path: root/man7/ipv6.7

.\" 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 $
.TH IPV6 7 1999-06-29 "Linux Man Page" "Linux Programmer's Manual"
.SH NAME
ipv6, PF_INET6 \- Linux IPv6 protocol implementation
.SH SYNOPSIS
.B #include <sys/socket.h>
.br
.B #include <netinet/in.h> 
.sp
.sp
.IB tcp6_socket " = socket(PF_INET6, SOCK_STREAM, 0);"
.br 
.IB raw6_socket " = socket(PF_INET6, SOCK_RAW, " protocol ");"
.br
.IB udp6_socket " = socket(PF_INET6, SOCK_DGRAM, " protocol ");"
.SH 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
.BR socket (7). 
.PP
The IPv6 API aims to be mostly compatible with the 
.BR ip (7) 
v4 API. Only differences are described in this man page. 
.PP
To bind an 
.I AF_INET6
socket to any process the local address should be copied from the 
.B in6addr_any
variable which has 
.I in6_addr 
type.
In static initializations 
.B IN6ADDR_ANY_INIT
may also be used, which expands to a constant expression.
Both of them are in network order.
.PP
The IPv6 loopback address (::1) is available in the global
.B in6addr_loopback
variable. For initializations
.B IN6ADDR_LOOPBACK_INIT
should be used.
.PP
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. 
.PP
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.
.SH "ADDRESS FORMAT"
.sp
.RS
.nf
.ta 4n 5n 20n
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 */
};
.ta
.fi
.RE
.sp
.B sin6_family 
is always set to 
.B AF_INET6; 
.B sin6_port 
is the protocol port (see
.B sin_port
in 
.BR ip (7));
.B sin6_flowinfo
is the IPv6 flow identifier;
.B sin6_addr
is the 128bit IPv6 address.
.B 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
.I sin6_scope_id
contains the interface index (see
.BR netdevice (7))
.PP
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.
.PP
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.
.PP
The port space of IPv6 is shared with IPv4.
.SH "SOCKET OPTIONS"
IPv6 supports some protocol specific socket options that can be set with
.BR setsockopt (2)
and read with
.BR getsockopt (2).
The socket option level for IPv6 is 
.BR IPPROTO_IPV6 .
A boolean integer flag is zero when it is false, otherwise true.
.TP
.B 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.
.TP
.B 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.
.TP 
.B IPV6_MULTICAST_IF
Set the device for outgoing multicast packets on the socket.
This is only allowed
for 
.I SOCK_DGRAM
and 
.I SOCK_RAW
socket.
The argument is an pointer to an interface index (see
.BR netdevice (7))
in an integer.
.TP
.B IPV6_ADDRFORM
Turn an 
.I AF_INET6
socket into a socket of a different address family. Only 
.I 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 
.B AF_INET. 
This is useful to pass v4-mapped sockets as filedescriptors to programs that 
don't know how to deal with the IPv6 API.
.TP 
.B IPV6_PKTINFO
Set delivery of the 
.B IPV6_PKTINFO 
control message on incoming datagrams. Only allowed for
.B SOCK_DGRAM
or
.B SOCK_RAW
sockets. Argument is a pointer to a boolean value in an integer.
.TP
.nh
.B IPV6_RTHDR, IPV6_AUTHHDR, IPV6_DSTOPS, IPV6_HOPOPTS, IPV6_FLOWINFO, IPV6_HOPLIMIT
.hy
Set delivery of control messages for incoming datagrams containing extension
headers from the received packet. 
.I IPV6_RTHDR
delivers the routing header,
.I IPV6_AUTHHDR
delivers the authentication header,
.I IPV6_DSTOPTS
delivers the destination options,
.I IPV6_HOPOPTS
delivers the hop options, 
.I IPV6_FLOWINFO
delivers an integer containing the flow id,
.I 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 
.BR sendmsg (2).
Only allowed for
.B SOCK_DGRAM
or
.B SOCK_RAW
sockets. Argument is a pointer to a boolean value.
.TP
.B IPV6_MULTICAST_LOOP
Control whether the socket sees multicast packets that is has send itself.
Argument is a pointer to boolean.
.TP
.B IPV6_ADD_MEMBERSHIP, IPV6_DROP_MEMBERSHIP
Control membership in multicast groups. Argument is a pointer to a 
.B struct ipv6_mreq
structure.
.TP
.B 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.
.TP
.B IPV6_MTU_DISCOVER
Control path mtu discovery on the socket. See 
.I IP_MTU_DISCOVER
in 
.BR ip (7)
for details.
.TP
.B IPV6_RECVERR
Control receiving of asynchronous error options. See 
.I IP_RECVERR
in
.BR ip (7)
for details.
Argument is a pointer to boolean.
.TP
.B 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.
.\" FLOWLABEL_MGR, FLOWINFO_SEND
.SH VERSIONS
The older 
.I libinet6
libc5 based IPv6 API implementation for Linux is not described here
and may vary in details. 
.PP
Linux 2.4 will break binary compatibility for the sockaddr_in6 for 64bit 
hosts by changing the alignment of
.I in6_addr 
and adding an additional 
.I 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.
.PP
The
.B 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.
.SH "PORTING NOTES"
The
.B sockaddr_in6
structure is bigger than the generic
.B sockaddr. 
Programs that assume that all address types can be stored safely in a 
.B struct sockaddr
need to be changed to use 
.B struct sockaddr_storage
for that instead.
.SH BUGS
The IPv6 extended API as in RFC2292 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. 
.PP
IPSec support for EH and AH headers is missing.
.PP
Flow label management is not complete and not documented here.
.PP
This man page is not complete.
.SH "SEE ALSO"
.BR cmsg (3),
.BR ip (7)
.PP
RFC2553: IPv6 BASIC API. Linux tries to be compliant to this.
.PP
RFC2460: IPv6 specification.