The address structure depends on the IP addressing family. An IPv4 socket address in an IP addressing family is comprised of the following four fields:

Address family

Set to AF_INET in C, or to a decimal 2 in other languages.

Port

Port used by the application, in network byte order (which is explained in TCP/IP network byte ordering convention).

IPv4 address

The IPv4 address of the network interface used by the application. It is also in network byte order.

Character array

Should always be set to all zeros.

An IPv6 socket address in an IP addressing family is comprised of the following five fields:

Address family

Set to AF_INET6 in C or to a decimal 19 in other languages.

Port

Port used by the application, in network byte order (which is explained in TCP/IP network byte ordering convention).

Flow Information

Four bytes in binary format indicating traffic class and flow label. This field is currently not implemented.

IPv6 address

The IPv6 address of the network interface used by the application. It is in network byte order.

Scope ID

Used to specify link scope for an IPv6 address as a interface index. If specified, and the destination is not link local, the socket call fails.