Snort Version 2.6.0

by Martin Roesch and The Snort Team (http://www.snort.org/team.html)

Distribution Site:
http://www.snort.org

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COPYRIGHT

Copyright (C)2001-2007 Sourcefire Inc.
Copyright (C)1998-2001 Martin Roesch

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License Version 2 as
published by the Free Software Foundation.  You may not use, modify or
distribute this program under any other version of the GNU General
Public License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

Some of this code has been taken from tcpdump, which was developed
by the Network Research Group at Lawrence Berkeley National Lab,
and is copyrighted by the University of California Regents.

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DESCRIPTION

Snort is an open source network intrusion detection and prevention system.  It
is capable of performing real-time traffic analysis, alerting, blocking and 
packet logging on IP networks.  It utilizes a combination of protocol analysis 
and pattern matchingin order to detect a anomalies, misuse and attacks.  
Snort uses a flexible rules language to describe activity that can be considered
malicious or anomalous as well as an analysis engine that incorporates a 
modular plugin architecture.  Snort is capable of detecting and responding in
real-time, sending alerts, performing session sniping, logging packets, or
dropping sessions/packets when deployed in-line.

Snort has three primary functional modes.  It can be used as a packet sniffer 
like tcpdump(1), a packet logger (useful for network traffic
debugging, etc), or as a full blown network intrusion detection and prevention
system.

Please read the snort_manual.pdf file that should be included with this 
distribution for full documentation on the program as well as a guide to 
getting started.


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[*][USAGE]

Command line: 

	snort -[options] <filters>

Options:

    -A <alert>  Set <alert> mode to full, fast or none.  Full mode
            does normal "classic Snort"-style alerts to the alert
            file.  Fast mode just writes the timestamp, message, 
            IP's, and ports to the file.  None turns off alerting.
            There is experimental support for UnixSock alerts 
            that allow alerting to a separate process.  Use the 
            "unsock" argument to activate this feature.  There's also
            the "cmg" option that prints out the full packet dump
            with the alert information.  The "console" option prints
            "fast" mode alerts to stdout, great for testing new rules
            and debugging preprocessor anomaly detectors.

    -b	    Log packets in tcpdump format.  All packets are logged
            in their native binary state to a tcpdump formatted 
            log file called "snort.log".  This option results in
            much faster operation of the program since it doesn't
            have to spend time in the packet binary->text
            converters.  Snort can keep up pretty well with 100Mbps
            networks in "-b" mode.

    -B <mask> Obfuscate IP addresses in alerts and packet dumps using 
            the provided CIDR mask as a substitution for the destination
            IP addresses in events.

    -c <cf>	Use configuration file <cf>.  This is puts Snort into IDS mode
            and it reads the runtime configuration from <cf>.

    -C      Dump the ASCII characters in packet payloads only, no
            hex dump.

    -d      Dump the application layer data.

    -D      Run Snort in daemon mode.  Alerts are sent to
            /var/log/snort/alert unless otherwise specified.

    -e      Display/log the layer 2 packet header data.

    -E      *WIN32 ONLY* Log alerts to the Windows Event Log.

    -f      Activate PCAP line buffering.

    -F <bpf> Read BPF filters from file <bpf>.  Handy for those of
            you running Snort as a SHADOW replacement or with a
            love of super complex BPF filters.

    -g <gname> Run Snort as group ID <gname> after initialization. 
            This switch allows Snort to drop root privileges after
            it's initialization phase has completed as a security
            measure.

    -G <id> Set a base event_id value for event generation, useful for
            unified logging and alerting primarily.

    -h <hn>	Set the "home network" to <hn>, which is a class C IP 
            address something like 192.168.1.0 or whatever.  If you
            use this switch, traffic coming from external networks
            will be formatted with the directional arrow of the 
            packet dump pointing right for incoming external 
            traffic, and left for outgoing internal traffic.  Kind
            of silly, but it looks nice.

    -i <if> Sniff on network interface <if>.  

    -I      Add the interface name to alert printouts (first interface only)

    -J <port> When running in in-line mode on a system with divert sockets
            this switch will select which <port> to read packets from.

    -k <checksum mode>
            Set <checksum mode> to all, noip, notcp, noudp, noicmp, or none.
            Setting this switch modifies the checksum verification subsystem of
            Snort to tune for maximum performance.  For example, in many
            situations Snort is behind a router or firewall that doesn't allow
            packets with bad checksums to pass, in which case it wouldn't make
            sense to have Snort re-verify checksums that have already been 
            checked.  Turning off specific checksum verification subsystems can
            improve performance by reducing the amount of time required to 
            inspect a packet.

    -K <logging mode>
            Set the packet output mode for logging.  There are three modes
            available, pcap, ascii and none.  Pcap mode is the default, if
            you don't specify a logging mode pcap is used now.  Pcap format
            is the same as the -b switch, tcpdump format.  Ascii format is
            the old default, it logs in the text-based "directories and files"<             format.  Be careful using ascii mode on uncontrolled networks, it
            can exhaust your filesystem's inodes.  None mode turns off packet
            logging.

    -l <ld> Log packets to directory <ld>.  Sets up a hierarchical
            directory structure with the log directory as the base
            starting directory, and the IP address of the remote
            peer generating traffic as the directory which packets
            packets from that address are stored in.  If you do not 
            use the -l switch, the default logging directory is 
            /var/log/snort.
          
    -L <fn> Set the binary output file's filename to <fn>.            

    -M      Log messages to syslog when running in non-daemon mode.
            Has no impact on logging of alerts.

    -m <mask> Set the umask for all of Snort's output files to the indicated 
            mask.

    -n <cnt> Exit after processing <cnt> packets.

    -N      Turn off logging.  Alerts still function normally.

    -o      Change the order in which the rules are applied to 
            packets.  Instead of being applied in the standard
            Alert->Pass->Log order, this will apply them in 
            Pass->Alert->Log order, allowing people to avoid having
            to make huge BPF command line arguments to filter their
            alert rules.  

    -O      Obfuscate the IP addresses when in ASCII packet dump
            mode.  This switch changes the IP addresses that get
            printed to the screen/log file to "xxx.xxx.xxx.xxx".
            If the homenet address switch is set (-h), only 
            addresses on the homenet will be obfuscated while non-
            homenet IP's will be left visible.  Perfect for posting
            to your favorite security mailing list!

    -p		Turn off promiscuous mode sniffing.  Useful for places
            where that can screw up your host severely.

    -P <snaplen> Set the snaplen of Snort to <snaplen>.  This filters how much 
            of each packet gets into Snort, the default is the MTU for the 
            interface that Snort is currently listening on.

    -q	    Quiet. Don't show banner and status report.			

    -Q      When running in-line, read packets from iptables/IPQ (on Linux).

    -r <tf>	Read packets from the pcap formatted file <tf>.  This will cause 
            Snort to read and process the file fed to it as if the file was the
            network.  This is essentially the same as tcpdump's readback mode.

    -R <name> Add a custom sufffix to the snort pidfile.

    -s      Log alert messages to the syslog.  On Linux boxen, they
	        will appear in /var/log/secure, /var/log/messages on
            many other platforms.  You can change the logging facility 
            by using the syslog output plugin, at which point the -s
            switch should not be used (command line alert/log switches
            override any config file output variables).    

	-S <n=v> Set variable name "n" to value "v".  This is useful for
            setting the value of a defined variable name in a Snort
            rules file to a command line specified value.  For
            instance, if you define a HOME_NET variable name inside
            of a Snort rules file, you can set this value from
            it's predefined value at the command line.

    -t <chroot> Changes Snort's root directory to <chroot> after 
            initialization.  Please note that all log/alert filenames
            are relevant to chroot directory, if chroot is used.

    -T      Snort will start up in self-test mode, checking all the supplied
            command line switches and rules files that are handed to it and
            indicating that everything is ready to proceed.  This is a good
            switch to use if daemon mode is going to be used, it verifies that
            the Snort configuration that is about to be used is valid and 
            won't fail at run time.

    -u <uname> Change the UID Snort runs under to <uname> after 
            initialization.

    -U      Turn on UTC timestamps.            

    -v		Be verbose.  Prints packets out to the console.  There
            is one big problem with verbose mode: it's still kind
            of slow.  If you are doing IDS work with Snort, don't
            use the -v switch, you WILL drop packets (not many, but
            some).

    -V      Show the version number and exit.

    -w      If running on a 802.11 network, show management frames.

    -W      *WIN32 ONLY* Enumerate the network interfaces available.

    -X      Dump the raw packet data starting at the link layer.

    -y      Turn on the year field in packet timestamps.

    -Z <path> Set the perfmon path/filename to <path>.

    -?      Show the usage summary and exit.

Longname options and their corresponding single char version
    --logid <0xid>                 Same as -G

    --perfmon-file <file>          Same as -Z

    --pid-path <path>              Specify the path for the Snort PID file

    --snaplen <snap>               Same as -P

    --help                         Same as -?

    --dynamic-engine-lib <file>
            Load a dynamic detection engine specified by <file>.

    --dynamic-detection-lib <file>
            Load a dynamic rules library specified by <file>.

    --dynamic-detection-lib-dir <path>
            Load all dynamic rules libraries from directory specified
            by <path>.

    --dump-dynamic-rules <path>
            Creates stub rule files of all loaded rules libraries
            specified by <path>.  Required to be done prior to
            runing snort to detect those rules.  Generated rules stub
            files must be 'include'ed in snort.conf.

    --dynamic-preprocessor-lib <file>
            Load a dynamic preprocessor library specified by <file>.

    --dynamic-preprocessor-lib-dir <path>
            Load all dynamic preprocessor libraries from directory
            specified by <path>.

    --dump-dynamic-preproc-genmsg <path>
            Creates gen-msg.map files of all loaded preprocessor
            libraries in <path>.

    --alert-before-pass
            Process alert, drop, sdrop, or reject before pass.
            Default is pass before alert, drop, etc.

    --treat-drop-as-alert
            Converts drop, sdrop, and reject rules into alert rules
            during startup.

    --process-all-events
            Process all triggered events in group order, per Rule Ordering
            configuration.  Default stops after first group.

    --pid-path <path>
            Specify the path for Snort's PID file.

    --create-pidfile
            Create PID file, even when not in Daemon mode.

[*][FILTERS]:

     The "filters" are standard BPF style filters as seen in tcpdump.  Look
at the man page for snort for docs on how to use it properly.  In general,
you can give it a host, net or protocol to filter on and some logical statements
to tie it together and get the specific traffic you're interested in.  For 
example:

[zeus ~]# ./snort -h 192.168.1.0/24 -d -v host 192.168.1.1

records the traffic to and from host 192.168.1.1.

[zeus ~]# ./snort -h 192.168.1.0/24 -d -v net 192.168.1 and not host 192.168.1.1

records all traffic on the 192.168.1.0/24 class C subnet, but not traffic 
to/from 192.168.1.1.  Notice that the command line data specified after the
"-h" switch is formated differently from the BPF commands provided at the end 
of the command line.  Sorry for the confusion, but I like the CIDR notation and
I'm not rewriting libpcap to make it consistent!  Anyway, you get the picture.
Mail me if you have trouble with it.

You can use the -F switch to read your BPF filters in from a file.  


[*][RULES]:
      
-------------------------------------------------------------------------
NOTE: The "official" rules document these days is available at:

http://www.snort.org/docs/writing_rules/

and is also usually distributed as snort_manual.pdf in the distro.  If
you don't have this file in your distribution of Snort, you can get it from
www.snort.org.
-------------------------------------------------------------------------

Please read the USAGE file or the snort_manual.pdf for more info!

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/* $Id$ */
