Chapter 1: Network Models Flashcards by Melissa Nyberg

List each layer (7 to 1) of the OSI Seven-Layer Model.

L7 Application
L6 Presentation
L5 Session
L4 Transport
L3 Network
L2 Data Link
L1 Physical

Remember the mnemonic “All People Seem To Need Data Processing.”

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Define: Protocols

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

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What does a NIC or Network Interface Card do and what network layer does it operate in?

A NIC serves as the interface between the PC and the network. It operates at L2 and uses MAC addresses.

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Define: MAC or Media Access Control Address (aka. a physical address)

A 48-bit (6-byte) unique identifier that is burned onto a ROM chip in every NIC. It is in hexadecimal notation (12 hex digits).

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What are the two parts of a MAC address?

The first six hex digits represent the NIC manufacturer, referred to as the Organizationally Unique Identifier (OUI).

The last six hex digits are the manufacturer’s unique serial number for that NIC, referred too as the device ID.

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In Windows, type ______ from a command prompt to display the MAC address.

ipconfig /all

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In macOS, type ______ from a terminal to display the MAC address.

ifconfig

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In Linux, type ______ from a terminal to display the MAC address.

ip a

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Define: Protocol Data Unit (PDU)

It is the unit of data specified by a protocol at each layer of the OSI seven-layer model.

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What is the PDU for Layer 2, the Data Link layer?

Frame (Ethernet)

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What does a frame do and what creates and uses them?

A frame encapsulates information and data for easier transmission. The NIC creates and sends, as well as receives and reads frames.

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What are the first two fields of a generic frame?

Recipient’s MAC address
Sender’s MAC address

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What is in the Type field of a frame?

The Type field indicates what’s encapsulated in the frame.

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What is in the Data field of a frame?

The Data field contains what’s encapsulated.

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What is the purpose of the Frame Check Sequence (FCS) field of a frame?

The FCS uses a type of binary math called a Cyclic Redundancy Check (CRC) to calculate a value that the receiving NIC uses to verify that the data arrived intact.

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What is the max size of an Ethernet frame’s Data field?

1500 bytes

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What is the size of the FCS field?

4 bytes

What is the Layer 2 broadcast address?

FF-FF-FF-FF-FF-FF

Who receives a Layer 2 broadcast address?

Every single NIC on the network except the sending NIC.

What is contained in a Layer 2 broadcast address?

A request for a system’s MAC address, by the use of that system’s known IP address.

What are the two sublayers of the Data Link layer?

Logical Link Control (LLC)
Media Access Control (MAC)

What is the job of the Logical Link Control (LLC) sublayer?

It is the part of the NIC that talks to the system’s operating system (usually via device drivers), and handles multiple network protocols and provides flow control.

What is the job of the Media Access Control (MAC) sublayer?

It creates and addresses the frame, adds or checks the FCS, and sends the frame along the network cable.

What is a switch and at what layer does it operate.

A switch is a network device that handles network traffic using MAC addresses to direct the traffic. It operates at Layer 2.

What is the PDU for Layer 3, the Network layer?

Packet

What is the protocol used in the Network layer?

Internet Protocol (IP)

What does the Internet Protocol do?

It gives each device on the network a unique numeric identifier called an IP address (logical address). The Internet Protocol is the primary logical addressing protocol for TCP/IP.

What is an IP address?

An IP address is 32-bits (4 bytes) long. It uses dotted decimal notation based on four 8-bit numbers. Each byte is separated by a decimal (192.168.4.232).

What is a router and at what layer does it operate?

A router is a networking device that connects subnets and networks and forwards data using IP addresses. It operates at Layer 3 (Network).

Explain how packets and frames work.

As a frame travels, if it goes through routers, each router strips off the incoming frame, determines where to send the data according to the IP address in the packet, creates a new frame to encapsulate the packet, and then sends it all on its way to its next stop. The new frame type will be the appropriate technology for whatever connection technology connects to the next router. The IP packet remains unchanged.

What are the PDUs for the Transport Layer?

Segments (TCP) and Datagrams (UDP)

What is Transmission Control Protocol (TCP), including what Layer it operates?

TCP is a connection-oriented protocol at Layer 4. It breaks up data into chunks called segments that will fit into packets, and gives each segment a sequence number.

What does the Transport Layer do?

It is the segmentation/reassembly software, that breaks up data into segments to send and reassembles data from segments that it receives. It also initializes requests for packets that weren't received in good order.

What logical addressing is used in the Transport Layer?

Port addressing

What is a port?

A port - a number between 1 and 65,535 - is a logical value assigned to specific applications or services.

What is User Datagram Protocol, including what Layer it operates at?

UDP is a connectionless protocol at Layer 4. It creates datagrams with less fields than TCP segments because it doesn't care whether the receiving computer gets its data.

What 5 fields are in a UDP datagram?

Source Port Destination Port Length Checksum Data

What does the Session Layer do?

It uses session software to connect applications to other applications between computers/devices by creating sessions. It handles all the sessions for a system by initiating sessions, accepting incoming sessions, and opens and closes existing sessions.

What does the Presentation Layer do?

The Presentation Layer translates data from lower layers into a format usable by the Application Layer, and vice versa.

What is the Application Layer?

The Application Layer refers to the code built into operating systems that enables network-aware applications. All operating systems have Application Programming Interfaces (APIs) that programmers can use to make their programs network aware.

What is encapsulation?

The entire process of preparing data to go onto a network. This includes all the steps from the Application, Presentation, Session, Transport, Network, and Data Link layers. Each layer adds more information so that the data gets to the correct recipient and the recipient knows what to do with the data.