AWS Transit Gateway
AWS Transit Gateway is a centralized network transit hub that connects multiple Virtual Private Clouds (VPCs) and on-premises networks through a single gateway, eliminating the complexity of managing multiple peering connections and simplifying network architecture.
- Centralized Connectivity: Transit Gateway acts as a hub that connects multiple VPCs and on-premises networks, replacing complex mesh networking topologies with a simplified hub-and-spoke model
- Global Expansion: Inter-region peering connects transit gateways across different AWS regions using the AWS Global Infrastructure for worldwide network connectivity
- Automatic Encryption: All network traffic between AWS data centers is automatically encrypted at the physical layer, ensuring security without additional configuration
- Scalable Architecture: As your cloud infrastructure grows, Transit Gateway scales to accommodate thousands of VPCs and network connections
Transit Gateway simplifies network management by providing a single point of connectivity for complex multi-VPC and hybrid cloud architectures.
Use case: Transit Gateway is essential for enterprises with multiple VPCs across regions, hybrid cloud deployments, and complex network topologies requiring centralized routing and security policies.
Core Components and Concepts​
Attachments: Transit Gateway supports various attachment types that define what can be connected to the gateway, enabling flexible network designs.
Route Tables: Transit Gateway uses route tables to control traffic flow between attachments, providing granular control over network connectivity and security policies.
Associations: Each attachment connects to exactly one route table, while route tables can serve multiple attachments, creating flexible routing scenarios.
Route Propagation: Networks can dynamically advertise routes to Transit Gateway route tables, enabling automatic network discovery and simplified management.
Transit Gateway Attachment Types​
| Attachment Type | Description | Use Cases |
|---|---|---|
| VPC Attachments | Connect VPCs to the transit gateway | Multi-VPC connectivity, shared services |
| VPN Connections | Site-to-site VPN connections to on-premises networks | Hybrid cloud connectivity, remote office access |
| Direct Connect Gateway | High-bandwidth dedicated connections to on-premises | Enterprise connectivity, data center integration |
| Peering Connections | Connect to other transit gateways | Inter-region connectivity, multi-account networking |
| Connect Attachments | SD-WAN and third-party network appliance integration | Advanced routing, network function insertion |
Maximum Transmission Unit (MTU) Considerations​
Standard MTU: Transit Gateway supports an MTU of 8500 bytes for traffic between VPCs, AWS Direct Connect, Transit Gateway Connect, and peering attachments, allowing larger data payloads for improved efficiency.
VPN Limitations: VPN connections are limited to an MTU of 1500 bytes due to internet infrastructure constraints and encapsulation overhead.
Performance Impact: Larger MTU sizes reduce packet overhead and improve network throughput for bulk data transfers between high-bandwidth connections.
Route Table Management​
Default Route Table: Every Transit Gateway includes a default route table that handles routing for attachments unless custom route tables are configured.
Custom Route Tables: Additional route tables enable advanced routing scenarios, traffic isolation, and security segmentation between different network segments.
Dynamic Routes: Routes can be automatically propagated from VPN connections, Direct Connect gateways, and Connect attachments using Border Gateway Protocol (BGP).
Static Routes: VPC attachments and peering connections require manual static route configuration to direct traffic through the Transit Gateway.
Route Propagation Behaviors​
VPC Route Propagation: VPCs require static routes in their route tables to send traffic to Transit Gateway, as they do not automatically propagate routes.
VPN Route Propagation: VPN connections automatically propagate routes between Transit Gateway and on-premises routers using BGP, enabling dynamic network discovery.
Direct Connect Route Propagation: Direct Connect gateways use BGP to advertise allowed prefixes to on-premises routers, facilitating automatic route advertisement.
Connect Route Propagation: Connect attachments automatically propagate routes to Transit Gateway route tables by default, simplifying SD-WAN integration.
Transit Gateway Benefits and Advantages​
Simplified Network Topology: Replace complex mesh peering architectures with a centralized hub-and-spoke model that reduces management overhead and improves visibility.
Centralized Routing Control: Implement consistent routing policies and security controls across all connected networks from a single management point.
Cost Optimization: Reduce data transfer costs by eliminating redundant peering connections and optimizing traffic flow through centralized routing.
Operational Efficiency: Streamline network operations with unified monitoring, troubleshooting, and configuration management across all connected networks.
Security and Access Control​
Route Table Isolation: Use separate route tables to create network segments and control which attachments can communicate with each other.
Security Group Integration: Leverage existing VPC security groups to control traffic at the instance level while Transit Gateway handles network-level routing.
Network ACL Support: Apply subnet-level access controls within VPCs while Transit Gateway manages inter-VPC and hybrid connectivity.
Monitoring and Logging: Enable VPC Flow Logs and CloudWatch metrics to monitor traffic patterns and detect security anomalies across the entire network.
Inter-Region Connectivity​
Global Network Expansion: Connect Transit Gateways across different AWS regions to create a global network infrastructure that spans continents.
Automatic Encryption: All inter-region traffic is encrypted automatically at the physical layer without impacting performance or requiring additional configuration.
Bandwidth Scaling: Inter-region connections can scale bandwidth based on demand, providing flexible capacity for global data transfer requirements.
Latency Optimization: AWS Global Infrastructure ensures optimal routing paths between regions to minimize latency for critical applications.
Best Practices for Transit Gateway Implementation​
Network Segmentation: Design route tables to create logical network segments based on security requirements, compliance needs, and operational boundaries.
IP Address Planning: Carefully plan CIDR blocks across all connected VPCs and on-premises networks to avoid conflicts and ensure scalability.
Monitoring Strategy: Implement comprehensive monitoring using CloudWatch metrics, VPC Flow Logs, and AWS Config to maintain visibility across the entire network.
Cost Management: Monitor data transfer costs and optimize routing policies to minimize unnecessary cross-region or cross-availability-zone traffic.
Transit Gateway Shared Responsibility Model​
AWS manages the underlying Transit Gateway infrastructure, inter-region connectivity, and automatic encryption, while customers are responsible for route table configuration, attachment management, security policies, and network design.