Vpc Peering Non Transitive Routing Firewall

What VPC Network Peering and Firewall Rule Configuration Is

VPC Network Peering allows private RFC 1918 connectivity across distinct Virtual Private Cloud networks without using external IP addresses, VPN gateways, or intermediate network appliances. Traffic remains entirely within Google's software-defined network (Andromeda).

How it meets the requirements

• Non-transitive routing resolution: Google Cloud VPC Network Peering is strictly non-transitive. A network (hub-vpc) cannot route traffic between two other peered networks (spoke-a-vpc and spoke-b-vpc). Establishing a direct peering connection between spoke-a-vpc and spoke-b-vpc directly bridges their subnet route tables.
• Bidirectional peering requirement: VPC peering requires two matching peering configurations—one initiated from spoke-a-vpc to spoke-b-vpc, and another from spoke-b-vpc to spoke-a-vpc—before the peering state moves to ACTIVE.
• Firewall rule alignment: Peering exchanges routes but does not alter firewall evaluation. By default, Google Cloud enforces an implied deny ingress rule. Updating the ingress firewall rules to allow source ranges such as 10.2.0.0/16 in spoke-a-vpc and 10.1.0.0/16 in spoke-b-vpc (or broad RFC 1918 ranges) ensures the peer traffic is permitted.

Key advantages

• Zero bandwidth bottleneck: Communication occurs peer-to-peer at full line rate without traversing an intermediate hop.
• Subnet route automation: Peered subnet routes are dynamically propagated into each VPC's routing table.
• Lowest latency: Packets flow directly between virtual machines in Andromeda.
• Explicit security boundaries: Ingress firewall rules remain isolated to each VPC, maintaining granular least-privilege security.

Why this is optimal

Direct peering combined with explicit ingress firewall rules directly resolves the non-transitive routing constraint and firewall denial without adding intermediate routing appliances, operational overhead, or additional network latency.