Internet User Datagram Protocol
UDP is a simple, unreliable datagram protocol which is used to support the
abstraction for the Internet
protocol family. UDP sockets are connectionless, and are normally used with
calls, though the
call may also be used to fix the destination for future packets (in which case
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
Options at the IP transport level may be used with UDP; see
UDP_ENCAP socket option may be used at the IPPROTO_UDP level to encapsulate
ESP packets in UDP. Only one value is supported for this option:
UDP_ENCAP_ESPINUDP from RFC 3948, defined in
protocol implements a number of
variables in the
branch of the
- (udp.checksum) Enable udp checksums (enabled by default).
- (udp.maxdgram) Maximum outgoing UDP datagram size
- (udp.recvspace) Maximum space for incoming UDP datagrams
- For all udp datagrams, to ports on which there is no socket listening, log
the connection attempt (disabled by default).
- 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
A socket operation may fail with one of the following errors returned:
- 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;
- when trying to send a datagram, but no destination address is specified,
and the socket has not been connected;
- when the system runs out of memory for an internal data structure;
- when an attempt is made to create a socket with a port which has already
- when an attempt is made to create a socket with a network address for
which no network interface exists.
protocol appeared in