Odd traffic going out through an application-specific security rule

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Odd traffic going out through an application-specific security rule

L1 Bithead

I've got a rule that allows the following applications from any source in our trusted zone out to any destination in the untrust zone.

  • appdynamics
  • dns-over-https
  • dns-over-tls
  • github
  • ms-delve
  • net.tcp
  • ntp
  • ocsp
  • okta
  • paloalto-updates
  • paloalto-wildfire-cloud
  • pan-db-cloud
  • rtcp
  • service-now
  • skype
  • ssh
  • windows-azure
  • windows-push-notifications

The rule is set for application-default.


We have some legitimate traffic on our network that goes from trust to untrust with the destination port of tcp/37.


For some reason, this traffic is matching up to this rule.  None of the applications in the rule list tcp/37 as a default port.  Only two of those applications (skype and net.tcp) have dynamic default ports.

When the tcp/37 traffic hits this rule, the application always shows up as "insufficient-data"


I know what the traffic is - it is supposed to be the old "TIME" protocol.  I've actually created a rule specific for this further down the list.


Any idea why the traffic would match up to this rule?


Cyber Elite
Cyber Elite


Whenever you have a rule allowing application-default the firewall is going to allow enough traffic to identify the application. So the rule that this traffic is hitting is, if I would have to make an educated guess, the first entry in your security rulebase from trust to untrust that is based off of app-id. 

Thanks for the response.  The rule that the traffic is hitting is actually the 4th rule in the list going from trust to untrust that is based off of app-id.


Also as a suggestion, please use URL filtering as well as DNS sinkholes. Will make your security posture that much better.



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