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udp - Internet User Datagram Protocol



      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 data‐
                         gram 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 con‐
      [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.
      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 data‐
      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
      getsockopt(2), recv(2), send(2), socket(2), blackhole(4), inet(4),
      intro(4), ip(4)


      The udp protocol appeared in 4.2BSD.


Based on BSD UNIX
FreeBSD is an advanced operating system for x86 compatible (including Pentium and Athlon), amd64 compatible (including Opteron, Athlon64, and EM64T), UltraSPARC, IA-64, PC-98 and ARM architectures. It is derived from BSD, the version of UNIX developed at the University of California, Berkeley. It is developed and maintained by a large team of individuals. Additional platforms are in various stages of development.