Comprehensive and Detailed In-Depth Explanation:
InIS-IS, routes are distributed differently based onrouter levels:
Level-1 (L1) routers→ Maintainspecific routes only within their own area.
Level-2 (L2) routers→ Maintainspecific routes for the entire network(inter-area routing).
Level-1-2 (L1/L2) routers→ Storeboth L1 and L2 routesand act asarea border routers.
In the diagram,R2 and R3 are L1/L2 routers, meaning they storespecific routes for both their area and other areas.
R1 is only an L1 router, meaning it only hasintra-area routes, andR7 is an L2-only router, meaning it does not store all specific routes.
Therefore,R2 and R3havespecific routesfor the entire network.
????Reference:Huawei HCIA-Datacom Study Guide, IS-IS Routing Levels and Route Distribution.
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