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Enterprise Networking > Module 2 OSPF > Flashcards

Module 2 OSPF Flashcards

1
Q

What is an OSPF router ID?

A

A 32-bit value represented as an IPv4 address, used to uniquely identify an OSPF router.

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2
Q

What are the two ways an OSPF router ID can be defined?

A
  • Defined by an administrator
  • Automatically assigned by the router
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3
Q

What role does the router ID play in OSPF database synchronization?

A

During the Exchange State, the router with the highest router ID sends their database descriptor (DBD) packets first.

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4
Q

In a multiaccess LAN environment, how is the designated router (DR) elected?

A

The router with the highest router ID is elected as the DR.

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5
Q

What is the function of the backup designated router (BDR)?

A

The BDR serves as a backup in case the DR fails.

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6
Q

What command is used to verify OSPF router roles?

A

show ip ospf interface

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7
Q

What does the output of the ‘show ip ospf interface’ command indicate about R3?

A

R3 is the DR with router ID 3.3.3.3.

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8
Q

What is the default priority for OSPF routers?

A

1

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9
Q

What is the multicast address used by the DR for OSPF?

A

224.0.0.5

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10
Q

What is the address used by DROTHERs to send OSPF packets?

A

224.0.0.6

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11
Q

What state indicates a router is fully adjacent with a DR?

A

FULL/DR

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12
Q

What does the term FULL/DROTHER indicate?

A

A DR or BDR router that is fully adjacent with a non-DR or BDR router.

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13
Q

What happens to the DR if it fails?

A

The BDR is automatically promoted to DR.

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14
Q

What is the default reference bandwidth for OSPF cost calculation?

A

100,000,000 bps

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15
Q

What is the formula to calculate OSPF cost?

A

Cost = reference bandwidth / interface bandwidth

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16
Q

What command adjusts the reference bandwidth on OSPF routers?

A

auto-cost reference-bandwidth

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17
Q

True or False: A router with a priority of 0 can be elected as DR or BDR.

A

False

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18
Q

What command is used to change the OSPF priority of an interface?

A

ip ospf priority [value]

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19
Q

What happens if all routers have the same interface priority?

A

The router with the highest router ID is elected as DR.

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20
Q

What is a DROTHER?

A

A router that is neither the DR nor the BDR.

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21
Q

What does the command ‘show ip ospf neighbor’ verify?

A

It verifies the OSPFv2 adjacencies.

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22
Q

What is the state of a non-DR router that has a neighbor relationship with another non-DR router?

A

2-WAY/DROTHER

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23
Q

What must happen for a new BDR election to occur?

A

The current BDR must be promoted to DR.

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24
Q

If the DR fails, what will happen to the BDR?

A

The BDR is automatically promoted to DR.

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25
Q

What is the significance of the ‘show ip ospf neighbor’ command output for R2?

A

It confirms R2’s adjacencies with R1 and R3, showing their states.

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26
Q

What happens if the DR fails?

A

The BDR is automatically promoted to DR.

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27
Q

What is the result after a BDR is promoted to DR?

A

A new BDR election occurs.

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28
Q

What is the basic syntax for the OSPF network command?

A

Router(config-router)# network network-address wildcard-mask area area-id

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29
Q

What does the wildcard mask represent?

A

The inverse of the subnet mask configured on that interface.

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30
Q

How can a router ID be explicitly configured?

A

Using the command ‘router-id rid’ in router configuration mode.

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31
Q

What is the preferred method to reset the router ID?

A

Clearing the OSPF process.

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32
Q

What is the order of precedence for deriving the OSPF router ID?

A
  • Explicitly configured router ID
  • Highest IPv4 address of any configured loopback interfaces
  • Highest active IPv4 address of any physical interfaces
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33
Q

What command is used to configure OSPF directly on an interface?

A

ip ospf process-id area area-id

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34
Q

What is the default behavior of OSPF messages on interfaces?

A

OSPF messages are forwarded out all OSPF-enabled interfaces.

35
Q

What command can you use to prevent routing messages from being sent out an interface?

A

passive-interface

36
Q

True or False: Loopback interfaces are advertised as /32 host routes by default.

A

True

37
Q

What command can be used to verify OSPF operation?

A

show ip protocols and show ip route

38
Q

Fill in the blank: The _______ command can be used to configure passive interfaces.

A

passive-interface

39
Q

What command is used to enable a point-to-point network?

A

ip ospf network point-to-point

40
Q

What is the effect of sending unnecessary OSPF messages on a LAN?

A
  • Inefficient use of bandwidth
  • Inefficient use of resources
  • Increased security risk
41
Q

What is the recommended area ID to use with single-area OSPFv2?

A

Area ID 0

42
Q

What command syntax is used to configure the network command on R1?

A

network 10.10.1.0 0.0.0.255 area 0

43
Q

What does the command ‘clear ip ospf process’ do?

A

Resets all OSPF processes.

44
Q

What command shows the current router ID?

A

show ip protocols | include Router ID

45
Q

What should the IPv4 address for a loopback interface be configured with to serve as a router ID?

A

A 32-bit subnet mask (255.255.255.255)

46
Q

What is the advantage of specifying the exact interface IPv4 address using a quad zero wildcard mask?

A

No wildcard mask calculation is necessary.

47
Q

What command is used to verify the OSPF interface configuration?

A

show ip ospf interface

48
Q

What command is used to enable OSPFv2?

A

router ospf process-id

The process-id value is a number between 1 and 65,535 and is locally significant.

49
Q

What is considered best practice regarding OSPF process ID?

A

Use the same process-id on all OSPF routers

This helps maintain consistency across the OSPF network.

50
Q

What does the command ‘show ip protocols’ display?

A

Vital OSPF configuration information including:
* OSPFv2 process ID
* Router ID
* Interfaces configured to advertise OSPF routes
* Neighbors receiving updates
* Default administrative distance

51
Q

What is the default administrative distance for OSPF?

A

110

52
Q

What can cause two routers to not form an OSPFv2 adjacency?

A

The following issues can prevent adjacency:
* Subnet masks do not match
* OSPFv2 Hello or Dead Timers do not match
* OSPFv2 Network Types do not match
* Missing or incorrect OSPFv2 network command

53
Q

Fill in the blank: To adjust the reference bandwidth, use the command _______.

A

auto-cost reference-bandwidth Mbps

54
Q

What command can be used to verify OSPF neighbors?

A

show ip ospf neighbor

55
Q

What does the command ‘show ip ospf interface brief’ provide?

A

A quick summary of OSPFv2-enabled interfaces including:
* Interfaces participating in OSPF
* Advertised networks (IP Address/Mask)
* Cost of each link
* Network state
* Number of neighbors on each link

56
Q

How do you configure OSPF to propagate a default route?

A

Configure:
* A default static route using ‘ip route 0.0.0.0 0.0.0.0 [next-hop-address | exit-intf]’
* ‘default-information originate’ command

57
Q

True or False: The reference bandwidth must be configured on every router in the OSPF domain.

A

True

58
Q

What happens if the calculated cost value for OSPF is less than an integer?

A

OSPF rounds up to the nearest integer.

59
Q

What command is used to manually set the OSPF cost value on an interface?

A

ip ospf cost value

60
Q

What is the maximum number of paths OSPF can use?

A

4

61
Q

What command can be used to verify the OSPF process information?

A

show ip ospf

62
Q

What information does ‘show ip ospf interface’ provide?

A

Detailed list for every OSPFv2-enabled interface including:
* Process ID
* Local router ID
* Type of network
* OSPF cost
* DR and BDR information
* Adjacent neighbors

63
Q

What is the purpose of the ‘passive-interface’ command in OSPF?

A

Suppress routing updates on an interface

64
Q

What does the ‘redistribute’ command do in OSPF?

A

Redistribute information from another routing protocol

65
Q

What is the command to check the routing table for a specific network?

A

show ip route | include [network]

66
Q

What is the command to configure a router ID for OSPF?

A

router ospf [process-id]

The router ID is specified during OSPF configuration.

67
Q

Fill in the blank: The default reference bandwidth is _______.

A

100 Mbps

68
Q

What command is used to show the routing entry for a specific IP address?

A

show ip route [IP address]

For example, ‘show ip route 10.10.2.0’.

69
Q

What is the distance and metric for the OSPF route to 10.10.2.0/24?

A

Distance: 110, Metric: 11

The route is known via ‘ospf 10’.

70
Q

What is the total cost for R1 to reach the 10.10.2.0/24 network?

A

11

This is calculated as the link to R2 cost (10) plus the loopback default cost (1).

71
Q

What command can be used to verify the current OSPFv2 cost assigned to an interface?

A

show ip ospf interface

This command provides details on the OSPF configuration for that interface.

72
Q

How does OSPF accumulate cost?

A

The cost is the accumulated value from one router to the destination network.

The cost reflects the link costs and default costs of loopback interfaces.

73
Q

What happens if the link between R1 and R2 goes down?

A

The routing table updates to use R3 as the next-hop router.

R1 can reach the 10.1.1.4/30 network through R3 with a cost value of 50.

74
Q

What are the default Hello and Dead intervals for OSPF?

A

Hello interval: 10 seconds, Dead interval: 40 seconds

These values are configurable on a per-interface basis.

75
Q

What command is used to change the OSPF Hello interval?

A

ip ospf hello-interval [seconds]

This command is entered in interface configuration mode.

76
Q

What is the purpose of Hello packets in OSPF?

A

Hello packets establish and maintain neighbor relationships between routers.

They are transmitted every 10 seconds to multicast address 224.0.0.5.

77
Q

True or False: OSPF Hello packets are sent on passive interfaces.

A

False

Hello packets are not sent on interfaces set to passive by the passive-interface command.

78
Q

Fill in the blank: The _______ interval is the period that the router waits to receive a Hello packet before declaring the neighbor down.

A

Dead

If the Dead interval expires without receiving a Hello packet, OSPF will remove that neighbor from its LSDB.

79
Q

What command is used to verify the neighbor adjacencies in OSPF?

A

show ip ospf neighbor

This command displays the state and Dead Time of OSPF neighbors.

80
Q

What is the result of modifying the Hello interval to 5 seconds?

A

The Dead interval is automatically adjusted to 20 seconds.

This is four times the Hello interval.

81
Q

What is the significance of the ‘O*E2’ designation in the routing table?

A

‘O*E2’ indicates the route was learned using OSPFv2 and is an external route.

The asterisk identifies it as a valid candidate for the default route.

82
Q

How can you verify the default route settings on a router?

A

Use the command show ip route

This will display the routing table, including any default routes.

83
Q

What does the command ‘auto-cost reference-bandwidth 10000’ do in OSPF?

A

It sets the reference bandwidth for OSPF cost calculations.

This is important for adjusting OSPF costs based on the speed of links.

Enterprise Networking (1 decks)

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