182 lines
5.7 KiB
Groff
182 lines
5.7 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)tcp.4 8.1 (Berkeley) 6/5/93
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.\"
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.Dd June 5, 1993
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.Dt TCP 4
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.Os BSD 4.2
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.Sh NAME
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.Nm tcp
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.Nd Internet Transmission Control Protocol
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.Sh SYNOPSIS
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.Fd #include <sys/socket.h>
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.Fd #include <netinet/in.h>
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.Ft int
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.Fn socket AF_INET SOCK_STREAM 0
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.Sh DESCRIPTION
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The
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.Tn TCP
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protocol provides reliable, flow-controlled, two-way
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transmission of data. It is a byte-stream protocol used to
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support the
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.Dv SOCK_STREAM
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abstraction. TCP uses the standard
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Internet address format and, in addition, provides a per-host
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collection of
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.Dq port addresses .
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Thus, each address is composed
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of an Internet address specifying the host and network, with
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a specific
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.Tn TCP
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port on the host identifying the peer entity.
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.Pp
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Sockets utilizing the tcp protocol are either
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.Dq active
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or
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.Dq passive .
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Active sockets initiate connections to passive
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sockets. By default
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.Tn TCP
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sockets are created active; to create a
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passive socket the
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.Xr listen 2
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system call must be used
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after binding the socket with the
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.Xr bind 2
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system call. Only
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passive sockets may use the
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.Xr accept 2
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call to accept incoming connections. Only active sockets may
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use the
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.Xr connect 2
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call to initiate connections.
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.Pp
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Passive sockets may
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.Dq underspecify
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their location to match
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incoming connection requests from multiple networks. This
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technique, termed
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.Dq wildcard addressing ,
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allows a single
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server to provide service to clients on multiple networks.
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To create a socket which listens on all networks, the Internet
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address
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.Dv INADDR_ANY
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must be bound. The
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.Tn TCP
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port may still be specified
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at this time; if the port is not specified the system will assign one.
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Once a connection has been established the socket's address is
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fixed by the peer entity's location. The address assigned the
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socket is the address associated with the network interface
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through which packets are being transmitted and received. Normally
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this address corresponds to the peer entity's network.
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.Pp
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.Tn TCP
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supports one socket option which is set with
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.Xr setsockopt 2
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and tested with
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.Xr getsockopt 2 .
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Under most circumstances,
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.Tn TCP
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sends data when it is presented;
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when outstanding data has not yet been acknowledged, it gathers
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small amounts of output to be sent in a single packet once
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an acknowledgement is received.
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For a small number of clients, such as window systems
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that send a stream of mouse events which receive no replies,
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this packetization may cause significant delays.
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Therefore,
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.Tn TCP
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provides a boolean option,
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.Dv TCP_NODELAY
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(from
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.Aq Pa netinet/tcp.h ,
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to defeat this algorithm.
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The option level for the
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.Xr setsockopt
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call is the protocol number for
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.Tn TCP ,
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available from
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.Xr getprotobyname 3 .
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.Pp
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Options at the
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.Tn IP
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transport level may be used with
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.Tn TCP ;
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see
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.Xr ip 4 .
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Incoming connection requests that are source-routed are noted,
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and the reverse source route is used in responding.
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.Sh DIAGNOSTICS
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A socket operation may fail with one of the following errors returned:
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.Bl -tag -width [EADDRNOTAVAIL]
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.It Bq Er EISCONN
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when trying to establish a connection on a socket which
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already has one;
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.It Bq Er ENOBUFS
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when the system runs out of memory for
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an internal data structure;
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.It Bq Er ETIMEDOUT
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when a connection was dropped
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due to excessive retransmissions;
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.It Bq Er ECONNRESET
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when the remote peer
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forces the connection to be closed;
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.It Bq Er ECONNREFUSED
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when the remote
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peer actively refuses connection establishment (usually because
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no process is listening to the port);
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.It Bq Er EADDRINUSE
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when an attempt
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is made to create a socket with a port which has already been
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allocated;
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.It Bq Er EADDRNOTAVAIL
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when an attempt is made to create a
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socket with a network address for which no network interface
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exists.
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.It Bq Er EAFNOSUPPORT
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when an attempt is made to bind or connect a socket to a multicast
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address.
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.El
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.Sh SEE ALSO
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.Xr getsockopt 2 ,
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.Xr socket 2 ,
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.Xr intro 4 ,
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.Xr inet 4 ,
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.Xr ip 4
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.Sh HISTORY
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The
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.Nm
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protocol stack appeared in
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.Bx 4.2 .
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