How is the designated router (DR) determined by OSPF on a multi-access network segment?

A.
The lowest interface priority, then the highest RID

B.
The highest interface priority, then the highest RID

C.
The lowest interface priority, then the highest OSPF process ID

D.
The highest interface priority, then the highest OSPF process ID

Explanation:
OSPF routers elect a designated router (DR) and backup designated router (BDR) on multi-access network
segments in order to minimize the amount of update traffic sent between OSPF neighbors. All routers on multiaccess network segment form adjacencies with the DR and BDR, but not with each other. Network events are
communicated to the DR, and the DR distributes the event to the rest of the network.
The DR is determined by the router with the highest interface priority number. If the priority numbers tie (which
will be the case if they are left to the default of 1), then the router with the highest router ID (RID) becomes the
DR. The default priority number is 1, and can be configured as high as 255.
In many cases, it is desirable to intervene in this process and select the router you want to be the DR. If that is
the case and the selected router is not becoming the DR for whatever reason, the following options are
available to ensure that the selected router wins the election:
Change the priority value of the router to a value higher than the other routers
Set the priority value of the other routers to 0
Create a loopback address on the selected router with an IP address higher than the IP addresses used on
the other routers
Changing the priority to 0 makes the router ineligible to become the DR or BDR. The ip ospf priority # command
is used to manually configure a priority on a specific interface.
It is also worth noting that a single OSPF area can have more than one DR. The election is NOT performed per
area, but per network segment. So if you had six OSPF routers in area 0 with three in one IP subnet and three
in another, there would be two elections, one for each segment.
The lowest interface priority does not determine the DR.
The OSPF process ID has no effect on DR elections.
Objective:
Routing Fundamentals
Sub-Objective:
Configure, verify, and troubleshoot single area and multi-area OSPFv2 for IPv4 (excluding authentication,
filtering, manual summarization, redistribution, stub, virtual-link, and LSAs)

Cisco > Support > IP > IP Routing > Technology Information > Technology White Paper > OSPF Design Guide
> Document ID: 7039 > DR Election