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HP-UX 11i Version 3: February 2007

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inet — Internet protocol family


#include <sys/types.h> #include <netinet/in.h>


The internet protocol family is a collection of protocols layered on top of the Internet Protocol (IP) network layer, which utilizes the internet address format. The internet family supports the SOCK_STREAM and SOCK_DGRAM socket types.


Internet addresses are four byte entities. The include file <netinet/in.h> defines this address as the structure struct in_addr.

Sockets bound to the internet protocol family utilize an addressing structure called struct sockaddr_in. Pointers to this structure can be used in system calls wherever they ask for a pointer to a struct sockaddr.

There are three fields of interest within this structure. The first is sin_family, which must be set to AF_INET. The next is sin_port, which specifies the port number to be used on the desired host. The third is sin_addr, which is of type struct in_addr, and specifies the address of the desired host.


The internet protocol family is comprised of the IP network protocol, Internet Control Message Protocol (ICMP), Transmission Control Protocol (TCP), and User Datagram Protocol (UDP). TCP is used to support the SOCK_STREAM socket type while UDP is used to support the SOCK_DGRAM socket type. The ICMP message protocol and IP network protocol are not directly accessible.

The local port address is selected from independent domains for TCP and UDP sockets. This means that creating a TCP socket and binding it to local port number 10000, for example, does not interfere with creating a UDP socket and also binding it to local port number 10000 at the same time.

Port numbers in the range 1-1023 inclusive are reserved for use by the super-user only. Attempts to bind to port numbers in this range by non-super-users fail and result in an error returned.


inet was developed by the University of California, Berkeley.


TCP(7P), UDP(7P).

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