UDP(4)                    BSD Kernel Interfaces Manual                    UDP(4)

     udp — Internet User Datagram Protocol

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

     socket(AF_INET, SOCK_DGRAM, 0);

     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) and 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 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).

     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 has not been

     [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 exists.

     The udp protocol implements a number of variables in the net.inet branch of
     the sysctl(3) MIB.

     UDPCTL_CHECKSUM    (udp.checksum) Enable udp checksums (enabled by

     UDPCTL_MAXDGRAM    (udp.maxdgram) Maximum outgoing UDP datagram size

     UDPCTL_RECVSPACE   (udp.recvspace) Maximum space for incoming UDP datagrams

     udp.log_in_vain    For all udp datagrams, to ports on which there is no
                        socket listening, log the connection attempt (disabled
                        by default).

     udp.blackhole      When a datagram is received on a port where there is no
                        socket listening, do not return an ICMP port unreachable
                        message.  (Disabled by default.  See blackhole(4).)

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

     The udp protocol appeared in 4.2BSD.

BSD                               June 5, 1993                               BSD