UDP(4)                    386BSD Programmer's Manual                    UDP(4)

NAME
     udp - Internet User Datagram Protocol

SYNOPSIS
     Makefile:
     $(NONSTDINC) += $(INCNET)
     C:
     #include <sys/socket.h>
     #include "in.h"

     int
     socket(AF_INET, SOCK_DGRAM, 0)

DESCRIPTION
     UDP is a simple, unreliable datagram protocol which is used to support
     the SOCK_DGRAM abstraction for the Internet protocol family.  UDP sockets
     are connectionless, and are normally used with the sendto and recvfrom
     calls, though the connect(2) call may also be used to fix the destination
     for future packets (in which case the recv(2) or read(2) and send(2) or
     write(2) system calls may be used).

     UDP address formats are identical to those used by TCP. In particular UDP
     provides a port identifier in addition to the normal Internet address
     format.  Note that the UDP port space is separate from the TCP port space
     (i.e. a UDP port may not be ``connected'' to a TCP port).  In addition
     broadcast packets may be sent (assuming the underlying network supports
     this) by using a reserved ``broadcast address''; this address is network
     interface dependent.

     Options at the IP transport level may be used with UDP; see ip(4).

DIAGNOSTICS
     A socket operation may fail with one of the following errors returned:

     [EISCONN]        when trying to establish a connection on a socket which
                      already has one, or when trying to send a datagram with
                      the destination address specified and the socket is
                      already connected;

     [ENOTCONN]       when trying to send a datagram, but no destination
                      address is specified, and the socket hasn't been
                      connected;

     [ENOBUFS]        when the system runs out of memory for an internal data
                      structure;

     [EADDRINUSE]     when an attempt is made to create a socket with a port
                      which has already been allocated;

     [EADDRNOTAVAIL]  when an attempt is made to create a socket with a
                      network address for which no network interface exists.

SEE ALSO
     getsockopt(2),  recv(2),  send(2),  socket(2),  intro(4),  inet(4),
     ip(4)

HISTORY
     The udp protocol appeared in 4.2BSD.

4.2 Berkeley Distribution       March 28, 1991                               1