Understanding IS-IS for CLNS
IS-IS extensions provide the basic interior gateway protocol (IGP) support for collecting intradomain routing information for Connectionless Network Service (CLNS) destinations within a CLNS network. Routers that learn host addresses through End System-to-Intermediate System (ES-IS) can advertise the addresses to other routers (intermediate systems) by using IS-IS.
For more information about IS-IS, see the ISO 10589 standard.