[Snort-users] Snort multiple sensor configuration

Stephen Reese rsreese at ...11827...
Thu Oct 9 11:15:47 EDT 2008


> in a multi-nic deployment dropped packets are the biggest concern.
> Watch the dropped packet counts closely.  more than 5% means you're
> wasting your time.

I don't think I'm doing do bad in regards to the packet loss, the
links to the internet and branch networks are not very fast the the
machine is decent, 3.2 intel with 4 gigs of ram on a 64 debian OS.

Oct  9 06:55:05 atlas snort[5260]: Packet Wire Totals:
Oct  9 06:55:05 atlas snort[5260]:    Received:      5100680
Oct  9 06:55:05 atlas snort[5260]:    Analyzed:      5099871 (99.984%)
Oct  9 06:55:05 atlas snort[5260]:     Dropped:          808 (0.016%)
Oct  9 06:55:05 atlas snort[5260]: Outstanding:            1 (0.000%)

Oct  9 06:56:31 atlas snort[5257]: Packet Wire Totals:
Oct  9 06:56:31 atlas snort[5257]:    Received:      1855372
Oct  9 06:56:31 atlas snort[5257]:    Analyzed:      1855129 (99.987%)
Oct  9 06:56:31 atlas snort[5257]:     Dropped:          242 (0.013%)
Oct  9 06:56:31 atlas snort[5257]: Outstanding:            1 (0.000%)

Oct  9 06:57:08 atlas snort[5254]: Packet Wire Totals:
Oct  9 06:57:08 atlas snort[5254]:    Received:      1989644
Oct  9 06:57:08 atlas snort[5254]:    Analyzed:      1989643 (100.000%)
Oct  9 06:57:08 atlas snort[5254]:     Dropped:            0 (0.000%)
Oct  9 06:57:08 atlas snort[5254]: Outstanding:            1 (0.000%)

> Sniffing outside of a properly configured firewall is wasteful.  Do
> you really need an IDS to tell you that the firewall is blocking lots
> of bad traffic?  It's a firewall! That's what it does!  Make sure it's
> configured correctly, make sure it's a quality firewall, then let it
> do it's job.  If you don't trust your firewall, solve that before
> deploying an IDS.  Crappy firewalls are a curse because once it's
> installed you're usually stuck with it.  Most IT organizations cannot
> politically repace a "working" firewall with a "good quality"
> firewall.  It's usually not about money, it's usually about brand
> loyalty, training curves, fancy reporting tools, and religion.

I understand this, I'm probably just reading in to some of the
examples I've seen floating around. The firewall is a new Cisco ASA
model which is nice but only so nice as it's configuration, hmm, now
that I think about it maybe it has a method to monitor traffic on it's
interfaces.

> Once you trust the firewall, you can stop trying to process packets
> that are never going to reach your network anyway.  You can't defend a
> network that does not have rock-solid firewall protection.
>
> Don't load up "all the rules".  If you load up too many rules, you
> will be dropping packets. If you can keep the dropped packet counts
> down (<5%), your IDS will function very nicely.
>
> When the IDS is new, you need to find out what's "normal" for your
> network and tune the sensor to understand "normal".  Start by
> unloading application exploit rules and loading up "equipment
> misconfiguration" rules.  Load up rules that indicate heretofore
> unknown problem areas, like clear text passwords and devices sending
> out TFTP broadcast requests. Misconfigured devices, leaking firewalls.
> Solve all those problems first.  You can't defend a jacked-up network.
>
> Once all those rules go quiet, load up the malware and spyware rules.
> Fix those problems.  At this point you will observe that you need a
> black-hole DNS server.  Once all *those* rules go quiet, you can
> really run a tight defense against the remaining problems as they come
> up.
>
> Or you can just make pretty charts all day and possibly get a pay
> raise and a promotion.  ;)

mmm, charts, base :-) anyhow thank you for your insight, I'll keep
hammering away and see if I can get some useful information out of
this.




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