7646a84161
it will be output on its own line. Ns cancels this effect however. This change is also consistent with the rest of our manual pages.
762 lines
25 KiB
Groff
762 lines
25 KiB
Groff
.\"
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.\" Copyright (c) 2010 The FreeBSD Foundation
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.\" All rights reserved.
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.\"
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.\" Portions of this software were developed at the Centre for Advanced
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.\" Internet Architectures, Swinburne University of Technology, Melbourne,
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.\" Australia by Lawrence Stewart under sponsorship from the FreeBSD
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.\" Foundation.
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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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.\" without modification, immediately at the beginning of the file.
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.\" 2. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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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 FOR
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.\" 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 November 12, 2010
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.Dt SIFTR 4
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.Os
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.Sh NAME
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.Nm SIFTR
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.Nd Statistical Information For TCP Research
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.Sh SYNOPSIS
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To load
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the driver
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as a module at run-time, run the following command as root:
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.Bd -literal -offset indent
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kldload siftr
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.Ed
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.Pp
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Alternatively, to load
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the driver
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as a module at boot time, add the following line into the
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.Xr loader.conf 5
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file:
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.Bd -literal -offset indent
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siftr_load="YES"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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.Po
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.Em S Ns tatistical
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.Em I Ns nformation
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.Em F Ns or
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.Em T Ns CP
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.Em R Ns esearch
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.Pc
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kernel module logs a range of statistics on active TCP connections to
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a log file.
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It provides the ability to make highly granular measurements of TCP connection
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state, aimed at system administrators, developers and researchers.
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.Ss Compile-time Configuration
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The default operation of
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.Nm
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is to capture IPv4 TCP/IP packets.
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.Nm
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|
can be configured to support IPv4 and IPv6 by uncommenting:
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.Bd -literal -offset indent
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CFLAGS+=-DSIFTR_IPV6
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.Ed
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.Pp
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in
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.Aq sys/modules/siftr/Makefile
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and recompiling.
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.Pp
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In the IPv4-only (default) mode, standard dotted decimal notation (e.g.
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"136.186.229.95") is used to format IPv4 addresses for logging.
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In IPv6 mode, standard dotted decimal notation is used to format IPv4 addresses,
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and standard colon-separated hex notation (see RFC 4291) is used to format IPv6
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addresses for logging. Note that SIFTR uses uncompressed notation to format IPv6
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addresses.
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For example, the address "fe80::20f:feff:fea2:531b" would be logged as
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"fe80:0:0:0:20f:feff:fea2:531b".
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.Ss Run-time Configuration
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.Nm
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|
utilises the
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.Xr sysctl 8
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|
interface to export its configuration variables to user-space.
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|
The following variables are available:
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.Bl -tag -offset indent
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.It Va net.inet.siftr.enabled
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|
controls whether the module performs its
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measurements or not.
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|
By default, the value is set to 0, which means the module
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will not be taking any measurements.
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Having the module loaded with
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.Va net.inet.siftr.enabled
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|
set to 0 will have no impact on the performance of the network stack, as the
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packet filtering hooks are only inserted when
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.Va net.inet.siftr.enabled
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is set to 1.
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.El
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.Bl -tag -offset indent
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.It Va net.inet.siftr.ppl
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controls how many inbound/outbound packets for a given TCP connection will cause
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a log message to be generated for the connection.
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By default, the value is set to 1, which means the module will log a message for
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every packet of every TCP connection.
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The value can be set to any integer in the range [1,2^32], and can be changed at
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any time, even while the module is enabled.
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.El
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.Bl -tag -offset indent
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.It Va net.inet.siftr.logfile
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controls the path to the file that the module writes its log messages to.
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By default, the file /var/log/siftr.log is used.
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The path can be changed at any time, even while the module is enabled.
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.El
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.Bl -tag -offset indent
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.It Va net.inet.siftr.genhashes
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controls whether a hash is generated for each TCP packet seen by
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.Nm .
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By default, the value is set to 0, which means no hashes are generated.
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The hashes are useful to correlate which TCP packet triggered the generation of
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a particular log message, but calculating them adds additional computational
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overhead into the fast path.
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.El
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.Ss Log Format
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A typical
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.Nm
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log file will contain 3 different types of log message.
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All messages are written in plain ASCII text.
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.Pp
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Note: The
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.Qq \e
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present in the example log messages in this section indicates a
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line continuation and is not part of the actual log message.
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.Pp
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The first type of log message is written to the file when the module is
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enabled and starts collecting data from the running kernel. The text below
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shows an example module enable log. The fields are tab delimited key-value
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pairs which describe some basic information about the system.
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.Bd -literal -offset indent
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enable_time_secs=1238556193 enable_time_usecs=462104 \\
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siftrver=1.2.2 hz=1000 tcp_rtt_scale=32 \\
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sysname=FreeBSD sysver=604000 ipmode=4
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.Ed
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.Pp
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Field descriptions are as follows:
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.Bl -tag -offset indent
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.It Va enable_time_secs
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time at which the module was enabled, in seconds since the UNIX epoch.
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.El
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.Bl -tag -offset indent
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.It Va enable_time_usecs
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time at which the module was enabled, in microseconds since enable_time_secs.
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.El
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.Bl -tag -offset indent
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.It Va siftrver
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version of
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.Nm .
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.El
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.Bl -tag -offset indent
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.It Va hz
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tick rate of the kernel in ticks per second.
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.El
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.Bl -tag -offset indent
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.It Va tcp_rtt_scale
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smoothed RTT estimate scaling factor.
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.El
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.Bl -tag -offset indent
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.It Va sysname
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operating system name.
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.El
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.Bl -tag -offset indent
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.It Va sysver
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operating system version.
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.El
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.Bl -tag -offset indent
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.It Va ipmode
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IP mode as defined at compile time.
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An ipmode of "4" means IPv6 is not supported and IP addresses are logged in
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regular dotted quad format.
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An ipmode of "6" means IPv6 is supported, and IP addresses are logged in dotted
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quad or hex format, as described in the
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.Qq Compile-time Configuration
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subsection.
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.El
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.Pp
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|
The second type of log message is written to the file when a data log message
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is generated.
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The text below shows an example data log triggered by an IPv4
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TCP/IP packet.
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The data is CSV formatted.
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.Bd -literal -offset indent
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o,0xbec491a5,1238556193.463551,172.16.7.28,22,172.16.2.5,55931, \\
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1073725440,172312,6144,66560,66608,8,1,4,1448,936,1,996,255, \\
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33304,208,66608,0,208,0
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.Ed
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.Pp
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Field descriptions are as follows:
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.Bl -tag -offset indent
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.It Va 1
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Direction of packet that triggered the log message.
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Either
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.Qq i
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for in, or
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.Qq o
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for out.
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.El
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.Bl -tag -offset indent
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.It Va 2
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Hash of the packet that triggered the log message.
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.El
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.Bl -tag -offset indent
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.It Va 3
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Time at which the packet that triggered the log message was processed by
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the
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.Xr pfil 9
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hook function, in seconds and microseconds since the UNIX epoch.
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.El
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.Bl -tag -offset indent
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.It Va 4
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The IPv4 or IPv6 address of the local host, in dotted quad (IPv4 packet)
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or colon-separated hex (IPv6 packet) notation.
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.El
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.Bl -tag -offset indent
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.It Va 5
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The TCP port that the local host is communicating via.
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.El
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.Bl -tag -offset indent
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.It Va 6
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The IPv4 or IPv6 address of the foreign host, in dotted quad (IPv4 packet)
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or colon-separated hex (IPv6 packet) notation.
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.El
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.Bl -tag -offset indent
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.It Va 7
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The TCP port that the foreign host is communicating via.
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.El
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.Bl -tag -offset indent
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.It Va 8
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The slow start threshold for the flow, in bytes.
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.El
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.Bl -tag -offset indent
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.It Va 9
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The current congestion window for the flow, in bytes.
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.El
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.Bl -tag -offset indent
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.It Va 10
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The current bandwidth-controlled window for the flow, in bytes.
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.El
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.Bl -tag -offset indent
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.It Va 11
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The current sending window for the flow, in bytes.
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The post scaled value is reported, except during the initial handshake (first
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few packets), during which time the unscaled value is reported.
|
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.El
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.Bl -tag -offset indent
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.It Va 12
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The current receive window for the flow, in bytes.
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The post scaled value is always reported.
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.El
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.Bl -tag -offset indent
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.It Va 13
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The current window scaling factor for the sending window.
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.El
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.Bl -tag -offset indent
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.It Va 14
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The current window scaling factor for the receiving window.
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.El
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.Bl -tag -offset indent
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.It Va 15
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The current state of the TCP finite state machine, as defined
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in
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.Aq Pa netinet/tcp_fsm.h .
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.El
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.Bl -tag -offset indent
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.It Va 16
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The maximum segment size for the flow, in bytes.
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.El
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.Bl -tag -offset indent
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.It Va 17
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The current smoothed RTT estimate for the flow, in units of TCP_RTT_SCALE * HZ,
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where TCP_RTT_SCALE is a define found in tcp_var.h, and HZ is the kernel's tick
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timer.
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|
Divide by TCP_RTT_SCALE * HZ to get the RTT in secs. TCP_RTT_SCALE and HZ are
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reported in the enable log message.
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.El
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.Bl -tag -offset indent
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.It Va 18
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SACK enabled indicator. 1 if SACK enabled, 0 otherwise.
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.El
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.Bl -tag -offset indent
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.It Va 19
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The current state of the TCP flags for the flow.
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See
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.Aq Pa netinet/tcp_var.h
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for information about the various flags.
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.El
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.Bl -tag -offset indent
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.It Va 20
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The current retransmission timeout length for the flow, in units of HZ, where HZ
|
|
is the kernel's tick timer.
|
|
Divide by HZ to get the timeout length in seconds. HZ is reported in the
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enable log message.
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.El
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.Bl -tag -offset indent
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.It Va 21
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|
The current size of the socket send buffer in bytes.
|
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.El
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.Bl -tag -offset indent
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.It Va 22
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The current number of bytes in the socket send buffer.
|
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.El
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.Bl -tag -offset indent
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.It Va 23
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The current size of the socket receive buffer in bytes.
|
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.El
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.Bl -tag -offset indent
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.It Va 24
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The current number of bytes in the socket receive buffer.
|
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.El
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.Bl -tag -offset indent
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.It Va 25
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The current number of unacknowledged bytes in-flight.
|
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Bytes acknowledged via SACK are not excluded from this count.
|
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.El
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.Bl -tag -offset indent
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.It Va 26
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The current number of segments in the reassembly queue.
|
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.El
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.Pp
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|
The third type of log message is written to the file when the module is disabled
|
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and ceases collecting data from the running kernel.
|
|
The text below shows an example module disable log.
|
|
The fields are tab delimited key-value pairs which provide statistics about
|
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operations since the module was most recently enabled.
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.Bd -literal -offset indent
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disable_time_secs=1238556197 disable_time_usecs=933607 \\
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num_inbound_tcp_pkts=356 num_outbound_tcp_pkts=627 \\
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total_tcp_pkts=983 num_inbound_skipped_pkts_malloc=0 \\
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num_outbound_skipped_pkts_malloc=0 num_inbound_skipped_pkts_mtx=0 \\
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num_outbound_skipped_pkts_mtx=0 num_inbound_skipped_pkts_tcb=0 \\
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num_outbound_skipped_pkts_tcb=0 num_inbound_skipped_pkts_icb=0 \\
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num_outbound_skipped_pkts_icb=0 total_skipped_tcp_pkts=0 \\
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flow_list=172.16.7.28;22-172.16.2.5;55931,
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.Ed
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.Pp
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Field descriptions are as follows:
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.Bl -tag -offset indent
|
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.It Va disable_time_secs
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|
Time at which the module was disabled, in seconds since the UNIX epoch.
|
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.El
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.Bl -tag -offset indent
|
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.It Va disable_time_usecs
|
|
Time at which the module was disabled, in microseconds since disable_time_secs.
|
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.El
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|
.Bl -tag -offset indent
|
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.It Va num_inbound_tcp_pkts
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Number of TCP packets that traversed up the network stack.
|
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This only includes inbound TCP packets during the periods when
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.Nm
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was enabled.
|
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.El
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.Bl -tag -offset indent
|
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.It Va num_outbound_tcp_pkts
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Number of TCP packets that traversed down the network stack.
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This only includes outbound TCP packets during the periods when
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.Nm
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was enabled.
|
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.El
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.Bl -tag -offset indent
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.It Va total_tcp_pkts
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The summation of num_inbound_tcp_pkts and num_outbound_tcp_pkts.
|
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.El
|
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.Bl -tag -offset indent
|
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.It Va num_inbound_skipped_pkts_malloc
|
|
Number of inbound packets that were not processed because of failed malloc() calls.
|
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.El
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.Bl -tag -offset indent
|
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.It Va num_outbound_skipped_pkts_malloc
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Number of outbound packets that were not processed because of failed malloc() calls.
|
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.El
|
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.Bl -tag -offset indent
|
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.It Va num_inbound_skipped_pkts_mtx
|
|
Number of inbound packets that were not processed because of failure to add the
|
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packet to the packet processing queue.
|
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.El
|
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.Bl -tag -offset indent
|
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.It Va num_outbound_skipped_pkts_mtx
|
|
Number of outbound packets that were not processed because of failure to add the
|
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packet to the packet processing queue.
|
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.El
|
|
.Bl -tag -offset indent
|
|
.It Va num_inbound_skipped_pkts_tcb
|
|
Number of inbound packets that were not processed because of failure to find the
|
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TCP control block associated with the packet.
|
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.El
|
|
.Bl -tag -offset indent
|
|
.It Va num_outbound_skipped_pkts_tcb
|
|
Number of outbound packets that were not processed because of failure to find
|
|
the TCP control block associated with the packet.
|
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.El
|
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.Bl -tag -offset indent
|
|
.It Va num_inbound_skipped_pkts_icb
|
|
Number of inbound packets that were not processed because of failure to find the
|
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IP control block associated with the packet.
|
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.El
|
|
.Bl -tag -offset indent
|
|
.It Va num_outbound_skipped_pkts_icb
|
|
Number of outbound packets that were not processed because of failure to find
|
|
the IP control block associated with the packet.
|
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.El
|
|
.Bl -tag -offset indent
|
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.It Va total_skipped_tcp_pkts
|
|
The summation of all skipped packet counters.
|
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.El
|
|
.Bl -tag -offset indent
|
|
.It Va flow_list
|
|
A CSV list of TCP flows that triggered data log messages to be generated since
|
|
the module was loaded.
|
|
Each flow entry in the CSV list is
|
|
formatted as
|
|
.Qq local_ip;local_port-foreign_ip;foreign_port .
|
|
If there are no entries in the list (i.e. no data log messages were generated),
|
|
the value will be blank.
|
|
If there is at least one entry in the list, a trailing comma will always be
|
|
present.
|
|
.El
|
|
.Pp
|
|
The total number of data log messages found in the log file for a module
|
|
enable/disable cycle should equate to total_tcp_pkts - total_skipped_tcp_pkts.
|
|
.Sh IMPLEMENTATION NOTES
|
|
.Nm
|
|
hooks into the network stack using the
|
|
.Xr pfil 9
|
|
interface.
|
|
In its current incarnation, it hooks into the AF_INET/AF_INET6 (IPv4/IPv6)
|
|
.Xr pfil 9
|
|
filtering points, which means it sees packets at the IP layer of the network
|
|
stack.
|
|
This means that TCP packets inbound to the stack are intercepted before
|
|
they have been processed by the TCP layer.
|
|
Packets outbound from the stack are intercepted after they have been processed
|
|
by the TCP layer.
|
|
.Pp
|
|
The diagram below illustrates how
|
|
.Nm
|
|
inserts itself into the stack.
|
|
.Bd -literal -offset indent
|
|
----------------------------------
|
|
Upper Layers
|
|
----------------------------------
|
|
^ |
|
|
| |
|
|
| |
|
|
| v
|
|
TCP in TCP out
|
|
----------------------------------
|
|
^ |
|
|
|________ _________|
|
|
| |
|
|
| v
|
|
---------
|
|
| SIFTR |
|
|
---------
|
|
^ |
|
|
________| |__________
|
|
| |
|
|
| v
|
|
IPv{4/6} in IPv{4/6} out
|
|
----------------------------------
|
|
^ |
|
|
| |
|
|
| v
|
|
Layer 2 in Layer 2 out
|
|
----------------------------------
|
|
Physical Layer
|
|
----------------------------------
|
|
.Ed
|
|
.Pp
|
|
.Nm
|
|
uses the
|
|
.Xr alq 9
|
|
interface to manage writing data to disk.
|
|
.Pp
|
|
At first glance, you might mistakenly think that
|
|
.Nm
|
|
extracts information from
|
|
individual TCP packets.
|
|
This is not the case.
|
|
.Nm
|
|
uses TCP packet events (inbound and outbound) for each TCP flow originating from
|
|
the system to trigger a dump of the state of the TCP control block for that
|
|
flow.
|
|
With the PPL set to 1, we are in effect sampling each TCP flow's control block
|
|
state as frequently as flow packets enter/leave the system.
|
|
For example, setting PPL to 2 halves the sampling rate i.e. every second flow
|
|
packet (inbound OR outbound) causes a dump of the control block state.
|
|
.Pp
|
|
The distinction between interrogating individual packets vs interrogating the
|
|
control block is important, because
|
|
.Nm
|
|
does not remove the need for packet capturing tools like
|
|
.Xr tcpdump 1 .
|
|
.Nm
|
|
allows you to correlate and observe the cause-and-affect relationship between
|
|
what you see on the wire (captured using a tool like
|
|
.Xr tcpdump 1 Ns )
|
|
and changes in the TCP control block corresponding to the flow of interest.
|
|
It is therefore useful to use
|
|
.Nm
|
|
and a tool like
|
|
.Xr tcpdump 1
|
|
to gather the necessary data to piece together the complete picture.
|
|
Use of either tool on its own will not be able to provide all of the necessary
|
|
data.
|
|
.Pp
|
|
As a result of needing to interrogate the TCP control block, certain packets
|
|
during the lifecycle of a connection are unable to trigger a
|
|
.Nm
|
|
log message.
|
|
The initial handshake takes place without the existence of a control block and
|
|
the final ACK is exchanged when the connection is in the TIMEWAIT state.
|
|
.Pp
|
|
.Nm
|
|
was designed to minimise the delay introduced to packets traversing the network
|
|
stack.
|
|
This design called for a highly optimised and minimal hook function that
|
|
extracted the minimal details necessary whilst holding the packet up, and
|
|
passing these details to another thread for actual processing and logging.
|
|
.Pp
|
|
This multithreaded design does introduce some contention issues when accessing
|
|
the data structure shared between the threads of operation.
|
|
When the hook function tries to place details in the structure, it must first
|
|
acquire an exclusive lock.
|
|
Likewise, when the processing thread tries to read details from the structure,
|
|
it must also acquire an exclusive lock to do so.
|
|
If one thread holds the lock, the other must wait before it can obtain it.
|
|
This does introduce some additional bounded delay into the kernel's packet
|
|
processing code path.
|
|
.Pp
|
|
In some cases (e.g. low memory, connection termination), TCP packets that enter
|
|
the
|
|
.Nm
|
|
.Xr pfil 9
|
|
hook function will not trigger a log message to be generated.
|
|
.Nm
|
|
refers to this outcome as a
|
|
.Qq skipped packet .
|
|
Note that
|
|
.Nm
|
|
always ensures that packets are allowed to continue through the stack, even if
|
|
they could not successfully trigger a data log message.
|
|
.Nm
|
|
will therefore not introduce any packet loss for TCP/IP packets traversing the
|
|
network stack.
|
|
.Ss Important Behaviours
|
|
The behaviour of a log file path change whilst the module is enabled is as
|
|
follows:
|
|
.Bl -enum
|
|
.It
|
|
Attempt to open the new file path for writing.
|
|
If this fails, the path change will fail and the existing path will continue to
|
|
be used.
|
|
.It
|
|
Assuming the new path is valid and opened successfully:
|
|
.Bl -dash
|
|
.It
|
|
Flush all pending log messages to the old file path.
|
|
.It
|
|
Close the old file path.
|
|
.It
|
|
Switch the active log file pointer to point at the new file path.
|
|
.It
|
|
Commence logging to the new file.
|
|
.El
|
|
.El
|
|
.Pp
|
|
During the time between the flush of pending log messages to the old file and
|
|
commencing logging to the new file, new log messages will still be generated and
|
|
buffered.
|
|
As soon as the new file path is ready for writing, the accumulated log messages
|
|
will be written out to the file.
|
|
.Sh EXAMPLES
|
|
To enable the module's operations, run the following command as root:
|
|
sysctl net.inet.siftr.enabled=1
|
|
.Pp
|
|
To change the granularity of log messages such that 1 log message is
|
|
generated for every 10 TCP packets per connection, run the following
|
|
command as root:
|
|
sysctl net.inet.siftr.ppl=10
|
|
.Pp
|
|
To change the log file location to /tmp/siftr.log, run the following
|
|
command as root:
|
|
sysctl net.inet.siftr.logfile=/tmp/siftr.log
|
|
.Sh SEE ALSO
|
|
.Xr tcpdump 1 ,
|
|
.Xr tcp 4 ,
|
|
.Xr sysctl 8 ,
|
|
.Xr alq 9 ,
|
|
.Xr pfil 9
|
|
.Sh ACKNOWLEDGEMENTS
|
|
Development of this software was made possible in part by grants from the
|
|
Cisco University Research Program Fund at Community Foundation Silicon Valley,
|
|
and the FreeBSD Foundation.
|
|
.Sh HISTORY
|
|
.Nm
|
|
first appeared in
|
|
.Fx 7.4
|
|
and
|
|
.Fx 8.2 .
|
|
.Pp
|
|
.Nm
|
|
was first released in 2007 by Lawrence Stewart and James Healy whilst working on
|
|
the NewTCP research project at Swinburne University of Technology's Centre for
|
|
Advanced Internet Architectures, Melbourne, Australia, which was made possible
|
|
in part by a grant from the Cisco University Research Program Fund at Community
|
|
Foundation Silicon Valley.
|
|
More details are available at:
|
|
.Pp
|
|
http://caia.swin.edu.au/urp/newtcp/
|
|
.Pp
|
|
Work on
|
|
.Nm
|
|
v1.2.x was sponsored by the FreeBSD Foundation as part of
|
|
the
|
|
.Qq Enhancing the FreeBSD TCP Implementation
|
|
project 2008-2009.
|
|
More details are available at:
|
|
.Pp
|
|
http://www.freebsdfoundation.org/
|
|
.Pp
|
|
http://caia.swin.edu.au/freebsd/etcp09/
|
|
.Sh AUTHORS
|
|
.An -nosplit
|
|
.Nm
|
|
was written by
|
|
.An Lawrence Stewart Aq lstewart@FreeBSD.org
|
|
and
|
|
.An James Healy Aq jimmy@deefa.com .
|
|
.Pp
|
|
This manual page was written by
|
|
.An Lawrence Stewart Aq lstewart@FreeBSD.org .
|
|
.Sh BUGS
|
|
Current known limitations and any relevant workarounds are outlined below:
|
|
.Bl -dash
|
|
.It
|
|
The internal queue used to pass information between the threads of operation is
|
|
currently unbounded.
|
|
This allows
|
|
.Nm
|
|
to cope with bursty network traffic, but sustained high packet-per-second
|
|
traffic can cause exhaustion of kernel memory if the processing thread cannot
|
|
keep up with the packet rate.
|
|
.It
|
|
If using
|
|
.Nm
|
|
on a machine that is also running other modules utilising the
|
|
.Xr pfil 9
|
|
framework e.g.
|
|
.Xr dummynet 4 ,
|
|
.Xr ipfw 8 ,
|
|
.Xr pf 4 Ns ,
|
|
the order in which you load the modules is important.
|
|
You should kldload the other modules first, as this will ensure TCP packets
|
|
undergo any necessary manipulations before
|
|
.Nm
|
|
.Qq sees
|
|
and processes them.
|
|
.It
|
|
There is a known, harmless lock order reversal warning between the
|
|
.Xr pfil 9
|
|
mutex and tcbinfo TCP lock reported by
|
|
.Xr witness 4
|
|
when
|
|
.Nm
|
|
is enabled in a kernel compiled with
|
|
.Xr witness 4
|
|
support.
|
|
.It
|
|
There is no way to filter which TCP flows you wish to capture data for.
|
|
Post processing is required to separate out data belonging to particular flows
|
|
of interest.
|
|
.It
|
|
The module does not detect deletion of the log file path.
|
|
New log messages will simply be lost if the log file being used by
|
|
.Nm
|
|
is deleted whilst the module is set to use the file.
|
|
Switching to a new log file using the
|
|
.Em net.inet.siftr.logfile
|
|
variable will create the new file and allow log messages to begin being written
|
|
to disk again.
|
|
The new log file path must differ from the path to the deleted file.
|
|
.It
|
|
The hash table used within the code is sized to hold 65536 flows. This is not a
|
|
hard limit, because chaining is used to handle collisions within the hash table
|
|
structure.
|
|
However, we suspect (based on analogies with other hash table performance data)
|
|
that the hash table look up performance (and therefore the module's packet
|
|
processing performance) will degrade in an exponential manner as the number of
|
|
unique flows handled in a module enable/disable cycle approaches and surpasses
|
|
65536.
|
|
.It
|
|
There is no garbage collection performed on the flow hash table.
|
|
The only way currently to flush it is to disable
|
|
.Nm .
|
|
.It
|
|
The PPL variable applies to packets that make it into the processing thread,
|
|
not total packets received in the hook function.
|
|
Packets are skipped before the PPL variable is applied, which means there may be
|
|
a slight discrepancy in the triggering of log messages.
|
|
For example, if PPL was set to 10, and the 8th packet since the last log message
|
|
is skipped, the 11th packet will actually trigger the log message to be
|
|
generated.
|
|
This is discussed in greater depth in CAIA technical report 070824A.
|
|
.It
|
|
At the time of writing, there was no simple way to hook into the TCP layer
|
|
to intercept packets.
|
|
.Nm Ap s
|
|
use of IP layer hook points means all IP
|
|
traffic will be processed by the
|
|
.Nm
|
|
.Xr pfil 9
|
|
hook function, which introduces minor, but nonetheless unnecessary packet delay
|
|
and processing overhead on the system for non-TCP packets as well.
|
|
Hooking in at the IP layer is also not ideal from the data gathering point of
|
|
view.
|
|
Packets traversing up the stack will be intercepted and cause a log message
|
|
generation BEFORE they have been processed by the TCP layer, which means we
|
|
cannot observe the cause-and-affect relationship between inbound events and the
|
|
corresponding TCP control block as precisely as could be.
|
|
Ideally,
|
|
.Nm
|
|
should intercept packets after they have been processed by the TCP layer i.e.
|
|
intercept packets coming up the stack after they have been processed by
|
|
tcp_input(), and intercept packets coming down the stack after they have been
|
|
processed by tcp_output().
|
|
The current code still gives satisfactory granularity though, as inbound events
|
|
tend to trigger outbound events, allowing the cause-and-effect to be observed
|
|
indirectly by capturing the state on outbound events as well.
|
|
.It
|
|
The
|
|
.Qq inflight bytes
|
|
value logged by
|
|
.Nm
|
|
does not take into account bytes that have been
|
|
.No SACK Ap ed
|
|
by the receiving host.
|
|
.It
|
|
Packet hash generation does not currently work for IPv6 based TCP packets.
|
|
.It
|
|
Compressed notation is not used for IPv6 address representation.
|
|
This consumes more bytes than is necessary in log output.
|
|
.El
|