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

1. 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?

Two-way

Full

Exchange

Loading

Neighboring OSPF routers that complete the database exchange are considered fully adjacent and rest in a Full neighbor state.

Explanation

Neighboring OSPF routers that complete the database exchange are considered fully adjacent and rest in a Full neighbor state.

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

Bandwidth

Delay

Load

Reliability

MTU

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

Explanation

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

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

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.

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.

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

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.

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.

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

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.

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.

Submit

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

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

Explanation

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

Submit

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

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.

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.

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

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.

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.

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.

Submit

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.

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.

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.

Submit

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

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.

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.

Submit