FQDN objects are failing to resolve when DNS Proxy object is configured

• After upgrading to PAN-OS 9.0, FQDN objects are failing to resolve when DNS Proxy object is configured under GUI: Device > Setup > Services > Global > DNS Proxy  > <object-name>
• "show dns-proxy fqdn all" command displays the URLs with IP address as 0.0.0.0

• PAN-OS 9.0.
• Palo Alto Firewall.
• DNS Proxy object configured.

This is expected behavior if DNS Cache in not selected under GUI: Network > DNS Proxy > Advanced > Cache

Starting from PAN-OS 9.0 and onward, FQDN address object's refresh is TTL driven, instead of a batch process at static interval. TTL driven means DNS Proxy daemon will track the TTL value received for each DNS response for a FQDN address object.

When the dictated number of seconds expired, by TTL, DNS Proxy daemon will initiate a request to check if FQDN resolution has changed.  In order for this to work properly, it's a requirement to enable cache for DNS Proxy objects under advanced settings.

1. Enable the DNS Proxy object Cache  GUI: Network > DNS Proxy > Advanced > Cache and commit the configuration.

2. Using "request system fqdn refresh", the "show dns-proxy all" command will now display the correct IP address.