Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
IP6(4)		       FreeBSD Kernel Interfaces Manual			IP6(4)

NAME
     ip6 -- Internet Protocol version 6	(IPv6) network layer

SYNOPSIS
     #include <sys/socket.h>
     #include <netinet/in.h>

     int
     socket(AF_INET6, SOCK_RAW,	proto);

DESCRIPTION
     The IPv6 network layer is used by the IPv6	protocol family	for transport-
     ing data.	IPv6 packets contain an	IPv6 header that is not	provided as
     part of the payload contents when passed to an application.  IPv6 header
     options affect the	behavior of this protocol and may be used by high-
     level protocols (such as the tcp(4) and udp(4) protocols) as well as
     directly by ``raw sockets'', which	process	IPv6 messages at a lower-level
     and may be	useful for developing new protocols and	special-purpose	appli-
     cations.

   Header
     All IPv6 packets begin with an IPv6 header.  When data received by	the
     kernel are	passed to the application, this	header is not included in
     buffer, even when raw sockets are being used.  Likewise, when data	are
     sent to the kernel	for transmit from the application, the buffer is not
     examined for an IPv6 header: the kernel always constructs the header.  To
     directly access IPv6 headers from received	packets	and specify them as
     part of the buffer	passed to the kernel, link-level access	(bpf(4), for
     example) must instead be utilized.

     The header	has the	following definition:

	   struct ip6_hdr {
		union {
		     struct ip6_hdrctl {
			  u_int32_t ip6_un1_flow;  /* 20 bits of flow ID */
			  u_int16_t ip6_un1_plen;  /* payload length */
			  u_int8_t  ip6_un1_nxt;   /* next header */
			  u_int8_t  ip6_un1_hlim;  /* hop limit	*/
		     } ip6_un1;
		     u_int8_t ip6_un2_vfc;   /*	version	and class */
		} ip6_ctlun;
		struct in6_addr	ip6_src;   /* source address */
		struct in6_addr	ip6_dst;   /* destination address */
	   } __packed;

	   #define ip6_vfc	   ip6_ctlun.ip6_un2_vfc
	   #define ip6_flow	   ip6_ctlun.ip6_un1.ip6_un1_flow
	   #define ip6_plen	   ip6_ctlun.ip6_un1.ip6_un1_plen
	   #define ip6_nxt	   ip6_ctlun.ip6_un1.ip6_un1_nxt
	   #define ip6_hlim	   ip6_ctlun.ip6_un1.ip6_un1_hlim
	   #define ip6_hops	   ip6_ctlun.ip6_un1.ip6_un1_hlim

     All fields	are in network-byte order.  Any	options	specified (see Options
     below) must also be specified in network-byte order.

     ip6_flow specifies	the flow ID.  ip6_plen specifies the payload length.
     ip6_nxt specifies the type	of the next header.  ip6_hlim specifies	the
     hop limit.

     The top 4 bits of ip6_vfc specify the class and the bottom	4 bits specify
     the version.

     ip6_src and ip6_dst specify the source and	destination addresses.

     The IPv6 header may be followed by	any number of extension	headers	that
     start with	the following generic definition:

	   struct ip6_ext {
		u_int8_t ip6e_nxt;
		u_int8_t ip6e_len;
	   } __packed;

   Options
     IPv6 allows header	options	on packets to manipulate the behavior of the
     protocol.	These options and other	control	requests are accessed with the
     getsockopt(2) and setsockopt(2) system calls at level IPPROTO_IPV6	and by
     using ancillary data in recvmsg(2)	and sendmsg(2).	 They can be used to
     access most of the	fields in the IPv6 header and extension	headers.

     The following socket options are supported:

     IPV6_UNICAST_HOPS int *
	     Get or set	the default hop	limit header field for outgoing	uni-
	     cast datagrams sent on this socket.  A value of -1	resets to the
	     default value.

     IPV6_MULTICAST_IF u_int *
	     Get or set	the interface from which multicast packets will	be
	     sent.  For	hosts with multiple interfaces,	each multicast trans-
	     mission is	sent from the primary network interface.  The inter-
	     face is specified as its index as provided	by if_nametoindex(3).
	     A value of	zero specifies the default interface.

     IPV6_MULTICAST_HOPS int *
	     Get or set	the default hop	limit header field for outgoing	multi-
	     cast datagrams sent on this socket.  This option controls the
	     scope of multicast	datagram transmissions.

	     Datagrams with a hop limit	of 1 are not forwarded beyond the
	     local network.  Multicast datagrams with a	hop limit of zero will
	     not be transmitted	on any network but may be delivered locally if
	     the sending host belongs to the destination group and if multi-
	     cast loopback (see	below) has not been disabled on	the sending
	     socket.  Multicast	datagrams with a hop limit greater than	1 may
	     be	forwarded to the other networks	if a multicast router (such as
	     mrouted(8)) is attached to	the local network.

     IPV6_MULTICAST_LOOP u_int *
	     Get or set	the status of whether multicast	datagrams will be
	     looped back for local delivery when a multicast datagram is sent
	     to	a group	to which the sending host belongs.

	     This option improves performance for applications that may	have
	     no	more than one instance on a single host	(such as a router dae-
	     mon) by eliminating the overhead of receiving their own transmis-
	     sions.  It	should generally not be	used by	applications for which
	     there may be more than one	instance on a single host (such	as a
	     conferencing program) or for which	the sender does	not belong to
	     the destination group (such as a time-querying program).

	     A multicast datagram sent with an initial hop limit greater than
	     1 may be delivered	to the sending host on a different interface
	     from that on which	it was sent if the host	belongs	to the desti-
	     nation group on that other	interface.  The	multicast loopback
	     control option has	no effect on such delivery.

     IPV6_JOIN_GROUP struct ipv6_mreq *
	     Join a multicast group.  A	host must become a member of a multi-
	     cast group	before it can receive datagrams	sent to	the group.

	     struct ipv6_mreq {
		     struct in6_addr ipv6mr_multiaddr;
		     unsigned int    ipv6mr_interface;
	     };

	     ipv6mr_interface may be set to zeroes to choose the default mul-
	     ticast interface or to the	index of a particular multicast-capa-
	     ble interface if the host is multihomed.  Membership is associ-
	     ated with a single	interface; programs running on multihomed
	     hosts may need to join the	same group on more than	one interface.

	     If	the multicast address is unspecified (i.e., all	zeroes), mes-
	     sages from	all multicast addresses	will be	accepted by this
	     group.  Note that setting to this value requires superuser	privi-
	     leges.

     IPV6_LEAVE_GROUP struct ipv6_mreq *
	     Drop membership from the associated multicast group.  Memberships
	     are automatically dropped when the	socket is closed or when the
	     process exits.

     IPV6_PORTRANGE int	*
	     Get or set	the allocation policy of ephemeral ports for when the
	     kernel automatically binds	a local	address	to this	socket.	 The
	     following values are available:

	     IPV6_PORTRANGE_DEFAULT  Use the regular range of non-reserved
				     ports (varies, see	sysctl(8)).
	     IPV6_PORTRANGE_HIGH     Use a high	range (varies, see sysctl(8)).
	     IPV6_PORTRANGE_LOW	     Use a low,	reserved range (600-1023).

     IPV6_PKTINFO int *
	     Get or set	whether	additional information about subsequent	pack-
	     ets will be provided as ancillary data along with the payload in
	     subsequent	recvmsg(2) calls.  The information is stored in	the
	     following structure in the	ancillary data returned:

	     struct in6_pktinfo	{
		     struct in6_addr ipi6_addr;	   /* src/dst IPv6 address */
		     unsigned int    ipi6_ifindex; /* send/recv	if index */
	     };

     IPV6_HOPLIMIT int *
	     Get or set	whether	the hop	limit header field from	subsequent
	     packets will be provided as ancillary data	along with the payload
	     in	subsequent recvmsg(2) calls.  The value	is stored as an	int in
	     the ancillary data	returned.

     IPV6_HOPOPTS int *
	     Get or set	whether	the hop-by-hop options from subsequent packets
	     will be provided as ancillary data	along with the payload in sub-
	     sequent recvmsg(2)	calls.	The option is stored in	the following
	     structure in the ancillary	data returned:

	     struct ip6_hbh {
		     u_int8_t ip6h_nxt;	     /*	next header */
		     u_int8_t ip6h_len;	     /*	length in units	of 8 octets */
	     /*	followed by options */
	     } __packed;

	     The inet6_option_space() routine and family of routines may be
	     used to manipulate	this data.

	     This option requires superuser privileges.

     IPV6_DSTOPTS int *
	     Get or set	whether	the destination	options	from subsequent	pack-
	     ets will be provided as ancillary data along with the payload in
	     subsequent	recvmsg(2) calls.  The option is stored	in the follow-
	     ing structure in the ancillary data returned:

	     struct ip6_dest {
		     u_int8_t ip6d_nxt;	     /*	next header */
		     u_int8_t ip6d_len;	     /*	length in units	of 8 octets */
	     /*	followed by options */
	     } __packed;

	     The inet6_option_space() routine and family of routines may be
	     used to manipulate	this data.

	     This option requires superuser privileges.

     IPV6_RTHDR	int *
	     Get or set	whether	the routing header from	subsequent packets
	     will be provided as ancillary data	along with the payload in sub-
	     sequent recvmsg(2)	calls.	The header is stored in	the following
	     structure in the ancillary	data returned:

	     struct ip6_rthdr {
		     u_int8_t ip6r_nxt;	     /*	next header */
		     u_int8_t ip6r_len;	     /*	length in units	of 8 octets */
		     u_int8_t ip6r_type;     /*	routing	type */
		     u_int8_t ip6r_segleft;  /*	segments left */
	     /*	followed by routing-type-specific data */
	     } __packed;

	     The inet6_option_space() routine and family of routines may be
	     used to manipulate	this data.

	     This option requires superuser privileges.

     IPV6_PKTOPTIONS struct cmsghdr *
	     Get or set	all header options and extension headers at one	time
	     on	the last packet	sent or	received on the	socket.	 All options
	     must fit within the size of an mbuf (see mbuf(9)).	 Options are
	     specified as a series of cmsghdr structures followed by corre-
	     sponding values.  cmsg_level is set to IPPROTO_IPV6, cmsg_type to
	     one of the	other values in	this list, and trailing	data to	the
	     option value.  When setting options, if the length	optlen to
	     setsockopt(2) is zero, all	header options will be reset to	their
	     default values.  Otherwise, the length should specify the size
	     the series	of control messages consumes.

	     Instead of	using sendmsg(2) to specify option values, the ancil-
	     lary data used in these calls that	correspond to the desired
	     header options may	be directly specified as the control message
	     in	the series of control messages provided	as the argument	to
	     setsockopt(2).

     IPV6_CHECKSUM int *
	     Get or set	the byte offset	into a packet where the	16-bit check-
	     sum is located.  When set,	this byte offset is where incoming
	     packets will be expected to have checksums	of their data stored
	     and where outgoing	packets	will have checksums of their data com-
	     puted and stored by the kernel.  A	value of -1 specifies that no
	     checksums will be checked on incoming packets and that no check-
	     sums will be computed or stored on	outgoing packets.  The offset
	     of	the checksum for ICMPv6	sockets	cannot be relocated or turned
	     off.

     IPV6_V6ONLY int *
	     Get or set	whether	only IPv6 connections can be made to this
	     socket.  For wildcard sockets, this can restrict connections to
	     IPv6 only.

     IPV6_FAITH	int *
	     Get or set	the status of whether faith(4) connections can be made
	     to	this socket.

     IPV6_USE_MIN_MTU int *
	     Get or set	whether	the minimal IPv6 maximum transmission unit
	     (MTU) size	will be	used to	avoid fragmentation from occurring for
	     subsequent	outgoing datagrams.

     IPV6_AUTH_LEVEL int *
	     Get or set	the ipsec(4) authentication level.

     IPV6_ESP_TRANS_LEVEL int *
	     Get or set	the ESP	transport level.

     IPV6_ESP_NETWORK_LEVEL int	*
	     Get or set	the ESP	encapsulation level.

     IPV6_IPCOMP_LEVEL int *
	     Get or set	the ipcomp(4) level.

     The IPV6_PKTINFO, IPV6_HOPLIMIT, IPV6_HOPOPTS, IPV6_DSTOPTS, and
     IPV6_RTHDR	options	will return ancillary data along with payload contents
     in	subsequent recvmsg(2) calls with cmsg_level set	to IPPROTO_IPV6	and
     cmsg_type set to respective option	name value (e.g., IPV6_HOPTLIMIT).
     These options may also be used directly as	ancillary cmsg_type values in
     sendmsg(2)	to set options on the packet being transmitted by the call.
     The cmsg_level value must be IPPROTO_IPV6.	 For these options, the	ancil-
     lary data object value format is the same as the value returned as
     explained for each	when received with recvmsg(2).

     Note that using sendmsg(2)	to specify options on particular packets works
     only on UDP and raw sockets.  To manipulate header	options	for packets on
     TCP sockets, only the socket options may be used.

     In	some cases, there are multiple APIs defined for	manipulating an	IPv6
     header field.  A good example is the outgoing interface for multicast
     datagrams,	which can be set by the	IPV6_MULTICAST_IF socket option,
     through the IPV6_PKTINFO option, and through the sin6_scope_id field of
     the socket	address	passed to the sendto(2)	system call.

     Resolving these conflicts is implementation dependent.  This implementa-
     tion determines the value in the following	way: options specified by
     using ancillary data (i.e., sendmsg(2)) are considered first, options
     specified by using	IPV6_PKTOPTIONS	to set ``sticky'' options are consid-
     ered second, options specified by using the individual, basic, and	direct
     socket options (e.g., IPV6_UNICAST_HOPS) are considered third, and
     options specified in the socket address supplied to sendto(2) are the
     last choice.

   Multicasting
     IPv6 multicasting is supported only on AF_INET6 sockets of	type
     SOCK_DGRAM	and SOCK_RAW, and only on networks where the interface driver
     supports multicasting.  Socket options (see above)	that manipulate	mem-
     bership of	multicast groups and other multicast options include
     IPV6_MULTICAST_IF,	IPV6_MULTICAST_HOPS, IPV6_MULTICAST_LOOP,
     IPV6_LEAVE_GROUP, and IPV6_JOIN_GROUP.

   Raw Sockets
     Raw IPv6 sockets are connectionless and are normally used with the
     sendto(2) and recvfrom(2) calls, although the connect(2) call may be used
     to	fix the	destination address for	future outgoing	packets	so that
     send(2) may instead be used and the bind(2) call may be used to fix the
     source address for	future outgoing	packets	instead	of having the kernel
     choose a source address.

     By	using connect(2) or bind(2), raw socket	input is constrained to	only
     packets with their	source address matching	the socket destination address
     if	connect(2) was used and	to packets with	their destination address
     matching the socket source	address	if bind(2) was used.

     If	the proto argument to socket(2)	is zero, the default protocol
     (IPPROTO_RAW) is used for outgoing	packets.  For incoming packets,	proto-
     cols recognized by	kernel are not passed to the application socket	(e.g.,
     tcp(4) and	udp(4))	except for some	ICMPv6 messages.  The ICMPv6 messages
     not passed	to raw sockets include echo, timestamp,	and address mask
     requests.	If proto is non-zero, only packets with	this protocol will be
     passed to the socket.

     IPv6 fragments are	also not passed	to application sockets until they have
     been reassembled.	If reception of	all packets is desired,	link-level
     access (such as bpf(4)) must be used instead.

     Outgoing packets automatically have an IPv6 header	prepended to them
     (based on the destination address and the protocol	number the socket was
     created with).  Incoming packets are received by an application without
     the IPv6 header or	any extension headers.

     Outgoing packets will be fragmented automatically by the kernel if	they
     are too large.  Incoming packets will be reassembled before being sent to
     the raw socket, so	packet fragments or fragment headers will never	be
     seen on a raw socket.

EXAMPLES
     The following determines the hop limit on the next	packet received:

     struct iovec iov[2];
     u_char buf[BUFSIZ];
     struct cmsghdr *cm;
     struct msghdr m;
     int found,	optval;
     u_char data[2048];

     /*	Create socket. */

     (void)memset(&m, 0, sizeof(m));
     (void)memset(&iov,	0, sizeof(iov));

     iov[0].iov_base = data;	     /*	buffer for packet payload */
     iov[0].iov_len = sizeof(data);  /*	expected packet	length */

     m.msg_name	= &from;	     /*	sockaddr_in6 of	peer */
     m.msg_namelen = sizeof(from);
     m.msg_iov = iov;
     m.msg_iovlen = 1;
     m.msg_control = (caddr_t)buf;   /*	buffer for control messages */
     m.msg_controllen =	sizeof(buf);

     /*
      *	Enable the hop limit value from	received packets to be
      *	returned along with the	payload.
      */
     optval = 1;
     if	(setsockopt(s, IPPROTO_IPV6, IPV6_HOPLIMIT, &optval,
	 sizeof(optval)) == -1)
	     err(1, "setsockopt");

     found = 0;
     while (!found) {
	     if	(recvmsg(s, &m,	0) == -1)
		     err(1, "recvmsg");
	     for (cm = CMSG_FIRSTHDR(&m); cm !=	NULL;
		  cm = CMSG_NXTHDR(&m, cm)) {
		     if	(cm->cmsg_level	== IPPROTO_IPV6	&&
			 cm->cmsg_type == IPV6_HOPLIMIT	&&
			 cm->cmsg_len == CMSG_LEN(sizeof(int)))	{
			     found = 1;
			     (void)printf("hop limit: %d\n",
				 *(int *)CMSG_DATA(cm));
			     break;
		     }
	     }
     }

DIAGNOSTICS
     A socket operation	may fail with one of the following errors returned:

     [EISCONN]	      when trying to establish a connection on a socket	which
		      already has one or when trying to	send a datagram	with
		      the destination address specified	and the	socket is
		      already connected.

     [ENOTCONN]	      when trying to send a datagram, but no destination
		      address is specified, and	the socket has not been	con-
		      nected.

     [ENOBUFS]	      when the system runs out of memory for an	internal data
		      structure.

     [EADDRNOTAVAIL]  when an attempt is made to create	a socket with a	net-
		      work address for which no	network	interface exists.

     [EACCES]	      when an attempt is made to create	a raw IPv6 socket by a
		      non-privileged process.

     The following errors specific to IPv6 may occur when setting or getting
     header options:

     [EINVAL]	      An unknown socket	option name was	given.

     [EINVAL]	      An ancillary data	object was improperly formed.

SEE ALSO
     getsockopt(2), recv(2), send(2), setsockopt(2), socket(2),
     if_nametoindex(3),	bpf(4),	icmp6(4), inet6(4), netintro(4), tcp(4),
     udp(4)

     W.	Stevens	and M. Thomas, Advanced	Sockets	API for	IPv6, RFC 2292,
     February 1998.

     S.	Deering	and R. Hinden, Internet	Protocol, Version 6 (IPv6)
     Specification, RFC	2460, December 1998.

     R.	Gilligan, S. Thomson, J. Bound,	and W. Stevens,	Basic Socket Interface
     Extensions	for IPv6, RFC 2553, March 1999.

     W.	Stevens, B. Fenner, and	A. Rudoff, UNIX	Network	Programming, third
     edition.

STANDARDS
     Most of the socket	options	are defined in RFC 2292	or RFC 2553.  The
     IPV6_V6ONLY socket	option is defined in RFC 3542.	The IPV6_PORTRANGE
     socket option and the conflict resolution rule are	not defined in the
     RFCs and should be	considered implementation dependent.

FreeBSD	10.1		       December	29, 2004		  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | DIAGNOSTICS | SEE ALSO | STANDARDS

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=ip6&sektion=4&manpath=FreeBSD+5.4-RELEASE>

home | help