Snort Version 2.4.2

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)2001-2005 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 as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

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

-n <num> Exit after processing <num> 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 Enumerate the network interfaces available on a win32 system.

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

-y Turn on the year field in packet timestamps.

-z The -z switch is deprecated.

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

-? Show the usage summary and exit.


[*][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: README,v 1.23.6.3 2005/09/28 02:32:29 roesch Exp $ */