Volume 1 - Chapter 23: Implementing Optional OSPF Features

Question 1

Which OSPF network type supports the use of a DR/BDR?

Answer 1

Broadcast

Question 2

Which OSPF network type does not support the use of a DR/BDR?

Answer 2

Point-to-Point

Question 3

An OSPF-enabled router has a connection to a LAN on its Gi0/1 interface, but no other routers share that LAN.

What role will the Gi0/1 be by default?

Answer 3

The designated router

Question 4

Describe the process for electing a BR/BDR.

Answer 4

The router elected to become the DR is the router with the highest OSPF interface priority.

If all priorities tie, then the router with the highest RID wins.

Question 5

What is the range of values available for an OSPF interface priority?

Answer 5

0 to 255.

Question 6

What OSPF interface priority will prevent a router from ever becoming a DR?

Answer 6

0

Question 7

What is the default OSPF interface priority?

Answer 7

1

Question 8

A technician configures R2 with an interface priority of 95 to attempt to make it the DR on a LAN shared with 3 other routers. All other routers use default priorities, what happens when the technician updates the priority?

Answer 8

Nothing, changing the interface priority does not cause a new DR/BDR election. Only a failure on the network will cause the routers to elect R2 as the DR.

Question 9

What is the default setting enabled on Serial interfaces?

Answer 9

ip ospf network point-to-point

Question 10

What type of OSPF network type is used on E-Line (Private Wire Services)?

Answer 10

Point to Point

Question 11

A technician connects R1 & R2 together over a direct point-to-point link. What neighbor state would you expect to see on either router when running the following command?:

show ip ospf neighbor

Answer 11

FULL/-

Question 12

Describe how the OSPF process changes on a port when a technician configures it to be a passive interface?

Answer 12

1) OSPF will continue to advertise the subnet.

2) OSPF no longer sends hello messages on the interface.

3) OSPF no longer processes any received hellos.

Question 13

What commands can be used to configure passive interfaces?

Answer 13

passive-interface type number

Or

passive-interface default

Question 14

A technician has configured all interfaces to be passive by default. What command is used stop interface Gi0/0/1 from being passive?

Answer 14

no passive-interface GigabitEthernet0/0/1

Question 15

What command(s) are used to advertise a default route to 0.0.0.0 /0 to OSPF enabled routers?

Answer 15

1) Set the default route on the edge router:
ip route 0.0.0.0 0.0.0.0 nexthop

2) Configure the router to advertise the default route:
default-information originate

Question 16

What command is used in OSPF to advertise a default route, even when no default route currently exists?

Answer 16

default-information originate always

Question 17

What interface subcommand can be used to statically set a port’s cost metric?

Answer 17

ip ospf cost x

Question 18

What is the command to set an interfaces bandwidth metric?

Answer 18

bandwidth speed

Question 19

How does OSPF calculate the cost of an interface that does not have a cost statically configured?

Answer 19

Using the following formula:

Cost = ref_bandwidth (kbps) / interface bandwidth (kbps)

Question 20

What is the default reference bandwidth used on Cisco routers?

Answer 20

100 Mbps

Question 21

What is the minimum OSPF interface cost?

Answer 21

1

Question 22

Describe the problem with utilizing the default reference bandwidth?

Answer 22

All links that are 100 Mbps or faster are treated the same in terms of cost:

Cost = ref_bandwidth (kbps) / interface bandwidth (kbps)

100,000 / 100,000 = 1
100,000 / 1,000,000 = 1 (minimum is 1)
100,000 / 10,000,000 = 1 (minimum is 1)

Question 23

What command is used to change the default interface reference bandwidth?

Answer 23

auto-cost reference-bandwidth speed

Speed is in Mbps

Question 24

What are the range of values for a statically assigned OSPF interface cost?

Answer 24

Between 1 and 65,535.

Question 25

What is the default hello interval on OSPF enabled interfaces for IOS?

Answer 25

10 seconds.

Question 26

What is the default dead interval on OSPF enabled interfaces for IOS?

Answer 26

40 seconds.

Question 27

What interface subcommands are configured to statically set the hello and dead intervals?

Answer 27

ip ospf hello-interval x
ip ospf dead-interval x