What’s Up With CCENT/CCNA Icnd2 Chapt. 9

2.

Which of the following affects the calculation of OSPF routes when all possible default values are used?

Bandwidth
Delay
Load
Reliability
MTU

Correct Answer

A. Bandwidth

Explanation

OSPF calculates metrics based on the cost associated with each interface. OSPF, by default, calculates interface cost based on the bandwidth setting.

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3.

Which of the following network commands, following the command router ospf 1, tells this router to start using OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1?

Network 10.0.0.0 255.0.0.0 area 0
Network 10.0.0.0 0.255.255.255 area 0
Network 10.0.0.1 255.0.0.255 area 0
Network 10.0.0.1 0.255.255.0 area 0

Correct Answer

A. Network 10.0.0.0 0.255.255.255 area 0

Explanation

The network 10.0.0.0 0.255.255.255 area 0 command works, because it matches all interfaces whose first octet is 10. The network 10.0.0.1 0.255.255.0 area 0 command uses matching logic that matches all interfaces whose first octet is 10 and last octet is 1, which matches all three interface IP addresses. However, the wildcard mask used in OSPF network commands can have only one string of consecutive binary 1s, with all other digits as binary 0s, and this wildcard mask breaks that rule.

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4.

Which of the following network commands, following the command router ospf 1, tells this router to start using OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1?

Network 0.0.0.0 255.255.255.255 area 0
Network 10.0.0.0 0.255.255.0 area 0
Network 10.1.1.0 0.x.1x.0 area 0
Network 10.1.1.0 255.0.0.0 area 0
Network 10.0.0.0 255.0.0.0 area 0

Correct Answer

A. Network 0.0.0.0 255.255.255.255 area 0

Explanation

The network 0.0.0.0 255.255.255.255 area 0 command matches all IP addresses as a result of the 255.255.255.255 wildcard mask, so this command enables OSPF in Area 0 on all interfaces. The answer with wildcard mask 0.255.255.0 is illegal, because it represents more than one string of binary 0s separated by binary 1s. The answer with x’s is syntactically incorrect. The answer with wildcard mask 255.0.0.0 means “Match all addresses whose last 3 octets are 0.0.0,” so none of the three interfaces are matched.

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5.

Two OSPF routers connect to the same VLAN using their Fa0/0 interfaces. Which of the following settings on the interfaces of these two potentially neighboring routers would prevent the two routers from becoming OSPF neighbors?

IP addresses of 10.1.1.1/24 and 10.1.1.254/25, respectively
The addition of a secondary IP address on one router's interface, but not the other
Both router interfaces assigned to area 3
One router is configured to use MD5 authentication, and the other is not configured to use authentication

Correct Answer(s)

A. IP addresses of 10.1.1.1/24 and 10.1.1.254/25, respectively
A. One router is configured to use MD5 authentication, and the other is not configured to use authentication

Explanation

Routers must use the same authentication type and, if so, the same authentication key. Additionally, the subnet number and range of addresses, as calculated from the interfaces’ IP addresses and masks, must be the same subnet.

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6.

OSPF runs an algorithm to calculate the currently best route. Which of the following terms refer to that algorithm?

SPF
DUAL
Feasible successor
Dijkstra
Good old common sense

Correct Answer(s)

A. SPF
A. Dijkstra

Explanation

OSPF uses the SPF algorithm, conceived by a mathematician named Dijkstra.

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7.

An OSPF router learns about five possible routes to reach subnet 10.1.1.0/24. All five routes have a cost of 55, and all five are interarea routes. By default, how many of these routes are placed in the routing table?

1
2
3
4
5

Correct Answer

A. 4

Explanation

The OSPF maximum-paths number router subcommand sets the number of equalcost routes added to the routing table. This command defaults to a setting of 4.

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8.

Which of the following is true about an existing OSPF designated router?

A newly connected router in the same subnet, with a higher OSPF priority, preempts the existing DR to become the new DR.
A newly connected router in the same subnet, with a lower OSPF priority, preempts the existing DR to become the new DR.
The DR may be elected based on the lowest OSPF Router ID.
The DR may be elected based on the highest OSPF Router ID.
The DR attempts to become fully adjacent with every other neighbor on the subnet.

Correct Answer(s)

A. The DR may be elected based on the highest OSPF Router ID.
A. The DR attempts to become fully adjacent with every other neighbor on the subnet.

Explanation

The DR is elected based on the highest OSPF priority. If there is a tie, it is based on the highest OSPF RID. However, after the DR is elected, the DR role cannot be taken over by a better router until the DR and BDR have lost connectivity to the subnet. The DR attempts to be fully adjacent to all other routers on the subnet as part of the optimized database exchange process.

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9.

OSPF routers R1, R2, and R3 attach to the same VLAN. R2 has been configured with the ip ospf authentication message-digest interface subcommand on the LAN interface connected to the common VLAN. The show ip ospf neighbor command lists R1 and R3 as neighbors, in an Init and Full state, respectively. Which of the following are true?

R3 must have an ip ospf authentication message-digest interface subcommand configured.
R3 must have an ip ospf authentication message-digest-key interface subcommand configured.
R1's failure must be because of having configured an incorrect OSPF authentication type.
R1's failure may or may not be related to authentication.

Correct Answer(s)

A. R3 must have an ip ospf authentication message-digest-key interface subcommand configured.
A. R1's failure may or may not be related to authentication.

Explanation

For R2’s neighbor state for neighbor R3 to be Full, R2 and R3 must have passed the authentication process as required by R2’s configuration. The authentication key must be configured with the ip ospf authentication messagedigest-key interface subcommand. However, the authentication type does not have to be configured with the ip ospf authentication message-digest-key interface subcommand. R1 is in an Init state because of one of several issues that can occur that prevent neighbors from communicating, so it cannot be determined if R1’s problem is an authentication problem.

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10.

Which of the following commands list the OSPF neighbors off interface serial 0/0?

Show ip ospf neighbor
Show ip ospf interface
Show ip neighbor
Show ip interface
Show ip ospf neighbor interface serial 0/0

Correct Answer(s)

A. Show ip ospf neighbor
A. Show ip ospf interface
A. Show ip ospf neighbor interface serial 0/0

Explanation

The correct answer is "show ip ospf neighbor" because this command specifically lists the OSPF neighbors. The other options do not provide information about OSPF neighbors or the interface serial 0/0. "show ip ospf interface" lists the OSPF interfaces, "show ip neighbor" lists the IP neighbors, "show ip interface" lists the IP interfaces, and "show ip ospf neighbor interface serial 0/0" is not a valid command.

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What’s Up With CCENT/CCNA Icnd2 Chapt. 9

Which of the following OSPF neighbor states is expected when the exchange of topology information is complete so that neighboring routers have the same LSDB?

Quiz Preview

Which of the following affects the calculation of OSPF routes when all possible default values are used?

Which of the following network commands, following the command router ospf 1, tells this router to start using OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1?

Which of the following network commands, following the command router ospf 1, tells this router to start using OSPF on interfaces whose IP addresses are 10.1.1.1, 10.1.100.1, and 10.1.120.1?

Two OSPF routers connect to the same VLAN using their Fa0/0 interfaces. Which of the following settings on the interfaces of these two potentially neighboring routers would prevent the two routers from becoming OSPF neighbors?

OSPF runs an algorithm to calculate the currently best route. Which of the following terms refer to that algorithm?

An OSPF router learns about five possible routes to reach subnet 10.1.1.0/24. All five routes have a cost of 55, and all five are interarea routes. By default, how many of these routes are placed in the routing table?

Which of the following is true about an existing OSPF designated router?

Which of the following commands list the OSPF neighbors off interface serial 0/0?