1130b656e5
This will make a number of things easier in the future, as well as (finally!) avoiding the Id-smashing problem which has plagued developers for so long. Boy, I'm glad we're not using sup anymore. This update would have been insane otherwise.
267 lines
7.7 KiB
Groff
267 lines
7.7 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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.\" From: @(#)tcp.4 8.1 (Berkeley) 6/5/93
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.\" $FreeBSD$
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.\"
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.Dd February 14, 1995
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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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.Tn TCP
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also supports a more datagram-like mode, called Transaction
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.Tn TCP ,
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which is described in
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.Xr ttcp 4 .
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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 a number of socket options which can be 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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.Bl -tag -width TCP_NODELAYx
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.It Dv TCP_NODELAY
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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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The boolean option
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.Dv TCP_NODELAY
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defeats this algorithm.
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.It Dv TCP_MAXSEG
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By default, a sender\- and receiver-TCP
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will negotiate among themselves to determine the maximum segment size
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to be used for each connection. The
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.Dv TCP_MAXSEG
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option allows the user to determine the result of this negotiation,
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and to reduce it if desired.
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.It Dv TCP_NOOPT
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.Tn TCP
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usually sends a number of options in each packet, corresponding to
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various
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.Tn TCP
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extensions which are provided in this implementation. The boolean
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option
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.Dv TCP_NOOPT
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is provided to disable
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.Tn TCP
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option use on a per-connection basis.
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.It Dv TCP_NOPUSH
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By convention, the sender-TCP
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will set the
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.Dq push
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bit and begin transmission immediately (if permitted) at the end of
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every user call to
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.Xr write 2
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or
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.Xr writev 2 .
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The
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.Dv TCP_NOPUSH
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option is provided to allow servers to easily make use of Transaction
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TCP (see
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.Xr ttcp 4 ).
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When the option is set to a non-zero value,
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.Tn TCP
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will delay sending any data at all until either the socket is closed,
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or the internal send buffer is filled.
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.El
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.Pp
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The option level for the
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.Xr setsockopt 2
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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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or
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.Dv IPPROTO_TCP .
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All options are declared in
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.Aq Pa netinet/tcp.h .
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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 MIB VARIABLES
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The
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.Nm
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protocol implements three variables in the
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.Li net.inet
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branch of the
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.Xr sysctl 3
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MIB.
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.Bl -tag -width TCPCTL_DO_RFC1644
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.It Dv TCPCTL_DO_RFC1323
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.Pq tcp.rfc1323
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Implement the window scaling and timestamp options of RFC 1323
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(default true).
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.It Dv TCPCTL_DO_RFC1644
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.Pq tcp.rfc1644
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Implement Transaction
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.Tn TCP ,
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as described in RFC 1644.
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.It Dv TCPCTL_MSSDFLT
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.Pq tcp.mssdflt
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The default value used for the maximum segment size
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.Pq Dq MSS
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when no advice to the contrary is received from MSS negotiation.
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.El
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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 sysctl 3 ,
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.Xr inet 4 ,
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.Xr intro 4 ,
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.Xr ip 4 ,
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.Xr ttcp 4
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.Rs
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.%A V. Jacobson, R. Braden, and D. Borman
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.%T "TCP Extensions for High Performance"
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.%O RFC 1323
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.Re
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.Rs
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.%A R. Braden
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.%T "T/TCP \- TCP Extensions for Transactions"
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.%O RFC 1644
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.Re
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.Sh HISTORY
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The
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.Nm
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protocol appeared in
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.Bx 4.2 .
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The RFC 1323 extensions for window scaling and timestamps were added
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in
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.Bx 4.4 .
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