Day 12 - Fine-Tuning and Troubleshooting OSPF

Question 1

R1 has a link to the internet which makes it an ASBR (autonomous system boundary router). Configure a default route on R1 that will propagate throughout the network. Use a process ID of 10

Answer 1

R1
ip route 0.0.0.0 0.0.0.0 serial 0/1/0

router ospf 10
default-information originate

Question 2

With R1’s default route successfully propagated what should R2 and R3’s routing tables show?

Answer 2

O*E2 routes that point to R1

Question 3

What is the default OSPF hello interval on multiaccess and point-to-point networks?

Answer 3

10 seconds

Question 4

What is the nonbroadcast multiaccess network default hello interval?

Answer 4

30 seconds

Question 5

What is the default OSPF dead interval?

Answer 5

40 seconds OR 4 times the hello interval

Question 6

True or False:

The default hello and dead intervals are configured at the interface level

Answer 6

True

Question 7

Based on the topology, configure a hello interval of 5 for interface S0/0/0 (don’t forget the dead interval as well)

Answer 7

int serial 0/0/0
ip ospf hello-interval 5
ip ospf dead-interval 20

Question 8

True or False:

Hello and Dead intervals don’t need to be consistent between neighbors

Answer 8

False

Question 9

What are the 5 types of OSPF networks?

Answer 9

Point-to-point
Broadcast multiaccess
NBMA (Nonbroadcast multiaccess)
Point-to-multipoint
Virtual links

Question 10

The solution to managing the number of adjacencies and the flooding of LSAs on a multiaccess network is the use of a __________ __________

Answer 10

Designated Router

Question 11

To reduce the amount of OSPF traffic on multiaccess networks, OSPF elects a __________ and a __________

Answer 11

DR
BDR

Question 12

The __________ __________ is responsible for updating all other OSPF routers when a change occurs in the multiaccess network

Answer 12

Designated Router

Question 13

The DR is the router with the highest __________ ___________ __________

Answer 13

OSPF interface priority

Question 14

The BDR is the router with second highest __________ __________ __________

Answer 14

OSPF interface priority

Question 15

When the DR is elected, it remains the DR until what of any of 3 conditions occurs?

Answer 15

The DR fails
The OSPF process on the DR fails
The multiaccess interface on the DR fails

Question 16

What is the range of OSPF priority numbers?

Answer 16

0 - 255

Question 17

What is the default priority value for all router interfaces unless manually changed?

Answer 17

1

Question 18

What does a value of 0 indicate when it comes to priority and electing DR and BDRs?

Answer 18

It makes the router ineligible to become the DR or BDR

Question 19

Based on the topology, why would R3 and R2 be DR and BDR respectively?

Answer 19

Because R3 has a router ID 3.3.3.3 and R2 has a router ID of 2.2.2.2

3.3.3.3 is the highest router id and 2.2.2.2 is the second highest

Question 20

Based on the topology, elect R1 and R2 as DR and BDR

Answer 20

R1
int gi0/0
ip ospf priority 200

R2
int gi0/0
ip ospf priority 100

Question 21

What are the general steps for Neighbor State Summary?

Answer 21

1. Down - No active neighbor detected
2. Initilialization - Hello packets sent and received by neighbors
3. 2 WAY - Bi-Directional communication. Can see it’s own router ID received in Hello packets
4. Exstart - Primary and secondary roles determined
5. Exchange - DBD packets sent
6. Loading - Exchange of LSRs and LSU (With LSAs within the LSU)
7. Full - Neighbors full adjacent

Question 22

What settings must be matched for a pair of OSPF routers to form an adjacency?

Answer 22

• They must be in each other’s neighbor list
• Hello & Dead Intervals
• Area ID
• IP Subnet
• Authentication Flag
• Stub Area Flag
• MTU and MTU IP Size

Question 23

Solve for definition of the correct show command when verifying OSPF:

Verifies vital OSPF configuration information, including the OSPF process ID, the router ID, networks the router is advertising, neighbors the router is receiving updates from, default AD, etc.

Answer 23

show ip protocols

Question 24

Solve for definition of the correct show command when verifying OSPF:

Verifies that the router has formed an adjacency with its neighboring router

Answer 24

show ip ospf neighbor

Question 25

Solve for definition of the correct show command when verifying OSPF:

Displays the OSPF parameters configured on an interface, such as the process ID, area, cost and timer intervals

Answer 25

show ip ospf interface

Question 26

Solve for definition of the correct show command when verifying OSPF:

Displays only the OSPF learned routes in the routing table

Answer 26

show ip route ospf

Question 27

This command clears and resets the OSPFv2 neighbor adjacencies

Answer 27

clear ip ospf process

Question 28

What 3 out of 7 OSPF states are establishing neighbor adjacencies?

Answer 28

Down State
Init State
Two-Way State

Question 29

What 3 out of the 7 OSPF states are synchronizing the OSPF database?

Answer 29

ExStart State
Exchange State
Loading State

Question 30

What is the last of the 7 states of OSPF?

Answer 30

Full State

Question 31

What 3 things / questions should you check or ask when troubleshooting OSPF?

Answer 31

Is the neighbor table correct? (show ip ospf neighbor)

Is the routing table correct? (show ip route ospf)

Does the traffic take the desired path? (show ip route ospf)

Question 32

What OSPF network type is assigned to Ethernet interfaces of directly connected neighbors?

Answer 32

Broadcast

Question 33

What is the default number of paths that OSPF will load balance packets?

Answer 33

4 equal cost paths

Question 34

Where is OSPF priority for DR and BDRs configured?

Answer 34

On the interface level