In IS-IS , routes are distributed differently based on router levels :
Level-1 (L1) routers → Maintain specific routes only within their own area .
Level-2 (L2) routers → Maintain specific routes for the entire network (inter-area routing).
Level-1-2 (L1/L2) routers → Store both L1 and L2 routes and act as area border routers .
In the diagram, R2 and R3 are L1/L2 routers , meaning they store specific routes for both their area and other areas .
R1 is only an L1 router , meaning it only has intra-area routes , and R7 is an L2-only router , meaning it does not store all specific routes.
Therefore, R2 and R3 have specific routes for the entire network.
???? Reference: Huawei HCIA-Datacom Study Guide, IS-IS Routing Levels and Route Distribution.
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