7.3.3 The Access Layer Quiz Answers. Networking Basics Module 7 quiz exam answers
1. What will a Layer 2 switch do when the destination MAC address of a received frame is not in the MAC table?
- It initiates an ARP request.
- It broadcasts the frame out of all ports on the switch.
- It notifies the sending host that the frame cannot be delivered.
- It forwards the frame out of all ports except for the port at which the frame was received.
Explanation: A Layer 2 switch determines how to handle incoming frames by using its MAC address table. When an incoming frame contains a destination MAC address that is not in the table, the switch forwards the frame out all ports, except for the port on which it was received.
2. Which network device has the primary function to send data to a specific destination based on the information found in the MAC address table?
- hub
- router
- switch
- modem
Explanation: If a MAC address is found in the MAC address table, then data is sent to the associated switch port. If the MAC address is not found in the MAC address table, the data is sent to all switch ports that have devices attached to the same network.
3. What addressing information is recorded by a switch to build its MAC address table?
- the destination Layer 3 address of incoming packets
- the destination Layer 2 address of outgoing frames
- the source Layer 3 address of outgoing packets
- the source Layer 2 address of incoming frames
Explanation: A switch builds a MAC address table by inspecting incoming Layer 2 frames and recording the source MAC address found in the frame header. The discovered and recorded MAC address is then associated with the port used to receive the frame.
4. What is the purpose of the FCS field in a frame?
- to obtain the MAC address of the sending node
- to verify the logical address of the sending node
- to compute the CRC header for the data field
- to determine if errors occurred in the transmission and reception
Explanation: The FCS field in a frame is used to detect any errors in the transmission and receipt of a frame. This is done by comparing the CRC value within the frame against a computed CRC value of the frame. If the two values do not match, then the frame is discarded.
5. What is one function of a Layer 2 switch?
- forwards data based on logical addressing
- duplicates the electrical signal of each frame to every port
- learns the port assigned to a host by examining the destination MAC address
- determines which interface is used to forward a frame based on the destination MAC address
Explanation: A switch builds a MAC address table of MAC addresses and associated port numbers by examining the source MAC address found in inbound frames. To forward a frame onward, the switch examines the destination MAC address, looks in the MAC address for a port number associated with that destination MAC address, and sends it to the specific port. If the destination MAC address is not in the table, the switch forwards the frame out all ports except the inbound port that originated the frame.
6. Which information does a switch use to keep the MAC address table information current?
- the destination MAC address and the incoming port
- the destination MAC address and the outgoing port
- the source and destination MAC addresses and the incoming port
- the source and destination MAC addresses and the outgoing port
- the source MAC address and the incoming port
Explanation: To maintain the MAC address table, the switch uses the source MAC address of the incoming packets and the port that the packets enter. The destination address is used to select the outgoing port.
7. What process is used to place one message inside another message for transfer from the source to the destination?
- access control
- decoding
- encapsulation
- flow control
- the source MAC address and the incoming port
Explanation: Encapsulation is the process of placing one message format into another message format. An example is how a packet is placed in its entirety into the data field as it is encapsulated into a frame.
8. Refer to the exhibit. The exhibit shows a small switched network and the contents of the MAC address table of the switch. PC1 has sent a frame addressed to PC3. What will the switch do with the frame?
7.3.3 The Access Layer Quiz Answers
- The switch will discard the frame.
- The switch will forward the frame only to port 2.
- The switch will forward the frame to all ports except port 4.
- The switch will forward the frame to all ports.
- The switch will forward the frame only to ports 1 and 3.
Explanation: The MAC address of PC3 is not present in the MAC table of the switch. Because the switch does not know where to send the frame that is addressed to PC3, it will forward the frame to all the switch ports, except for port 4, which is the incoming port.
9. Which three fields are found in an 802.3 Ethernet frame? (Choose three.)
- source physical address
- source logical address
- media type identifier
- frame check sequence
- destination physical address
- destination logical address
Explanation: The fields of an Ethernet frame are the preamble, destination and source address, length, data, and FCS.
10. What will a host on an Ethernet network do if it receives a frame with a unicast destination MAC address that does not match its own MAC address?
- It will discard the frame.
- It will forward the frame to the next host.
- It will remove the frame from the media.
- It will strip off the data-link frame to check the destination IP address.
Explanation: In an Ethernet network, each NIC in the network checks every arriving frame to see if the destination MAC address in the frame matches its own MAC address. If there is no match, the device discards the frame. If there is a match, the NIC passes the frame up to the next OSI layer.
11. Which statement is correct about Ethernet switch frame forwarding decisions?
- Frame forwarding decisions are based on MAC address and port mappings in the MAC Address table.
- Frames addressed to unknown MAC addresses are dropped.
- Switches build up their MAC Address tables based on the destination MAC address of incoming frames.
- Unicast frames are always forwarded regardless of the destination MAC address.
Explanation: Switches build their MAC Address tables based on the source MAC addresses of incoming frames. Broadcast frames and frames with a destination MAC address that is not in the MAC Address table are flooded out all active ports except the one that received the frame. Unicast frames are not always forwarded. Received frames with a destination MAC address that is associated with the switch port on which it is received are not forwarded because the destination exists on the network segment connected to that port.