OSPF routers use these criteria to select the best route to be installed in the routing table:
A) When there are multiple routes available to the same network with different route types, routers use this order of preference (from highest to lowest):
- 1. Intra-area routes
- 2. Inter-area routes
- 3. External Type-1 routes (N1 or E1)
- 4. External Type-2 routes (N2 or E2)
B) If there are multiple routes to a network with the same route type, the route with the lowest value for cost is chosen as the best route.
C) If there are multiple routes to a network with the same route type and cost:
- If both N1 & E1 have the same cost, P-bit in N1 will be used to break the tide.
- Chooses all the routes to be installed in the routing table, and the router does equal cost load balancing across multiple paths. Otherwise if maximum-path = 1, LSA with Higher Router-ID will get installed