In Cisco SD-Access, the border node serves as the gateway for communication between the fabric (SD-Access domain) and external networks (nonfabric devices). It is essential for allowing traffic to flow in and out of the fabric. The control plane node, on the other hand, maintains the full mapping database of RLOC (Routing Locator) to EID (Endpoint Identifier), which is crucial for the fabric's routing and forwarding decisions. References: Cisco SD-Access Solution Design Guide