AF_INET6 address family

This address family provides support for the Internet Protocol version 6 (IPv6). AF_INET6 address family uses a 128 bit (16 byte) address.

The basic architecture of these addresses includes 64 bits for a network number and another 64 bits for the host number. You can specify AF_INET6 addresses as x:x:x:x:x:x:x:x, where the x's are the hexadecimal values of eight 16–bit pieces of the address. For example, a valid address looks like this: FEDC:BA98:7654:3210:FEDC:BA98:7654:3210.

For a socket application that uses TCP, User Datagram Protocol (UDP) or RAW, the AF_INET6 address family uses the sockaddr_in6 address structure. This address structure changes if you use _XOPEN_SOURCE macro to implement BSD 4.4/ UNIX^® 98 specifications. For the sockaddr_in6 address structure, these differences are summarized in this table:

Table 1. Differences between BSD 4.3 and BSD 4.4/ UNIX 98 for sockaddr_in6 address structure
BSD 4.3 sockaddr_in6 address structure	BSD 4.4/ UNIX 98 sockaddr_in6 address structure
struct sockaddr_in6 { sa_family_t sin6_family; in_port_t sin6_port; uint32_t sin6_flowinfo; struct in6_addr sin6_addr; uint32_t sin6_scope_id; };	struct sockaddr_in6 { uint8_t sin6_len; sa_family_t sin6_family; in_port_t sin6_port; uint32_t sin6_flowinfo; struct in6_addr sin6_addr; uint32_t sin6_scope_id; };

Table 1. Differences between BSD 4.3 and BSD 4.4/ UNIX 98 for sockaddr_in6 address structure

BSD 4.3 sockaddr_in6 address structure

BSD 4.4/ UNIX 98 sockaddr_in6 address structure

 struct sockaddr_in6 {
  sa_family_t     sin6_family;
  in_port_t       sin6_port;
  uint32_t        sin6_flowinfo;
  struct in6_addr sin6_addr;
  uint32_t        sin6_scope_id;
 };

 struct sockaddr_in6 {
  uint8_t         sin6_len;
  sa_family_t     sin6_family;
  in_port_t       sin6_port;
  uint32_t        sin6_flowinfo;
  struct in6_addr sin6_addr;
  uint32_t        sin6_scope_id;
 };

Table 2. AF_INET6 address structure
Address structure field	Definition
sin6_len	This field contains the length of the address for UNIX 98 specifications. Note: The: sin6_len field is only provided for BSD 4.4 compatibility. It is not necessary to use this field even when using BSD 4.4/ UNIX 98 compatibility. The field is ignored on input addresses.
sin6_family	This field specifies the AF_INET6 address family.
sin6_port	This field contains the transport layer port.
sin6_flowinfo	This field contains two pieces of information: the traffic class and the flow label. Note: This field is currently not supported and should be set to zero for upward compatibility.
sin6_addr	This field specifies the IPv6 address.
sin6_scope_id	This field identifies a set of interfaces as appropriate for the scope of the address carried in the sin6_addr field.