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NAME    [Toc]    [Back]

     udp - Internet User Datagram Protocol

SYNOPSIS    [Toc]    [Back]

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

     socket(AF_INET, SOCK_DGRAM, 0);

     socket(AF_INET6, SOCK_DGRAM, 0);

DESCRIPTION    [Toc]    [Back]

     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(2)
     recvfrom(2)  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
     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) or

DIAGNOSTICS    [Toc]    [Back]

     A socket operation may fail with one of the following errors

     [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

     [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

     [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

SEE ALSO    [Toc]    [Back]

     getsockopt(2), recv(2),  send(2),  socket(2),  inet(4),  inet6(4), ip(4),
     ip6(4), netintro(4)

HISTORY    [Toc]    [Back]

     The udp protocol appeared in 4.2BSD.

OpenBSD      3.6                           June      5,      1993
[ Back ]
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