Firewall Wizards: Additional TPC/IP stack

["Franco RUGGIERI" <fruggieri () selfin net>]

An NT based firewall I've been reading about is marketted as using an
additional TCP/IP stack, which performs additional checking before
transerring the packets to the native NT TCP/IP stack. (The firewall in
question is Cisco's Centri)  My questions are:
        Do you feel that such additional checking in an ad hoc IP stack is
valuable?
        What kind of additional checks would make sense?
        Is this a valid/reasonable approach or is it just hype?
TIA
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Franco RUGGIERI
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fruggieri () selfin net