Manual page for ng_tcpmss.
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Gleb Smirnoff
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@ -209,6 +209,7 @@ MAN= aac.4 \
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ng_sppp.4 \
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ng_sscfu.4 \
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ng_sscop.4 \
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ng_tcpmss.4 \
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ng_tee.4 \
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ng_tty.4 \
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ng_ubt.4 \
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126
share/man/man4/ng_tcpmss.4
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126
share/man/man4/ng_tcpmss.4
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.\" Copyright (c) 2005 Gleb Smirnoff
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.\" 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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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.\" $FreeBSD$
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.\"
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.Dd June 9, 2005
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.Dt NG_TCPMSS 4
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.Os
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.Sh NAME
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.Nm ng_tcpmss
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.Nd netgraph node to adjust TCP MSS option
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.Sh SYNOPSIS
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.In netgraph/ng_tcpmss.h
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.Sh DESCRIPTION
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The
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.Nm tcpmss
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node type is designed to alter the Maximum Segment Size option
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of TCP packets.
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This node accepts an arbitrary number of hooks.
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Initially a new hook is considered unconfigured.
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To configure a hook, user should send
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.Dv NG_TCPMSS_CONFIG
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control message to node.
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.Sh CONTROL MESSAGES
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This node type supports the generic control messages, plus the following.
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.Bl -tag -width foo
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.It Dv NGM_TCPMSS_CONFIG Pq Ic config
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This control message configures node to do given MSS adjusting on
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particular hook.
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It requires the
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.Vt "struct ng_tcpmss_config"
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to be supplied as argument:
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.Bd -literal
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struct ng_tcpmss_config {
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char inHook[NG_HOOKSIZ];
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char outHook[NG_HOOKSIZ];
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uint16_t maxMSS;
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}
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.Ed
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.Pp
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This means: packets received on
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.Qq inHook
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would be checked for TCP MSS option and the latter would be
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reduced down to
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.Qq maxMSS ,
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if it exceeds
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.Qq maxMSS .
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After that packets would be sent to hook
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.Qq outHook .
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.It Dv NGM_TCPMSS_GET_STATS Pq Ic getstats
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This control message obtains statistics for the given hook.
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The statistics are returned in
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.Vt "struct ng_tcpmss_hookstat" :
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.Bd -literal
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struct ng_tcpmss_hookstat {
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uint64_t Octets; /* total bytes */
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uint64_t Packets; /* total packets */
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uint16_t maxMSS; /* maximum MSS */
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uint64_t SYNPkts; /* TCP SYN packets */
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uint64_t FixedPkts; /* changed packets */
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};
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.Ed
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.Pp
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.It Dv NGM_TCPMSS_CLR_STATS Pq Ic clrstats
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This control message clears statistics for the given hook.
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.It Dv NGM_TCPMSS_GETCLR_STATS Pq Ic getclrstats
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This control message obtains and clears statistics for the given hook.
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.El
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.Sh EXAMPLES
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In the following example packets are injected into
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.Nm
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node with help of
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.Xr ng_ipfw 4
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node.
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.Bd -literal -offset indent
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# Create tcpmss node and connect it to ng_ipfw node
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ngctl mkpeer ipfw: tcpmss 100 qqq
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# Adjust MSS to 1452
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ngctl msg ipfw:100 config '{ inHook="qqq" outHook="qqq" maxMSS=1452 }'
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# Divert traffic into tcpmss node
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ipfw add 300 netgraph 100 tcp from any to any tcpflags syn out via fxp0
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# Let packets continue with ipfw after being hacked
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sysctl net.inet.ip.fw.one_pass=0
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.Ed
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.Sh SHUTDOWN
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This node shuts down upon receipt of an
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.Dv NGM_SHUTDOWN
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control message, or when all hooks have been disconnected.
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.Sh SEE ALSO
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.Xr netgraph 4 ,
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.Xr ng_ipfw 4
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.Sh HISTORY
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The
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.Nm
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node type was implemented in
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.Fx 6.0 .
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.Sh AUTHORS
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.An Alexey Popov Aq lollypop@flexuser.ru
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and
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.An Gleb Smirnoff Aq glebius@FreeBSD.org
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.Sh BUGS
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When running on SMP system statistics may be broken.
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