AWS Transit Gateway
AWS Transit Gateway provides a hub and spoke design for connecting VPCs and on-premises networks as a fully managed service without requiring you to provision virtual appliances like the Cisco CSRs. No VPN overlay is required, and AWS manages high availability and scalability.
Transit Gateway enables customers to connect thousands of VPCs. You can attach all your hybrid connectivity (VPN and Direct Connect connections) to a single Transit Gateway instance, consolidating and controlling your organization's entire AWS routing configuration in one place (refer to the figure under Transit VPC Solution). Transit Gateway controls how traffic is routed among all the connected spoke networks using route tables. This hub-and-spoke model simplifies management and reduces operational costs because VPCs only connect to the Transit Gateway instance to gain access to the connected networks.
Hub-and-spoke design with AWS Transit Gateway
Transit Gateway is a Regional resource and can connect thousands of VPCs within the same AWS Region. You can create multiple Transit Gateway instances per Region, and you can connect to a maximum of three Transit Gateway instances over a single Direct Connect connection for hybrid connectivity. Typically, you can use just one Transit Gateway instance connecting all your VPC instances in a given Region, and use Transit Gateway routing tables to isolate them wherever needed. There is a valid case for creating multiple Transit Gateway instances to limit misconfiguration blast radius, segregate control plane operations and administrative ease-of-use.
With Transit Gateway peering, customers can peer their Transit Gateway instances within same or multiple
Regions and route traffic between them. It uses the same underlying infrastructure as VPC
peering, and is therefore encrypted. For more information, refer to Building a global network using AWS Transit Gateway Inter-Region peering
Place your organization’s Transit Gateway instance in its Network Services account. This enables
centralized management by network engineers who manage the Network services account. Use AWS
Resource Access Manager (RAM) to share a Transit Gateway instance for connecting VPCs across multiple
accounts in your AWS Organization within the same Region. AWS RAM enables you to easily and
securely share AWS resources with any AWS account, or within your AWS Organization. For more
information, refer to the Automating AWS Transit Gateway attachments to a transit gateway in a central
account
Transit Gateway also allows you to establish connectivity between SD-WAN infrastructure and AWS
using Transit Gateway Connect. Use Transit GatewayConnect Border Gateway Protocol (BGP) for dynamic routing
and Generic Routing Encapsulation (GRE) tunnel protocol for high performance, delivering up to
20 Gbps total bandwidth per Connect attachment (up to four Transit Gateway Connect peers per Connect
attachment). By using Transit Gateway Connect, you can integrate both on-premises SD-WAN
infrastructure or SD-WAN appliances running in the cloud through VPC attachment, or AWS Direct Connect
attachment as the underlying transport layer. Refer to Simplify SD-WAN connectivity with AWS Transit Gateway Connect
