OSPF cost in a point-to-multipoint setup

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When 3 routers are connected to each other on a single broadcast medium the definition of cost can be cumbersome. Normally in point-to-point connections we just put the cost on the specific interface.

In a point-to-multipoint setup you must define the cost specific for the neighbor.

For example in the following situation. We have 3 routers in Vlan10 and the range is 10.100.21.0/24. We want different cost towards 10.100.21.1 and 10.100.21.2.

OSPF Multi point setup

On Cisco IOS this can be done as following:

router ospf 1
 router-id 10.100.20.1
 neighbor 10.100.21.1 cost 20
 neighbor 10.100.21.2 cost 10