230 lines
6.6 KiB
Groff
230 lines
6.6 KiB
Groff
.\" Copyright 1994, 1995 Massachusetts Institute of Technology
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.\"
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.\" Permission to use, copy, modify, and distribute this software and
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.\" its documentation for any purpose and without fee is hereby
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.\" granted, provided that both the above copyright notice and this
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.\" permission notice appear in all copies, that both the above
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.\" copyright notice and this permission notice appear in all
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.\" supporting documentation, and that the name of M.I.T. not be used
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.\" in advertising or publicity pertaining to distribution of the
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.\" software without specific, written prior permission. M.I.T. makes
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.\" no representations about the suitability of this software for any
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.\" purpose. It is provided "as is" without express or implied
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.\" warranty.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY M.I.T. ``AS IS''. M.I.T. DISCLAIMS
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.\" ALL EXPRESS OR IMPLIED WARRANTIES WITH REGARD TO THIS SOFTWARE,
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.\" INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
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.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT
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.\" SHALL M.I.T. BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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.\" SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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.\" LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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.\" USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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.\" ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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.\" 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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.\" $FreeBSD$
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.\"
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.Dd January 18, 1995
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.Dt TTCP 4
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.Os FreeBSD
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.Sh NAME
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.Nm ttcp
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.Nd Transmission Control Protocol Extensions for Transactions
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.Sh SYNOPSIS
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.Fd #include <sys/types.h>
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.Fd #include <sys/socket.h>
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.Fd #include <netinet/in.h>
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.Fd #include <netinet/tcp.h>
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.Ft int
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.Fn setsockopt sock IPPROTO_TCP TCP_NOPUSH &One "sizeof One"
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.Ft ssize_t
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.Fn sendto sock msg len MSG_EOF &sin "sizeof sin"
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.Ft ssize_t
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.Fn sendto sock msg len MSG_EOF 0 0
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.Sh DESCRIPTION
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.Tn T/TCP
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refers to a set of extensions to the
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.Tn TCP
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protocol (see
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.Xr tcp 4 )
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which permit hosts to reliably exchange a small amount of data in a
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two-packet exchange, thus eliminating the extra round-trip delays
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inherent in a standard
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.Tn TCP
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connection. The socket interface includes modifications to support
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.Tn T/TCP ,
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detailed here for the specific case, and in the
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.Xr socket 2
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and
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.Xr send 2
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manual pages for the protocol-independent support.
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.Tn T/TCP
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is defined in RFC 1644.
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.Pp
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The
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.Tn T/TCP
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extensions work by including certain options in all segments of a
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particular connection, which enable the implementation to avoid the
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three-way handshake for all but the first connection between a pair of
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hosts. These same options also make it possible to more reliably
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recognize old, duplicate packets, which in turn reduces the amount of
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time the
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.Tn TCP
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protocol must maintain state after a connection closes. The
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.Dq Li net.inet.tcp.rfc1644
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MIB variable can be used to disable
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.Tn T/TCP
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negotiation at run time; however, the protocol has been designed to
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ensure that attempts by non-T/TCP
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systems to communicate with T/TCP-enhanced
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ones automatically degenerate into standard
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.Tn TCP .
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.Sh TRANSACTION MODEL
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The expected model of a
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.Dq transaction
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as used by
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.Tn T/TCP
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is a fairly simple one:
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.Bl -enum
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.It
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A client program generates a request to be sent to the server, which
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is small enough to fit in a single
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.Tn TCP
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segment, and sends a SYN PUSH FIN segment with options and data to the
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server.
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.It
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The server program accepts the request in the same manner as for
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regular
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.Tn TCP
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connections, interprets it, and generates a reply which may be small
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enough to fit in a single segment. If it is, the reply is sent in a
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single SYN PUSH FIN ACK segment with (different) options and data back
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to the client. If not, then the connection degenerates into (almost)
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the usual case for
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.Tn TCP .
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The server then closes its socket.
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.It
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The client reads the reply and closes its socket.
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.El
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.Sh CLIENT SUPPORT
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Support on the client side is provided by extending the semantics of
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the
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.Xr sendto 2
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and
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.Xr sendmsg 2
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system calls to understand the notion of
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.Dq implied connect
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and
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.Dq send and shutdown.
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To send the request in a transaction, the
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.Xr sendto 2
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system call is typically used, as in the following example:
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.Bd -literal -offset indent
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char request[REQ_LEN];
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struct sockaddr_in sin;
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int sock, req_len;
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sock = socket(PF_INET, SOCK_STREAM, 0);
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/* prepare request[] and sin */
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err = sendto(sock, request, req_len, MSG_EOF,
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(struct sockaddr *)&sin, sin.sin_len);
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/* do something if error */
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req_len = read(sock, request, sizeof request);
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close(sock);
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/* do something with the reply */
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.Ed
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.Pp
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Note that, after the
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call to
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.Fn sendto ,
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the socket is now in the same state as if the
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.Xr connect 2
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and
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.Xr shutdown 2
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system calls had been used. That is to say, the only reasonable
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operations to perform on this socket are
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.Xr read 2
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and
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.Xr close 2 .
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(Because the client's
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.Tn TCP
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sender is already shut down, it is not possible to
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.Xr connect 2
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this socket to another destination.)
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.Sh SERVER SUPPORT
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There are two different options available for servers using
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.Tn T/TCP :
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.Bl -enum
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.It
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Set the
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.Dv TCP_NOPUSH
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socket option, and use normal
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.Xr write 2
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calls when formulating the response.
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.It
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Use
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.Xr sendto 2
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with the
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.Dv MSG_EOF
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flag, as in the client, but with the destination unspecified.
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.El
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.Pp
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The first option is generally the appropriate choice when converting
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existing servers to use
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.Tn T/TCP
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extensions; simply add a call to
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.Fn setsockopt sock IPPROTO_TCP TCP_NOPUSH &One "sizeof One"
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(where
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.Va One
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is an integer variable with a non-zero value). The server socket must
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be closed before any data is sent (unless the socket buffers fill up).
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.Pp
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The second option is preferable for new servers, and is sometimes easy
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enough to retrofit into older servers. In this case, where the reply
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phase would ordinarily have included a call to
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.Fn write ,
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one substitutes:
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.Pp
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.Dl "sendto(sock, buf, len, MSG_EOF, (struct sockaddr *)0, 0)"
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.Pp
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In this case, the reply is sent immediately, but as in the client
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case, the socket is no longer useful for anything and should be
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immediately closed.
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.Sh MIB VARIABLES
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The
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.Tn T/TCP
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extensions require the
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.Dq Li net.inet.tcp.rfc1644
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MIB variable to be true in order for the appropriate
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.Tn TCP
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options to be sent. See
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.Xr tcp 4
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for more information.
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.Sh SEE ALSO
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.Xr send 2 ,
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.Xr setsockopt 2 ,
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.Xr inet 4 ,
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.Xr tcp 4
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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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Support for
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.Tn T/TCP
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first appeared in
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.Fx 2.1 ,
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based on code written by Bob Braden and Liming Wei at the
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University of Southern California, Information Sciences Institute, and
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ported by Andras Olah at the University of Twente.
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