OSPF Basics

Question 1

What is the protocol number for OSPF?

Answer 1

89

Question 2

Which version of OSPF supports ipv6?

Answer 2

OSPFv3

Question 3

Which RFC(s) describes OSPFv2?

Answer 3

1247 and 2348

Question 4

Multicast addresses used by OSPF

Answer 4

224. 0.0.5 for all OSPF routers

224. 0.0.6 for DR or BDR routers

Question 5

What does LSA stand for?

Answer 5

Link State Advertisement

Question 6

Three basic OSPF operation steps

Answer 6

1. Discover all directly connected OSPF-speaking neighbor routers
2. Exchange link state information that describes the topology of the OSPF area
3. Perform best path calculation

Question 7

What does ASBR stand for?

Answer 7

Autonomous System Border Router

Question 8

Two requirements for backbone areas

Answer 8

1. Must connect to all other non-backbone areas

2. Must be contiguous - not allowed to be split

Question 9

What is the purpose and type of a HELLO packet?

Answer 9

To discover neighbors and build adjacencies (type 1)

Question 10

What is the purpose and type of a DBD packet?

Answer 10

To check for database synchronization between routers (type 2)

Question 11

What type of packet is used to request LSAs from another router?

Answer 11

LSR packet (type 3)

Question 12

What type of packet is used to send LSAs?

Answer 12

LSU packet (type 4)

Question 13

Command to verify DR/BDR status

Answer 13

show ip ospf neighbor

Question 14

Command to verify OSPF configuration

Answer 14

show ip protocols

Question 15

View OSPF neighborship

Answer 15

show ip ospf neighbor

Question 16

View OSPF enabled interfaces

Answer 16

show ip ospf interface

Question 17

What is an intra-area route?

Answer 17

An intra-area route is a route which originates and is learned in the same local area to which the router belongs

Question 18

What is an interarea route?

Answer 18

Routes which originate in other areas and are inserted into the local area to which the router belongs

Question 19

Command to investigate hello and dead timers

Answer 19

show ip ospf interface interface-name

Question 20

State in which no active OSPF neighbors have been detected?

Answer 20

Down

Question 21

INIT state

Answer 21

Interface has received a hello packet but no bi-directional communication has been established with a neighbor

Question 22

State in which bidirectional communication occurs?

Answer 22

2-Way

Question 23

Full State

Answer 23

Neighbors have become fully adjacent

Question 24

State in which a router has received its own router ID in a hello packet?

Answer 24

2-Way

Question 25

Exstart State

Answer 25

Establishes which router will exchange DBD packets first

Question 26

State in which DBD packets are exchanged and compared?

Answer 26

Exchange

Question 27

Loading State

Answer 27

Exchange of LSRs and LSUs in order to synchronize the link state databases between two routers

Question 28

Command to change OSPF network type

Answer 28

Enter interface configuration mode | ip ospf network network_type

Question 29

OSPF network types

Answer 29

1. Point-to-Point 2. Broadcast 3. NonBroadcast 4. Point-to-multipoint 5. Point-to-multipoint NonBroadcast 6. Loopback

Question 30

Which OSPF network types do not use BRs/BDRs?

Answer 30

1. Point-to-Point because only two routers in subnet 2. Point-to-Multipoint because one router acts as hub 3. Loopback because it is a logical interface

Question 31

Which OSPF network types do not use dynamic neighbor discovery?

Answer 31

1. NonBroadcast | 2. Loopback

Question 32

Steps to configure OSPF passive interface

Answer 32

router ospf # | passive-interface interface-name

Question 33

When would you use passive interfaces?

Answer 33

Whenever you do not expect the interface to form neighbor adjacencies.

Question 34

Command to investigate ospf database

Answer 34

show ip ospf database

Question 35

Command to verify OSPF type 1 LSAs

Answer 35

show ip ospf database router

Question 36

Command to verify locally generated type 1 LSAs

Answer 36

show ip ospf database router self-originate

Question 37

What is a type 2 LSA?

Answer 37

A LSA generated by a designated router within its area. It includes a list of attached routers on the transit link and the subnet mask of the link

Question 38

Command to investigate type 2 LSAs on a router

Answer 38

show ip ospf database network

Question 39

What is the function of a type 3 LSA?

Answer 39

To advertise network information to areas outside of the originating area within the OSPF AS. They are regenerated by ABRs.

Question 40

Command to investigate type 3 LSAs on a router

Answer 40

show ip ospf database summary

Question 41

What is the function of a type 4 LSA?

Answer 41

To advertise the metric to the autonomous system border router. They contain the router id of the ASBR and are regenerated by ABRs.

Question 42

Command to view type 4 LSAs on a router

Answer 42

show ip ospf database asbr-summary

Question 43

What is the function a type 5 external LSA?

Answer 43

To advertise networks from other autonomous systems. They are advertised and owned by the originating ASBR.

Question 44

Command to view details of type 5 external LSA

Answer 44

show ip ospf database external

Question 45

Command to examine the OSPF cost of an interface

Answer 45

show ip ospf interface | [brief]

Question 46

How do you prevent router from becoming the DR or BDR?

Answer 46

Manually set its OSPF priority to 0 1. interface 2. ip ospf priority 0

Question 47

Command to create summary route on an ASBR

Answer 47

router ospf # | summary-address

Question 48

What's unique about OSPF stub areas?

Answer 48

They do not allow type 5 LSAs

Question 49

When and where would you use 'default-information originate'?

Answer 49

Whenever you want to direct traffic to the internet through an ASBR.

Question 50

What is unique about totally stub areas?

Answer 50

They do not allow type 3 LSAs

Question 51

What is unique about NSSAs?

Answer 51

They do not allow type 5 LSAs