Cisco CCNA mock exam questions sample test – Question 64

.In the network exhibit, the routers are running OSPF and are set to the default configurations. (Click the Exhibit(s) button.)
What would be the effect of configuring a loopback interface on RouterA with an address of 192.168.1.50/24?

A. Router B would become the DR
B. Router A would become the DR
C. Router C would become the DR
D. Router A would become the BDR

Correct Answer: B

Explanation:
Configuring a loopback interface on RouterA with an address of 192.168.1.50/24 would cause Router A to become the designated router (DR). The designated router (DR) is
determined by the router with the highest interface priority number. If the priority numbers are tied, 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. Changing the priority to 0 would make the router ineligible to become the DR or the backup designated router
(BDR). The ip ospf priority # command is used to manually configure a priority on a specific interface.
Router IDs are determined first by the highest loopback IP address, followed by the highest IP address on an active physical interface. Thus, in the case of a priority tie, the router with
the highest loopback IP address will have the highest RID, and will become the DR for the network segment.
The current Router ID for a router can be determined by executing the show ip interface brief command. In the sample output of the show ip interface brief command below, the RID
will be 10.108.200.5.
Router# show ip interface brief
Interface IP-Address OK? Method Status Protocol
Ethernet0 10.108.00.5 YES NVRAM up up
Ethernet1 unassigned YES unset administratively down down
Loopback0 10.108.200.5 YES NVRAM up up
Serial0 10.108.100.5 YES NVRAM up up
Serial1 10.108.40.5 YES NVRAM up up
Serial2 10.108.100.5 YES manual up up
Serial3 unassigned YES unset administratively down down
Neither Router B nor C will be the DR because the IP addresses on their physical interfaces are lower than 192.168.1.50/24.
Router A will not be the backup designated router. Since it is the DR, it cannot also be the BDR.
Router C will not be the BDR because its IP address is lower than that of Router B. Router B will be the BDR.
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)
References:
Cisco > Support > IP > IP Routing > Technology Information > Technology White Paper > OSPF Design Guide > Document ID: 7039 > DR Election