This chapter covered the control plane aspects of TRILL and FabricPath. Both TRILL and FabricPath use IS-IS with some extensions as their control protocol. A brief overview of IS-IS was given followed by a detailed description of the changes that were made in IS-IS to support TRILL. This chapter focused primarily on the IS-IS–related changes including the packet format of the newly introduced TLVs for TRILL. The forwarding and architecture concepts in TRILL and FabricPath were touched upon briefly to give some context. Study Chapters 4 and Chapter 5 to get a thorough understanding of the architecture and forwarding concepts.