GRE Tunnel with TGW Use Cases

Question

Hi all, im just prepping for my AWS Network Specaility and I was wondering what the use cases's are with GRE Tunneling and Transit Gateway Connect.
Im just wondering based of some of the documentation where they peer a VPC to TGW and use GRE to tunnel to an appliance, what benefits this would bring to the consumers infrastructure from a SDN perpsective..

Im intrested to hear peoples views and thoughts to as and why it may be a good use case.

Thanks
Gary

Answer

Connecting on-premises networks to AWS - GRE tunnels can be used to connect VPN appliances or routers on-prem to TGW, providing secure connectivity to VPCs and on-prem networks. This avoids the need for each VPC having its own VPN connection.

Traffic inspection/security services - The GRE tunnels can send traffic to a firewall or IPS appliance before routing it to the destination VPC. This allows you to apply security policies and inspect traffic.

Answer

Hello.

The following documentation may be helpful.  
https://aws.amazon.com/jp/blogs/networking-and-content-delivery/simplify-sd-wan-connectivity-with-aws-transit-gateway-connect/

Answer

Another use case that I've personally deployed for some customers is to connect the VPC (or VPCs) to different on-premises VRF networks. This is the case mainly for CSPs or Telcos which have different routing-domains or VRFs on-premises and need to connect these networks to AWS, keeping this separation of routing. 
This is usually done by using TGW Connect peers (GRE tunnels) or Private IP IPSec VPNs, which both terminate on TGW. From here, you can create multiple TGW route-tables to keep the routing separated/segregated, similar to how it's done on-premises with VRFs.

GRE Tunnel with TGW Use Cases

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