Chapter 7

Question 1

*To properly configure link-state routing, which of the following is mandatory within an area?

• External
• Stub
• Backbone
• Perimeter

Answer 1

-Backbone
EXPLANATION
Within each area, a contiguous backbone area must be defined. Non-backbone areas communicate through the backbone area. Non-backbone areas may include one or more stub areas. Only the backbone area is required.

Question 2

*You are currently using EIGRP on your network. Which of the following would you gain by switching to OSPF? (Select two.)

Correct Answer:

• Autosummarization
• Unequal-cost load balancing
• Open standard
• Hierarchical network design
• VLSM support
• Multiprotocol support

Answer 2

-Open standard

-Hierarchical network design
OSPF is an open standard routing protocol, while EIGRP is a Cisco-proprietary protocol. OSPF uses a hierarchical design for the network, while EIGRP uses a less-structured design.

OSPF supports equal-cost load balancing, but does not support unequal-cost load balancing. Both OSPF and EIGRP provide VLSM support. OSPF only supports manual summarization between areas, while EIGRP supports both manual and automatic summarization. OSPF is an IP-only routing protocol; multiprotocol support is provided by EIGRP.

Question 3

*You have configured Router A, Router B, and Router C as shown. No loopback interfaces have been configured.

hostname C
…
router ospf 600
network 172.16.32.1 0.0.0.0 area 100
network 192.168.2.1 0.0.0.0 area 100
…

What is the default router ID of Router C?

• 172.16.32.1
• 100
• 600
• 192.168.2.1

Answer 3

-192.168.2.1

Question 4

What are DRs and BDRs used for when using the OSPF routing protocol?

• Reduce routing table updates in a point-to-point network.
• Divide the network into a hierarchical configuration.
• Ensure a loopfree path between two networks.
• Reduce routing table updates in a broadcast network.
• Identify preferred and backup routes to improve recovery from link failure.

Answer 4

-Reduce routing table updates in a broadcast network.

EXPLANATION

OSPF uses designated routers (DR) and backup designated routers (BDR) on broadcast networks (such as Ethernet) where multiple routers are on the same subnet to reduce the amount of traffic from routing table updates. Routing updates are sent to the DR, with the DR being responsible for propagating changes to other routers on the subnet.

On a point-to-point network, the DR and BDRs are not used. Instead, routers begin exchanging routing information immediately following neighbor discovery. OSPF uses areas to organize the network into a hierarchical design. By design, OSPF is a link-state routing method, which includes built-in mechanisms for eliminating routing loops. Preferred and backup routes are characteristics of successor and feasible successor routes in EIGRP.

Question 5

*You have a medium-sized business network with twelve subnets (192.168.1.0/24 through 192.168.12.0/24). You use OSPF for your routing protocol. One Ethernet subnet has five routers, all in the same OSPF area as shown.

You want to ensure that RouterC (192.168.12.0/24) becomes the designated router on the subnet. Assuming that no additional configuration parameters are configured other than what is shown, how could you accomplish this task? (Select three. Each option is a complete solution.)

• Configure a loopback interface IP address of 1.1.1.1.
• For the OSPF process, set the router-id to 200.1.1.1.
• Change the IP address on the interface connected to the 192.168.12.0/24 subnet to 192.168.12.1.
• For the interface connected to the 192.168.12.0/24 subnet, set the OSPF priority to 2.
• For the OSPF process, set the router-id to 172.16.1.1.
• Change the IP address on the interface connected to the 192.168.12.0/24 subnet to 192.168.12.254.
• For the router, set its OSPF priority to 2.

Answer 5

• For the OSPF process, set the router-id to 200.1.1.1.
• For the interface connected to the 192.168.12.0/24 subnet, set the OSPF priority to 2.
• Change the IP address on the interface connected to the 192.168.12.0/24 subnet to 192.168.12.254.

Question 6

You are running OSPF as your routing protocol. One Ethernet subnet has five OSPF routers on the subnet. A partial configuration for two of the routers is shown. Both routers are connected to the subnet through the Fa0/1 interface. All interfaces are up.

hostname RouterA
!
interface loopback0
ip address 199.1.1.1 255.255.255.255
!
interface FastEthernet0/0
ip address 172.17.1.41 255.255.255.192
!
interface FastEthernet0/1
ip address 172.16.1.250 255.255.255.128
!
router ospf 200
network 172.16.1.128 0.0.0.127 area 0
network 172.17.1.0 0.0.0.63 area 0
!
–additional output omitted

==============================

hostname RouterB
!
interface FastEthernet0/0
ip address 172.18.1.12 255.255.255.192
!
interface FastEthernet0/1
ip address 172.16.1.200 255.255.255.128
!
router ospf 300
network 172.16.1.128 0.0.0.127 area 0
network 172.18.1.0 0.0.0.63 area 0
!
–additional output omitted

Assuming that either RouterA or RouterB will become the DR, which one will be elected the DR for the subnet?

• RouterB will be the DR because of the Fa0/0 interface IP address.
• RouterA will be the DR because of the loopback interface IP address.
• RouterA will be the DR because of the Fa0/1 interface IP address.
• Router B will be the DR because of the OSPF process number.