ISIS architecture

• ISIS as a POINT-TO-POINT architecture
• You can build full-mesh or hub-and-spoke ISIS topologies using point-to-point, but each link will require its own address space. The rest of this discussion assumes an ISIS full-mesh/hub-and-spoke using one subnet.
• ISIS as a FULL-MESH architecture.
• ISIS will works if all routers are using main interface (requires CLNS MAP statements).
• ISIS will works if all routers are using multipoint subinterface (requires CLNS MAP statements).
• Some ISIS routers using the main interface, and some ISIS routers using multipoint = FAIL
• ISIS as a HUB-AND-SPOKE architecture.
• Using main interface for ISIS doesn't work (hub forms neighbor relationships with both spokes, but drops all routes except for one spoke).
• Using multipoint subinterface for ISIS doesn't work (hub forms neighbor relationships with both spokes, but drops all routes except for one spoke).