Chapter 6 - Study

Question 1

Ethernet Frames -

Preamble and Start Frame Delimiter Fields

Answer 1

The Preamble (7 bytes) and Start Frame Delimiter (SFD), also called the Start of Frame (1 byte), fields are used for synchronization between the sending and receiving devices. These first eight bytes of the frame are used to get the attention of the receiving nodes. Essentially, the first few bytes tell the receivers to get ready to receive a new frame.

Question 2

Ethernet Frames -

Destination MAC Address Field

Answer 2

This 6-byte field is the identifier for the intended recipient. As you will recall, this address is used by Layer 2 to assist devices in determining if a frame is addressed to them. The address in the frame is compared to the MAC address in the device. If there is a match, the device accepts the frame. Can be a unicast, multicast or broadcast address.

Question 3

Ethernet Frames -

Source MAC Address Field

Answer 3

This 6-byte field identifies the originating NIC or interface of the frame. A source MAC address can only be a unicast address.

Question 4

Ethernet Frames -

Type / Length

Answer 4

This 2-byte field identifies the upper layer protocol encapsulated in the Ethernet frame. Common values are, in hexadecimal, 0x800 for IPv4, 0x86DD for IPv6 and 0x806 for ARP.
Note: You may also see this field referred to as EtherType, Type, or Length.

Question 5

Ethernet Frames -

Data Field

Answer 5

This field (46 - 1500 bytes) contains the encapsulated data from a higher layer, which is a generic Layer 3 PDU, or more commonly, an IPv4 packet. All frames must be at least 64 bytes long. If a small packet is encapsulated, additional bits called a pad are used to increase the size of the frame to this minimum size.

Question 6

Ethernet Frames -

Frame Check Sequence Field

Answer 6

The Frame Check Sequence (FCS) field (4 bytes) is used to detect errors in a frame. It uses a cyclic redundancy check (CRC). The sending device includes the results of a CRC in the FCS field of the frame. The receiving device receives the frame and generates a CRC to look for errors. If the calculations match, no error occurred. Calculations that do not match are an indication that the data has changed; therefore, the frame is dropped. A change in the data could be the result of a disruption of the electrical signals that represent the bits.

Question 7

Which Ethernet frame field assists a host in determining if the frame that is received is addressed to it?

Answer 7

Destination

Question 8

Which Ethernet frame field notifies destinations to get ready for a new frame?

Answer 8

Preamble

Question 9

Which Ethernet frame field describes the higher-layer protocol that is encapsulated?

Answer 9

Type / Length

Question 10

Which part of the Ethernet frame helps a destination detect if there are errors in a frame?

Answer 10

Frame Check Sequence

Question 11

Which OSI layer sends segments to be encapsulated in an IPv4 or IPv6 packet?

Answer 11

Transport

Question 12

Which layer is responsible for taking an IP packet and preparing it for transmission over the communications medium?

Answer 12

Data Link

Question 13

What is the term for splitting up an IP packet when forwarding it from one medium to another medium with a smaller MTU?

Answer 13

Fragmentation

Question 14

Which delivery method does not guarantee that the packet will be delivered fully without errors?

Answer 14

Best Effort