This image shows the east-west traffic flow from the database to the web or application in a regional hub and spoke topology that uses a VM Series firewall. It includes three virtual cloud networks (VCNs): Hub VCN (192.168.0.0/16):

• The hub VCN houses the VM Series firewalls. The trust subnet uses vNIC2 for internal traffic to or from the VM Series firewall. The hub VCN communicates with spoke VCNs through a dynamic routing gateway (DRG).
• Web or application tier spoke VCN (10.0.0.0/24): The VCN contains a single subnet. A load balancer manages traffic to the web or application VMs. The application tier VCN is connected to the hub VCN over the DRG.
• Database tier spoke VCN (10.0.1.0/24): The VCN contains a single subnet that contains the primary database system. The database tier VCN is connected to the hub VCN over the DRG.

East-west traffic flows from the database to the web or application in the following steps:

1. Traffic that moves from the database tier to the web or application load balancer (10.0.0.10) is routed through the database subnet route table (destination 0.0.0.0/0).
2. Traffic moves from the database subnet route table to the DRG for the database tier spoke VCN.
3. Traffic moves from the DRG through the hub VCN ingress route table to VM Series Firewall VMs using the internal network load balancer. The network load balancer has more than one backend pointing to trust interfaces (vNIC2) of the VM Series firewall.
4. Traffic from the VM Series firewall is routed through the trust subnet route table (destination 10.0.0.0/16). The firewall performs source translation on incoming packet to ensure that it uses the trust interface private IP address as the source translation object so that the spoke VCN (Web) sees traffic coming from the trust interface of the firewalls.
5. Traffic moves from the trust subnet route table to the DRG for the web spoke VCN.
6. Traffic moves from the DRG for the web, application, or load balancer for the web or application through the web spoke VCN attachment.