sin6_flowinfo field of the sockaddr_in6 structure is used to carry
the flow information between the application and the system. An
application may specify a flow label and priority to use in the
transmitted packets of an actively opened TCP connection by setting the
sin6_flowinfo field of the destination address sockaddr_in6 structure
passed in the connect() function. An application may specify the flow
label and priority to use in transmitted UDP packets by setting the
sin6_flowinfo field of the destination address sockaddr_in6 structure
passed in the sendto() function. If an application does not care what
values are used, it should set the flowinfo value to zero.
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 in the bind() function.
The flow label and priority that appeared in received UDP packets are
passed up to the application in the sin6_flowinfo field of the source
address sockaddr_in6 structure that is returned in the recvfrom() call.
The flow information that appeared in the received SYN segment of a
passively accepted TCP connection is returned to the application in the
source address sin6_flowinfo field of the sockaddr_in6 structure that is
passed in the accept() call.
4.10. Handling IPv6 Source Routes
IPv6 makes more use of the source routing mechanism than IPv4. In order IPv6 makes more use of the source routing mechanism than IPv4. In order
for source routing to operate properly, the node receiving a request for source routing to operate properly, the node receiving a request
packet that bears a source route must reverse that source route when packet that bears a source route must reverse that source route when
sending the reply. In the case of TCP, the reversal can be done in the sending the reply. In the case of TCP, the reversal can be done in the
transport protocol implementation transparently to the application. But transport protocol implementation transparently to the application. But
in the case of UDP, the application must perform the reversal itself. in the case of UDP, the application must perform the reversal itself.
The transport protocol code can not perform the reversal for UDP packets The transport protocol code can not perform the reversal for UDP packets
because a UDP application may receive a number of requests and generate because a UDP application may receive a number of requests and generate
replies asynchronously. A "reply" sent by an application may not match replies asynchronously. A "reply" sent by an application may not match
the "request" most recently passed up to the application. the "request" most recently passed up to the application.
The API for source routing has two components: providing a source route The API for source routing has two components: providing a source route
to be used with originated traffic -- actively opened TCP connections to be used with originated traffic -- actively opened TCP connections
and UDP packets being sent -- and retrieving the source route of and UDP packets being sent; and retrieving the source route of received
received traffic -- passively accepted TCP connections and received UDP traffic -- passively accepted TCP connections and received UDP packets.
packets. An application may always provide a source route with TCP An application may always provide a source route with TCP connections
connections being originated and UDP packets being sent. But to receive being originated and UDP packets being sent. But to receive source
source routes, the application must enable an option. routes, the application must enable an option.
To provide a source route, an application simply provides an array of To provide a source route, an application simply provides an array of
sockaddr_in6 data structures in the address argument of the sendto() sockaddr_in6 data structures in the msg_name field of the msghdr
function (when sending a UDP packet), or the connect() function (when structure of a sendmsg() function, or the address argument of the
actively opening a TCP connection). The length argument of the function sendto() function (when sending a UDP packet), or the address argument
is the total length, in octets, of the array. The elements of the array of the connect() function (when actively opening a TCP connection). For
represent the full source route, including both source and destination sendto() and connect(), the length argument of the function is the total
endpoint address. The elements of the array are ordered from length, in octets, of the array. For sendmsg(), the msg_namelen field
destination to source. That is, the first element of the array of the msghdr structure specifies the total length of the array. The
represents the destination endpoint address, and the last element of the elements of the array represent the full source route, including both
array represents the source endpoint address. If the application source and destination endpoint address. The elements of the array are
ordered from destination to source. That is, the first element of the
array represents the destination endpoint address, and the last element
of the array represents the source endpoint address. If the application
provides a source route, the source endpoint address can not be omitted. provides a source route, the source endpoint address can not be omitted.
The sin6_addr field of the source endpoint address may be set to zero, The sin6_addr field of the source endpoint address may be set to zero,
however, in which case the system will select an appropriate source however, in which case the system will select an appropriate source
address. The sin6_port field of the destination endpoint address must address. The sin6_port field of the destination endpoint address must
be assigned. The sin_port field of the source endpoint address may be be assigned. The sin6_port field of the source endpoint address may be
set to zero, in which case the system will select an appropriate source set to zero, in which case the system will select an appropriate source
port number. The sin6_port fields of the intermediate port number. The sin6_port fields of the intermediate addresses must be
addresses must be set to zero. set to zero.
The application also has control over the loose/strict source routing
flag that is defined in the IPv6 specification [1]. It does this by
setting or clearing the loose/strict flag contained in the sin6_flowinfo
field of the destination and intermediate addresses. On the receive
side, the implementation uses the loose/strict flag in the address array
returned to the application to indicate the loose/strict status of each
hop.
The implementation provides a set of constant definitions to simplify
getting and setting the loose/strict flag for each of the hops of a
source route. The following constant is used to select the loose/strict
flag from the sin6_flowinfo field:
IPV6_FLOWINFO_SRFLAG
In addition, two constants are provided which represent the two states
of this flag:
IPV6_SRFLAG_STRICT
IPV6_SRFLAG_LOOSE
These constants can be used to inspect the source route flags of
received addresses, for example:
struct sockaddr_in6 sin6[3];
. . .
if ((sin6[0].sin6_flowinfo & IPV6_FLOWINFO_SRFLAG) ==
IPV6_SRFLAG_STRICT)
. . .
And they can also be used to set the source route flags:
struct sockaddr_in6 sin6[3];
. . .
sin6[0].sin6_flowinfo =
(sin6[0].sin6_flowinfo & ~IPV6_FLOWINFO_SRFLAG) |
IPV6_SRFLAG_STRICT;
The flow label and priority sub-fields of the sin6_flowinfo field of the The flow label and priority sub-fields of the sin6_flowinfo field of the
destination endpoint address may be set, but the these fields must be destination endpoint address may be set, but the these fields must be
set to zero in the intermediate and source endpoint address.
set to zero in the intermediate and source endpoint address. The
loose/strict flag of the sin6_flowid field of the destination endpoint
address and the intermediate addresses may be set to 0 or 1. If the
flag is set to one, the leg of the end-to-end path TO that address
should be treated as a strict source route. If the flag is 0, that leg
should be treated as a loose source route. The loose/strict flag of the
source endpoint address must be set to 0.
The arrangement of the address structures in the address buffer passed The arrangement of the address structures in the address buffer passed
to connect() or sendto() is shown in the figure below: to sendmsg(), connect() or sendto() is shown in the figure below:
+--------------------+ +--------------------+
| | | |
| sockaddr_in6[0] | Destination Endpoint Address | sockaddr_in6[0] | Destination Endpoint Address
| | | |
+--------------------+ +--------------------+
| | | |
| sockaddr_in6[1] | Last Source-Route Hop Address | sockaddr_in6[1] | Last Source-Route Hop Address
| | | |
+--------------------+ +--------------------+
skipping to change at page 13, line 40 skipping to change at page 16, line 29
| sockaddr_in6[N-1] | First Source-Route Hop Address | sockaddr_in6[N-1] | First Source-Route Hop Address
| | | |
+--------------------+ +--------------------+
| | | |
| sockaddr_in6[N] | Source Endpoint Address | sockaddr_in6[N] | Source Endpoint Address
| | | |
+--------------------+ +--------------------+
Address buffer when sending a source route Address buffer when sending a source route
The IP_RCVSRCRT setsockopt() option controls the reception of source The IPV6_RECVSRCRT setsockopt() option controls the reception of source
routes. The option is disabled by default. Applications must routes. The option is disabled by default. Applications must
explicitly enable the option using the setsockopt() function in order to explicitly enable the option using the setsockopt() function in order to
receive source routes. receive source routes.
The macro definition for IP_RCVSRCRT is in <netinet/in.h>. The IPV6_RECVSRCRT option is at the IPPROTO_IPV6 level. An example of
how an application might use this option is:
The IP_RCVSRCRT option is at the IPPROTO_IP level. An example of how an
application might use this option is:
int on = 1; /* value == 1 means enable the option */ int on = 1; /* value == 1 means enable the option */
if (setsockopt(s, IPPROTO_IP, IP_RCVSRCRT, (char *) &on, if (setsockopt(s, IPPROTO_IPV6, IPV6_RECVSRCRT, (char *) &on,
sizeof(on)) == -1) sizeof(on)) == -1)
perror("setsockopt IP_RCVSRCRT"); perror("setsockopt IPV6_RECVSRCRT");
When the IP_RCVSRCRT option is disabled, only a single sockaddr_in6 When the IPV6_RECVSRCRT option is disabled, only a single sockaddr_in6
address structure is returned to applications in the address argument address structure is returned to applications in the address argument of
of the recvfrom() and accept() functions. This address represents the the recvfrom() and accept() functions. This address represents the
source endpoint address of the UDP packet received or the TCP source endpoint address of the UDP packet received or the TCP connection
connection accepted. accepted.
When the IP_RCVSRCRT option is enabled, the address argument of the When the IPV6_RECVSRCRT option is enabled, the msg_name field of the
msghdr of the recvmsg() function, or the address argument of the
recvfrom() function (when receiving UDP packets) and the accept() recvfrom() function (when receiving UDP packets) and the accept()
functions (when passively accepting TCP connections) points to an array functions (when passively accepting TCP connections) points to an array
of sockaddr_in6 structures. When the function returns, the array will of sockaddr_in6 structures. When the function returns, the array will
hold two elements -- source and destination address -- when the received hold two elements -- source and destination address -- when the received
UDP packet or TCP SYN packet does not carry a source route. The array UDP packet or TCP SYN packet does not carry a source route. The array
will hold more than two elements when the received packet carries a will hold more than two elements when the received packet carries a
source route. source route.
The addresses in the array are ordered from source to destination. That The addresses in the array are ordered from source to destination. That
is, the first element of the array holds source endpoint address of the is, the first element of the array holds source endpoint address of the
received packet. Following this in the array are the intermediate hops received packet. Following this in the array are the intermediate hops
in the order in which they were visited. The last element of the array in the order in which they were visited. The last element of the array
skipping to change at page 14, line 28 skipping to change at page 17, line 17
UDP packet or TCP SYN packet does not carry a source route. The array UDP packet or TCP SYN packet does not carry a source route. The array
will hold more than two elements when the received packet carries a will hold more than two elements when the received packet carries a
source route. source route.
The addresses in the array are ordered from source to destination. That The addresses in the array are ordered from source to destination. That
is, the first element of the array holds source endpoint address of the is, the first element of the array holds source endpoint address of the
received packet. Following this in the array are the intermediate hops received packet. Following this in the array are the intermediate hops
in the order in which they were visited. The last element of the array in the order in which they were visited. The last element of the array
holds the destination endpoint address. Note that this is the opposite holds the destination endpoint address. Note that this is the opposite
of the order specified for sending. This ordering was chosen so that of the order specified for sending. This ordering was chosen so that
the address array received in a recvfrom() call can be used in a the address array returned in a recvmsg() or recvfrom() call can be used
subsequent sendto() call without requiring the application to re-order in a subsequent sendmsg() or sendto() call without requiring the
the addresses in the array. Similarly, the address array received in an application to re-order the addresses in the array. Similarly, the
accept() call can be used unchanged in a subsequent connect() call. address array received in an accept() call can be used unchanged in a
subsequent connect() call.
The address length argument of the recvfrom() and accept() functions The address length argument of the recvfrom() and accept() functions,
and the msg_namelen field of the msghdr field in the recvmsg() function,
indicate the length, in octets, of the full address array. This indicate the length, in octets, of the full address array. This
argument is a value-result parameter. The application sets the maximum argument is a value-result parameter. The application sets the maximum
size of the address buffer when it makes the call, and the system size of the address buffer when it makes the call, and the system
modifies the value to return the actual size of the buffer to the modifies the value to return the actual size of the buffer to the
application. application.
The sin6_port field of the first and last array elements (source and The sin6_port field of the first and last array elements (source and
destination endpoint address) will hold the source and destination UDP destination endpoint address) will hold the source and destination UDP
or TCP port number of the received packet. The sin6_port field of the or TCP port number of the received packet. The sin6_port field of the
intermediate elements of the array will be zero. intermediate elements of the array will be zero.
The flow label and priority sub-fields of the sin6_flowinfo field of the The flow label and priority sub-fields of the sin6_flowinfo field of the
source endpoint address will hold the flow label and priority values of source endpoint address will hold the flow label and priority values of
the received packet. The flow label and priority sub-fields of the the received packet. The flow label and priority sub-fields of the
intermediate addresses and the destination endpoint address will be intermediate addresses and the destination endpoint address will be
zero. The loose/strict flag of the sin6_flowinfo field of the source zero. The loose/strict flag of the sin6_flowinfo field of the source
endpoint address and the intermediate addresses will be 1 if the leg of endpoint address and the intermediate addresses will be set according to
the end-to-end path originating FROM that address was strict. The the flags in the received packet. The macros defined above can be used
to inspect the loose/strict flag of each hop.
loose/strict flag of the destination endpoint address will be 0.
The address buffer returned to the application in the recvfrom() or The address buffer returned to the application in the recvfrom() or
accept() functions when the IP_RCVSRCRT option is enabled is shown accept() functions when the IPV6_RECVSRCRT option is enabled is shown
below: below:
+--------------------+ +--------------------+
| | | |
| sockaddr_in6[0] | Source Endpoint Address | sockaddr_in6[0] | Source Endpoint Address
| | | |
+--------------------+ +--------------------+
| | | |
| sockaddr_in6[1] | First Source-Route Hop Address | sockaddr_in6[1] | First Source-Route Hop Address
| | | |
skipping to change at page 15, line 35 skipping to change at page 18, line 29
| sockaddr_in6[N-1] | Last Source-Route Hop Address | sockaddr_in6[N-1] | Last Source-Route Hop Address
| | | |
+--------------------+ +--------------------+
| | | |
| sockaddr_in6[N] | Destination Endpoint Address | sockaddr_in6[N] | Destination Endpoint Address
| | | |
+--------------------+ +--------------------+
Address buffer when receiving a source route Address buffer when receiving a source route
Since IPv6 allows the number of elements in a source route to be very IPv6 allows a source route with up to 23 intermediate hops. Since the
large, it is impractical for all applications that have enabled the it must also receive the source and destination endpoint addresses, the
reception of source routes to provide buffer space to hold the maximum application must provide a buffer capable of holding 25 addresses to
number of elements. Some applications may choose a buffer size that is receive such a source route. Implementations provide the following
appropriate for their own use. This means that it is possible that a constant declaration in order to allow applications to simply declare
received source route may be too large to fit into the buffer provided storage for the largest possible source route:
by the application. In this circumstance, the system should return only
a single address element -- the source endpoint address -- to the
application. This case is clearly distinguishable to the application
because in all other cases, the system returns at least two address
elements -- the source and destination endpoint addresses.
4.11. Unicast Hop Limit IPV6_SR_MAXADDR
Applications can use this constant like this:
struct sockaddr_in6 sin6[IPV6_SR_MAXADDR];
It may be impractical for some applications to allocate space to hold
the largest possible source route. Thus a received source route may be
too large to fit into the buffer provided by the application. In this
circumstance, the system should return only a single address element --
the source endpoint address -- to the application. This case is clearly
distinguishable to the application because in all other cases, the
system returns at least two address elements -- the source and
destination endpoint addresses.
4.3. Receiving Interface Determination
Some applications run on multi-homed hosts need to determine which
interface UDP packets were received on or TCP connections are bound to.
While the source routing interface described in the previous section
returns the destination address of the packet, this does not necessarily
identify the receiving interface. Some cases where it does not are:
- When the received packet is multicast. The destination address
in this case is an IPv6 multicast address, not the address of an
interface.
- When the node is operating as an IPv6 router. The node may
receive packets on interfaces other than the one they are
addressed to.
- When the received packet is sent to the node's link-local
address which is being used on multiple interfaces.
The address of the receiving interface is returned to the application
similarly to the way that source routes are returned. A new
setsockopt() option named IPV6_RECVIF is provided at the IPPROTO_IPV6
level. If this option is enabled, the system returns an additional
sockaddr_in6 structure to the application, holding the IPv6 address of
the receiving interface, in the recvfrom(), recvmsg(), or accept()
functions.
The option is enabled like this:
int on = 1; /* value == 1 means enable the option */
if (setsockopt(s, IPPROTO_IPV6, IPV6_RECVIF, (char *) &on,
sizeof(on)) == -1)
perror("setsockopt IPV6_RECVIF");
This option can be used in conjunction with the IP_RECVSRCRT option.
When the IPV6_RECVIF option is enabled, the buffer returned to the
application is structured like this:
+--------------------+ - - - - - - - - - - - - - - -
| |
| sockaddr_in6[0] |
| |
+--------------------+
. . Source Address, or
. . Full Source Route
. .
+--------------------+
| |
| sockaddr_in6[N-1] |
| |
+--------------------+ - - - - - - - - - - - - - - -
| |
| sockaddr_in6[N] | Receiving Interface Address
| |
+--------------------+ - - - - - - - - - - - - - - -
Address buffer with receiving interface address
The last address in the array is an IPv6 address of the receiving
interface. Since interfaces in IPv6 may have more than one address, and
some addresses (e.g. link-local addresses) may be used on more than one
interface, the system should select an address that uniquely identifies
the interface.
4.4. Sending Interface Specification
Applications may also need to specify the outgoing interface that
originated UDP or TCP packets should use. This is accomplished like
source route selection. The application may provide an additional
sockaddr_in6 structure in its sendto(), sendmsg() or connect() call
specifying the address of the outgoing interface. Unlike source route
selection, the outgoing interface address can only be included if a new
option is enabled. The new option is needed so that the system can
differentiate between the application's specification of an outgoing
interface address and a source route.
The new option option is named IPV6_SENDIF and is at the IPPROTO_IPV6
level. It can be enabled like this:
int on = 1; /* value == 1 means enable the option */
if (setsockopt(s, IPPROTO_IPV6, IPV6_SENDIF, (char *) &on,
sizeof(on)) == -1)
perror("setsockopt IPV6_SENDIF");
This option can be used in conjunction with source route specification.
If this option is enabled, the application passes in an address array
structured as follows:
+--------------------+ - - - - - - - - - - - - - - -
| |
| sockaddr_in6[0] |
| |
+--------------------+
. . Destination Address, or
. . Full Source Route
. .
+--------------------+
| |
| sockaddr_in6[N-1] |
| |
+--------------------+ - - - - - - - - - - - - - - -
| |
| sockaddr_in6[N] | Sending Interface Address
| |
+--------------------+ - - - - - - - - - - - - - - -
Address buffer with sending interface address
The last address in the array is an IPv6 address of the sending
interface. Applications should use an address that uniquely identifies
the interface to use.
4.5. Unicast Hop Limit
A new setsockopt() option is used to control the hop limit used in A new setsockopt() option is used to control the hop limit used in
outgoing unicast IPv6 packets. The name of this option is outgoing unicast IPv6 packets. The name of this option is
IP_UNICAST_HOPS, and it is used at the IPPROTO_IP layer. The macro IPV6_UNICAST_HOPS, and it is used at the IPPROTO_IPV6 layer. The
definition for IP_UNICAST_HOPS resides in the <netinet/in.h> header following example illustrates how it is used:
file. The following example illustrates how it is used:
int hoplimit = 10; int hoplimit = 10;
if (setsockopt(s, IPPROTO_IP, IP_UNICAST_HOPS, (char *) &hoplimit, if (setsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS, (char *) &hoplimit,
sizeof(hoplimit)) == -1) sizeof(hoplimit)) == -1)
perror("setsockopt IP_UNICAST_HOPS); perror("setsockopt IPV6_UNICAST_HOPS");
When the IP_UNICAST_HOPS option is set with setsockopt(), the option When the IPV6_UNICAST_HOPS option is set with setsockopt(), the option
value given is used as the hop limit for all subsequent unicast packets value given is used as the hop limit for all subsequent unicast packets
sent via that socket. If the option is not set, the system selects a sent via that socket. If the option is not set, the system selects a
default value. default value.
The IP_UNICAST_HOPS option may be used in the getsockopt() function to The IPV6_UNICAST_HOPS option may be used in the getsockopt() function 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;
int len = sizeof(hoplimit); int len = sizeof(hoplimit);
if (getsockopt(s, IPPROTO_IP, IP_UNICAST_HOPS, (char *) &hoplimit, if (getsockopt(s, IPPROTO_IPV6, IPV6_UNICAST_HOPS, (char *) &hoplimit,
&len) == -1) &len) == -1)
perror("getsockopt IP_UNICAST_HOPS); perror("getsockopt IPV6_UNICAST_HOPS");
else else
printf("Using %d for hop limit.\n", hoplimit); printf("Using %d for hop limit.\n", hoplimit);
4.12. Sending and Receiving Multicast Packets 4.6. Sending and Receiving Multicast Packets
IPv6 applications may send UDP multicast packets by simply specifying an IPv6 applications may send UDP multicast packets by simply specifying an
IPv6 multicast address in the address argument of the sendto() function. IPv6 multicast address in the address argument of the sendto() function.
A few setsockopt options at the IPPROTO_IP layer are used to control A few setsockopt options at the IPPROTO_IPV6 layer are used to control
some of the parameters of sending multicast packets. These options are some of the parameters of sending multicast packets. These options are
optional: applications may send multicast packets without using these optional: applications may send multicast packets without using these
options. The setsockopt() options for controlling the sending of options. The setsockopt() options for controlling the sending of
multicast packets are summarized below: multicast packets are summarized below:
IP_MULTICAST_IF Set the interface to use for outgoing IPV6_MULTICAST_IF
multicast packets.
IP_MULTICAST_HOPS Set the hop limit to use for outgoing Set the interface to use for outgoing multicast packets.
multicast packets. (Note a separate The argument is an IPv6 address of the interface to use.
option - IP_UNICAST_HOPS - is provided
to set the hop limit to use for outgoing Argument type: struct in6_addr
IPV6_MULTICAST_HOPS
Set the hop limit to use for outgoing multicast packets.
(Note a separate option - IPV6_UNICAST_HOPS - is
provided to set the hop limit to use for outgoing
unicast packets.) unicast packets.)
IP_MULTICAST_LOOP Controls whether outgoing multicast Argument type: unsigned int
packets sent should be delivered back to
the local application. A toggle. IPV6_MULTICAST_LOOP
Controls whether outgoing multicast packets sent should
be delivered back to the local application. A toggle.
If the option is set to 1, multicast packets are looped
back. If it is set to 0, they are not.
Argument type: unsigned int
The reception of multicast packets is controlled by the two setsockopt() The reception of multicast packets is controlled by the two setsockopt()
options summarized below: options summarized below:
IP_ADD_MEMBERSHIP Join a multicast group. Requests IPV6_ADD_MEMBERSHIP
that multicast packets sent to a
particular multicast address
be delivered to this socket.
IP_DROP_MEMBERSHIP Leave a multicast group. Requests that Join a multicast group. Requests that multicast packets
multicast packets sent to a particular sent to a particular multicast address be delivered to
multicast address no longer be delivered this socket. The argument is the IPv6 multicast address
to this socket. of the group to join.
4.13. Name-to-Address Translation Functions Argument type: struct in6_addr
We have defined two new functions analogous to gethostbyname() and IPV6_DROP_MEMBERSHIP
gethostbyaddr() which support addresses in both the IPv4 and IPv6
address families. The names of the new functions are hostname2addr()
and addr2hostname(). These functions were designed to have semantics
similar to gethostbyname() and gethostbyaddr(), so that existing IPv4
applications can be easily ported to IPv6.
Hostname2addr() is defined similarly to gethostbyname(), but enables Leave a multicast group. Requests that multicast
packets sent to a particular multicast address no longer
be delivered to this socket. The argument is the IPv6
multicast address of the group to join.
Argument type: struct in6_addr
5. Library Functions
New library functions are needed to lookup IPv6 addresses in the name
service, and to manipulate IPv6 addresses.
5.1. Name-to-Address Translation Functions
Two new functions analogous to gethostbyname() and gethostbyaddr() have
been defined which support both IPv4 and IPv6 addresses. The names of
the new functions are hostname2addr() and addr2hostname(). These
functions were designed to have semantics similar to gethostbyname() and
gethostbyaddr(), so that existing IPv4 applications can be easily ported
to IPv6.
The new functions differ from the old in one important way that is not
related to IPv6: The old functions could not safely be used by
multi-threaded applications, while the new ones can. There are two
multi-threading problems with the old functions. First, the return
value of the old functions is a pointer to a single static buffer
belonging to the library. The new functions return a dynamically
allocated buffer, and a third new function, named freehostent(), is
provided to free that storage. Second, the old functions returned their
error code in a global variable (h_errno). The new functions carry a
pointer that allows the library to return the error code into storage
provided by the caller.
The hostname2addr() function is similar to gethostbyname(), but enables
applications to specify the type of address to be looked up: applications to specify the type of address to be looked up:
struct hostent *hostname2addr(const char *name, int af); struct hostent *hostname2addr(
const char *name,
int af,
int *error);
This new function looks up the given name in the name service and This function looks up the hostname argument name in the name service
returns the completed hostent structure if the lookup succeeds, and NULL and, if the lookup succeeds, returns a completed hostent structure. If
otherwise. The name argument is the domain name of the host to look up. the lookup fails, the function returns NULL and an error code is
The af argument specifies the type of the address -- IPv4 (AF_INET) or returned in the buffer pointed to by the argument error. The af argument
IPv6 (AF_INET6) -- to return to the caller in the h_addr_list field of specifies the type of the address -- IPv4 (AF_INET) or IPv6 (AF_INET6)
the hostent structure. -- to return to the caller in the h_addr_list field of the hostent
structure.
If the af argument is AF_INET, hostname2addr() queries the name service If the af argument is AF_INET, hostname2addr() behaves much like
gethostbyname. It queries the name service for IPv4 addresses and, if
any are found, returns a hostent structure that includes an array of
IPv4 addresses. Each IPv4 address is encoded in network byte order.
for IPv4 addresses and, if any are found, returns a hostent structure If the af argument is AF_INET6, hostname2addr() queries the name service
that includes an array of IPv4 addresses. Each IPv4 address is encoded for IPv6 addresses. The function may also query the name service for
in network byte order. IPv4 records. If this is done, any IPv4 addresses found are returned to
If the af argument is AF_INET6, the processing is as follows: the the application encoded as IPv4-compatible IPv6 addresses. The
hostname2addr() function first queries the name service for IPv6 determination of whether to query for IPv4 addresses is system specific.
addresses. If IPv6 addresses are found, they are returned in an array in Systems that support querying for IPv4 addresses should provide a
the hostent structure. If no IPv6 addresses are found, the function system-wide configuration switch allowing the system administrator to
queries the name service for IPv4 addresses. If IPv4 addresses are enable or disable that feature.
found, they are returned as IPv4-mapped IPv6 addresses. As in IPv4,
each IPv6 address returned in the hostent structure is encoded in IPv6 addresses returned by the hostname2addr() function are encoded in
network byte order. network byte order.
The second new function, called addr2hostname(), is defined in exactly The second new function, called addr2hostname(), is like the
the same way as the gethostbyaddr() function, except that it now gethostbyaddr() function, but supports both the IPv4 and IPv6 address
supports both the IPv4 and IPv6 address families: families:
struct hostent *addr2hostname(const void *addr, int len, int af); struct hostent *addr2hostname(
const void *addr,
int addrlen,
int af,
int *error);
addr2hostname() performs an address-to-name lookup on the address The addr2hostname() function performs an address-to-name lookup on the
specified, returning a completed hostent structure if the lookup address specified by the addr argument, returning a completed hostent
succeeds, or NULL, if the lookup fails. This function supports both the structure if the lookup succeeds. If the lookup fails, the function
AF_INET and AF_INET6 address families. If the af argument is AF_INET, returns NULL and an error code is returned in the buffer pointed to by
then len must be specified to be 4-octets and addr must refer to an IPv4 the argument error.
address. If af is AF_INET6, then len must be specified as 16-octets and
addr must refer to an IPv6 address. If the addr argument is an The addrlen argument specifies the length of the address (in octets)
IPv4-mapped IPv6 address, an IPv4 address-to-name lookup is performed on pointed to by the addr argument.
the embedded IPv4 address.
The af argument specifies the address family of the addr argument. This
function supports both the AF_INET and AF_INET6 address families. If
the af argument is AF_INET, then addr refers to an IPv4 address and
addrlen must have the value 4. If af is AF_INET6, addr represents an
IPv6 address and addrlen must have the value 16. In the latter case,
the caller may present an IPv4-mapped IPv6 address in the addr argument.
If this is done, an IPv4 address-to-name lookup is performed on the
embedded IPv4 address.
The hostent structure returned by both of these functions is allocated
by the library. Applications use the freehostent() function to return
the hostent structure to the library after they are done using it:
void freehostent(
struct hostent *hp);
Applications may not access the hostent structure after they have
returned it to the library.
Another new name-to-address translation library function is now under
A new name-to-address translation library function is now under
development at Berkeley. This new function, named getconninfo(), will development at Berkeley. This new function, named getconninfo(), will
subsume the functionality of gethostbyname(), hostname2addr(), as well subsume the functionality of gethostbyname(), hostname2addr(), as well
as the getservbyname() and getservbyport() functions. The new as the getservbyname() and getservbyport() functions. The new function
function is specifically designed to be "transport independent", so it is specifically designed to be "transport independent", so it should be
should be directly usable by IPv6 applications. directly usable by IPv6 applications.
System implementations should provide the addr2hostname() and System implementations should provide the addr2hostname() and
hostname2addr() functions in order to simplify the porting of existing hostname2addr() functions in order to simplify the porting of existing
IPv4 applications to IPv6. System implementations may also provide IPv4 applications to IPv6. System implementations may also provide the
the getconninfo() function, once it is defined, so that newly written getconninfo() function, once it is defined, so that newly written
applications can be transport independent. applications can be transport independent.
Specification of the getconninfo() function is published as a separate The specification of the getconninfo() function is published as a
specification document [2], not included in this spec. separate document [2], not included in this spec.
Implementations must retain the BSD gethostbyname() and gethostbyaddr() Implementations must retain the BSD gethostbyname() and gethostbyaddr()
functions in order to provide source and binary compatibility for functions in order to provide source and binary compatibility for
existing applications. existing applications.
4.14. Address Conversion Functions Applications obtain the function prototype declarations for
hostname2addr() and addr2hostname() by including the header file
<netdb.h>.
5.3. Address Conversion Functions
BSD Unix provides two functions, inet_addr() and inet_ntoa(), to convert BSD Unix provides two functions, inet_addr() and inet_ntoa(), to convert
an IPv4 address between binary and printable form. IPv6 applications an IPv4 address between binary and printable form. IPv6 applications
need similar functions. We have defined the following two functions to need similar functions. The following two functions convert both IPv6
convert both IPv6 and IPv4 addresses: and IPv4 addresses:
int ascii2addr(int af, const char *cp, void *ap); int ascii2addr(
int af,
const char *cp,
void *ap);
and and
char *addr2ascii(int af, const void *ap, int len, char *cp); char *addr2ascii(
int af,
const void *ap,
int len,
char *cp);
The first function converts an ascii string to an address in the address The first function converts an ascii string to an address in the address
family specified by the af argument. Currently AF_INET and AF_INET6 family specified by the af argument. Currently AF_INET and AF_INET6
address families are supported. The cp argument points to the ascii address families are supported. The cp argument points to the ascii
string being passed in. The ap argument points to a buffer into which string being passed in. The ap argument points to a buffer into which
the function stores the address. Ascii2addr() returns the length of the the function stores the address. Ascii2addr() returns the length of the
address in octets if the conversion succeeds, and -1 otherwise. The address in octets if the conversion succeeds, and -1 otherwise. The
function does not modify the storage pointed to by ap if the conversion function does not modify the storage pointed to by ap if the conversion
fails. The application must ensure that the buffer referred to by ap is fails. The application must ensure that the buffer referred to by ap is
large enough to hold the converted address. large enough to hold the converted address.
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
skipping to change at page 19, line 51 skipping to change at page 27, line 34
AF_INET6. The ap argument points to a buffer holding an IPv4 address if AF_INET6. The ap argument points to a buffer holding an IPv4 address if
the af argument is AF_INET, and an IPv6 address if the af argument is the af argument is AF_INET, and an IPv6 address if the af argument is
AF_INET6. The len field specifies the length in octets of the address AF_INET6. The len field specifies the length in octets of the address
pointed to by ap, and must be 4 if af is AF_INET, or 16 if af is pointed to by ap, and must be 4 if af is AF_INET, or 16 if af is
AF_INET6. The cp argument points to a buffer that the function can use AF_INET6. The cp argument points to a buffer that the function can use
to store the ascii string. If the cp argument is NULL, the function to store the ascii string. If the cp argument is NULL, the function
uses its own private static buffer. If the application specifies a cp uses its own private static buffer. If the application specifies a cp
argument, it must be large enough to hold the ascii conversion of the argument, it must be large enough to hold the ascii conversion of the
address specified as an argument, including the terminating null octet. address specified as an argument, including the terminating null octet.
For IPv6 addresses, the buffer must be at least 46-octets. For IPv4 For IPv6 addresses, the buffer must be at least 46-octets. For IPv4
addresses, the buffer must be at least 16-octets. addresses, the buffer must be at least 16-octets. In order to allow
applications to easily declare buffers of the proper size to store IPv4
and IPv6 addresses in string form, implementations should provide the
following constants, made available to applications that include
<netinet/in.h>:
#define INET_ADDRSTRLEN 16
#define INET6_ADDRSTRLEN 46
The addr2ascii() function returns a pointer to the buffer containing the The addr2ascii() function returns a pointer to the buffer containing the
ascii string if the conversion succeeds, and NULL otherwise. The ascii string if the conversion succeeds, and NULL otherwise. The
function does not modify the storage pointed to by cp if the conversion function does not modify the storage pointed to by cp if the conversion
fails. fails.
5. Security Considerations Applications obtain the prototype declarations for addr2ascii() and
ascii2addr() by including the header file <arpa/inet.h>.
5.3. Embedded IPv4 Addresses
The IPv4-mapped IPv6 address format is used to represent IPv4 addresses
as IPv6 addresses. Most applications should be able to to manipulate
IPv6 addresses as opaque 16-bit 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_isipv4addr (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 true (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_isipv4addr() function to the returned
address.
Applications obtain the prototype for this function by including the
header file <arpa/inet.h>.
6. Security Considerations
IPv6 provides a number of new security mechanisms, many of which need to IPv6 provides a number of new security mechanisms, many of which need to
be accessible to applications. A companion document detailing the be accessible to applications. A companion document detailing the
extensions to the socket interfaces to support IPv6 security is being extensions to the socket interfaces to support IPv6 security is being
written [4]. At some point in the future, that document and this one written [4]. At some point in the future, that document and this one
may be merged into a single API specification. may be merged into a single API specification.
6. Change History 7. Change History
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 file
<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 receving interface determination and sending interface
selection options.
- Added definitions of ipv6addr_any and ipv6addr_loopback.
- Added text making the lookup of IPv4 addresses by
hostname2addr() optional.
Changes from the June 1995 Edition Changes from the June 1995 Edition
- Added capability for application to select loose or strict - Added capability for application to select loose or strict
source routing. source routing.
Changes from the March 1995 Edition Changes from the March 1995 Edition
- Changed the definition of the ipv6_addr structure to be an array - Changed the definition of the ipv6_addr structure to be an array
of sixteen chars instead of four longs. This change is of sixteen chars instead of four longs. This change is
skipping to change at page 21, line 28 skipping to change at page 31, line 7
- Removed specification of numeric values for AF_INET6, - Removed specification of numeric values for AF_INET6,
IP_ADDRFORM, and IP_RCVSRCRT, since they need not be the same on IP_ADDRFORM, and IP_RCVSRCRT, since they need not be the same on
different implementations. different implementations.
- Added a definition for the in_addr6 IPv6 address data - Added a definition for the in_addr6 IPv6 address data
structure. Added this so that applications could use structure. Added this so that applications could use
sizeof(struct in_addr6) to get the size of an IPv6 address, sizeof(struct in_addr6) to get the size of an IPv6 address,
and so that a structured type could be used in the and so that a structured type could be used in the
is_ipv4_addr(). is_ipv4_addr().
7. Open Issues 8. Open Issues
A few open issues for IPv6 socket interface API specification remain, A few open issues for IPv6 socket interface API specification remain,
including: including:
- The multicast API needs to be documented in more detail.
- Should we add a timeout parameter to hostname2addr() and - Should we add a timeout parameter to hostname2addr() and
addr2hostname()? DNS lookups need to be given some finite addr2hostname()? DNS lookups need to be given some finite
timeout interval, so it might be nice to let the application timeout interval, so it might be nice to let the application
specify that interval. specify that interval.
- Can the IPV6_ADDRFORM option really be implemented?
- An interface is needed to allocate flow labels. Should one be
defined in this spec, or left for another document?
- Can existing IPv4 applications interoperate with IPv6 nodes? - Can existing IPv4 applications interoperate with IPv6 nodes?
This issue is discussed in more detail in the following section.
7.1. IPv4 Applications Interoperating with IPv6 Nodes 8.1. IPv4 Applications Interoperating with IPv6 Nodes
This problem primarily has to do with the how IPv4 applications This problem primarily has to do with the how IPv4 applications
represent addresses of IPv6 nodes. What address should be returned to represent addresses of IPv6 nodes. What address should be returned to
the application when an IPv6/UDP packet is received, or an IPv6/TCP the application when an IPv6/UDP packet is received, or an IPv6/TCP
connection is accepted? The peer's address could be any arbitrary connection is accepted? The peer's address could be any arbitrary
128-bit IPv6 address. But the application is only equipped to deal with 128-bit IPv6 address. But the application is only equipped to deal with
32-bit IPv4 addresses encoded in sockaddr_in data structures. 32-bit IPv4 addresses encoded in sockaddr_in data structures.
We have not discovered any solution that provides complete transparent We have not discovered any solution that provides complete transparent
interoperability with IPv6 nodes for applications using the original interoperability with IPv6 nodes for applications using the original
skipping to change at page 22, line 33 skipping to change at page 32, line 17
have to make sure that these cookie values did not escape into have to make sure that these cookie values did not escape into
the Internet as the source or destination addresses of IPv4 the Internet as the source or destination addresses of IPv4
packets. packets.
Both of these techniques have drawbacks. This is an area for further Both of these techniques have drawbacks. This is an area for further
study. System implementors may use one of these techniques or implement study. System implementors may use one of these techniques or implement
another solution. another solution.
Acknowledgments 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 to the numerous revisions of this document, including: Marc Hasson, to the numerous revisions of this document, including: Ran Atkinson,
Dave Borman, Alan Cox, Wan-Yen Hsu, Alex Conta, Richard Stevens, Dan Fred Baker, Dave Borman, Andrew Cherenson, Alex Conta, Alan Cox, Steve
McDonald, Alan Lloyd, Christian Huitema, Steve Deering, Andrew Deering, Francis Dupont, Robert Elz, Marc Hasson, Tom Herbert, Christian
Cherenson, Charles Lynn, Ran Atkinson, Erik Nordmark, Josh Osborne, Huitema, Wan-Yen Hsu, Alan Lloyd, Charles Lynn, Dan McDonald, Erik
Glenn Trewitt, Fred Baker, Robert Elz, Dean D. Throop, and Francis Nordmark, Josh Osborne, Richard Stevens, Dean D. Throop, Glenn Trewitt,
Dupont. Craig Partridge suggested the addr2ascii() and ascii2addr() and Carl Williams. Craig Partridge suggested the addr2ascii() and
functions. ascii2addr() functions.
Ramesh Govindan made a number of contributions and co-authored an Ramesh Govindan made a number of contributions and co-authored an
earlier version of this paper. earlier version of this paper.
References References
[1] R. Hinden. "Internet Protocol, Version 6 (IPv6) Specification". [1] R. Hinden. "Internet Protocol, Version 6 (IPv6) Specification".
Internet Draft. June 1995. Internet Draft. June 1995.
[2] Keith Sklower. "Getconninfo(): An alternative to Gethostbyname()" [2] Keith Sklower. "Getconninfo(): An alternative to Gethostbyname()"
skipping to change at page 23, line 20 skipping to change at page 33, line 4
Draft. January 1995. Draft. January 1995.
Authors' Address Authors' Address
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
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 Telephone: +1 201 829 4514
Email: set@thumper.bellcore.com Email: set@thumper.bellcore.com
Robert E. Gilligan Robert E. Gilligan
Mailstop MPK 17-202
Sun Microsystems, Inc. Sun Microsystems, Inc.
2550 Garcia Avenue 2550 Garcia Avenue
Mailstop UMTV05-44
Mountain View, CA 94043-1100 Mountain View, CA 94043-1100
Phone: +1 415 336 1012 Phone: +1 415 786 5151
Email: bob.gilligan@eng.sun.com Email: gilligan@eng.sun.com
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