Networking Basics Questions and Answers

Q: Which router command allows you to view the entire contents of all access lists?

Correct answer: show access-listsshow access-lists displays every access list configured on the router, of all protocols, with each statement and the number of packets it has matched - those counters being invaluable when diagnosing a list that is not behaving as intended. show ip interface reveals where a list is applied but not what is in it, and the interface commands show neither.

Q: Which class of IP address has the most host addresses available by default?

Correct answer: AA class A address uses one octet for the network and three for hosts, giving\[ 2^{24} - 2 = 16{,}777{,}214 \text{ hosts per network} \]Class B gives \( 2^{16} - 2 = 65{,}534 \) and class C only 254. The two subtracted addresses are the network address and the broadcast address, neither of which can be assigned to a host.

Q: In a network with dozens of switches, how many root bridges would you have?

Correct answer: 1Spanning tree elects exactly one root bridge per broadcast domain, however many switches there are, and every other switch computes its shortest path to that root. The election is by lowest bridge ID - priority first, then MAC address as the tiebreaker - which is why the priority is normally set deliberately on the switch that should win, rather than left to the accident of which switch has the lowest MAC address.

Q: What PPP protocol provides dynamic addressing, authentication, and multilink?

Correct answer: LCPThe Link Control Protocol negotiates the characteristics of the PPP link itself: authentication with PAP or CHAP, dynamic addressing, callback, compression, error detection and multilink. NCP is the layer above it, negotiating one control protocol for each network layer protocol carried. The division is worth holding: LCP concerns the link, NCP concerns what is carried over it.

Q: If your router is facilitating a CSU/DSU, which of the following commands do you need to use to provide the router with a 64000bps serial link?

Correct answer: RouterA(config-if)#clock rate 64000Where the router provides the DCE function it must supply the clocking, and clock rate is set in bits per second under the interface, hence 64000 rather than 64. bandwidth is a quite different command: it sets a value used by routing protocols in their metric calculations and by QoS, and changing it has no effect whatever on the actual line speed.

Q: What is the main reason the OSI model was created?

Correct answer: So different networks could communicate.The OSI reference model was produced by ISO to allow equipment from different manufacturers, running different proprietary protocol stacks, to interoperate. Dividing the problem into seven layers with defined interfaces means each layer can be implemented independently, and a change at one layer need not disturb the others. It is a reference model rather than a protocol suite, and it long predates any single vendor’s use of it.

Q: How many collision domains are created when you segment a network with a 12-port switch?

Correct answer: 12Every port on a switch is its own collision domain, which is exactly what distinguishes a switch from a hub: frames are forwarded only towards the port where the destination MAC address resides, so two conversations on different ports never collide. Twelve ports therefore give twelve collision domains, while all twelve remain in one broadcast domain unless VLANs are configured.

141.

Which router command allows you to view the entire contents of all access lists?

A.show all access-lists
B.show access-lists
C.show ip interface
D.show interface

Answer: B

Correct answer: show access-lists

show access-lists displays every access list configured on the router, of all protocols, with each statement and the number of packets it has matched - those counters being invaluable when diagnosing a list that is not behaving as intended. show ip interface reveals where a list is applied but not what is in it, and the interface commands show neither.

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142.

Which class of IP address has the most host addresses available by default?

A.A
B.B
C.C
D.A and B

Answer: A

Correct answer: A

A class A address uses one octet for the network and three for hosts, giving

\[ 2^{24} - 2 = 16{,}777{,}214 \text{ hosts per network} \]

Class B gives \( 2^{16} - 2 = 65{,}534 \) and class C only 254. The two subtracted addresses are the network address and the broadcast address, neither of which can be assigned to a host.

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143.

In a network with dozens of switches, how many root bridges would you have?

A.1
B.2
C.5
D.12

Answer: A

Correct answer: 1

Spanning tree elects exactly one root bridge per broadcast domain, however many switches there are, and every other switch computes its shortest path to that root. The election is by lowest bridge ID - priority first, then MAC address as the tiebreaker - which is why the priority is normally set deliberately on the switch that should win, rather than left to the accident of which switch has the lowest MAC address.

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144.

What PPP protocol provides dynamic addressing, authentication, and multilink?

A.NCP
B.HDLC
C.LCP
D.X.25

Answer: C

Correct answer: LCP

The Link Control Protocol negotiates the characteristics of the PPP link itself: authentication with PAP or CHAP, dynamic addressing, callback, compression, error detection and multilink. NCP is the layer above it, negotiating one control protocol for each network layer protocol carried. The division is worth holding: LCP concerns the link, NCP concerns what is carried over it.

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145.

What is a stub network?

A.A network with more than one exit point.
B.A network with more than one exit and entry point.
C.A network with only one entry and no exit point.
D.A network that has only one entry and exit point.

Answer: D

Correct answer: A network that has only one entry and exit point.

A stub network reaches the rest of the internetwork through a single point, so there is only one possible path in or out. Because no routing decision is available, it needs no dynamic routing protocol - a default route out of it and a static route into it are sufficient, which is why stubs are used to reduce routing overhead. A network with no exit at all would be isolated rather than a stub.

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146.

If your router is facilitating a CSU/DSU, which of the following commands do you need to use to provide the router with a 64000bps serial link?

A.RouterA(config)#bandwidth 64
B.RouterA(config-if)#bandwidth 64000
C.RouterA(config-if)#clock rate 64
D.RouterA(config-if)#clock rate 64000

Answer: D

Correct answer: RouterA(config-if)#clock rate 64000

Where the router provides the DCE function it must supply the clocking, and clock rate is set in bits per second under the interface, hence 64000 rather than 64. bandwidth is a quite different command: it sets a value used by routing protocols in their metric calculations and by QoS, and changing it has no effect whatever on the actual line speed.

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147.

Which one of the following is true regarding VLANs?

A.Two VLANs are configured by default on all Cisco switches.
B.VLANs only work if you have a complete Cisco switched internetwork. No off-brand switches are allowed.
C.You should not have more than 10 switches in the same VTP domain.
D.VTP is used to send VLAN information to switches in a configured VTP domain.

Answer: D

Correct answer: VTP is used to send VLAN information to switches in a configured VTP domain.

VLAN Trunking Protocol propagates the VLAN database from a server switch to the clients in the same VTP domain, so a VLAN created once appears throughout. The other statements are false: only VLAN 1 exists by default, not two; VLANs are a standard function that works with equipment from any manufacturer; and there is no ten-switch limit on a VTP domain.

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148.

What does a VLAN do?

A.Acts as the fastest port to all servers.
B.Provides multiple collision domains on one switch port.
C.Breaks up broadcast domains in a layer 2 switch internetwork.
D.Provides multiple broadcast domains within a single collision domain.

Answer: C

Correct answer: Breaks up broadcast domains in a layer 2 switch internetwork.

A switch by itself puts every port in one broadcast domain. Assigning ports to different VLANs divides them into separate broadcast domains within the same physical switch, so a broadcast in one VLAN is never seen in another, and traffic between VLANs requires a router or a layer 3 switch. Each port already has its own collision domain, VLAN or not; that is what makes it a switch.

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149.

What is the main reason the OSI model was created?

A.To create a layered model larger than the DoD model.
B.So application developers can change only one layer's protocols at a time.
C.So different networks could communicate.
D.So Cisco could use the model.

Answer: C

Correct answer: So different networks could communicate.

The OSI reference model was produced by ISO to allow equipment from different manufacturers, running different proprietary protocol stacks, to interoperate. Dividing the problem into seven layers with defined interfaces means each layer can be implemented independently, and a change at one layer need not disturb the others. It is a reference model rather than a protocol suite, and it long predates any single vendor’s use of it.

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150.

How many collision domains are created when you segment a network with a 12-port switch?

A.1
B.2
C.5
D.12

Answer: D

Correct answer: 12

Every port on a switch is its own collision domain, which is exactly what distinguishes a switch from a hub: frames are forwarded only towards the port where the destination MAC address resides, so two conversations on different ports never collide. Twelve ports therefore give twelve collision domains, while all twelve remain in one broadcast domain unless VLANs are configured.

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