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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.Dd August 1, 2022 29.Dt UDP 4 30.Os 31.Sh NAME 32.Nm udp 33.Nd Internet User Datagram Protocol 34.Sh SYNOPSIS 35.In sys/types.h 36.In sys/socket.h 37.In netinet/in.h 38.Ft int 39.Fn socket AF_INET SOCK_DGRAM 0 40.Sh DESCRIPTION 41.Tn UDP 42is a simple, unreliable datagram protocol which is used 43to support the 44.Dv SOCK_DGRAM 45abstraction for the Internet 46protocol family. 47.Tn UDP 48sockets are connectionless, and are 49normally used with the 50.Xr sendto 2 51and 52.Xr recvfrom 2 53calls, though the 54.Xr connect 2 55call may also be used to fix the destination for future 56packets (in which case the 57.Xr recv 2 58or 59.Xr read 2 60and 61.Xr send 2 62or 63.Xr write 2 64system calls may be used). 65.Pp 66.Tn UDP 67address formats are identical to those used by 68.Tn TCP . 69In particular 70.Tn UDP 71provides a port identifier in addition 72to the normal Internet address format. 73Note that the 74.Tn UDP 75port 76space is separate from the 77.Tn TCP 78port space (i.e., a 79.Tn UDP 80port 81may not be 82.Dq connected 83to a 84.Tn TCP 85port). 86In addition broadcast 87packets may be sent (assuming the underlying network supports 88this) by using a reserved 89.Dq broadcast address ; 90this address 91is network interface dependent. 92.Pp 93Options at the 94.Tn IP 95transport level may be used with 96.Tn UDP ; 97see 98.Xr ip 4 . 99.Tn UDP_ENCAP 100socket option may be used at the 101.Tn IPPROTO_UDP 102level to encapsulate 103.Tn ESP 104packets in 105.Tn UDP . 106Only one value is supported for this option: 107.Tn UDP_ENCAP_ESPINUDP 108from RFC 3948, defined in 109.In netinet/udp.h . 110.Sh MIB (sysctl) Variables 111The 112.Nm 113protocol implements a number of variables in the 114.Va net.inet.udp 115branch of the 116.Xr sysctl 3 117MIB, which can be also read or modified with 118.Xr sysctl 8 : 119.Bl -tag -width ".Va log_in_vain" 120.It Va blackhole 121When a datagram is received on a port where there is no socket 122listening, do not return an ICMP port unreachable message. 123(Disabled by default. 124See 125.Xr blackhole 4 . ) 126.It Va checksum 127Enable UDP checksums (enabled by default). 128.It Va log_in_vain 129For all UDP datagrams, to ports on which there is no socket 130listening, log the connection attempt (disabled by default). 131.It Va maxdgram 132Maximum outgoing UDP datagram size 133.It Va recvspace 134Maximum space for incoming UDP datagrams 135.El 136.Sh ERRORS 137A socket operation may fail with one of the following errors returned: 138.Bl -tag -width Er 139.It Bq Er EISCONN 140when trying to establish a connection on a socket which 141already has one, or when trying to send a datagram with the destination 142address specified and the socket is already connected; 143.It Bq Er ENOTCONN 144when trying to send a datagram, but 145no destination address is specified, and the socket has not been 146connected; 147.It Bq Er ENOBUFS 148when the system runs out of memory for 149an internal data structure; 150.It Bq Er EADDRINUSE 151when an attempt 152is made to create a socket with a port which has already been 153allocated; 154.It Bq Er EADDRNOTAVAIL 155when an attempt is made to create a 156socket with a network address for which no network interface 157exists. 158.El 159.Sh SEE ALSO 160.Xr getsockopt 2 , 161.Xr recv 2 , 162.Xr send 2 , 163.Xr socket 2 , 164.Xr blackhole 4 , 165.Xr inet 4 , 166.Xr intro 4 , 167.Xr ip 4 , 168.Xr udplite 4 169.Sh HISTORY 170The 171.Nm 172protocol appeared in 173.Bx 4.2 . 174