16.6 The Internet Namespace

This section describes the details of the protocols and socket naming conventions used in the Internet namespace.

Originally the Internet namespace used only IP version 4 (IPv4). With the growing number of hosts on the Internet, a new protocol with a larger address space was necessary: IP version 6 (IPv6). IPv6 introduces 128-bit addresses (IPv4 has 32-bit addresses) and other features, and will eventually replace IPv4.

To create a socket in the IPv4 Internet namespace, use the symbolic name PF_INET of this namespace as the namespace argument to socket or socketpair. For IPv6 addresses you need the macro PF_INET6. These macros are defined in sys/socket.h.

A socket address for the Internet namespace includes the following components:

• The address of the machine you want to connect to. Internet addresses can be specified in several ways; these are discussed in Internet Address Formats, Host Addresses and Host Names.
• A port number for that machine. See Ports.

You must ensure that the address and port number are represented in a canonical format called network byte order. See Byte Order, for information about this.

• Internet Address Formats: How socket addresses are specified in the Internet namespace.
• Host Addresses: All about host addresses of Internet host.
• Protocols Database: Referring to protocols by name.
• Ports: Internet port numbers.
• Services Database: Ports may have symbolic names.
• Byte Order: Different hosts may use different byte ordering conventions; you need to canonicalize host address and port number.
• Inet Example: Putting it all together.