See comments inline.
On 8/21/07, Jason <security@brvenik.com> wrote:
bleh wrote:
This would seem to be dependent on a lot of factors.
database event rate
snort alert rate
cpu/memory/io
system load
network kbps
type of traffic (protocols etc.)
enabled rules / quality of rules
enabled preprocessors
snort variable assignment
I think you are getting a bit pedantic. You are not concerned about "a
user" you are concerned about the environment surrounding the sensor.
Why would you needlessly add another risk factor to performance when
there are clear solutions to it?
The job of any systems, network or ids administrator is to look at the
systems and network as a whole. Network and systems profiling is far from
being pedantic, this is called performing your job.
Do not let perfection be the enemy of good.
A user can do a lot more damage to a sensor with any combination of the
above items. For example I can make Snort stop inspecting any traffic
for quite a while with a single (badly written) pcre rule. There are a
number of preprocesors that can turn a sensor into a brick under the
right conditions as well. Does this mean all users should stop using
pcre and the smtp preprocessor? I do not believe so.
Do you have something in the preprocessors you care to share with the
development team so it can be addressed or is this conjecture?
Portscan, SMTP, DNS and BO just to name a few.
Just because you can write a poor rule does not invalidate that you
should not do direct writes to the database. As always, there must be a
car analogy.
I agree, a car analogy does work. Sure, I know that having on the A/C has
the potential to impact performance. However, there are still many key
factors involved such as the engine size, transmition, fuel and weight.
These factors are very similar in nature to those I addressed above. You
telling me I should *always* run with my A/C off is a blanket statement and
has very little bearing when you have no idea what kind of car I drive and
how I drive it.
Just because you can go faster than conditions warrant does not mean you
should.
As with anything else on a sensor you need evaluate your situation and
set up the system accordingly. There is no one size fits all, and this
(IMHO) includes output plugins. For example, I have two sensors in my
lab (for validating new config options, new snort versions etc.)
watching the same traffic one with unified and one with db. I
continually receive the same number of alerts from both systems.
I humbly assert that you are incorrect in every sense of the word. There
is absolutely no practical advantage to using direct DB writes from the
engine compared to using unified output and there are certainly clear
disadvantages to using them.
My statement states there is not a "one size fits all" solution. You stating
that I am "incorrect in every sense of the word" asserts that there is a
"one size fits all" solution. Therefore, please tell me which config,
preprocessors, rules, hardware and OS everyone in the Snort community should
be running.
-bleh
-bleh
On 8/21/07, *Joel Esler* <joel.esler@sourcefire.com
<mailto:joel.esler@sourcefire.com>> wrote:
When snort logs to db, it takes resources away from inspecting
traffic. Missing packets.
--
Joel Esler
Sent from the road.
On Aug 21, 2007, at 10:33 AM, bleh <mailbox.size.limit@gmail.com
<mailto:mailbox.size.limit@gmail.com>> wrote:
Can you explain what you mean by Snort "has to stop being an IDS"?
If Snort is no longer an IDS when logging directly to a DB what is
it?
> In order for Snort to do an insert, it has to stop being an IDS.
> Personally, I don't want my IDS to miss any packets, regardless
of the
> extremely short amount of time it takes to do a DB insert.
(Unless you
> have a very busy DB).
>
> Still would rather you use Barnyard and Unified.
>
> Joel
>
> Jason Haar wrote:
>> Joel Esler wrote:
>>> As a general recommendation for everyone on the list, Snort
should never be logging directly to the DB.
>>>
>>>
>> Can you tell me why that is? I mean, surely directly accessing a
DB
>> doesn't introduce much latency/load *unless* it continually
generates
>> events?
>>
>> i.e. if a particular installation of snort only generates 1
event per
>> minute, is there really any difference between snort->mysql and
>> snort->barnyard?
>>
>> I could understand it being a problem if snort is having to
queue up
>> events while INSERTs are going on, but if that are spaced many
seconds
>> apart...?
>>
>
> --
>
>
> --
> joel esler | security consultant | Sourcefire | pgp is public
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