# VOSS fabric identifier decoder > Decode an Extreme SPBM fabric identifier - a 24-bit I-SID, a 20-bit nickname (X.XX.XX), or a system-id / B-MAC. Auto-detected, all in your browser. - Tool: https://ronutz.com/en/tools/voss-fabric-id - Family: Networking --- ## What it does Extreme's Fabric Connect (SPBM) names things with three numbers, and this tool decodes whichever one you paste, auto-detecting it by shape: - an **I-SID**, a 24-bit service identifier (1 to 16,777,215) that names a service instance in the fabric; - a **nickname**, a 20-bit node identifier written `X.XX.XX` in hex; and - a **system-id / B-MAC**, a 48-bit MAC-form address written as a dotted triple like `00bb.0021.0001`. It runs entirely in your browser. ## The I-SID The I-SID is the heart of a fabric service. A customer VLAN mapped to an I-SID is a Layer 2 VSN; a VRF mapped to an I-SID is a Layer 3 VSN; the global routing table carried over IS-IS with no I-SID is IP Shortcuts. The number itself does not encode which of these it is - that is set by how you provision it - so the tool validates the 24-bit range and explains usage rather than guessing a type. The default Fabric Attach network I-SID (FAN) is 16777001, which the tool calls out. ## The nickname Every SPBM node carries a 20-bit nickname, written as one hex digit, a dot, two hex digits, a dot, two hex digits (for example `C.30.00`). It must be unique across the fabric, including across adjacent IS-IS areas. The tool converts the `X.XX.XX` form to and from its integer value and range-checks it. Dynamic nickname assignment hands out nicknames from a server prefix range such as `C.30.00-C.3F.FF`. ## The system-id / B-MAC The nodal B-MAC, configured as the IS-IS system-id, is a 48-bit address. The tool reads the two significant bits of its first octet: the U/L bit (Extreme's guidance is to use a locally administered address, first octet `02`) and the I/G bit (a node address should be individual, not group). ## Using it Paste a decimal I-SID, an `X.XX.XX` nickname, or a dotted-triple B-MAC. Detection is by shape, so there is nothing to select. ## Standards and references - [Extreme VOSS User Guide: I-SID (24-bit service identifier)](https://documentation.extremenetworks.com/VOSS/SW/89/VOSSUserGuide/GUID-B71193C3-7579-4917-8FE3-839F01ABDCA9.shtml) - the 24-bit I-SID and its role in Layer 2 and Layer 3 VSNs - [Extreme VOSS User Guide: SPBM and IS-IS Infrastructure Fundamentals](https://documentation.extremenetworks.com/VOSS/SW/89/vossuserguide/GUID-1BC71501-66E0-4458-807F-CB320C884AD4.shtml) - nicknames, B-VLANs, B-MAC forwarding, and the IS-IS control plane - [Extreme VOSS User Guide: Configure Dynamic Nickname Assignment](https://documentation.extremenetworks.com/VOSS/SW/89/VOSSUserGuide/GUID-227C21E8-9EA7-4AA7-891D-02A1A7F22C27.shtml) - the X.XX.XX nickname format and nick-name server prefix ranges ## Related reading - [Fabric Attach: Auto-Provisioning the Edge (Where VOSS Meets EXOS)](https://ronutz.com/en/learn/voss-fabric-attach.md): How Fabric Attach lets an edge device signal the service it needs so the fabric provisions the I-SID automatically, the FA Server / Proxy / Client roles, how it rides LLDP, and how an EXOS switch attaches to a VOSS fabric without running SPBM itself. - [Fabric Connect and SPBM: Why VOSS Retires Spanning Tree](https://ronutz.com/en/learn/voss-fabric-connect-spbm.md): What Extreme's Fabric Connect actually is - Shortest Path Bridging MAC (SPBM, IEEE 802.1aq) with an IS-IS control plane and a MAC-in-MAC data plane - and why collapsing the core to a single link-state protocol replaces spanning tree and the usual overlay stack. - [IS-IS, Nicknames, and B-MACs: The VOSS Control Plane](https://ronutz.com/en/learn/voss-isis-and-nicknames.md): How SPBM uses IS-IS as its single link-state control plane on fabric links only, what a 20-bit node nickname is and why it must be unique, and how the system-id / backbone MAC drives MAC-in-MAC forwarding. - [SMLT and vIST: Dual-Homing a Fabric Edge](https://ronutz.com/en/learn/voss-smlt-and-vist.md): How Split MultiLink Trunking dual-homes an edge device to a pair of switches with active-active links and no spanning tree, how virtual IST runs the inter-switch trunk through the SPBM fabric itself, and the smlt-peer-system-id and smlt-virtual-bmac that make the cluster one logical node. - [The I-SID: How VOSS Replaces VLAN Stretching](https://ronutz.com/en/learn/voss-i-sid-and-vsns.md): Why Extreme's Fabric Connect provisions services at the edge instead of trunking VLANs hop by hop, what the 24-bit I-SID is, and how Layer 2 VSN, Layer 3 VSN, and IP Shortcuts all ride the same mechanism over an SPBM MAC-in-MAC core. - [VOSS vs EXOS: Two Extreme Operating Systems](https://ronutz.com/en/learn/voss-vs-exos.md): Extreme ships universal hardware that boots either EXOS or VOSS (Fabric Engine). This is what actually differs - a traditional-Ethernet OS with an intuitive CLI versus a fabric-native OS built on SPBM - and the three boundaries at which they interconnect.