UDP(4P)                                                                UDP(4P)



NAME
       udp - Internet User Datagram Protocol

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

       s = 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 sock‐
       ets  are  connectionless,  and  are  normally  used with the _s_e_n_d_t_o and
       _r_e_c_v_f_r_o_m calls, though the _c_o_n_n_e_c_t(2) call may also be used to fix  the
       destination  for  future  packets (in which case the _r_e_c_v(2) or _r_e_a_d(2)
       and _s_e_n_d(2) or _w_r_i_t_e_(_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 _i_p(4P).

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  con‐
                      nected;

       [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 net‐
                      work address for which no network interface exists.

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



4.2 Berkeley Distribution        May 16, 1986                          UDP(4P)