[sockets] What is AF_INET, and why do I need it?

I'm getting started on socket programming, and I keep seeing this AF_INET.

Yet, I've never seen anything else used in its place. My lecturers are not that helpful and just say "You just need it".

So my questions:

• What is the purpose of AF_INET?
• Is anything else ever used instead of it?
  • If not, why is it there? For possible changes in the future?
  • If so, what and why?

You need arguments like AF_UNIX or AF_INET to specify which type of socket addressing you would be using to implement IPC socket communication. AF stands for Address Family.

As in BSD standard Socket (adopted in Python socket module) addresses are represented as follows:

1. A single string is used for the AF_UNIX/AF_LOCAL address family. This option is used for IPC on local machines where no IP address is required.

2. A pair (host, port) is used for the AF_INET address family, where host is a string representing either a hostname in Internet domain notation like 'daring.cwi.nl' or an IPv4 address like '100.50.200.5', and port is an integer. Used to communicate between processes over the Internet.

AF_UNIX , AF_INET6 , AF_NETLINK , AF_TIPC , AF_CAN , AF_BLUETOOTH , AF_PACKET , AF_RDS are other option which could be used instead of AF_INET.

This thread about the differences between AF_INET and PF_INET might also be useful.

Socket are characterized by their domain, type and transport protocol. Common domains are:

1. AF_UNIX: address format is UNIX pathname

2. AF_INET: address format is host and port number

(there are actually many other options which can be used here for specialized purposes).usually we use AF_INET for socket programming

Reference: http://www.cs.uic.edu/~troy/fall99/eecs471/sockets.html

The primary purpose of AF_INET was to allow for other possible network protocols or address families (AF is for address family; PF_INET is for the (IPv4) internet protocol family). For example, there probably are a few Netware SPX/IPX networks around still; there were other network systems like DECNet, StarLAN and SNA, not to mention the ill-begotten ISO OSI (Open Systems Interconnection), and these did not necessarily use the now ubiquitous IP address to identify the peer host in network connections.

The ubiquitous alternative to AF_INET (which, in retrospect, should have been named AF_INET4) is AF_INET6, for the IPv6 address family. IPv4 uses 32-bit addresses; IPv6 uses 128-bit addresses.

You may see some other values - but they are unusual. It is there to allow for alternatives and future directions. The sockets interface is actually very general indeed - which is one of the reasons it has thrived where other networking interfaces have withered.

Life has (mostly) gotten simpler - be grateful.

it defines the protocols address family.this determines the type of socket created. pocket pc support AF_INET.

the content in the following page is quite decent http://etutorials.org/Programming/Pocket+pc+network+programming/Chapter+1.+Winsock/Streaming+TCP+Sockets/