The single control plane

SPBM's control plane is IS-IS - the same link-state interior gateway protocol used for IP routing, adapted to carry Ethernet fabric information. Nodes form adjacencies on their fabric links, exchange link-state PDUs, and each independently computes the shortest path to every other node. Onto standard IS-IS, 802.1aq adds TLVs (and sub-TLVs) that carry the SPBM-specific data: node nicknames, backbone MACs, and I-SID service membership. When you provision a service on a Backbone Edge Bridge, its I-SID membership floods through the topology inside these TLVs.

IS-IS runs in the core, not at the edge

A detail that trips people up: IS-IS is the fabric's Network-to-Network Interface (NNI) protocol. It runs between fabric nodes, not on the User-to-Network Interface (UNI) edge ports where hosts and non-fabric devices attach. You will not bring up an IS-IS adjacency to a server or a plain access switch. That is also why extending IP routing to a non-fabric neighbor - an EXOS switch, for instance - uses OSPF, BGP, or RIP redistribution rather than IS-IS, and why Layer 2 attachment uses Fabric Attach; both are covered in later articles. The fabric is typically one IS-IS area, configured with a manual area address such as 49.0000.

The nickname

Every SPBM node has a nickname: a 20-bit identifier written in hex as X.XX.XX (for example C.30.00 or 1.21.01). The nickname identifies the node when the fabric builds its multicast distribution trees, and it must be unique across the fabric - including across adjacent IS-IS areas, where duplicate nicknames are not allowed. You can assign nicknames statically, or use dynamic nickname assignment, where a nickname server hands them out from a configured prefix range such as C.30.00 to C.3F.FF.

The system-id and the B-MAC

Each node also has a system-id: a 48-bit value in MAC form, written as a dotted triple like 00bb.0021.0001, that serves as the node's backbone MAC. In MAC-in-MAC forwarding, a BEB uses its own nodal B-MAC as the source and the destination node's B-MAC as the destination of the backbone header, and the Backbone Core Bridges switch on exactly these addresses. Extreme's guidance is to make the system-id a locally administered address - the U/L bit set, so the first octet is 02 - which keeps it clearly distinct from a burned-in vendor MAC.

How it comes together

Put the pieces in order. IS-IS forms adjacencies over the NNI links and floods, in its link-state PDUs, each node's nickname, its B-MAC, and the I-SIDs it serves. Every node runs the same shortest-path computation and programs its B-VLAN forwarding tables accordingly. From then on, a customer frame entering a BEB is encapsulated toward the right destination B-MAC and follows the precomputed shortest path: no flooding, no spanning tree, no per-service core configuration. The fabric-identifier tool decodes any nickname, I-SID, or B-MAC you pull from show output while you are still learning to read it.