Intra-Area Routes
A network route learned from another router within the same area is known as a intra-area route.
In show ip route ospf , any routes learned this way are displayed with the key symbol O
These routes are advertised using a Type 1 LSA, and are preferred over Type 3 LSAs.
If multiple intra-area routes exist, the path with the lowest total metric is preferred and installed in the routing table. If there are multiple routes with the same lowest metric, they are installed into the routing table up to a total number of four by default
Inter-Area Routes
Network routes learned from other OSPF routers in a different area through an Area Border Router (ABR) are known as an inter-area route.
show ip route ospf shows any routes learned this way with the key O IA
Interarea routes are similar that the path with the lowest metric is installed into the routing table. It is the same case that if multiple equal lowest metric paths exist, they are installed into the routing table up to a default value of four.
Equal Cost Multipathing
The default number of equal cost metric paths in the routing table can be changed from the default of four. The command maximum-paths <number> in the routing process configuration mode will do this.
OSPF Path Type Selection Priority
Inra area routes are preferred first, followed by Interarea, then External Routes.
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