Figure D-2 Dynamic transition from TCP to SMC-R The hybrid model of SMC-R uses the following key attributes: GLYPH<SM590000> It follows the standard TCP/IP connection setup. GLYPH<SM590000> The hybrid model switches to RDMA (SMC-R) dynamically. GLYPH<SM590000> The TCP connection remains active (idle) and is used to control the SMC-R connection. GLYPH<SM590000> The hybrid model preserves the following critical operational and network management  TCP/IP features: – Minimal (or zero) IP topology changes – Preservation of the existing IP security model,such as IP filters, policies, virtual LANs  (VLANs), and Secure Sockets Layer (SSL) – Compatibility with TCP conne ction-level load balancers – Minimal network administration and management changes GLYPH<SM590000> Host application software is not required to change; therefore, all host application  workloads can benefit immediately. 478  IBM z14 (3906) Technical Guide ETH RNIC TCP IP Interface Sockets Middleware/Application SMC-R enabled platform SMC-R ETH RNIC TCP IP Interface Sockets Middleware/Application SMC-R enabled platform SMC-R TCP connection establishment over IP IP Network (Ethernet) RDMA Network RoCE (CEE) TCP connection transitions to SMC-R allowing application data to be exchanged using RDMA Dynamic (in-line) negotiation for SMC-R is initiated by presence of TCP Option (SMCR)  TCP syn flows (TCP Option SMCR) data exchanged using RDMA data exchanged using RDMA