what is the difference between state full inspection and deep packet inspection ?

what is the difference between state full inspection and deep packet inspection ?

thanks !!!
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SPI basically inspects to see whether the packet is part of a valid session. For example, if I try to send a packet to try to terminate a session that doesn't exist, this will get rejected. Because it checks so much less than DPI does, it is a lot less taxing on the firewall's hardware. However, it is far less secure.

DPI looks a lot deeper into packets to get an idea of whether the packet is valid for acceptance. As pointed out, this requires a lot more processing power. However, because the firewall is being more finicky about what it allows through, it is also the far more secure way to go.

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atlas_shudderedSr. Network EngineerCommented:
Simple answer:

Stateful inspection confirms that traffic is part of a legitimate SYN/ACK session.  Uses a session table to track outbound SYN requests and only allows return traffic that corresponds to these known requests.  Used to combat the following:

1. SYN Flood attacks by actively tracking sessions and automatically closing orphaned embryonic sessions
2. Gratuitous ACK attempts against internal hosts wherein an attack generates crafted ACK packets against a host in the effort to illicit a bogus session response or resource flood.

Deep Packet Inspection takes the above to the next level by doing at least one and sometimes two main things:

1. - Always - Inspects each packet to insure it complies with RFC standards.  Used to counter attackers attempts to inject malformed packets
2. - Sometimes - Inspects actual payload to insure the packet doesn't contain malicious content in payload (malware/sploit/etc.).  This is usually found with beefier boxes that are making use of sandboxing and application level inspections.

Easy Peasy.
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