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@(#)udp.4 8.1 (Berkeley) 6/5/93
.Dd June 5, 1993 .Dt UDP 4 .Os BSD 4.2 .Sh NAME .Nm udp .Nd Internet User Datagram Protocol .Sh SYNOPSIS .Fd #include <sys/socket.h> .Fd #include <netinet/in.h> .Ft int .Fn socket AF_INET SOCK_DGRAM 0 .Sh DESCRIPTION .Tn UDP is a simple, unreliable datagram protocol which is used to support the .Dv SOCK_DGRAM abstraction for the Internet protocol family. .Tn UDP sockets are connectionless, and are normally used with the .Xr sendto and .Xr recvfrom calls, though the .Xr connect 2 call may also be used to fix the destination for future packets (in which case the .Xr recv 2 or .Xr read 2 and .Xr send 2 or .Xr write 2 system calls may be used).
p .Tn UDP address formats are identical to those used by .Tn TCP . In particular .Tn UDP provides a port identifier in addition to the normal Internet address format. Note that the .Tn UDP port space is separate from the .Tn TCP port space (i.e. a .Tn UDP port may not be .Dq connected to a .Tn TCP port). In addition broadcast packets may be sent (assuming the underlying network supports this) by using a reserved .Dq broadcast address ; this address is network interface dependent.
p Options at the .Tn IP transport level may be used with .Tn UDP ; see .Xr ip 4 . .Sh DIAGNOSTICS A socket operation may fail with one of the following errors returned: l -tag -width [EADDRNOTAVAIL] t Bq Er 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; t Bq Er ENOTCONN when trying to send a datagram, but no destination address is specified, and the socket hasn't been connected; t Bq Er ENOBUFS when the system runs out of memory for an internal data structure; t Bq Er EADDRINUSE when an attempt is made to create a socket with a port which has already been allocated; t Bq Er EADDRNOTAVAIL when an attempt is made to create a socket with a network address for which no network interface exists. .El .Sh SEE ALSO .Xr getsockopt 2 , .Xr recv 2 , .Xr send 2 , .Xr socket 2 , .Xr inet 4 , .Xr intro 4 , .Xr ip 4 .Sh HISTORY The .Nm protocol appeared in x 4.2 .