Technical data

SunOS 5.5 Protocols inet(7P)

ADDRESSING IP addresses are four byte quantities, stored in network byte order. IP addresses should

be manipulated usingthe byte order conversion routines (see byteorder(3N)).

Addresses in the Internetprotocol family use the sockaddr_in structure, which has that

following members:

short sin_family;

u_short sin_port;

struct in_addr sin_addr;

char sin_zero[8];

Library routines are provided to manipulate structures of this form; See inet(3N).

The sin_addr ﬁeld of the sockaddr_in structure speciﬁes a local or remote IP address.

Each network interface has its own uniqueIP address. The special value INADDR_ANY

may be used in this ﬁeld to effect “wildcard” matching. Given in a bind(3N) call, this

value leaves the local IP address of the socket unspeciﬁed, so that the socket will receive

connections or messages directed at any of the validIP addresses of the system. This can

prove useful when a process neither knows nor cares what the local IP address is or when

a process wishes to receive requests using all of its network interfaces. The sockaddr_in

structure given in the bind(3N) call must specify an in_addr value of either

IPADDR_ANY or one of the system’s valid IP addresses. Requests to bind any other

address will elicit the error EADDRNOTAVAI. When a connect(3N) call is made for a

socket that has a wildcard local address, the system sets the sin_addr ﬁeld of the socket

to the IP address of the network interface that the packets for that connection are routed

via.

The sin_port ﬁeld of the sockaddr_in structure speciﬁes a port number used byTCP or

UDP. The local port address speciﬁed in a bind(3N) call is restricted to be greater than

IPPORT_RESERVED (deﬁned in <netinet/in.h>) unless the creating process is running

as the super-user, providing a space of protected port numbers. In addition, the local

port address must not be in use by any socket of same address family and type. Requests

to bind sockets to port numbers being used by other sockets return the error EAD-

DRINUSE. If the local port address is speciﬁed as 0, then the system picks a unique port

address greater than IPPORT_RESERVED. A unique local port address is also picked

when a socket which is not bound is used in a connect(3N) or sendto (see send(3N)) call.

This allows programs which do not care which local port number is used to set up TCP

connections by simply calling socket(3N) and then connect(3N), and to send UDP

datagrams with a socket(3N) call followed by a sendto() call.

modiﬁed 3 Jul 1990 7P-143