Routing Hierarchy Area-Border Backbone areas Router Lower-evel areas Partition Network into“ Areas” k Within area k each node has routes to every other node k Outside area Each node has routes for other top-level areas only Inter-area packets are routed to nearest appropriate border router Constraint: no path between two sub-areas of an area can 2021/1/exit that areaRouting Hierarchy  Partition Network into “Areas”  Within area  Each node has routes to every other node  Outside area  Each node has routes for other top-level areas only  Inter-area packets are routed to nearest appropriate border router  Constraint: no path between two sub-areas of an area can 2021/1/31exit that area 7 Backbone Areas Lower-level Areas Area-Border Router