| UDP(4) | Device Drivers Manual | UDP(4) | 
udp —
#include <sys/socket.h>
#include <netinet/in.h>
int
  
  socket(AF_INET,
    SOCK_DGRAM,
    0);
int
  
  socket(AF_INET6,
    SOCK_DGRAM,
    0);
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.
There are two UDP-level
    setsockopt(2)/getsockopt(2)
    options. UDP_OPTIONS may be used to change the
    default behavior of the socket. For example:
setsockopt(s, IPPROTO_UDP, UDP_OPTIONS, NULL, 0);
The UDP_ENCAP option can be used to
    encapsulate ESP packets in UDP. There is one valid encapsulation option:
    UDP_ENCAP_ESPINUDP from RFC3948 defined in
    <netinet/udp.h>.
Options at the IP transport level may be used with UDP; see ip(4) or ip6(4).
EADDRINUSE]EADDRNOTAVAIL]EISCONN]ENOBUFS]ENOTCONN]User Datagram Protocol, RFC, 768, August 28, 1980.
Requirements for Internet Hosts — Communication Layers, RFC, 1122, October 1989.
udp protocol appeared in
  4.2BSD.
| May 31, 2018 | NetBSD 10.1 |