FQDN not working vs Resolved IP address
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FQDN not working vs Resolved IP address

L1 Bithead

I created a new FQDN address object to facilitate a new Policy(rule).

 When tested the FQDN resolves internal to the Palo Alto Firewall.

The rule contains one destination address which is the new company.fqdn.com FQDN

The rule contains one source address

Application SSL with Application-Default Service

Action Allow

 

When attempts are made to connect  to this destination via the new rule with the FQDN set(destination), the traffic is denied(fails) and logs point to(identify) the "interzone-default" rule instead of the "new rule" that is set up to facilitate this connection 

 

But when I replace the FQDN(destination) with it's resolved IP in the new rule, it works fine(allowed) and logs point the occurrence to the "new rule" (not the interzone-default) as to be expected since that is normal behavior 

Questions:

  1. Why would the interzone-default rule become a part of the failed attempt to connect to the new rule
  2. Anyone know why connection fails with the FQDN set as destination rather than it's resolved IP address
  3. As anyone had a similar experience

Thanks in advance.

1 ACCEPTED SOLUTION

Accepted Solutions

Cyber Elite
Cyber Elite

@rockfort 

Questions:

1. Why would the interzone-default rule become a part of the failed attempt to connect to the new rule

Because the new rule isn't properly matching the traffic. I would verify with the 'request system fqdn show' or ''show dns-proxy fqdn all' depending on your currently installed version of PAN-OS to verify that the firewall is actually properly resolving the FQDN object to the proper address.

 

2. Anyone know why connection fails with the FQDN set as destination rather than it's resolved IP address

99.8% of the time, this is due to the FQDN object either not refreshing properly or the rule not properly being built to accommodate for the traffic that's actually being seen by the firewall. Once you've verified the FQDN object is resolving properly, you'll want to test the rulebase entry and look at the recorded logs and make sure that your rulebase entry as configured properly accounts for the traffic. 

View solution in original post

3 REPLIES 3

Cyber Elite
Cyber Elite

@rockfort 

Questions:

1. Why would the interzone-default rule become a part of the failed attempt to connect to the new rule

Because the new rule isn't properly matching the traffic. I would verify with the 'request system fqdn show' or ''show dns-proxy fqdn all' depending on your currently installed version of PAN-OS to verify that the firewall is actually properly resolving the FQDN object to the proper address.

 

2. Anyone know why connection fails with the FQDN set as destination rather than it's resolved IP address

99.8% of the time, this is due to the FQDN object either not refreshing properly or the rule not properly being built to accommodate for the traffic that's actually being seen by the firewall. Once you've verified the FQDN object is resolving properly, you'll want to test the rulebase entry and look at the recorded logs and make sure that your rulebase entry as configured properly accounts for the traffic. 

View solution in original post

Thank you very much

L2 Linker

I Have similar problem however in my case on firewall when I create fqdn object it resolve to  IP and when I use same object in rule that rule doesnt work, then I need to add IPs manualy based on deny logs in same rule.

 

I observe one strange thing when I resolved fqdn address object it resolved to some different IPs and when I nslookup fqdn in cmd it resolved to some  completely different subnet  IPs and same IPs when I allowed in rule then rule works.

I guess  firewall is not resolving to correct IPs .

 

 

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