In an OSPF network when are DR and BDR elections required?

Question:
In an OSPF network when are DR and BDR elections required?

• when the two adjacent neighbors are interconnected over a point-to-point link
• when all the routers in an OSPF area cannot form adjacencies
• when the routers are interconnected over a common Ethernet network
• when the two adjacent neighbors are in two different networks

Explanation: When the routers are interconnected over a common Ethernet network, then a designated router (DR) and a backup DR (BDR) must be elected.

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