CCNA LAN Switching Questions and Answers

By | October 16, 2017

This is an Updated LAN Switching CCNA common exam question (October 2016). You might see a different IP addressing, VLAN configuration and Port allocation.

As usual, take time to read through the question so as to clearly understand what the question is all about.

Note: These LAN Switching Questions are used for demonstration only, you will see different IP addressing,  configuration and Port allocation in the real CCNA exam. But it all works the same way, try and understand the technique.

I suggest you use packet tracer for practice.

Download Cisco Packet Tracer




Question 1.

How many broadcast domains are present in the network in the following exhibit?

A. One broadcast domain
B. Two broadcast domains
C. Three broadcast domains
D. Seven broadcast domains
Answer A

Explanation
There is only one broadcast domain exists in the exhibit switch above because a PC on the left hub can send an ARP request,  and the PC on the right hub can receive it.
A broadcast domain includes all devices that would receive the same broadcast traffic.

Question 2.

Which benefit to a LAN does a switch provide?
A. Breaks up broadcast domains
B. Breaks up collision domains
C. Forces full-duplex on all ports
D. Allows for a fast uplink port
Answer B.

Explanation
Switches break up collision domains by allowing full-duplex.
Unlike a hub, a switch forwards a message from various devices connected to it to a specific host its intended to. Switches can be used to connect PCs, Printers, Routers together on a LAN.

Question 3.

Where are MAC address tables stored?
A. Flash
B. CPU registers
C. RAM
D. NVRAM
Answer C.

Explanation

MAC address tables also called CAM tables, are always built and stored
temporarily in RAM. When the switch is turned off or the clear command is issued, the table no longer exists.

Question 4.

How do switches forward frames only to the destination computer?
A. Forward filter decisions based on the MAC address table
B. Forward filter decisions based on the routing table
C. Flooding ports for the destination MAC address
D. Broadcasting for the MAC address

Answer A.

Explanation

Switches make forward/filter decisions based upon the MAC address to the port association in the MAC address table.
Ok…now
PC1 wants to send traffic to PC5 on the network,

PC 1 has a MAC address of 00:00:00:00:00:03.
When the frame gets to the switch, it will create a new entry in its MAC address table for PC1’s MAC address. The switch would then do a lookup on its MAC address table to determine which port to send the traffic to; if no matching entries exist in the switch’s tables, it would flood/send out the frame out all of its interfaces (except the receiving port). The message would be received by the target port.
But if the PC5’s mac address is found in the MAC address table, the frame will be sent to the connection port direct.




Question 5.

Which mechanism does a switch employ to stop switching loops?
A. Port channels
B. Spanning Tree Protocol
C. Ether channels
D. Trunks
Answer B.

Explanation

Switching loops are data traffic that starts out as unicast but is continuously cycled between a set of switches on a network due to the wrong configuration in redundant switching. This is where STP steps in…STP is a mechanism that switches use for loop avoidance on a network, this process is implemented by using spanning tree algorithm in disabling unwanted links and blocking ports that could cause a loop.

STP is a mechanism that switches use for loop avoidance on a network, this process is implemented by using spanning tree algorithm in disabling unwanted links and blocking ports that could cause a loop.

Question 6.

How are MAC addresses learned and associated with the port?
A. Destination MAC address learning
B. Source MAC address learning
C. Port listen/learning
D. Frame type learning
Answer B.

Explanation

Switches learn MAC addresses by inspecting the frame’s source MAC address on the incoming port. They then associate the source MAC address with the port it came in on.

Question 6.

In the following exhibit, what will happen first when Computer A wants to send Computer B a message?

A. The switch will forward the frame to all ports on the switch.
B. The switch will direct communication to port Fa0/1.
C. The switch will record computer A’s MAC address on port Fa0/0.
D. The switch will record computer B’s MAC address on port Fa0/1.

Answer B.

Explanation

Since the switch MAC address table stored/has the MAC address for Computer B, the switch will direct the frame to port Fa0/1 only. If it doesn’t, it will flood the frame to all ports.

Question 7.

In the following exhibit, what will happen if the computers on ports Fa0/1 (Computer A) and Fa0/4 (Computer B) are swapped?

A. Computer A’s frames will only be forwarded to port Fa0/1.
B. Computer A’s frames will be forwarded to ports Fa0/1 and Fa0/4.
C. Computer A’s frames will only be forwarded to port Fa0/4.
D. Computer B’s frames will be forwarded to all ports.

Answer A

Explanation

The switch Fa0/1 had been configured as static. Computer A will no longer forward traffic because the static entry will override a dynamic entry.




Question 9.

Which statement is true of an ARP request entering into a switch?
A. The source MAC address of the frame will be all Fs.
B. The destination MAC address of the frame will be all Fs.
C. The switch will only forward the ARP request to the port for the destination
computer.
D. The switch will respond directly back with an ARP reply.

Answer B.

In brief:

The destination MAC address for broadcasts are always all Fs, such as
ffff.ffff.ffff.

Question 10.

Which is a consequence of not using loop avoidance with layer 2 switching?
A. Duplicate unicast frames
B. Broadcast storms
C. MAC address thrashing
D. All the above

Answer D.

Explanation

Trick question…check keyword…” Which is a consequence of not using loop avoidance”
When loop avoidance such as STP is not configured on a network and loops exist, you will encounter duplicate unicast frames and broadcast storms. This will inevitably thrash the MAC address table and degrade bandwidth to nothing.