Shortest Path Bridging MAC (SPBM) is a next generation virtualization technology that revolutionizes the design, deployment, and operations of carriers and service providers, along with enterprise campus core networks and the enterprise data center. SPBM provides massive scalability while at the same time reducing the complexity of the network.
SPBM eliminates the need for multiple overlay protocols in the core of the network by reducing the core to a single Ethernet based link-state protocol that provides all virtualization services in an integrated model. In addition, by relying on endpoint service provisioning only, the idea of building your network once and not touching it again becomes a true reality. This technology provides all the features and benefits required by carrier-grade, enterprise and service provider deployments without the complexity of alternative technologies, for example, Multiprotocol Label Switching (MPLS).
SPBM simplifies deployments by eliminating the need to configure multiple points throughout the network. When you add new connectivity services to an SPBM network you do not need intrusive core provisioning. The simple endpoint provisioning is done where the application meets the network, with all points in between automatically provisioned through the robust link-state protocol, Intermediate-System-to-Intermediate-System (IS-IS).
Most Ethernet based networks use 802.1Q tagged interfaces between the routing switches. SPBM uses two Backbone VLANs (B-VLANs) that are used as the transport instance. A B-VLAN is not a traditional VLAN in the sense that it does not flood unknown, broadcast or multicast traffic, but only forwards based on IS-IS provisioned backbone MAC (BMAC) tables. After you configure the B-VLANs and the IS-IS protocol is operational, you can map the services to service instances.
SPBM uses IS-IS to discover and advertise the network topology, which enables it to compute the shortest path to all nodes in the SPBM network. SPBM uses IS-IS shortest path trees to populate forwarding tables for the individual BMAC addresses of each participating node.
To forward customer traffic across the core network backbone, SPBM uses IEEE 802.1ah Provider Backbone Bridging (PBB) MAC-in-MAC encapsulation, which hides the customer MAC (CMAC) addresses in a backbone MAC (BMAC) address pair. MAC-in-MAC encapsulation defines a BMAC destination address (BMAC-DA) and a BMAC source address (BMAC-SA). Encapsulating customer MAC addresses in BMAC addresses improves network scalability (no end-user CMAC learning is required in the core) and also significantly improves network robustness (loops have no effect on the backbone infrastructure.)
The SPBM BMAC header includes a Service Instance Identifier (I-SID) with a length of 32 bits with a 24-bit ID. I-SIDs identify and transmit virtualized traffic in an encapsulated SPBM frame. You can use I-SIDs in a Virtual Services Network (VSN) for VLANs or VRFs across the MAC-in-MAC backbone:
Unicast
For a Layer 2 VSN, the device associates the I-SID with a customer VLAN, which the device then virtualizes across the backbone. Layer 2 VSNs associate one VLAN per I-SID.
With Layer 3 VSN, the device associates the I-SID with a customer VRF, which the device virtualizes across the backbone. Layer 3 VSNs associate one VRF per I-SID.
With Inter-VSN routing, Layer 3 devices, routers, or hosts connect to the SPBM cloud using the SPBM Layer 2 VSN service. The Backbone Core Bridge can transmit traffic between different VLANs with different I-SIDs.
With IP shortcuts, no I-SID is required, forwarding for the Global Routing Table (GRT) is done using IS-IS based shortest path BMAC reachability.
For more information on Fabric Layer 3 services, see Fabric Layer 3 Services.
Multicast
With Layer 2 VSN with IP multicast over Fabric Connect, the BEB associates a data I-SID with the multicast stream and the scope I-SID is based on the Layer 2 VSN I-SID.
With Layer 3 VSN with IP multicast over Fabric Connect, the BEB associates a data I-SID with the multicast stream and the scope I-SID is based on the Layer 3 VSN I-SID.
With IP Shortcuts with IP multicast over Fabric Connect, the BEB associates a data I-SID with the multicast stream, but there is no I-SID for the scope, which is the Global Routing Table (GRT).
For more information on IP multicast over Fabric Connect, see IP Multicast over Fabric Connect.
Note
Inter-VSN routing for IP multicast over Fabric Connect is not supported.
The switch supports the IEEE 802.1aq standard of SPBM, which allows for larger Layer 2 topologies and permits faster convergence.
The following figure shows multiple tenants using different services within an SPBM metro network. In this network, you can use some or all of the SPBM implementation options to meet the needs of the community while maintaining the security of information within VLAN members.
To illustrate the versatility and robustness of SPBM even further, the following figure shows a logical view of multiple tenants in a ring topology. In this architecture, each tenant has its own domain where some users have VLAN requirements and are using Layer 2 VSNs and others have VRF requirements and are using Layer 3 VSNs. In all three domains, they can share data center resources across the SPBM network.
