Tier-0 logical routers have downlink ports to connect to NSX-T Data Center tier-1 logical routers and uplink ports to connect to external networks.
While creating Tier-0 gateway, we need to configure uplink interfaces to top-of-the-rack (TOR) to form BGP neighbor ship. To connect your uplink to TOR we need VLAN based logical switches which are provided by IBM Cloud Classic Network Infrastructure. One can see in the below diagram, how a Tier-0 router gets connected to Backend Customer Switch on the private network and further to Backend Customer Router.
Note: The image is just for depiction. Subnets will vary as per IBM Cloud Specifications. One should refer the IBM Cloud documentation for subnet details. Below diagram depicts the components which are managed by IBM.
Each NSX Edge node can have two uplinks. One for public network and one for private network. As one can see below, any connectivity through FCR will connect public network, while through BCR it will be private network.
One can refer standard reference architectures mentioned on IBM Cloud Docs.References:a) https://cloud.ibm.com/docs/vmwaresolutions?topic=vmwaresolutions-managing_imib) https://www.vmware.com/in/cloud-solutions/ibm-cloud.html