SPBM introduces a service instance identifier called I-SID. SPBM uses I-SIDs to separate services from the infrastructure. After you create an SPBM infrastructure, you can add additional services (such as VLAN extensions or VRF extensions) by provisioning the endpoints only. The SPBM endpoints are Backbone Edge Bridges (BEBs), which mark the boundary between the core MAC-in-MAC SPBM domain and the edge customer 802.1Q domain. I-SIDs are provisioned on the BEBs to be associated with a particular service instance. In the SPBM core, the bridges are Backbone Core Bridges (BCBs). BCBs forward encapsulated traffic based on the BMAC-DA.
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 a service instance for 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:
For a Layer 2 VSN, the I-SID is associated with a customer VLAN, which is then virtualized across the backbone. Layer 2 VSNs offer an any-any LAN service type. Layer 2 VSNs associate one VLAN per I-SID.
For a Layer 2 VSN with IP multicast over Fabric Connect, the BEB associates a data I-SID with the multicast stream and a scope I-SID that defines the scope as Layer 2 VSN. A multicast stream with a scope of Layer 2 VSN can only transmit a multicast stream for the same Layer 2 VSN.
For a Transparent Port UNI, the I-SID is associated with a port or MLT, which is then virtualized across the backbone. Transparent Port UNI associates multiple ports or MLT to an I-SID.
For a Layer 3 VSN, the I-SID is associated with a customer VRF, which is also virtualized across the backbone. Layer 3 VSNs are always full-mesh topologies. Layer 3 VSNs associate one VRF per I-SID.
For a Layer 3 VSN with IP multicast over Fabric Connect, the BEB associates a data I-SID with the multicast stream and a scope I-SID that defines the scope as Layer 3 VSN. A multicast stream with a scope of Layer 3 VSN can only transmit a multicast stream for the same Layer 3 VSN.
For IP Shortcuts with IP multicast over Fabric Connect, the BEB associates a data I-SID with the multicast stream and defines the scope as Layer 3 GRT. A multicast stream with a scope of Layer 3 GRT can only transmit a multicast stream for a Layer 3 GRT.
Note
I-SID configuration is required only for virtual services such as Layer 2 VSN and Layer 3 VSN. With IP Shortcuts with unicast, no I-SID is required, forwarding for the Global Routing table is done using IS-IS based shortest path BMAC reachability.
I-SID to VLAN binding is used to automatically determine the path between client and server in order to attach network devices to FA Zero touch services.