# ipv6

## NAME



           ipv6 - Linux IPv6 protocol implementation
    


## SYNOPSIS



           **#include <sys/socket.h>**
           **#include <netinet/in.h>**
    
           _tcp6_socket_ **= socket(AF_INET6, SOCK_STREAM, 0);**
           _raw6_socket_ **= socket(AF_INET6, SOCK_RAW,**_protocol_**);**
           _udp6_socket_ **= socket(AF_INET6, SOCK_DGRAM,**_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 **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 byte 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 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 */
               };
    
           _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 128-bit IPv6 address.  _sin6_scope_id_
           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 _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 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 ipv6_mreq_.
    
           **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) 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)) 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_
                  _in6_pktinfo_ , 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).  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) 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



           **ENODEV** The user tried to bind(2) to a link-local IPv6 address, but
                  the _sin6_scope_id_ in the supplied _sockaddr_in6_ structure is
                  not a valid interface index.
    


## VERSIONS



           Linux 2.4 will break binary compatibility for the _sockaddr_in6_ for
           64-bit 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 32-bit
           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.
    
           **SOL_IP** , **SOL_IPV6** , **SOL_ICMPV6** , and other **SOL_*** socket options are
           nonportable variants of **IPPROTO_***.  See also ip(7).
    


## 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.
    


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