pfSense

Dynamic DNS service configured for Cloudflare DNS fails when WAN IP is configured with DHCP on bridge0 (vtnet0 + vtnet1) when neither underlying interface has IP connectivity, and only one of the interfaces is operational.

The interface to use for curl (CURLOPT_INTERFACE) is fetched via function get_failover_interface, which returns vtnet0 (the underlying enabled interface for bridge0; vtnet1 is disconnected). The result is an "UNKNOWN ERROR" in the logs. Further digging and debugging shows curl_errno returns error 7 (CURLE_COULDNT_CONNECT) without any additional details anywhere.

Manual override in the code, changing the interface used to bridge0 where the WAN IP is configured, circumvents this problem and Dynamic DNS towards Cloudflare is operational.

For more details see my post in the forums: https://forum.netgate.com/topic/188716/cloudflare-ddns-unknown-error