title: TransitGatewayRouteTableId for default TransitGatewayRouteTable
body: <p>I am using the following settings for creating a transit gateway through CloudFormation.</p>
  <pre><code>AutoAcceptSharedAttachments: disable
  DefaultRouteTableAssociation: enable
  DefaultRouteTablePropagation: enable
  </code></pre>
  <p>I want to know how can one get the &quot;TransitGatewayRouteTableId&quot; in this situation? It is a necessary property for creating a static route in the <strong>default</strong> transit gateway route table.</p>
  <pre><code>Type: AWS::EC2::TransitGatewayRoute
  Properties: 
    Blackhole: Boolean
    DestinationCidrBlock: String
    TransitGatewayAttachmentId: String
    TransitGatewayRouteTableId: String
  </code></pre>
  <p>I have already tried the following <code>!GetAtt</code> intrinsic function but it doesn't work since it seems that the only return value for a transit gateway resource is the <code>id</code> <a href="https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-ec2-transitgateway.html" rel="nofollow noreferrer">https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-ec2-transitgateway.html</a></p>
  <p><code>TransitGatewayRouteTableId: !GetAtt TransitGateway.AssociationDefaultRouteTableId</code></p>