Networking and Interconnect Connectivity for Multicloud Architectures
Connectivity choices
Multicloud networking connects VCNs, VNets, VPCs, on-premises networks, and partner services. Options are IPsec VPN over the internet for quick or backup links; dedicated private interconnect such as OCI FastConnect, Azure ExpressRoute, AWS Direct Connect, and Google Cloud Interconnect for predictable latency; and Oracle cross-cloud interconnects where offered. Design at least two diverse paths for production.
Routing and naming
- Use non-overlapping CIDRs; overlapping ranges force NAT and break route symmetry.
- Advertise only the specific subnets that need reachability over BGP; use hub-and-spoke or transit gateways to control paths.
- Configure return routes on both sides; asymmetry causes dropped sessions.
- Private DNS zones and conditional forwarding must resolve database names to private addresses in each cloud.
- Security groups, NSGs, network firewalls, and private endpoints enforce least privilege; databases should not have public IPs.
Worked example
An OCI VCN 10.0.0.0/16 hosts EBS; an Azure VNet 10.1.0.0/16 hosts the app. The architect uses FastConnect plus ExpressRoute through an interconnect provider, establishes BGP, advertises 10.1.1.0/24 (app subnet) to OCI and 10.0.2.0/24 (database subnet) to Azure, and keeps a VPN as backup with longer AS paths. Private DNS forwards db.corp to the OCI resolver. A failover test confirms sessions reconnect.
Traps
Overlapping CIDRs; advertising 0.0.0.0/0; forgetting return routes; relying on one circuit; using public DNS or public IPs; ignoring MTU and fragmentation; assuming interconnect implies encryption, so use TLS or VPN where required.