My two cents:

Stateful Packet Inspection ("SPI") firewalls maintain (or keep) the
state of network connections passing through them. "Keeping the state"
enables the firewalls to accurately distinguish legitimate packets for
various connections from rogue unwanted packets. While the legitimate
packets are allowed, the rogue packets are rejected.

I remember when Checkpoint used "Stateful Inspection" as a marketing
term and claimed to be the company with the only commercial firewall
with the stateful inspection capability. In my opinion stateful
inspection doesn't provide much of a security benefit when weighed
against today's attack methodologies, but it does do what it was
designed to do very well.

Regards,
Adriel T. Desautels
Chief Technology Officer
Netragard, LLC.
Office : 617-934-0269
Mobile : 617-633-3821
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Andrea Gatta wrote:
> Hi Juan,
> a stateful inspection firewall can greatly improve the security of
> your perimeter even in case of a port scan. Think about the following
> scenario: an attacker is trying to "fly under the radar" using common
> scanning techniques, let's say using a FYN scan. In that case a static
> packet filter will not see and - most important - LOG such activity.
> So you won't be aware a reconnaissance is taking place.
>
> On the other hand, a stateful inspection firewall - and I mean with
> that expression a device that has the concept of 'session' and at the
> same time is capable to work both on the header and the payload -
> might help preventing attacks even on open and exposed applications.
> An example of that is an IPS which is nothing more than a stateful
> inspection firewall which uses signatures to patter match stuff
> happening on the wire.
>
> Another thing I have learned is that what stateful really means can
> change from vendor to vendor. So one good point would be to clearly
> understand if we are talking about stateful packet filtering and/or
> stateful inspection. They are not clearly the same thing.
>
> Hope that helps.
>
> Andrea
> On Wed, Aug 20, 2008 at 7:04 AM, Juan B <juanbabi (at) yahoo (dot) com [email concealed]> wrote:
>>
>> Hi,
>>
>> Can someone please explain why statefull inspection Fw helps against hackers? I know that those FW keep track of the sessions but I dont understand how the feature might help against a port scan from the internet or other ways to mitigate hackers attacks.
>>
>> Thanks
>>
>> Juan
>>
>>
>>
>>
>>
>>
>>
>>

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