UDP(4) BSD Programmer's Manual UDP(4)
udp - Internet User Datagram Protocol
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 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
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 al-
[ENOTCONN] when trying to send a datagram, but no destination ad-
dress is specified, and the socket hasn't been connect-
[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 net-
work address for which no network interface exists.
getsockopt(2), recv(2), send(2), socket(2), intro(4), inet(4),
The udp protocol appeared in 4.2BSD.
4.2 Berkeley Distribution June 5, 1993 1