OSPF Path Selection

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:

  1. If both N1 & E1 have the same cost, P-bit in N1 will be used to break the tide.
  2. 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
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