Cisco Certified Network Associate (CCNA) Practice Exam

How is the OSPF designated router (DR) selected?

1. Routers with the highest cost

2. Lowest router ID

3. Highest priority, then highest router ID

4. Random selection

The correct answer is: Highest priority, then highest router ID

The OSPF designated router (DR) selection process indeed prioritizes routers based on their interface priority first and then utilizes the router ID in case of ties. Each OSPF router has a priority value configured on each interface, which can be set to a value from 0 to 255. When OSPF neighbors form an adjacency, if the priority values are different, the router with the highest priority becomes the DR. If two or more routers have the same priority, the router with the highest router ID will be selected as the DR. This method of selection helps ensure that the most capable router (as indicated by its higher priority) is chosen for sending and receiving OSPF routing updates in broadcast and non-broadcast multi-access networks, which reduces unnecessary routing update traffic and helps maintain a more stable routing environment. In summary, the correct answer reflects the two-step process of DR selection in OSPF: first considering the priority, and if needed, resorting to the router ID for final selection.