rent areas is performed in two steps: first the route is individuated in the area topology, then, knowing for each traversed areas the incoming and the outcoming nodes, the path route is specified also within areas. Following the same network representation, IS-IS routing entities are hierarchically ordered depending on their ability to route GLSPs only within their area or also toward other routing areas. In particular routing entities that are only able to route paths within their area are called Level 1 routers (not to confound with Layer 1 entities; this is a specific IS-IS hierarchy completely different from the network layering). Following the same criterion, routing entities that can route GLSPs only between vir- tual nodes that represents routing areas are called Level 2 routers (or inter area routers) and finally routing entities that are able to route GLSPs both inside the area and between different areas are considered logically as a superposition of communicating Level 1 and Level 2 routers and are called Level 1-2 routers. Level 2 routers are interarea routers that can only form relationships with other Level 2 routers; in other words, they can route through the area topology constituted by virtual nodes representing the routing areas. Similarly Level 1 routers can exchange information only with other Level 1 routers. Level 1-2 routers exchange information with both levels and are used to connect the interarea routers with the intraarea routers. Integrated IS-IS uses the legacy CLNP node-based addresses [35-37] to identify routers even in pure IP environments. The CLNP addresses, which are known as network service access points (NSAPs), are made up of three components: an area identifier (area ID) prefix, Telecommunication Networks followed by a system identifier (SysID), and an N-selector. The N-selector refers to the net- work service user, such as a transport protocol or the routing layer. A group of routing entities belongs to the same area if they share a common area ID. Note that all routing en