ipv6(7) - Linux manual page (original) (raw)
ipv6(7) Miscellaneous Information Manual ipv6(7)
NAME top
ipv6 - Linux IPv6 protocol implementationSYNOPSIS top
**#include <sys/socket.h>**
**#include <netinet/in.h>**
_tcp6socket_ **= socket(AF_INET6, SOCK_STREAM, 0);**
_raw6socket_ **= socket(AF_INET6, SOCK_RAW,** _protocol_**);**
_udp6socket_ **= socket(AF_INET6, SOCK_DGRAM,** _protocol_**);**DESCRIPTION top
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)](../man7/socket.7.html).
The IPv6 API aims to be mostly compatible with the IPv4 API (see
[ip(7)](../man7/ip.7.html)). 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 _in6addrany_ variable which has _in6addr_
type. In static initializations, **IN6ADDR_ANY_INIT** may also be
used, which expands to a constant expression. Both of them are in
network byte order.
The IPv6 loopback address (::1) is available in the global
_in6addrloopback_ 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 needs to support only
this API type to support both protocols. This is handled
transparently by the address handling functions in the C library.
IPv4 and IPv6 share the local port space. When you get an IPv4
connection or packet to an IPv6 socket, its source address will be
mapped to v6.Address format struct sockaddr_in6 { sa_family_t sin6_family; /* AF_INET6 / in_port_t sin6_port; / port number / uint32_t sin6_flowinfo; / IPv6 flow information / struct in6_addr sin6_addr; / IPv6 address / uint32_t sin6_scope_id; / Scope ID (new in Linux 2.4) */ };
struct in6_addr {
unsigned char s6_addr[16]; /* IPv6 address */
};
_sin6family_ is always set to **AF_INET6**; _sin6port_ is the protocol
port (see _sinport_ in [ip(7)](../man7/ip.7.html)); _sin6flowinfo_ is the IPv6 flow
identifier; _sin6addr_ is the 128-bit IPv6 address. _sin6scopeid_
is an ID depending on the scope of the address. It is new in
Linux 2.4. Linux supports it only for link-local addresses, in
that case _sin6scopeid_ contains the interface index (see
[netdevice(7)](../man7/netdevice.7.html))
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 an IPv4 host, and other reserved address
types.
The address notation for IPv6 is a group of 8 4-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 allowed only for IPv6 sockets that are
connected and bound to a v4-mapped-on-v6 address. The
argument is a pointer to an 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 ipv6mreq_.
**IPV6_MTU**
**getsockopt**(): Retrieve the current known path MTU of the
current socket. Valid only when the socket has been
connected. Returns an integer.
**setsockopt**(): 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)](../man7/ip.7.html) 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 allowed only for **SOCK_DGRAM** and **SOCK_RAW**
socket. The argument is a pointer to an interface index
(see [netdevice(7)](../man7/netdevice.7.html)) 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_RECVPKTINFO** (since Linux 2.6.14)
Set delivery of the **IPV6_PKTINFO** control message on
incoming datagrams. Such control messages contain a _struct_
_in6pktinfo_, as per RFC 3542. Allowed only for **SOCK_DGRAM**
or **SOCK_RAW** sockets. Argument is a pointer to a boolean
value in an integer.
**IPV6_RTHDR, IPV6_AUTHHDR, IPV6_DSTOPTS, 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)](../man2/sendmsg.2.html). Allowed only 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)](../man7/ip.7.html) for details. Argument is a pointer to
boolean.
**IPV6_ROUTER_ALERT**
Pass forwarded packets containing a router alert hop-by-hop
option to this socket. Allowed only for **SOCK_RAW** sockets.
The tapped packets are not forwarded by the kernel, it is
the user's responsibility to send them out again. Argument
is a pointer to an integer. A positive integer indicates a
router alert option value to intercept. Packets carrying a
router alert option with a value field containing this
integer will be delivered to the socket. A negative
integer disables delivery of packets with router alert
options to this socket.
**IPV6_UNICAST_HOPS**
Set the unicast 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_V6ONLY** (since Linux 2.4.21 and 2.6)
If this flag is set to true (nonzero), then the socket is
restricted to sending and receiving IPv6 packets only. In
this case, an IPv4 and an IPv6 application can bind to a
single port at the same time.
If this flag is set to false (zero), then the socket can be
used to send and receive packets to and from an IPv6
address or an IPv4-mapped IPv6 address.
The argument is a pointer to a boolean value in an integer.
The default value for this flag is defined by the contents
of the file _/proc/sys/net/ipv6/bindv6only_. The default
value for that file is 0 (false).ERRORS top
**ENODEV** The user tried to [bind(2)](../man2/bind.2.html) to a link-local IPv6 address, but
the _sin6scopeid_ in the supplied _sockaddrin6_ structure is
not a valid interface index.VERSIONS top
Linux 2.4 will break binary compatibility for the _sockaddrin6_ for
64-bit hosts by changing the alignment of _in6addr_ and adding an
additional _sin6scopeid_ field. The kernel interfaces stay
compatible, but a program including _sockaddrin6_ or _in6addr_ into
other structures may not be. This is not a problem for 32-bit
hosts like i386.
The _sin6flowinfo_ 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 top
The _sockaddrin6_ 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_
_sockaddrstorage_ for that instead.
**SOL_IP**, **SOL_IPV6**, **SOL_ICMPV6**, and other **SOL_*** socket options are
nonportable variants of **IPPROTO_***. See also [ip(7)](../man7/ip.7.html).BUGS top
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 top
[cmsg(3)](../man3/cmsg.3.html), [ip(7)](../man7/ip.7.html)
RFC 2553: IPv6 BASIC API; Linux tries to be compliant to this.
RFC 2460: IPv6 specification.COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-05-02 ipv6(7)
Pages that refer to this page:bind(2), recv(2), send(2), socket(2), sd_is_fifo(3), sockaddr(3type), nfs(5), systemd.socket(5), address_families(7), ip(7), socket(7), udplite(7)