Name
ipv6, PF_INET6 — Linux IPv6 protocol
implementation
DESCRIPTION
Linux 2.2 optionally implements the Internet Protocol,
version 6. This man page contains a description of the IPv6
basic API as implemented by the Linux kernel and glibc 2.1.
The interface is based on the BSD sockets interface; see
socket(7).
The IPv6 API aims to be mostly compatible with the
ip(7) v4 API. Only
differences are described in this man page.
To bind an AF_INET6 socket
to any process the local address should be copied from the
in6addr_any
variable which has in6_addr type. In static
initializations IN6ADDR_ANY_INIT may also be used, which
expands to a constant expression. Both of them are in network
order.
The IPv6 loopback address (::1) is available in the global
in6addr_loopback
variable. For initializations IN6ADDR_LOOPBACK_INIT should be used.
IPv4 connections can be handled with the v6 API by using
the v4-mapped-on-v6 address type; thus a program only needs
only to support this API type to support both protocols. This
is handled transparently by the address handling functions in
libc.
IPv4 and IPv6 share the local port space. When you get an
IPv4 connection or packet to a IPv6 socket its source address
will be mapped to v6 and it'll be mapped to v6.
Address Format
| struct |
sockaddr_in6 { |
|
|
u_int16_t |
|
sin6_family; |
/* AF_INET6 */ |
|
|
u_int16_t |
|
sin6_port; |
/* port number */ |
|
|
u_int32_t |
|
sin6_flowinfo; |
/* IPv6 flow information */ |
|
|
struct in6_addr |
|
sin6_addr; |
/* IPv6 address */ |
|
|
u_int32_t |
|
sin6_scope_id; |
/* Scope ID (new in 2.4) */ |
| }; |
|
| struct |
in6_addr { |
|
|
unsigned char |
|
s6_addr[16]; |
/* IPv6 address */ |
| }; |
sin6_family is
always set to AF_INET6;
sin6_port is the
protocol port (see sin_port in ip(7)); sin6_flowinfo is the IPv6
flow identifier; sin6_addr is the 128bit
IPv6 address. sin6_scope_id is an ID of
depending of on the scope of the address. It is new in
Linux 2.4. Linux only supports it for link scope addresses,
in that case sin6_scope_id contains the
interface index (see netdevice(7))
IPv6 supports several address types: unicast to address
a single host, multicast to address a group of hosts,
anycast to address the nearest member of a group of hosts
(not implemented in Linux), IPv4-on-IPv6 to address a IPv4
host, and other reserved address types.
The address notation for IPv6 is a group of 16 2 digit
hexadecimal numbers, separated with a ':'. '::' stands for
a string of 0 bits. Special addresses are ::1 for loopback
and ::FFFF:<IPv4 address> for
IPv4-mapped-on-IPv6.
The port space of IPv6 is shared with IPv4.
Socket Options
IPv6 supports some protocol specific socket options that
can be set with setsockopt(2) and read
with getsockopt(2). The socket
option level for IPv6 is IPPROTO_IPV6. A boolean integer flag is
zero when it is false, otherwise true.
IPV6_ADDRFORM-
Turn an AF_INET6
socket into a socket of a different address family.
Only AF_INET is
currently supported for that. It is only allowed for
IPv6 sockets that are connected and bound to a
v4-mapped-on-v6 address. The argument is a pointer to
a integer containing AF_INET. This is useful to pass
v4-mapped sockets as file descriptors to programs
that don't know how to deal with the IPv6 API.
- IPV6_ADD_MEMBERSHIP,
IPV6_DROP_MEMBERSHIP
-
Control membership in multicast groups. Argument
is a pointer to a struct
ipv6_mreq structure.
IPV6_MTU-
Set the MTU to be used for the socket. The MTU is
limited by the device MTU or the path mtu when path
mtu discovery is enabled. Argument is a pointer to
integer.
IPV6_MTU_DISCOVER-
Control path mtu discovery on the socket. See
IP_MTU_DISCOVER in
ip(7) for
details.
IPV6_MULTICAST_HOPS-
Set the multicast hop limit for the socket.
Argument is a pointer to an integer. −1 in the
value means use the route default, otherwise it
should be between 0 and 255.
IPV6_MULTICAST_IF-
Set the device for outgoing multicast packets on
the socket. This is only allowed for SOCK_DGRAM and SOCK_RAW socket. The argument is an
pointer to an interface index (see netdevice(7)) in an
integer.
IPV6_MULTICAST_LOOP-
Control whether the socket sees multicast packets
that it has send itself. Argument is a pointer to
boolean.
IPV6_PKTINFO-
Set delivery of the IPV6_PKTINFO control message on
incoming datagrams. Only allowed for SOCK_DGRAM or SOCK_RAW sockets. Argument is a
pointer to a boolean value in an integer.
- IPV6_RTHDR, IPV6_AUTHHDR, IPV6_DSTOPS,
IPV6_HOPOPTS, IPV6_FLOWINFO,
IPV6_HOPLIMIT
-
Set delivery of control messages for incoming
datagrams containing extension headers from the
received packet. IPV6_RTHDR delivers the routing
header, IPV6_AUTHHDR
delivers the authentication header, IPV6_DSTOPTS delivers the
destination options, IPV6_HOPOPTS delivers the hop
options, IPV6_FLOWINFO
delivers an integer containing the flow ID,
IPV6_HOPLIMIT delivers
an integer containing the hop count of the packet.
The control messages have the same type as the socket
option. All these header options can also be set for
outgoing packets by putting the appropriate control
message into the control buffer of sendmsg(2). Only
allowed for SOCK_DGRAM
or SOCK_RAW sockets.
Argument is a pointer to a boolean value.
IPV6_RECVERR-
Control receiving of asynchronous error options.
See IP_RECVERR in
ip(7) for details.
Argument is a pointer to boolean.
IPV6_ROUTER_ALERT-
Pass all forwarded packets containing an router
alert option to this socket. Only allowed for
datagram sockets and for root. Argument is a pointer
to boolean.
IPV6_UNICAST_HOPS-
Set the unicast hop limit for the socket. Argument
is an pointer to an integer. −1 in the value
means use the route default, otherwise it should be
between 0 and 255.
VERSIONS
The older libinet6 libc5 based IPv6 API
implementation for Linux is not described here and may vary
in details.
Linux 2.4 will break binary compatibility for the
sockaddr_in6 for 64bit hosts by changing the alignment of
in6_addr and adding
an additional sin6_scope_id field. The
kernel interfaces stay compatible, but a program including
sockaddr_in6 or in6_addr into other structures may not be.
This is not a problem for 32bit hosts like i386.
The sin6_flowinfo field is new in
Linux 2.4. It is transparently passed/read by the kernel when
the passed address length contains it. Some programs that
pass a longer address buffer and then check the outgoing
address length may break.
NOTES
The sockaddr_in6
structure is bigger than the generic sockaddr. Programs that
assume that all address types can be stored safely in a
struct sockaddr need
to be changed to use struct
sockaddr_storage for that instead.
BUGS
The IPv6 extended API as in RFC 2292 is currently only
partly implemented; although the 2.2 kernel has near complete
support for receiving options, the macros for generating IPv6
options are missing in glibc 2.1.
IPSec support for EH and AH headers is missing.
Flow label management is not complete and not documented
here.
This man page is not complete.
SEE ALSO
cmsg(3), ip(7)
RFC 2553: IPv6 BASIC API. Linux tries to be compliant to
this.
RFC 2460: IPv6 specification.
This man page is Copyright (C) 2000 Andi Kleen <ak@muc.de>.
Permission is granted to distribute possibly modified copies
of this page provided the header is included verbatim,
and in case of nontrivial modification author and date
of the modification is added to the header.
$Id: ipv6.7,v 1.3 2000/12/20 18:10:31 ak Exp $
|
