Re: Difference of Alerts, Snort Logs, and Tcpdumps

[frederick sonnichsen <fsonnichsen () whoi edu>]

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 () whoi edu> 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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