Tag Archives: Transit Gateway

Native AWS VPC Connecting to VMware Cloud on AWS (Part 2) – Route Tables and Transit Gateway Attachments

Welcome to Part 2 of VPN connectivity to VMC via AWS VPN. For this post, I will walk through how to attach an AWS VPC to an AWS Transit Gateway in order for route tables to be learned by the VMC SDDC and AWS VPC that will ultimately allow communication from workloads in AWS and workloads in VMC. If you immediately try to ping across the VPN from an EC2 instance to a VMC VM, it will fail as there is more work to do in order to create communication pathways in the form of adding a VPC to the Transit Gateway as well as configure some NSX rules.

In the diagram above I created two EC2 instances with an AWS VPC. For the sake of testing and validation, I first had to create a jump VM with access to the internet in order to remote into the workload VM. This is because, in order for the workload VM to ping across the VPN, 0.0.0.0/0 must be routed through the Transit Gateway and not an Internet Gateway. The goal here is to have a VM on the 10.0.10.32/27 subnet ping a VM on the 10.250.10.0/24 subnet.

To start, the first thing to check is the routing table for the Transit Gateway. This is done by selecting “Transit Gateway Route Tables” on the sidebar with the VPC.

You will then see a list of learned routes from the VMC SDDC. For the sake of this blog, I have deployed AWS EC2 Instances on a subnet that I plan on attaching to the Transit Gateway (10.0.10.0/24). However, notice below that only the learned routes for the VPN to VMC are listed below. While the 10.250.10/0/24 subnet is learned, in order to open communication via the AWS VPC, we first need to attach the VPC to the Transit Gateway so the 10.0.10.0/27 subnet is included. Here are the steps to create the VPC attachment to the Transit Gateway.

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Step 1: Select “Transit Gateway Attachments” then “Create Transit Gateway Attachment”. Find correct Transit Gateway ID.

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Step 2: Add tag for attachment name.

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Step 3: Select the correct VPC and ensure you have the correct subnet selected. Select “Create Attachment”

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As you can see, now that the VPC is attached to the TGW, the 10.0.10.0/24 subnet is now listed. This will now allow for the routing of traffic from my EC2 instance to my VM on VMC.

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The final step is to create groups and add inbound and outbound firewall rules within the Network & Security section of the SDDC console. Make sure to apply the rule to the VPN Tunnel Interface and NOT “All Uplinks“. The reason for this is that a firewall rule applied to All Uplinks does not apply to the VPN Tunnel Interface (VTI), which is a virtual interface and not a physical uplink. The VPN Tunnel Interface must be specified explicitly in the Applied To parameter of any firewall rule that manages workload VM communications over a route-based VPN. In addition, you can see how groups are created on an earlier blog here.

Now that the routing table is complete and Compute Gateway Firewall rules are in place, you can test!

EC2 Windows VM
Ping results from EC2 VM to VMC VM