OSPF metric sum of outgoing interface costs
When using the OSPF routing protocol, the metric to a particular destination is determined by the sum of the cost of the outgoing interfaces along the path. Thus, if the cost is not the same on both ends of a link, return traffic may take another route.
Links:
https://forum.networklessons.com/t/how-to-configure-ospf-for-ccna-students/879/88?u=lagapides