NAME
ipv6 - Linux IPv6 protocol implementation SYNOPSIS
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tcp6socket = socket(AFINET6, SOCKSTREAM, 0); raw6socket = socket(AFINET6, SOCKRAW, protocol); udp6socket = socket(AFINET6, SOCKDGRAM, protocol); 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 IPv4 API (see ip(7)). Only differences are described in this man page. To bind an AFINET6 socket to any process, the local address should be copied from the in6addrany variable which has in6addr type. In static initializations, IN6ADDRANYINIT 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, IN6ADDRLOOPBACKINIT 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 to support 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 connec‐ tion or packet to a IPv6 socket, its source address will be mapped to v6 and it will be mapped to v6. Address format struct sockaddrin6 { safamilyt sin6family; /* AFINET6 */ inportt sin6port; /* port number */ uint32t sin6flowinfo; /* IPv6 flow information */ struct in6addr sin6addr; /* IPv6 address */ uint32t sin6scopeid; /* Scope ID (new in 2.4) */ }; struct in6addr { unsigned char s6addr[16]; /* IPv6 address */ }; sin6family is always set to AFINET6; sin6port is the protocol port (see sinport in ip(7)); sin6flowinfo is the IPv6 flow identifier;
sin6addr is the 128-bit IPv6 address. sin6scopeid is an ID depend‐ ing on the scope of the address. It is new in Linux 2.4. Linux sup‐
ports it only for link-local addresses, in that case sin6scopeid con‐ tains 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 8 4-digit hexadecimal num‐ bers, separated with a ':'. "::" stands for a string of 0 bits. Spe‐ cial addresses are ::1 for loopback and ::FFFF:
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 IPPROTOIPV6. A boolean integer flag is zero when it is false, otherwise true. IPV6ADDRFORM Turn an AFINET6 socket into a socket of a different address family. Only AFINET 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 inte‐
ger containing AFINET. This is useful to pass v4-mapped sock‐ ets as file descriptors to programs that don't know how to deal with the IPv6 API. IPV6ADDMEMBERSHIP, IPV6DROPMEMBERSHIP Control membership in multicast groups. Argument is a pointer to a struct ipv6mreq. IPV6MTU getsockopt(): Retrieve the current known path MTU of the current socket. Only valid 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 discov‐ ery is enabled. Argument is a pointer to integer. IPV6MTUDISCOVER
Control path-MTU discovery on the socket. See IPMTUDISCOVER in ip(7) for details. IPV6MULTICASTHOPS 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. IPV6MULTICASTIF Set the device for outgoing multicast packets on the socket. This is allowed only for SOCKDGRAM and SOCKRAW socket. The argument is a pointer to an interface index (see netdevice(7)) in an integer. IPV6MULTICASTLOOP Control whether the socket sees multicast packets that it has send itself. Argument is a pointer to boolean. IPV6RECVPKTINFO (since Linux 2.6.14) Set delivery of the IPV6PKTINFO control message on incoming datagrams. Such control messages contain a struct in6pktinfo, as per RFC 3542. Only allowed for SOCKDGRAM or SOCKRAW sock‐ ets. Argument is a pointer to a boolean value in an integer. IPV6RTHDR, IPV6AUTHHDR, IPV6DSTOPTS, IPV6HOPOPTS, IPV6FLOWINFO, IPV6HOPLIMIT Set delivery of control messages for incoming datagrams contain‐ ing extension headers from the received packet. IPV6RTHDR de‐ livers the routing header, IPV6AUTHHDR delivers the authentica‐ tion header, IPV6DSTOPTS delivers the destination options, IPV6HOPOPTS delivers the hop options, IPV6FLOWINFO delivers an integer containing the flow ID, IPV6HOPLIMIT delivers an inte‐ ger containing the hop count of the packet. The control mes‐ sages have the same type as the socket option. All these header options can also be set for outgoing packets by putting the ap‐ propriate control message into the control buffer of sendmsg(2). Only allowed for SOCKDGRAM or SOCKRAW sockets. Argument is a pointer to a boolean value. IPV6RECVERR Control receiving of asynchronous error options. See IPRECVERR in ip(7) for details. Argument is a pointer to boolean. IPV6ROUTERALERT
Pass forwarded packets containing a router alert hop-by-hop op‐ tion to this socket. Only allowed for SOCKRAW 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. IPV6UNICASTHOPS 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. IPV6V6ONLY (since Linux 2.4.21 and 2.6) If this flag is set to true (nonzero), then the socket is re‐ stricted 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
ENODEV The user tried to bind(2) to a link-local IPv6 address, but the sin6scopeid in the supplied sockaddrin6 structure is not a valid interface index. 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 sockaddrin6 for
64-bit hosts by changing the alignment of in6addr and adding an addi‐ tional 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 out‐ going address length may break. NOTES The sockaddrin6 structure is bigger than the generic sockaddr. Pro‐ grams 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. BUGS The IPv6 extended API as in RFC 2292 is currently only partly imple‐ mented; 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. COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2012-12-16 IPV6(7)