Explanation for why all applications are not available for PBF

[ccarter]

Hi All,

Just wondering if anyone can explain why the application objects have thousands of objects, but when attempting to create a policy based forwarding rule for a specific app (in my example, ms-teams), it does not appear in the drop down options in the Application drop down.

Can anyone guide me on the best way to setup PBF for ms-teams? 

Thanks All.

[reaper · Accepted solution]

this is how pbf works

consider how you redirect packets out to the internet: a syn packet goes out to establish a session: does it need to take a route or go through pbf? all we can see at this point is port 443

if pbf is set for ports, it will send via pbf, if it's set for applications, it can't know at this point,  so the packet is set out through regular route

so the syn/ack comes back and another ack is sent out via the regular route, still no clue what application we're talking and we're already 3 packets in

then comes payload and app-id can go to work. once a rudimentary application is identified, pbf can kick in. for this session however it's already late but app-id leanrs this session and stores it in the app cache so it can apply pbf on the next connection to the same source/destination/port combination

this is why it's recommended not to use applications in pbf, and why only some app-ids are available to begin with (because these are more easily identifiable and can use this 'bypass' without too many false positives)

hope this makes sense

[ccarter]

Many thanks for the answer @reaper. Clear and concise which is a very hard trait to have in the world of firewalls. Many people over complicate answers and this was spot on.

[reaper]

thanks for the compliment @ccarter ! glad my answer was helpful 🙂

[rmcrae]

Is there any workaround?  I've tried using a couple EDLs provided by Palo Alto for the Microsoft SharePoint and OneDrive endpoints and one for Microsoft Skype and Teams endpoints but there is too much cross over between the two EDLs so you cant force VOIP traffic to use a specific path via a PBF without also affecting filesharing traffic.  As you pointed out the Security Profiles with App-IDs don't work at this point because we are much lower in the OSI model.