How does OSPF on S series switches create ECMP routes

Question: Two routes learned from two areas with the same cost are not ECMP routes. Why?
Answer: According to RFC 2328, OSPF can generate ECMP routes only when the following conditions are met:
The routes are learned from the same area.
The routes have the same priority and cost.
RFC 2328 does not define selection rules of intra-area and inter-area routes for switches. When conditions of multiple routes are the same, a switch may not select the last advertised route. If routes are Type 5 external routes, the route with the largest area ID is preferentially selected, as defined in RFC 2328.

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