OSPF

Question 1

What are the issues with large single area OSPF configuration

Answer 1

• large routing table
• large link state database (topology)
• frequent SPF routing calculations

Question 2

In MOSPF, what are the routers which are connected to the backbone and to the other areas called?

Answer 2

Area border routers

Question 3

OSPF route summarization is enabled by default

Answer 3

False

Question 4

Internal routers in the same area have identical LSDB’s

Answer 4

True

Question 5

OSPF supports automatic summarization between areas

Answer 5

False

Question 6

OSPF supports automatic summarization for external routes injected with ASBR

Answer 6

False

Question 7

What are LSA’s used for?

Answer 7

Exchanging routing information between OSPF peers

Question 8

What are LSA’s (link state advertisement) carried inside of?

Answer 8

LSU (link state update) messages

Question 9

All routers generate type 1 LSA’s

Answer 9

True

Question 10

What types of routers are in OSPF?:

Answer 10

• designated routers
• backup designated routers
• designated router other (DROTHER)

Question 11

What OSPF router type can send type 2 network LSA’s?

Answer 11

designated routers

Question 12

What are LSA type 2 messages used for?

Answer 12

inform routers of the router ID of the DR in each area, and shows a list of attached routers

Question 13

What type of LSA’s do area border routers propagate?

Answer 13

• Type 3 OSPF summary
• type 4 OSPF ABR summary

Question 14

What is the OSPF Adjacency Table used for?:

Answer 14

• Neighbour table
• lists all neighbour routers

Question 15

What is the OSPF Link State Database used for?:

Answer 15

• topology table
• this is the same across all routers in same area

Question 16

What is the OSPF Forwarding Database used for?:

Answer 16

• routing table

Question 17

What is a routing metric?

Answer 17

a measurable value that is assigned to different routes based on the usefulness of that route

Question 18

What is an OSPF best path?:

Answer 18

a route with the lowest cost

Question 19

How is OSPF cost calculated?:

Answer 19

based on bandwidth

Question 20

What problems do Classful routing protocols have?:

Answer 20

• subnet mask information is not sent
• variable length subnet masks are not supported
• creates problems in dis-contiguous networks

Question 21

Classless routing protocols include subnet mask information in updates and support VLSMs

Answer 21

True

Question 22

Link-state protocols only send updates when there is a topology change (no periodic updates)

Answer 22

True

Question 23

What are the 5 types of OSPF packets?:

Answer 23

• hello
• database description (DBD)
• link state request (LSR)
• link state update (LSU)
• link state acknowledgement (LSAck)

Question 24

Which OSPF packet type contains LSAs?:

Answer 24

LSUs

Question 25

What purpose do LSU packets have?:

Answer 25

- forward OSPF routing updates - send specifically requested link state records

Question 26

What purpose do hello packets have?:

Answer 26

- discover OSPF neighbours - form neighbour adjacencies - advertise network parameters - elect DR and BDR on multiaccess networks (P2P does not require DRs and BDRs)

Question 27

True or False: -------------------- A neighbour adjacency will form between 2 routers if the hello and dead timers are different

Answer 27

False

Question 28

What is the all routers multicast address that the DR uses to send hello packets?:

Answer 28

224.0.0.5

Question 29

What information does the "show ip protocols" command display?:

Answer 29

- which interfaces are passive - OSPF process id - router id - routed networks - active interfaces - gateway routers

Question 30

What does the command "passive-interface default" do?:

Answer 30

makes all interfaces passive

Question 31

Which multiaccess network do DROTHERs use to send OSPF packets to the (B)DR?:

Answer 31

224.0.0.6

Question 32

True or False: ------------------- Only the DR and BDR listen to the 224.0.0.6 address

Answer 32

True

Question 33

What information will the command "show ip ospf interface" display?:

Answer 33

- priority - router state (DR, BDR, DROTHER) - neighbour adjacencies - DR and BDR router ids

Question 34

True or False: ------------------- hello packets are sent on passive interfaces

Answer 34

False