This document describes an optional mechanism within Intermediate
System to Intermediate Systems (IS-ISs) used today
by many ISPs for IGP routing within their clouds. This document
describes how to run, within a single IS-IS domain, a set of
independent IP topologies that we call Multi-Topologies (MTs).
This MT extension can be used for a variety of purposes, such as an
in-band management network "on top" of the original IGP topology,
maintaining separate IGP routing domains for isolated multicast or
IPv6 islands within the backbone, or forcing a subset of an address
space to follow a different topology. [STANDARDS-TRACK]