I have a MySQL database hosted in one Azure subscription, and I can connect to it from a Virtual Machine (VM) located in another Azure subscription from different region. However, I am unable to connect to the same MySQL database from a normal PC, even though there are no specific firewall rules allowing the VM’s IP address or subnet.

Here are some specifics:

• MySQL Database: Hosted in Azure Subscription A.
• VM: Hosted in Azure Subscription B.
• Firewall Rules: There are no explicit firewall rules set to allow connectivity from the VM’s IP or subnet to the MySQL database.
• External PC: Cannot connect to the MySQL database.
  I suspect it might be related to Azure’s internal networking, but I’m not sure how or why this connectivity is possible.

My Questions:

• Why can the Azure VM connect to the MySQL database despite the lack of specific firewall rules?
• What Azure features or configurations might allow this connectivity (e.g., VNet peering, Private Link, Service Endpoints)?
• How can I verify if any of these features are in place and are facilitating the connection?

Checked firewall rules for the MySQL database.

Attempted connection from an external PC (failed).

Verified that there are no explicit inbound rules allowing the VM’s IP range in the MySQL firewall settings.