udp(4) Internet User Datagram Protocol

SYNOPSIS

In sys/types.h In sys/socket.h In netinet/in.h Ft int Fn 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).

MIB VARIABLES

The 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).)

ERRORS

A socket operation may fail with one of the following errors returned:

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;
Bq Er ENOTCONN
when trying to send a datagram, but no destination address is specified, and the socket has not been connected;
Bq Er ENOBUFS
when the system runs out of memory for an internal data structure;
Bq Er EADDRINUSE
when an attempt is made to create a socket with a port which has already been allocated;
Bq Er EADDRNOTAVAIL
when an attempt is made to create a socket with a network address for which no network interface exists.

HISTORY

The protocol appeared in BSD 4.2

SEE ALSO

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