Week 4 - The Network Layer

Question 1

What Two Functions Does The Logical Link Control Perform?

Answer 1

• Handles Communication Between The Upper And Lower Layers And Fills In The Networking Protocol (Sending)/Passes It On To The Correct Networking Protocol (Receiving)
• Takes The Network Protocol Data And Adds Control Information To Help Deliver The Packet To The Destination (Flow Control And Reliability Of Connection!).

Question 2

1. What Networking Hardware Implements The MAC Layer 2 Sublayer?
2. What Are The Two Responsibilities Of The MAC Sublayer?

Answer 2

1. The Network Interface Card (NIC)
2. • Data Encapsulation (Packet To Frame).
   • Media Access Control (Allowing It Onto The
     Transmission Media)

Question 3

The MAC Layer Encapsulates Data Further From A Packet. What Is Added By The MAC Sublayer Upon A Packets Encapsulation Into A Frame.

Answer 3

A Header (Containing The Start Flag And The Data) And A Trailer (Containing The FCS (Frame Check Sequence) For The Cyclic Redundancy Check Are Added.

Question 4

What Are The Two Primary Responsibilities Of The MAC Sublayer?

Answer 4

• Data Encapsulation (Frame Packets)

- Media Access Control (Interacting With The Physical Layer Processot (PYH) To Get The Frame Onto The Media.

Question 5

In The MAC Sublayer, What Is Frame Delimiting?

Answer 5

Adding Groups Of Bits (Flags) To Indicate The Start And End Of A Frame.

Question 6

In The MAC Sublayer, What Is Addressing?

Answer 6

Adding A MAC Address To Deliver To A Destination Node.

Question 7

In The MAC Sublayer, What Is Error Dectection?

Answer 7

Using The Cyclic Redundancy Check To Perform A Polynomial Division And Verify The Integrity Of The Frame.

Question 8

Each NIC Views Each Recieved Frame To See If The …………………………. in the frame matches the devices’s ……………………………. stored in RAM.

Answer 8

Each NIC Views Each Recieved Frame To See If The Destination MAC Address in the frame matches the devices’s Physical MAC Address stored in RAM.

Question 9

If A Frame’s Destination MAC Address Does Not Match The MAC Address Of The Device Recieving The Frame, The Frame Is…….

Answer 9

Dropped.

Question 10

If The MAC Address Of The Incoming Frame Matches The MAC Address Of The Receiving Device……….

Answer 10

The NIC Passes The Frame Up The OSI Layers Where It Is Decapsulated And Passed Back To The Application.

Question 11

What is The:

1. Minimum Possible Size A Frame Can Be (In Bytes)?
2. Maxiumum Possible Size A Frame Can Be (In Bytes)?

Answer 11

1. 64 Bytes

2. 1518 Bytes (Jumbo Frame)

Question 12

How Many Bits Make Up A MAC Address?

Answer 12

48 Bits

Question 13

What Is The OUI Section Of A MAC Address. How Many Bytes Does It Occupy?

Answer 13

• The Organizationally Unique Identifier, It Identifies The Manufacturer Of The Device! It Occupies The First 3 Bytes Of A MAC Address.

Question 14

What Do The Last Three Bytes Of A MAC Address Represent? In Theory, What Should Property Should This Address Have?

Answer 14

• The Vendor Assigned Address. These Bytes Should Be Globally Unique! (No Other Device Should Share It!!!)

Question 15

What Fields Are Used To Direct A Packet To It’s Destination?

Answer 15

The Destination MAC and IP Addresses.

Question 16

What Are The First Three Bytes Used By A Frame’s Destination MAC When A Multicast Transmission Is Made?

Answer 16

01-00-5E

Question 17

What Range Of IP Addresses Are Used To Identify A Multicast Transmission?

Answer 17

224.0.0.0 to 239.255.255.255

(MAC Address Is Mapped Onto The Multicast IP - Hosts Then Join The Group And ‘Listen’ For Broadcasts Made To The Group.

Question 18

A MAC Address Does Not………. And Is Known As A ……………………. Address

Answer 18

A MAC Address Does Not Change And Is Known As A Physical Address

Question 19

An IP Address Is Based On Where The Host…………………………………………… And Is Known As A ………………………… Address.

Answer 19

An IP Address Is Based On Where The Host Is Actually Located And Is Known As A Logical Address.

Question 20

A Switch Examines…………………….

Answer 20

MAC Addresses

Question 21

A Router Examines……………………

Answer 21

IP Addresses.

Question 22

What Does ARP (Address Resoluton Protocol) Allow Nodes To Discover?

Answer 22

The MAC Address OF A Device Connected To A LAN

Question 23

ARP Protocol Allows:
- The ……………………………. of IPv4 Addresses To ……………………………………….

• Devices To Maintain A Table Of……………………………….

Answer 23

The Resolution of IPv4 Addresses To MAC Addresses.

Devices TO Maintain A Table Of Mappings

Question 24

What Does The ARP Table Do?

Answer 24

When A Node Recieves A Frame From The Media, It Records Which IP It Came From And Associates It With The MAC Address The Frame Was Sourced From.

Question 25

What Is An ARP Request?

Answer 25

A Layer 2 Device Broadcasts To All Devices With The Destination IP Address Of An Incoming Frame. If A Device Matches The IP Address, It Responds. The Router Then Updates The IP Stored In It’s ARP Table With The MAC Address Of The Responding Device.

Question 26

What Will The Destination MAC Address Of A Frame Be When Sent To A Device On The Same Network?

Answer 26

• The MAC Address Of The Recipient Host Device.

Question 27

1. What Will The Destination MAC Address Of A Frame Be When Sent To A Device That Is Not On The Same Network?

2.

Answer 27

• The MAC Address Of The Routing Interface Assigned As The Default Gateway.