Vpc Egress Firewall Restricted Vip Priority

What Egress Firewall Rule Priority Is

In Google Cloud VPC networks, firewall rules are evaluated sequentially based on their numerical priority (from 0 to 65535), where lower numerical values represent higher precedence. When traffic matches a rule with higher precedence, that rule is applied immediately, and subsequent lower-priority rules are ignored.

How It Meets The Requirements

• Exfiltration Prevention: Creating a custom deny egress rule for 0.0.0.0/0 ensures that all outbound traffic destined for external internet endpoints is blocked.
• Restricted VIP Access: Creating an allow egress rule targeting 199.36.153.4/30 on TCP port 443 explicitly permits communication with Google APIs.
• Priority Evaluation Order: Placing the allow rule at a priority before 1000 (e.g., 900) and the broad deny rule at a priority after 1000 (e.g., 1100) ensures that traffic to the restricted VIP is evaluated and allowed before the broad deny rule is reached.
• Connector and Internal Service Compatibility: Keeping the deny-all rule at a priority after 1000 prevents blocking internal infrastructure flows (such as Serverless VPC Access connectors or Direct VPC egress mechanisms) that rely on default priority ranges.

Key Advantages

• Granular Perimeter Security: Restricts outbound VPC communication strictly to validated Google services.
• Deterministic Rule Evaluation: Prevents accidental shadowing of specific allow rules by global deny rules.
• Operational Stability: Protects internal VPC management and serverless routing paths from unintended disruption.

Why This Is Optimal

This configuration ensures that traffic destined for 199.36.153.4/30 is processed and allowed first, while all other egress is systematically dropped without interfering with default VPC internal routing.