[Snort-users] Difference of Alerts, Snort Logs, and Tcpdumps

frederick sonnichsen fsonnichsen at ...315...
Tue Mar 4 13:46:46 EST 2008


OK and thanks Seth.
 It helps to undstand what the logs mean. For some reason the old way of 
controlling these no longer works. I have checked release notes and the 
FAQ but little is said there.

In my OLD implementation the configuration appears likes this:
snort.conf:
    output alert_syslog: LOG_LOCAL0 LOG_ALERT
    output log_tcpdump: tcpdump.log
syslog.conf
     local0.*                                                
/var/log/snort/snortlog.log
As expected I get a dump of ASCII alerts in snortlog.log and a bin dump 
in tcpdump.log

However when I try the same parms in my new implementation on Fedore 
Core6 with snort 2.8.0.2,
If I start with
24905 ?        Ss     0:02 /usr/sbin/snort -D -i eth3 -u root -g snort 
-c /etc/snort/snort.conf -l /var/log/snort

I get only the tcpdump log:
-rw------- 1 root snort 268022 Mar  4 13:06 tcpdump.log.1204653931
and my /var/log/messages receives all the alerts

I changed the startup to include -A and -b
25023 ?        Ss     0:00 /usr/sbin/snort -A fast -b -D -i eth3 -u root 
-g snort -c /etc/snort/snort.conf -l /var/log/snort
resulting files
-rw------- 1 root snort  84701 Mar  4 13:04 alert
-rw------- 1 root snort 298787 Mar  4 13:04 snort.log.1204653811

I am not sure if something changed in the snort.conf but I have tried 
several variations on the startup parms (-a, -M -b), on snort.conf and 
with the syslog.conf but I cannot get my original function back. (e.g. 
alerts in snortlog.log and dump in tcpdump.log.xxxxxxxx
==============================================================

>Fritz,
>
>Alerts are stored in ASCII.  You can cat, tail, less, etc. that file.
>snortlog.log is most likely in unified format (binary, so you can't
>view it in a text editor).
>tcpdump.log is stored in pcap format.  You can most likely read this
>file by typing: tcpdump -nr Tcpdump.log and it will show you the
>actual packets that were collected by snort rules that in fact log
>packets.
>
>Those three files are each the result of a separate output plugin.
>There has been a lot of them written as to which is best for each
>scenario.   ASCII logs are great for quickly checking what your sensor
>is seeing, but it slows down the instance of snort considerably.
>When running snort in daemon mode, you should almost always run snort
>without this option (-A fast on the command line)
>
>If you are upgrading the old sensor, and you want to keep all of your
>other tools the same, the important lines that have to do with logging
>can be found by doing this:
>
>cat snort.conf | grep output | grep -v /#
>
>Of course this just looks at the output part of the snort.conf
>configuration.  You will have to make sure you retain a whole lot of
>information from the previous snort.conf file including $HOME_NET and
>$EXTERNAL_NET, and a whole lot of others.   Check out some of the
>how-to documents on www.snort.org
>
>-Seth
>
>
>
>On Tue, Mar 4, 2008 at 12:07 PM, frederick sonnichsen
><fsonnichsen at ...315...> wrote:
>  
>
>>I am new  to snort and trying to upgrade a prior system. It appears that
>> the old system collects Alerts, Snortlog.log and Tcpdump.log, however
>> after reading the doc I am a little unclear on the meaning of  these.
>> Are the snortlogs basically uncompressed versions of the tcpdumps? Also
>> are the alerts a condensation of the snort logs?
>> Thanks,
>> Fritz
>>
>>
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>
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