udp(4) [debian man page]

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

NAME

     udp -- Internet User Datagram Protocol

SYNOPSIS

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

     int
     socket(AF_INET, SOCK_DGRAM, 0);

DESCRIPTION

     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).

ERRORS

     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 desti-
			nation 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 connected;

     [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 network address for which no network interface exists.

MIB VARIABLES

     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 default).

     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).)

SEE ALSO

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

HISTORY

     The udp protocol appeared in 4.2BSD.

BSD
								   June 5, 1993 							       BSD

udp(n)								 Tnm Tcl Extension							    udp(n)

__________________________________________________________________________________________________________________________________________________

NAME

       udp - Send and receive UDP datagrams.
_________________________________________________________________

DESCRIPTION

       The udp command allows to send and receive datagrams using the User Datagram Protocol (UDP) (RFC 768).

UDP COMMAND

       udp open [port]
	      The  udp	open  command opens a UDP datagram socket and returns an udp handle. The socket is bound to given port number or name.	An
	      unused port number is used if the port argument is missing.

       udp connect host port
	      The udp connect command opens a UDP datagram socket and connects it to a port on a remote host. A connected UDP socket  only  allows
	      to  send messages to a single destination. This usually allows to shorten the code since there is no need to specify the destination
	      address for each udp send command on a connected UDP socket. The command returns a udp handle.

       udp send handle [host port] message
	      The udp send command sends a datagram containing message to the destination specified by host and port. The host and port  arguments
	      may  not	be  used  if the UDP handle is already connected to a transport endpoint. If the UDP handle is not connected, you must use
	      these optional arguments to specify the destination of the datagram.

       udp receive handle
	      The udp receive command receives a datagram from the UDP socket associated with handle. This command  blocks  until  a  datagram	is
	      ready to be received. In most cases, it might be a good idea to check for pending datagrams using the udp bind command.

       udp close handle
	      The udp close command closes the UDP socket associated with handle.

       udp bind handle readable [script]
       udp bind handle writable [script]
	      The  udp	bind  command allows to bind scripts to a UDP handle. A script is evaluated once the UDP handle becomes either readable or
	      writable, depending on the third argument of the udp bind command. The script currently bound to a UDP handle can  be  retrieved	by
	      calling the udp bind command without a script argument. Bindings are removed by binding an empty string.

       udp info [handle]
	      The  udp	info  command without the handle argument returns a list of all existing UDP handles. Information about the state of a UDP
	      handle can be obtained by supplying a valid UDP handle. The result is a list containing the source IP address, the source port,  the
	      destination IP address and the destination port.

SEE ALSO

       scotty(1), Tnm(n), Tcl(n)

AUTHORS

       Juergen Schoenwaelder <schoenw@cs.utwente.nl>

Tnm																	    udp(n)