Which routers are likely to have been elected as DR?

The internetwork infrastructure of company XYZ consists of a single OSPF area as shown in the graphic. There is concern that a lack of router resources is impeding internetwork performance. As part of examining the router resources, the OSPF DRs need to be known. All the router OSPF priorities are at the default and the router IDs are shown with each router.

Which routers are likely to have been elected as DR? (Choose two.)
A .  Corp-1
B .  Corp-2
C .  Corp-3
D .  Corp-4
E .  Branch-1
F .  Branch-2

View Answer

Answer: D,F

Explanation: There are 2 segments on the topology above which are separated by Corp-3 router. Each segment will have a DR so we have 2 DRs. To select which router will become DR they will compare their router-IDs. The router with highest (best) router-ID will become DR. The router-ID is chosen in the order below:

The highest IP address assigned to a loopback (logical) interface. If a loopback interface is not defined, the highest IP address of all active router’s physical interfaces will be chosen. In this question, the IP addresses of loopback interfaces are not mentioned so we will consider IP addresses of all active router’s physical interfaces. Router Corp-4 (10.1.40.40) & Branch-2

(10.2.20.20) have highest “active” IP addresses so they will become DRs.