scope:

This document describes a mechanism that allows a single router to share one or more circuits among multiple Intermediate System to Intermediate System (IS-IS) routing protocol instances.

Multiple instances allow the isolation of resources associated with each instance. Routers will form instance-specific adjacencies. Each instance can support multiple topologies. Each topology has a unique Link State Database (LSDB). Each Protocol Data Unit (PDU) will contain a new Type-Length-Value (TLV) identifying the instance and the topology (or topologies) to which the PDU belongs.