Packet Flow Sequence and Application Override

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L1 Bithead

Packet Flow Sequence and Application Override

Hello everyone,

I have a question regarding the "AppID override" ,

In this article "https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA10g000000ClVLCA0" we can read the following:

"
Special Note about Content and Threat inspection
Application Override to a custom application will force the firewall to bypass Content and Threat inspection for the traffic that is matching the override rule. The exception to this is when you override to a pre-defined application that supports threat inspection. 
"

However, in the PaloAlto Packet Flow Sequence (available : http://live.paloaltonetworks.com//t5/image/serverpage/image-id/12862i950F549C7D4E6309) we can see this :


When the application override policy is matched the only step skiped is [Pattern-based application identification]. The "Content Inspection (SP3/CTD)" is allways performed, regardless of the application override. So the Content profiles seem to be applyed.

So my question is the following: is something missing from the diagram or am I wrongly reading the graph ?

Many thanks, 
Karim BENYELLOUL

L7 Applicator

Re: Packet Flow Sequence and Application Override

The graph is a bit confusing, so that's where the issue is. App override traffic does indeed skip content inspection unless you're overriding it to a pre-defined app.

 

Note that the diagram you referenced has "Content inspection setup" on the green Application Identification section, not actual content inspection. The "setup" is to do the tasks it lists:

- Setup SP3 if security profile is specified

- set session to discard if security rule action deny

- set QoS class from QoS policy lookup

It still has to do those things, even for app overridden traffic.

 

If you follow that box down to the next one ("Application is SSL and decryption policy match?"), the result is No, which moves us back to the pink/salmon FW Fastpath block.

 

There, it has another yes/no box "Content inspection applicable?". When you do app override, the answer to that is No, which skips all of the SP3/CTD (blue) box and moves to packet forwarding at the bottom.

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