Need help with logging in case of App-Id

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Need help with logging in case of App-Id

L1 Bithead



I have below rule in my Palo Alto and another default rules which are Intra-zone and Inter-zone.


Source Zone: Trust

Destination: Any

Destination Zone: Untrust

Application: ssl, web-browsing, dns, Facebook-base, YouTube-base, etc

Service: Application-default

Action: Allow

Log: At session end

I am trying to understand behaviour of Palo Alto in terms of Application-Id and traffic logs.


Let us suppose if someone tries to establish connection using for port udp/1194 or any other tcp port using nmap, which apps allowed in my explicit policy are not using. Which policy will this traffic be hitting when traffic is going from network to Untrust zone for Any destination. What will be I seeing in logs.


Cyber Elite
Cyber Elite

in terms of establisghing a connection, the 'application-default' setting will populate the rule with all the ports associated with the applications you list, so in your case 53, 80 and 443


any connection coning in on a different port will drop down to the interzone rule and be discarded


any connection coming in on one of the allowed ports will be accepted and will cause a session to be created and packets to flow

at this point (typically tcp handshake) the app-id will not be known yet so for a tcp session at least 3 packets will be allowed to flow back and forward, for DNS there would be an immediate decission to allow or drop down to intraone as the first packet already contains identifiable payload


when tcp starts to talk payload, app-id will be able to identify if an app is alowed or not, so if at some point SQL is identified while communicating over port 443, the session will no longer match your rule and drop down to the interzone rule and be discarded mid-flow

Tom Piens
PANgurus - (co)managed services and consultancy


Hi @reaper ... Thanks for your quick response.


We have allowed application "app-discovery-request" in list of allowed applications when traffic going from Inside to Outside Zone. As per you, while trying to install session it considers destination ports which are being used applications allowed in policy. In my case, application "app-discovery-request" uses udp dynamic range which means it can use or allow any udp port.


Let us suppose if someone tries to make connection for an application which uses udp port 1194 (for example, open-vpn application), should the traffic for this application using udp port 1194 hitting this existing policy where I did not allow open-vpn but allowed "app-discovery-request" which uses dynamic udp ports and 1194 can also be a part of this.


I have also attached logs from my firewall which I can see for udp port 1194. As per you, if application is not allowed in explicit rule, then it should be hitting default deny policy after application identification is completed. However, I see this behavior in logging of traffic logs. Is the firewall logging correctly traffic logs or is there any issues with logging behavior of PALO ALTO. Let me know your thoughts as it will clear a lot of things and I will be able to plan it accordingly for future cases.


Will  be waiting for your kind response.


Thanks & Regards

This KB might help. Basically 4 packets or 2000 bytes are allowed for the appid engine to try to identify the app.


- DM

Sr. Technical Support Engineer, Strata
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