title: AWS Transit Gatway to connect multiple VPC in a region (NEW AWS Service )
body: <p>I am trying to write a CloudFormation template to deploy a Transit Gateway and want to connect my all VPC of a region to that Gateway. I have written a template but not able to set the GatewayRoutetable routing </p>
  
  <pre><code>TransitGateway:
  Type: "AWS::EC2::TransitGateway"
  Properties:
    AmazonSideAsn: 65000
    Description: "TGW Route Integration "
    AutoAcceptSharedAttachments: "disable"
    DefaultRouteTableAssociation: "enable"
    DnsSupport: "enable"
    VpnEcmpSupport: "enable"
    Tags:
      - Key: Name
        Value: !Join ["-", ["ath", !Ref 'Env', "transit", "gateway", !Ref 'AWS::Region']]
      - Key: Env
        Value: !Ref 'Env'
      - Key: Region
        Value: !Ref 'AWS::Region'
     TransitGatewayAttachment:
     Type: "AWS::EC2::TransitGatewayAttachment"
     Properties:
       SubnetIds:
        - !Ref SubnetPublic1
      - !Ref SubnetPublic2
        - !Ref SubnetWorker1
      - !Ref SubnetWorker2
      TransitGatewayId: !Ref TransitGateway
      VpcId: !Ref 'VPC'
  
     TransitGatewayRouteTable:
      Type: "AWS::EC2::TransitGatewayRouteTable"
      Properties:
       Tags:
         - Key: Name
           Value: !Join ["-", ["ath", !Ref 'Env', "RouteTable", "TransitGateway", !Ref 'AWS::Region']]
        - Key: Env
          Value: !Ref 'Env'
        - Key: Region
          Value: !Ref 'AWS::Region'
    TransitGatewayId: !Ref TransitGateway
     TransitGatewayRouting:
     Type: "AWS::EC2::TransitGatewayRoute"
      Properties:
      Blackhole: true
      DestinationCidrBlock:
      TransitGatewayAttachmentId: !Ref TransitGatewayAttachment
      TransitGatewayRouteTableId: !Ref TransitGateway
  
       TransitGatewayRouteTableAssociation:
        Type: "AWS::EC2::TransitGatewayRouteTableAssociation"
        Properties:
        TransitGatewayAttachmentId: !Ref TransitGatewayAttachment
        TransitGatewayRouteTableId: !Ref TransitGatewayRouteTable
  
      TransitGatewayRouteTablePropagation:
       Type: "AWS::EC2::TransitGatewayRouteTablePropagation"
       Properties:
       TransitGatewayAttachmentId: !Ref TransitGatewayAttachment
       TransitGatewayRouteTableId: !Ref TransitGatewayRouteTable
  </code></pre>
  
  <p>Now I am able to deploy my Transit Gateway also able to attach it to a VPC  able to create a route table but, my problem is that when I come to TransitGatewayRouting it prompt me to enter CIDRdestination . I am confused about it referring to which CIDR Destination and what should I mention to get it working as of now as it does not keep the routing for the VPC.</p>
  
  <p>And another part of question is how would I manage to code so that even in future if there is a new VPC get created in same region I'll able to connect that VPC to this very same transit gateway.</p>