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
#include <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:
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.
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).)
