NAME¶

SYNOPSIS¶

DESCRIPTION¶

Header¶

struct ip6_hdr { 
     union { 
          struct ip6_hdrctl { 
               uint32_t ip6_un1_flow;	/* 20 bits of flow ID */ 
               uint16_t ip6_un1_plen;	/* payload length */ 
               uint8_t  ip6_un1_nxt;	/* next header */ 
               uint8_t  ip6_un1_hlim;	/* hop limit */ 
          } ip6_un1; 
          uint8_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

struct ip6_ext { 
     uint8_t ip6e_nxt; 
     uint8_t ip6e_len; 
} __packed;

Options¶

IPV6_UNICAST_HOPS int *

Get or set the default hop limit header field for outgoing unicast datagrams sent on this socket.

IPV6_MULTICAST_IF u_int *

Get or set the interface from which multicast packets will be sent. For hosts with multiple interfaces, each multicast transmission is sent from the primary network interface. The interface 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 multicast 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 multicast 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) (ports/net/mrouted)) 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 daemon) by eliminating the overhead of receiving their own transmissions. 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 destination 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 multicast 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 multicast interface or to the index of a particular multicast-capable interface if the host is multihomed. Membership is associated 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), messages from all multicast addresses will be accepted by this group. Note that setting to this value requires superuser privileges.

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 ip(4)).

IPV6_PORTRANGE_HIGH

Use a high range (varies, see ip(4)).

IPV6_PORTRANGE_LOW

Use a low, reserved range (600-1023, see ip(4)).

IPV6_PKTINFO int *

Get or set whether additional information about subsequent packets 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 subsequent recvmsg(2) calls. The option is stored in the following structure in the ancillary data returned:

struct ip6_hbh { 
	uint8_t ip6h_nxt;	/* next header */ 
	uint8_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 packets will be provided as ancillary data along with the payload in subsequent recvmsg(2) calls. The option is stored in the following structure in the ancillary data returned:

struct ip6_dest { 
	uint8_t ip6d_nxt;	/* next header */ 
	uint8_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_TCLASS int *

Get or set the value of the traffic class field used for outgoing datagrams on this socket. The value must be between -1 and 255. A value of -1 resets to the default value.

IPV6_RECVTCLASS int *

Get or set the status of whether the traffic class header field will be provided as ancillary data along with the payload in subsequent recvmsg(2) calls. The header field is stored as a single value of type int.

IPV6_RTHDR int *

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

struct ip6_rthdr { 
	uint8_t ip6r_nxt;	/* next header */ 
	uint8_t ip6r_len;	/* length in units of 8 octets */ 
	uint8_t ip6r_type;	/* routing type */ 
	uint8_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 corresponding 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 ancillary 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 checksum 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 computed and stored by the kernel. A value of -1 specifies that no checksums will be checked on incoming packets and that no checksums 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.

Multicasting¶

Raw Sockets¶

EXAMPLES¶

struct iovec iov[2]; 
u_char buf[BUFSIZ]; 
struct cmsghdr *cm; 
struct msghdr m; 
int optval; 
bool found; 
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 = false; 
do { 
	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 = true; 
			(void)printf("hop limit: %d\n", 
			    *(int *)CMSG_DATA(cm)); 
			break; 
		} 
	} 
} while (!found);

DIAGNOSTICS¶

[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 connected.

[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 network address for which no network interface exists.

[EACCES]

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

[EINVAL]

An unknown socket option name was given.

[EINVAL]

An ancillary data object was improperly formed.

SEE ALSO¶

STANDARDS¶