1. OSPF Path Selection Process
   1. OSPF always chooses an intra-area route over an inter-area route.
   2. ABR-s ignore type 3 LSA-s learned in a non-backbone area during SPF calculations. That prevents the ABR from choosing routes to Backbone via non-backbone areas.
2. The LSAs in the LSDB contain information to create a math equivalent of a figure of a network.
3. 1. Router
   1. One per router, per area.
   2. Lists: RID, all interface IP addresses in that area.
   3. Flooded only within the area.
4. 2. Network
   1. One per transit network.
   2. Created by DR on the subnet.
   3. Represents: the subnet and all interfaces in it.
   4. Flooded only within its area of origin.
5. 3. Net Summary
   1. Created by ABR.
   2. Represents: networks in an area when being advertised into another area. Defines the subnets in the origin area and their costs. Does not define the topology of the origin area.
   3. Flooded only within its area of the origin. Re-originated on ABRs.
6. 4. ASBR Summary
   1. Created by ABR.
   2. Advertises a host route to reach an ASBR Contains ASBR's RID and ABR's cost to reach it.
   3. Flooded only within its area of the origin. Re-originated on ABRs.
7. 5. AS External
   1. Created by ASBR for external routes injected in OSPF.
   2. Processed by other routers depending on the metric type: E1 -> Cost = Cost to reach ASBR + E1 (cost of the external network). E2 -> Cost = E2 (cost inside domain negligible when compared with E2). E1 is always preferred to E2 when both available.
   3. Flooded to all regular areas.
8. 6. Group membership - MOSPF
9. 7. NSSA External
   1. Created by ASBR inside NSSA.
   2. External route information carried in this type LSAto distinguish from LSA type 5 which is still prohibited in NSSA.
   3. ABR with the highest RID will translate to LSA type 5 and inject the external routes to other area.