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CCNA > Chapter 2 - Fundamentals of Ethernet LANs > Flashcards

Chapter 2 - Fundamentals of Ethernet LANs Flashcards

1
Q

Define Ethernet

A

Ethernet is a family of standards and protocols that define characteristics of data transmission.

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2
Q

What standard number is Ethernet?

A

802.3

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3
Q

What is UTP?

A

UTP (Unshielded Twisted Pair) is a form of Ethernet cable that transmits data over upto 4 pairs of copper wires.

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4
Q

What Suffix is used by the IEEE to define different types of cable?

A

T = UTP (Copper)
X = Fibre

Example - BASE-T is copper but BASE-X is fibre.

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5
Q

How does Fibre Cabling work? Include the different parts of the fibre cable.

A

Ethernet nodes at each end of the fibre cable transmit data by encoding bits as changes in light.
The Outer Jacket, Strengthener, and Buffer, are used to protect the interior of the cable and make them easier to install and manage.
The Optical Transmitter produces the light that passes over the cable.
The Inner Core and Cladding allow light to pass over the cable. Sometimes the light can pass through the core but the cladding reflects it back into the core.
It works the same as UTP in the sense that there are 2 cables, each of which transmits data in only one direction. The transmit on one device connects to the receive end on the other device and vice versa for the second cable.

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6
Q

Define Ethernet LAN

A

A network that uses a combination of different devices, LAN switches, and cabling that all adhere to Ethernet standards.

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7
Q

What is another name for:
10 BASE-T
100 BASE-T
1000 BASE-T

A

Ethernet
Fast Ethernet (FE)
Gigabit Ethernet (GE)

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8
Q

How does a UTP transmit data?

A
  • The wires in each pair in a UTP cable are connected at the nodes at either end of the cable to create a complete circuit.
  • They use an encoding scheme to define how the electrical signals are interpreted by each node.
  • 10BASE-T and 100BASE-T dedicate one pair to transmitting and one pair to receiving.
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9
Q

How does an Encoding Scheme work?

A

The transmitting node changes its electrical signal over time and the receiving node uses an encoding scheme to interpret these changes as either 0s or 1s. (e.g. 10 BASE-T using an encoding scheme that encodes a 0 as a change from a higher voltage to a lower voltage).

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10
Q

Advise how many twisted pairs each BASE-T standard uses.

A

10 BASE-T = 2
100 BASE-T = 2
1000 BASE-T = 4

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11
Q

Define GBIC

A

A Gigabit Interface Converter is the original form factor for a removable transceiver for a Gigabit interface.

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12
Q

Define SFP

A

A Small Form Pluggable is the replacement for GBICs. These are also used on Gigabit interfaces but are smaller. SFP+ is the same except it is used for 10 Gigabit interfaces.

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13
Q

What does Pinout mean?

A

A pinout confirms which colour wire is placed in which of the 8 RJ45 pin positions.

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14
Q

What is a Straight Through Cable Pinout?

A

This is necessary when two devices transmit on opposite pins (MDI to MDIX). This connects the pin on one end of the wire to the same pin on the other end of the wire. (e.g. Pin 1,2 on one end connects to pin 1,2 on the other).

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15
Q

Provide one reason that UTP cables are crossed over instead of being parallel.

A

Reduces the likelihood of Crosstalk by cancelling out EMI (Electro Magnetic Interference)

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16
Q

What is a Crossover Cable Pinout?

A

This is necessary when two devices transmit on the same pins (MDI to MDI or MDIX to MDIX). The connections are crossed at each end of the UTP so that the transmitting pins of device 1 connect to the receiving pins of device 2. (Pin 1 connects to pin 3 and pin 2 connects to pin 6.

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17
Q

Advise which pins these devices transmit on and whether they are MDI or MDIX:
Routers
Switches
PC NICs
Wireless Access Points
Hubs

A

PC NICs - 1,2 (MDI)
Hubs - 3,6 (MDIX)
Routers - 1,2 (MDI)
Wireless Access Points - 1,2 (MDI)
Switches - 3,6 (MDIX)

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18
Q

What is auto-mdix?

A

Auto-mdix adjusts a cable’s logic depending on whether it needs to be Straight Through or Crossover. This is automatically detected by switch ports that are auto-mdix enabled.

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19
Q

How does a 1000BASE-T Crossover cable differ from a 100BASE-T or 10BASE-T Crossover cable?

A

As there are 4 pairs in 1000BASE-T it crosses the two new pairs as well which are 4,5 and 7,8.

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20
Q

Explain the differences between Multi Mode and Single Mode fibre.

A

Multimode:
- Transmits over shorter distances without signal degradation (=<500m)
- Transmits more modes (angles) of light
- Transmits using an LED
- Cheaper
- Thicker core

Single Mode:
- Transmits over longer distances (<=40km)
- Transmits a single mode (angle) of light
- Transmits using a laser
- More expensive
- Smaller core

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21
Q

What is the approximate maximum transmission distance for:
UTP
Multimode
Singlemode

A

Multimode - 500m
UTP - 100m
Singlemode - 40km

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22
Q

Define MTU

A

The Maximum Transmission Unit is the maximum size of a packet that is allowed to be sent over a medium (in bits).

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23
Q

Define MAC address

A

Also known as Ethernet addresses MAC (Media Access Control) addresses are 6 byte long binary numbers that are hardcoded to devices upon manufacture. They are generally 12 digit long hexadecimal strings.
In order to keep MAC addresses unique, each organisation is assigned an OUI (Organizationally Unique Identifier) which is a 3 byte, unique code that is assigned to an organisation by the IEEE (Institute of Electronics and Electrical engineers).

24
Q

Define Unicast Ethernet (MAC) address

A

This address only represents one interface or device.

25
Q

Define the structure of a Unicast MAC address

A

OUI takes up the first 24 bits (6 hex digits) and defines the manufacturer
The last 24 bits (6 hex digits) are a random sequence assigned by the manufacturer

26
Q

Define Broadcast Ethernet (MAC) address

A

Frames sent to this address should be delivered to all devices on the same broadcast domain. It has a value of FFFF.FFFF.FFFF (FF:FF:FF:FF:FF:FF).

27
Q

Define Multicast Ethernet (MAC) address

A

Frames sent to one of these addresses will be copied and forwarded to a subset of devices on an Ethernet LAN that volunteer to receive frames sent to this address.

28
Q

Define Ethernet Type

A

Identifies the type of packet that resides inside the Ethernet frame (E.g. it may say that the Ethernet frame contains an IPv4 packet using the hexadecimal code 0x0800).

29
Q

What is FCS?

A

Frame Check Sequence is a way for receiving nodes to find out whether a frame’s bits have changed while traversing an Ethernet link (e.g. due to interference). The sending node applies a complex math formula to the frame before sending it and stores the results in the FCS field of the frame (located in the trailer). The receiver then compares its own results from this formula with the sender’s results. If the results are the same then this means that the bits have not changed. If the results are different then the frames are discarded. Unlike TCP, this is not error recovery as the receiver doesn’t attempt to rectify this.

30
Q

Define Half Duplex

A

Two devices on a LAN segment can send and received data but not simultaneously. Devices that use half duplex logic use an algorithm called CSMA/CD (Carrier Sense Multiple Access with Collision Detection) to avoid collissions and react to them in the event that one does occur.

31
Q

Define Full Duplex

A

A device can send and receive data at the same time over a LAN segment without data collissions occurring.

32
Q

What is a LAN hub?

A

A LAN hub allows multiple devices to connect to its RJ45 ports, however, unlike switches hubs are layer 1 devices (not layer 2). When an electrical signal is received on one interface it then forwards this signal to all other interfaces in hopes that it will reach the correct destination. Hubs use half duplex logic so if two devices send data at the same time it will cause a collission and the signal could become muddled.

33
Q

What is a data collision?

A

Occurs when multiple devices on a collision domain attempt to send data at the same time.

34
Q

What is 802.3z?

A

1000BASE - LX

Supports a gigabit Ethernet connection over fibre cabling.

35
Q

What is 802.3u?

A

Supports Fast Ethernet over copper cabling

36
Q

What is 802.3ab?

A

Supports Gigabit Ethernet over copper cabling

37
Q

What is 802.3an?

A

Supports 10gig Ethernet over copper cabling

38
Q

Label and describe the different parts of an Ethernet frame

A
  1. Preamble (7 bytes) - Lists a recognizable bit pattern so that the receiving nodes realise a new frame is arriving. Also allows the receiver to synchronize its clock with the sender.
  2. Start Frame Delimiter (SFD) (1 byte) - Signifies that the next byte begins the Destination MAC Address field
    (The Preamble and SFD aren’t actually standard parts of an Ethernet header so are not included in the minimum size of an Ethernet header. Although they are always included when sending Ethernet frames)
  3. Destination MAC Address (6 bytes) - Identifies the intended recipient of this frame
  4. Source MAC Address (6 bytes) - Identifies the sender of this frame
  5. Type (replaced Length) (2 bytes) - If this field has a value of 1536 or greater then it defines the protocol of the packet encapsulated inside the frame. If this field has a value of 1500 or less then it will only define the length of the encapsulated packet.
  6. Data and Padding - Holds data from a higher layer. Padding can be added by the sender (all bytes of which are made up entirely of 0s, so 10 padding bytes would be 10 consecutive 0s) to meet the minimum length requirement for this field (46 bytes)
  7. Frame Check Sequence (FCS) (4 bytes) - Provides a method for the receiving device to determine whether the frame experienced transmission errors (CRC algorithm - Cyclic Redundancy Check).
39
Q

What is a MAC Address Table?

A

A MAC Address Table maps layer 2 addresses to specific interfaces so that a switch knows what ports to forward frames to when given a MAC address.

40
Q

What is a Collision Domain?

A

Part of a network where collisions can occur. This is often seen when hubs are in use as all ports on a hub are in the same collision domain. All ports on a switch are in a different collision domain.

41
Q

What is a Broadcast Domain?

A

A domain in which a broadcast is forwarded. This contains all devices that can reach each other at later 2 using broadcast. All ports on a switch and a hub are in the same broadcast domain. All ports on a router are in different broadcast domains. Routers don’t forward broadcasts from one domain to another.

42
Q

True or False. When interfaces don’t have auto negotiation they need to use the exact same standards (e.g. Speed, Duplex) in order to communicate.

A

Both, speed needs to match but duplexes do not.

43
Q

Which speed of Ethernet cable is bi-directional?

A

1000BASE-T and 10GBASE-T meaning each pair isn’t dedicated to transmitting or receiving data. This is partially why they can attain higher speeds than 10BASE-T and 100BASE-T cables.

44
Q

What is 802.3ae (10GBASE - SR)

A

10G Ethernet over multimode fibre

45
Q

What is 802.3ae (10GBASE - LR)

A

10G Ethernet over single mode fibre upto 10km

46
Q

What is 802.3ae (10BASE - ER)

A

10G Ethernet over single mode fibre upto 30km

47
Q

True or False. A MAC address is also known as a Kept-In Address.

A

False. Another name for a MAC address is a Burned-In Address.

48
Q

What numbers and characters are part of the Hexadecimal numbering system?

A

0-9
A-F

A=10
F=15

If you start at 00, 01, 02, etc. once you reach 0F you would then restart at 10, 11, 12 etc.

49
Q

True or False. Hexadecimal is a base 16 numbering system.

A

True. This means that each digit increases by 16 times (16^0, 16^1, 16^2, etc.). For example:

Decimal = 3294
Hexadecimal = CDE

The first digit (E) is multiplied by 1 which would be 14.

The second digit is multiplied by 16 which would be 208.

The third digit is multiplied by 256 (16*16=256) which would be 3072

If there was a fourth digit then this would be multiplied by 4096 (16*256)

50
Q

True or False. Decimal is a base 10 numbering system.

A

True. This means that each digit increases by 10 times.

51
Q

True or False. Binary is a base 1 numbering system.

A

False. Binary is a base 2 numbering. This means that each digit increases by 2 times.

52
Q

What is CSMA/CD?

A

CSMA/CD (Carrier Sense Multiple Access with Collision Detection) attempts to rectify and avoid collisions by making it so that:
- Each sending device that detects a collision sends a jamming signal to advise all nodes that a collision happened.
- They then each choose random times to wait before trying again.

53
Q

What is the minimum and maximum size of an Ethernet header?

A
  • Minimum 64 bytes
  • Maximum 1518 bytes
54
Q

What is the format of a layer 2 multicast addres

A

Any MAC beginning 01:00:5E

55
Q

Out of band vs in band management

A
  • In band uses the same network as normal data traffic for management (e.g. Access over the standard LAN)
  • Out of band uses its own network or method specific for management (e.g. Access via a console port)

CCNA (50 decks)

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