1.\" Copyright (c) 2005 Gleb Smirnoff 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.Dd June 9, 2005 26.Dt NG_TCPMSS 4 27.Os 28.Sh NAME 29.Nm ng_tcpmss 30.Nd "netgraph node to adjust TCP MSS option" 31.Sh SYNOPSIS 32.In netgraph.h 33.In netgraph/ng_tcpmss.h 34.Sh DESCRIPTION 35The 36.Nm tcpmss 37node type is designed to alter the Maximum Segment Size option 38of TCP packets. 39This node accepts an arbitrary number of hooks. 40Initially a new hook is considered unconfigured. 41The 42.Dv NG_TCPMSS_CONFIG 43control message is used to configure a hook. 44.Sh CONTROL MESSAGES 45This node type supports the generic control messages, plus the following. 46.Bl -tag -width foo 47.It Dv NGM_TCPMSS_CONFIG Pq Ic config 48This control message configures node to do given MSS adjusting on 49a particular hook. 50It requires the 51.Vt "struct ng_tcpmss_config" 52to be supplied as an argument: 53.Bd -literal 54struct ng_tcpmss_config { 55 char inHook[NG_HOOKSIZ]; 56 char outHook[NG_HOOKSIZ]; 57 uint16_t maxMSS; 58} 59.Ed 60.Pp 61This means: packets received on 62.Va inHook 63would be checked for TCP MSS option and the latter would be 64reduced down to 65.Va maxMSS 66if it exceeds 67.Va maxMSS . 68After that, packets would be sent to hook 69.Va outHook . 70.It Dv NGM_TCPMSS_GET_STATS Pq Ic getstats 71This control message obtains statistics for a given hook. 72The statistics are returned in 73.Vt "struct ng_tcpmss_hookstat" : 74.Bd -literal 75struct ng_tcpmss_hookstat { 76 uint64_t Octets; /* total bytes */ 77 uint64_t Packets; /* total packets */ 78 uint16_t maxMSS; /* maximum MSS */ 79 uint64_t SYNPkts; /* TCP SYN packets */ 80 uint64_t FixedPkts; /* changed packets */ 81}; 82.Ed 83.It Dv NGM_TCPMSS_CLR_STATS Pq Ic clrstats 84This control message clears statistics for a given hook. 85.It Dv NGM_TCPMSS_GETCLR_STATS Pq Ic getclrstats 86This control message obtains and clears statistics for a given hook. 87.El 88.Sh EXAMPLES 89In the following example, packets are injected into the 90.Nm tcpmss 91node using the 92.Xr ng_ipfw 4 93node. 94.Bd -literal -offset indent 95# Create tcpmss node and connect it to ng_ipfw node 96ngctl mkpeer ipfw: tcpmss 100 qqq 97 98# Adjust MSS to 1452 99ngctl msg ipfw:100 config '{ inHook="qqq" outHook="qqq" maxMSS=1452 }' 100 101# Divert traffic into tcpmss node 102ipfw add 300 netgraph 100 tcp from any to any tcpflags syn out via fxp0 103 104# Let packets continue with ipfw after being hacked 105sysctl net.inet.ip.fw.one_pass=0 106.Ed 107.Sh SHUTDOWN 108This node shuts down upon receipt of an 109.Dv NGM_SHUTDOWN 110control message, or when all hooks have been disconnected. 111.Sh SEE ALSO 112.Xr netgraph 4 , 113.Xr ng_ipfw 4 114.Sh HISTORY 115The 116.Nm 117node type was implemented in 118.Fx 6.0 . 119.Sh AUTHORS 120.An Alexey Popov Aq Mt lollypop@flexuser.ru 121.An Gleb Smirnoff Aq Mt glebius@FreeBSD.org 122.Sh BUGS 123When running on SMP, system statistics may be broken. 124