Definitions/Abbreviations

Question 1

OSI seven-layer model

Answer 1

Open Systems Interconnection

• Layer 7 (L7) - Application
• Layer 6 (L6) - Presentation
• Layer 5 (L5) - Session
• Layer 4 (L4) - Transport
• Layer 3 (L3) - Network
• Layer 2 (L2) - Data Link - any device that deals with a MAC address. Ex: switches, NICs. *Only layer that has sublayers (Logical Link Control and Media Access Control)*
• Layer 1 (L1) - Physical - anything that moves data from one system to another. Ex: copper cabling, fiber optics, even radio waves and hubs. NICs appear here as well.

Mnemonic: “Please Do Not Throw Spicy Pizza Away”

Question 2

ISO

Answer 2

International Organization for Standardization
*Note: not misspelled

(Greek word “isos” means “equal”. The ISO sets standards that promote equality among network designers and manufacturers.)

Question 3

Protocol

Answer 3

A set of clearly defined rules, regulations, standards, and procedures that enable hardware and software developers to make devices and applications that function properly at a particular layer.

Question 4

UTP

Answer 4

Unshielded Twisted Pair
(Usually) contains four pairs of wires that can transmit and receive data.

Question 5

NIC

Answer 5

Network Interface Card
The interface between the PC and the network.

Question 6

IEEE

Answer 6

Institute of Electrical and Electronics Engineers

Question 7

MAC Address

Answer 7

Media Access Control Address
Unique identifier - like a telephone number - with a 48 bit-value to ensure data is delivered to the correct system.

The first six digits in a MAC address represent the unique number of the NIC manufacturer; referred to as the Organizationally Unique Identifier (OUI). The last six digits are the manufacturer’s unique serial number for that specific NIC; often referred to as the device ID. No two manufacturers may have the same OUI, and no two NICs from the same manufacturer may have the same device ID.

Note 1: MAC addresses are always written in hex, using 0-9 for numbers 0-9, and A-F for numbers 10-15.
Windows uses the dash as a delimiter for the MAC address. Linux and macOS use a colon.
Example:
48-A4-72-F6-A2–ED on Windows would be
48:A4:72:F6:A2:ED on Linux and macOS

Note 2: MAC addresses are also known as physical addresses. (ipconfig refers to MAC addresses as such.) The exam will test on this.

Note 3: The IEEE forms MAC addresses from a numbering name space originally called MAC-48, which simply means that the MAC address is 48 bits, with the first 24 bits defining the OUI, just as described here. The current term for this numbering name space is EUI-48. EUI stands for Extended Unique Identifier. (IEEE apparently went with the latter term because they could trademark it.)
Most techs just call them MAC addresses, as you should, but you might see MAC-48 or EUI-48 on the CompTIA Network+ exam.

Question 8

OUI

Answer 8

Organizationally Unique Identifier
The first six digits in a MAC address representing the unique number of the NIC manufacturer.

Question 9

Device ID

Answer 9

The last six digits in a MAC address representing the manufacturer’s unique serial number for that specific NIC.

Question 10

EUI-48

Answer 10

Extended Unique Identifier
The IEEE forms MAC addresses from a numbering name space originally called MAC-48, which simply means that the MAC address is 48 bits, with the first 24 bits defining the OUI. The current term for this numbering name space is EUI-48. (IEEE apparently went with the latter term because they could trademark it.)
Most techs just call them MAC addresses, as you should, but you might see MAC-48 or EUI-48 on the CompTIA Network+ exam.

Question 11

Frame

Answer 11

Discrete chunk of data (such as files, print jobs, webpages, and so forth) moving across the Physical layer of a network. A frame encapsulates - puts a wrapper around - information and data for easier transmission.

The frame begins with the MAC address of the NIC to which the data is to be sent, followed by the MAC address of the sending NIC. Next comes the Type field, which indicates what’s encapsulated in the frame. Then comes the Data field that contains what’s encapsulated, followed by a special piece of checking information called the frame check sequence (FCS). The FCS uses a type of binary math called a cyclic redundancy check (CRC) that the receiving NIC uses to verify that the data arrived intact.

You can think of a frame in a different way as having three sections. The header (MAC addresses and Type) starts, followed by the payload (whatever is encapsulated in the frame); this is followed by the trailer (the FCS).

Note 1: Different frame types are used in different networks. All NICs on the same network must use the same frame type, or they will not be able to communicate with other NICs.

Note 2: Frames used in Ethernet networks hold at most 1500 bytes of data.

Question 12

PDU

Answer 12

Protocol Data Unit
The unit of data specified by a protocol at each layer of the OSI seven-layer model.

PDUs by layer:
Layer 3: packet
Layer 2: frame

Question 13

Type field

Answer 13

Indicates what’s encapsulated in the frame.

Question 14

Data field

Answer 14

Contains what’s encapsulated in the frame.

Question 15

FCS

Answer 15

Frame Check Sequence
Special piece of checking information using a type of binary math called a cyclic redundancy check (CRC) that the receiving NIC uses to verify that the data arrived intact.

Note: All FCSs are only 4 bytes long.

Question 16

CRC

Answer 16

Cyclic Redundancy Check
A type of binary math that the receiving NIC uses to verify that the data being delivered in a frame arrived intact.

Note: Think of the CRC as just the remainder of a division problem. The NIC sending the frame does a little math to make the CRC. The receiving NIC applies the same math. If the receiving NIC’s answer is the same as the CRC, it knows the data is good; if it’s not good, the frame is dropped.

Question 17

Hub

Answer 17

A central box in the early days of networking (essentially a repeater). When the hub received a frame, the hub made an exact copy of that frame, sending a copy of the original frame out of all connected ports except the port on which the message originated.

Question 18

Switch

Answer 18

Newer central boxes replacing the hub. Switches filter traffic by MAC address. Rather than sending all incoming frames to all network devices connected to it, a switch sends the frame only to the interface associated with the destination MAC address.

Question 19

Broadcast (frame)

Answer 19

A sending NIC function to identify the MAC address of a receiving NIC. The MAC address of FF-FF-FF-FF-FF-FF is the Layer 2 broadcast address. If a NIC sends a frame using the broadcast address, every single NIC on the network will process that frame. That broadcast frame’s data will contain a request for a system’s MAC address. Without knowing the MAC address to begin with, the requesting computer will use an IP address to pick the target computer out of the crowd.

Question 20

Broadcast Address

Answer 20

FF-FF-FF-FF-FF-FF

If a NIC sends a frame using the broadcast address, every single NIC on the network will process that frame. That broadcast frame’s data will contain a request for a system’s MAC address. Without knowing the MAC address to begin with, the requesting computer will use an IP address to pick the target computer out of the crowd.

Question 21

FF-FF-FF-FF-FF-FF

Answer 21

Broadcast address

If a NIC sends a frame using the broadcast address, every single NIC on the network will process that frame. That broadcast frame’s data will contain a request for a system’s MAC address. Without knowing the MAC address to begin with, the requesting computer will use an IP address to pick the target computer out of the crowd.

Question 22

Unicast frame

Answer 22

Any frame addressed specifically to another device is MAC address.

Question 23

Unicast addressing

Answer 23

The one-to-one addressing scheme.

Note: Seen in other layers as well as Layer 2.

Question 24

LLC

Answer 24

Logical Link Control
First job of two distinct jobs a NIC performs to keep data moving. The LLC is the aspect of the NIC that talks to the system’s operating system (usually via device drivers). The LLC handles multiple network protocols and provides flow control.

Question 25

MAC

Answer 25

Media Access Control
Second job of two distinct jobs a NIC performs to keep data moving. Creates and addresses the frame. It adds the NIC’s own MAC address and attaches MAC addresses to the frames. The MAC sublayer adds or checks the FCS. The MAC also ensures that the frames, now complete with their MAC addresses, are then sent along the network cabling.