Data Link Layer

Front 1

What is the data link layer responsible for

Back 1

Allowing upper layers to access media

Prepare network data for physical network

Exchange frames BTW nodes over physical network

Front 2

What layer performs error detection

Back 2

Data link

Front 3

What are the two sublets of data link

Back 3

LLC logical link control

MAC Media access control

Front 4

What does the LLC do

Back 4

Upper sublayer

Communicates with the network layer

Allows multiple layer 3 protocols to use the same network interface and media.

Front 5

What are some layer 3 protocols

Back 5

Ipv4 and 6

Front 6

What does media access control do

Back 6

Lower sub layer

Defines media access process performed by hardware.

Front 7

Technique used to get frames on and off the media

Back 7

Media Access Control Method

Front 8

What layer governs how to format a frame for use on different media

Back 8

Data link layer

Front 9

At each hop along the path, a router does what to the frame. 4 steps

Back 9

Accepts a frame from a medium

DE encapsulates the frame

RE encapsulates the packet into new frame

Forwards frame to next segment of the network.

Front 10

What layer is responsible for controlling the transfer of frames across media

Back 10

Data link

Front 11

Example of changing frames across network.

Back 11

A router changing ethernet frames to WiFi frames.

Front 12

Media Access Control sublayer is the frame equivalent to

Back 12

Traffic rules.

Front 13

WANS are connected with these 3 physical topologies

Back 13

Point to point

HUB and Spoke

Mesh

Front 14

Point to point topology

Back 14

A permanent link between two endpoints.

Front 15

Hub and spoke topology

Back 15

A cent site interconnects branch sites using point to point

Front 16

Mesh topology

Back 16

Every end system is connected to every other end system.

Each link is a point to point link to other node

Front 17

What is a virtual circuit

Back 17

A point to point connection BTW two nodes even if they aren't in the same physical location

Front 18

What is half duplex

Back 18

Both devices can transfer and receive on media but not at the same time

Front 19

What does CSMA/CD stand for

Back 19

Carrier sense multiple access/collision detection

Front 20

When is cmsa/CD used

Back 20

Used in half duplex

Front 21

Explain the CSMA/CD process

Back 21

Pc 1 wants to send ethernet frame to pc 3

Pc 1's NIC checks for traffic on network, if none, sends frame.

If other device wants to send but is receiving frames, it must wait.

All other devices will receive the frame but ignore it if it's not for them.

Front 22

What happens when a collision occurs

Back 22

Both devices will detect collision(known as CD)

Done by NIC noticing higher signal amplitude or comparing data transferred to data sent.

Front 23

What is CA collision avoidance

Back 23

Doesn't detect collisions but tries to avoid by waiting before transmitting.

Waits to receive ACK that a transmission is done on network

Front 24

What are the 3 things included in a frame

Back 24

Header

Data

Trailer

Front 25

What are frame start and stop indicator flages

Back 25

ID the beginning and end limits of frame

Front 26

Frane fields included in the header of a frame

Back 26

Frame start

Addressing

Type

Control

Front 27

Frane fields included in the trailer of a frame

Back 27

Error detection

Frane stop

Front 28

How to determine MAC address of a node knowing only the IP address

Back 28

Broadcast ARP query packet with the IP

The right compt replies to node with MAC

The node saves MAC in ARP table until it becomes old (TTL time to live)

Front 29

What layers does ethernet operate in

Back 29

Data link

Physical layer

Front 30

Name each part of the ethernet frame. 6 parts

Back 30

Preamble

Destination address

Sure address

Ethernet type

Data plus pad

FCS

Front 31

Ethernet frane: preamble

Back 31

Used to alert stations that data is being transmitted.

Front 32

Ethernet frame: type

Back 32

Indicates higher layer protocol

Most likely IP

Front 33

Ethernet frame: FCS

Back 33

Detects errors. Uses CRC cycle redund check

Checked at receiver, if error detected, frame dropped

Front 34

Min and max ethernet frame size

Back 34

64 bytes min

1518 max

Front 35

Why is ethernet unreliable

Back 35

It's conectionless (no handshaking)

It doesn't send ACKs or to sending NIC

Front 36

What does the 802.2 header and data do

Back 36

Uses pad to increase frame field to at least 64 bytes

Front 37

Start of frame delimiter

Back 37

Syncs sending and receiving devices for frane delivery

Front 38

Frame field how big is the length

Back 38

2 bytes

Front 39

What does CSMA do if it detects another transmission while transmitting

Back 39

Aborts and sends jam signal

Then enter exponential back off (random number)

Front 40

What is a jam signal

Back 40

Makes sure all other transmitters are aware of collision.

Front 41

What is a collision domain

Back 41

Where data packets can collide with one another being sent on a shared medium

Front 42

What happens when a switch does not have the destination address I'm it's ARP table

Back 42

It floods it out to all ports

Front 43

Frame forwarding method: store and forward

Back 43

Switch receives the entire frame. It computes the CRC. If valid it looks up destination address, determines the outgoing interface and forwards it to correct port.

Front 44

Frame forwarding: cut through

Back 44

This switch forwards frane before it's entirely received. At minimum the destination address must be read before sent.

Front 45

What is a switch

Back 45

Link layer device

Store and forward ethernet frames

Front 46

Can a switch forward more than one frame at a time

Back 46

Yes because each port can make forwarding decisions

Front 47

What does a switch do

Back 47

Learns which hosts can be reached through which interfaces by receiving frames from that destination

Front 48

Purpose of layer 2 switches

Back 48

Segment broadcast domains into separate collision domains

Front 49

How do VLANS work

Back 49

They are created on a switch and act as 2 different switches

No communication BTW LANS

Front 50

How to share data between LANS

Back 50

With a router

Front 51

What standard allows devices from different vendors to communicate

Back 51

IEEE 802.1q

Front 52

What does a layer 3 switch do

Back 52

Allows for routing between VLANS

Front 53

What is ppp and how does it work

Back 53

Point to point protocol data link control

One sender one receiver one link

Just needs error detection and packet framing

Front 54

What is a CAM table

Back 54

Contains a list of MAC addresses available on a port of a switch.

Front 55

How to do a CAM table overflow attack

Back 55

Attacker floods a switch with large amount of flash source MAC addresses until table fills up.

When full switch floods all ports on a VLANS it's connected to.

Front 56

How to prevent cam overflow

Back 56

Make any invalid mac address be blocked or shut down the port they are using.

Front 57

What does ARP do

Back 57

Maps IP address to MAC

Front 58

What is an ARP attack

Back 58

When ARP table is nodded by attacker with false info allowing for address spoofing. To perform mitm or dos attack

Front 59

What does the physical layer standard IEEE cover

Back 59

Ethernet

Wireless

Bluetooth