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CCNP Core > Chap 8 - OSPF > Flashcards

Chap 8 - OSPF Flashcards

1
Q

What is SPT

A

Shortest Path Tree

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2
Q

How does OSPF provide for scaling?

A

By using multiple areas within the routing domain.

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3
Q

What multicast addresses does OSPF use?

A

224.0.0.5 and 224.0.0.6

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4
Q

What multicast MAC address do all OSPF routers use?

A

01:00:5E:00:00:05

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5
Q

What multicast MAC address is used for all DR routers?

A

01:00:5E:00:00:06

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6
Q

What are the 5 types of packets used by OSPF?

A
  • Hello
  • DD
  • Link State Request (LSR)
  • Link State Update (LSU)
  • Link State Ack
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7
Q

What are OSPF Hello packets used for?

A
  • Discovering neighbors
  • Periodic checks to make sure the neighbor is still alive
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8
Q

What are DD packets used for?

A

Summarizing database contents when adjacency is first formed

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9
Q

What are Link State Requests used for?

A

Sent by a router requesting LSAs from its neighbor

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10
Q

What are Link State Updates for?

A

Sent in response to an LSR containing database updates

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11
Q

What are Link State Acknowledgements for?

A
  • Acknowledges the flooding of LSAs.
  • Provides reliable transport
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12
Q

What are 9 fields in a Hello packet?

A
  • Router ID
  • Authentication options
  • Area ID
  • Interface mask
  • Interface priority
  • Hello Interval
  • Dead Interval
  • DR and BDR IP addresses
  • Active neighbors
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13
Q

What are the 8 neighbor states?

A
  • Down
  • Attempt
  • Init
  • 2-way
  • ExStart
  • Exchange
  • Loading
  • Full
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14
Q

Describe the Down state.

A

When the router has not received any Hello packets

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15
Q

Describe the Attempt state.

A

On NBMA networks, no information has been received recently but its still trying.

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16
Q

Describe the Init state.

A

Router has received a hello packet from its neighbor, but the receiving router’s ID was not included in the hello packet.

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17
Q

What happens in the 2-way state.

A

Bidirectional communication has started. DR and BDR elected at the end of this state

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18
Q

What 2 things happen during the ExStart state.

A
  • Master/Slave roles are determined. Highest router-id is Master
  • Initial sequence number is decided.
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19
Q

What happens during the Exchange state.

A

DD’s are exchanged summarizing the contents of the LSDB

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20
Q

What 3 things happen during the Loading state.

A
  • Routers send link-state request packets based on the DD summary it received
  • Neighbor responds with Link State Update packets
  • All LSUs are acknowledged with Link-state Acks
21
Q

Describe the Full state.

A

LSDBs are in sync, routers are fully adjacent.

22
Q

What are 2 methods of enabling OSPF on an interface?

A
  • network statement
  • interface config ‘ip ospf (process_id) area (area_number)
23
Q

If 2 network statements are entered that both include an interface what happens?

A

The more specific network statement wins.

24
Q

If the interface configuration is used will it match on secondary interfaces?

A

Yes, unless the ‘secondaries none’ parameter is added to the command.

25
Q

If an OSPF configuration includes both a network statement and an interface command which takes precedence?

A

The interface command takes precedence.

26
Q

If a router ID is not specified what is used for the router ID?

A
  • Highest loopback IP address first
  • Highest physical interface IP address second
27
Q

Will the network on an interface still be advertised if the network is configured as passive?

A

Yes, network still advertised but interface won’t send out Hellos, won’t process received OSPF packets and won’t establish neighborships.

28
Q

What are the 8 requirements for OSPF routers to become neighbors?

A
  • Unique router IDs
  • Authentication matches
  • Area ID matches
  • Area flags match
  • Interfaces on a common subnet
  • MTUs match
  • Hello and Dead timers match
  • DR enablement matches
29
Q

When a default route is advertised what kind of route is it?

A

E2 External

30
Q

What is the reference bandwidth in OSPF?

A

100 Mbps

31
Q

What is the formula used to calculate the cost of an interface?

A

100 Mbps / interface bandwidth

32
Q

What are 5 interface costs?

A
  • T1 = 64
  • 10 Mbps Ethernet = 10
  • 100 Mbps Ethernet = 1
  • 1 Gbps Ethernet =1
  • 10 Gbps Ethernet = 1
33
Q

If the reference bandwidth is changed what does it affect and where else should it be done?

A
  • Affects all interfaces in that OSPF process
  • Should be made the same on all OSPF routers
34
Q

For LSA purposes what range does an interface cost need to be in?

A

1 - 65,535

35
Q

What happens when you change the Hello timer?

A

The Dead timer changes to 4 times the Hello timer.

36
Q

What should be taken into consideration when you choose which routers should be DR and BDR?

A

DR and BDR routers need to have adequate memory and CPU

37
Q

How are DR and BDR routers elected?

A

Router with the highest interface priority is DR, second highest is BDR. If interface priorities tie then routers with highest and second highest router IDs win.

38
Q

After the DR has been elected and the BDR election takes place what does the DR do?

A

The DR does not place its RID in the BDR field of the Hello packet.

39
Q

What has to happen in order to elect an new DR or BDR?

A

The OSPF process on the DR or BDR has to have gone down or restarted.

40
Q

What is the default priority of OSPF interfaces?

A

The default is 1.

41
Q

How does a router know it needs to elect a DR / BDR?

A

If Hellos don’t contain a DR/BDR the router initiates a Wait timer (equal to the Dead timer). Once Wait timer expires router participates in the election.

42
Q

What is the best way to modify a router so that it becomes the DR or BDR?

A

Change the interface priority to a value higher than the default (1).

43
Q

Can the DR or BDR roles be preempted?

A

No. The OSPF process on the DR or BDR needs to be restarted.

44
Q

How can you make sure a router doesn’t participate in the DR / BDR election?

A

Change its interface priority to 0.

45
Q

What will happen if the priority of an interface on the DR is changed to 0?

A

Router will remove itself as the DR. The BDR will become the DR and a new BDR will be elected.

46
Q

What are the 5 OSPF media types?

A
  • Broadcast
  • Non-broadcast
  • Point-to-point
  • Point-to-multipoint
  • Loopback
47
Q

Display the Hello and Dead timers.

A

show ip ospf interface

48
Q

Determine if a router is the DR or BDR of a network.

A

show ip ospf interface brief (appears under State)

49
Q

Identify the Network Type of an interface.

A

show ip ospf interfaces gig0/1

CCNP Core (46 decks)

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