Security Basics: Re: statefull inspection FW and hackers

[aditya.mukadam () gmail com]

my take on SPI:

Stateful inspection can be best understood with security zones/level.

By default, most of the firewall dont allow anything to come from low security zone to high (ie lets say from internet 
to internal resources). This would mean that if internal user accesses internet his response will be blocked. This is 
not desirable because we donot want to keep on opening hole from internet to internal host on the
firewall. We need some mechanism to allow this response/reply back to the internal user.SPI helps us to achieve it !

As mentioned in the thread and also to keep it simple, SPI maintains a state table of requests and opens the incoming 
requests for that
connection  !Rest all the requests from low security zone to high are denied (if not explicitly allowed)

Thanks,
Aditya Govind Mukadam