Fundamentals of Ethernet LAN Flashcards

1
Q

Ethernet

A

Family of LAN standards with standard names that begin with 802.3 that together define the physical and data-link layers of the world’s most popular WIRED LAN technology

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2
Q

Wireless LANs

A

Defined by the IEEE using standards that begin with 802.11, use radio waves to send the bits from one node to the next

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3
Q

Unshielded Twisted Pair (UTP)

A

Transmits data over electrical circuits via the copper wires inside the cable.
Suffix includes T (Twisted pairs)
Up to 100 meters

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4
Q

Fiber-optic

A

Sends light over glass fibers in the center of the cable.
Although more expensive, optical cables typically allow longer cabling distances between nodes.
Suffix includes X

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5
Q

Ethernet header and trailer

A

Bytes of overhead data that Ethernet uses to do its job of sending data over a LAN, with the same format no matter the speed or the medium

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6
Q

Ethernet Frame

A

Refers to the header and trailer of a data-link protocol, plus the data encapsulated inside that header and trailer

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7
Q

10BASE-T

A

Standard Ethernet 10Mbps

2 pairs of wires

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8
Q

100BASE-T

A
Fast Ethernet (FE) 100Mbps
2 pairs of wires
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9
Q

1000BASE-T

A

Gigabit Ethernet (GE)
1000Mbps
4 pairs of wires

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10
Q

Electro Magnetic Interference (EMI)

A

When electrical current passes over any wire, it creates electromagnetic interference that interferes with the electrical signals in nearby wires, including the wires in the same cable.

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11
Q

Crosstalk

A

Electro Magnetic Interference (EMI) between wire pairs in the same cable

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12
Q

Ethernet link

A

Any physical cable between two Ethernet nodes

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13
Q

Network Interface Card (NIC)

A

Standard name for PC network Card

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14
Q

Gigabit Ethernet Interface Converter (GBIC)

A

The original form factor for a removable transceiver for Gigabit interfaces

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15
Q

Small Form Pluggable (SFP)

A

The replacement for GBICs, used on Gigabit interfaces, with a smaller size, taking less space on the side of the networking card or switch

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16
Q

Small Form Pluggable Plus (SFP+)

A

Same size as the SFP, but used on 10-Gbps interfaces.

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17
Q

10BASE-T and 100BASE-T Straight-Through Cable Pinout

A

For transmission, pin 1 and 2 on one end of the cable to pin 1 and 2 at the other end of the cable
For receiving, pin 3 and 6 on one end of the cable to pin 3 and 6 at the other end of the cable

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18
Q

10BASE-T and 100BASE-T Crossover Cable Pinout

A

Pin 1 and 2 on one end of the cable to pin 3 and 6 at the other end of the cable, and viceversa

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19
Q

Straight-through vs Crossover cable

A

Straight-through cable, if the endpoints transmit on different pin pairs
Crossover cable, if the endpoints transmit on the same pin pairs

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20
Q

Devices which transmit on Pins 1,2

A

PC NICs
Routers
Wireless access point (Ethernet interface)

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21
Q

Devices which transmit on Pins 3,6

A

Hubs

Switches

22
Q

Auto mdix

A

Cisco switches feature that notices when the wrong cable is used and automatically changes its logic to make the link work

23
Q

1000BASE-T Cable Pinout

A

1,2 > 3,6

4,5 > 7,8

24
Q

Multimode fiber

A

The cable allows for multiple angles (modes) of light waves emitted by a LED trasmitter entering the core

25
Q

Single mode fiber

A

To transmit light into a much smaller core, a laser-based transmitter sends light at a single angle (hence the name single-mode)
Smaller-diameter core, around one-fifth the diameter of common multimode cables

26
Q

Fiber transmission between devices

A

Two cables, one for each direction, like having two electrical circuits with the original UTP Ethernet standards.
Transmit port on one device connects to a cable that connects to a receive port on the other device, and vice versa with the other cable

27
Q

Comparisons Between UTP, MM, and SM

A

Relative Cost of Cabling Low > Medium > Medium
Relative Cost of a Switch Port Low > Medium > High
Approximate Max Distance 100m > 500m > 40km
Relative Susceptibility to Interference Some > None > None
Relative Risk of Copying from Cable Emissions Some > None > None

28
Q

Ethernet Frame Format

A
Header
   Preamble (7)
   SFD (1)
   Destination (6)
   Source (6)
   Type (2)

Data and Pad (46-1500)

Trailer
FCS (4)

29
Q

Ethernet Frame Header - Preamble

A

Synchronization (7 bytes)

30
Q

Ethernet Frame Header - Start Frame Delimiter (SFD)

A

Signifies that the next byte begins the Destination MAC Address field (1 byte)

31
Q

Ethernet Frame Header - Destination MAC Address

A

Identifies the intended recipient of this frame (6 bytes)

32
Q

Ethernet Frame Header - Source MAC Address

A

Identifies the sender of this frame (6 bytes)

33
Q

Ethernet Frame Header - Type

A

Defines the type of protocol listed inside the frame
Today, most likely identifies IP version 4 (IPv4) or IP version 6 (IPv6)
(2 bytes)

34
Q

Ethernet Frame - Data and Pad

A

Holds data from a higher layer, typically an L3PDU (usually an IPv4 or IPv6 packet).
The sender adds padding to meet the minimum length requirement for this field (46-1500 bytes)

35
Q

Ethernet Frame Trailer - Frame Check Sequence (FCS)

A

Provides a method for the receiving NIC to determine whether the frame experienced transmission errors (4 bytes)

36
Q

Maximum Transmission Unit (MTU)

A

The maximum Layer 3 packet that can be sent over a medium.
Because the Layer 3 packet rests inside the data portion of an Ethernet frame, 1500 bytes is the largest IP MTU allowed over an Ethernet.

37
Q

Media Access Control (MAC)

A

6-byte-long binary numbers.
For convenience, most computers list MAC addresses as 12-digit hexadecimal numbers.
Cisco devices typically add some periods to the number for easier readability as well (0000.0C12.3456)

38
Q

Organizationally unique identifier (OUI)

A

Universally unique 3-byte code assigned to the manufacturer by IEEE

39
Q

Ethernet address aliases

A
LAN address
Hardware address
Burned-in address (BIA) 
Physical address
Universal address
MAC address.
40
Q

Unicast address

A

A term for a MAC address that represents a single LAN interface

41
Q

Broadcast address

A

An address that means “all devices that reside on this LAN right now.”
It has a value of FFFF.FFFF.FFFF.

42
Q

Multicast address

A

On Ethernet, a multicast address implies some subset of all devices currently on the Ethernet LAN (that volunteers to receive frames sent to a specific multicast address.)

43
Q

EtherType

A

Hexadecimal number which identifies the type of network layer (Layer 3) packet that sits inside the Ethernet frame.
0800 IPv4
86DD IPv6

44
Q

Error Detection with FCS

A

The sender applies a complex math formula to the frame before sending it, storing the result of the formula in the FCS field. The receiver applies the same math formula to the received frame. The receiver then compares its own results with the sender’s results. If the results are the same, the frame did not change; otherwise, an error occurred, and the receiver discards the frame.

45
Q

Error Detection vs Error Recovery

A

Ethernet defines that the errored frame should be discarded, but Ethernet does not attempt to recover the lost frame. Other protocols, notably TCP, recover the lost data by noticing that it is lost and sending the data again.

46
Q

Half Duplex

A

The device must wait to send if it is currently receiving a frame; in other words, it cannot send and receive at the same time

47
Q

Full Duplex

A

The device does not have to wait before sending; it can send and receive at the same time

48
Q

LAN Hub

A

Forward data using physical layer standards rather than data-link standards and are therefore considered to be Layer 1 devices. When an electrical signal comes in one hub port, the hub repeats that electrical signal out all other ports (except the incoming port)

49
Q

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

A

Enforce rules that allow only one device to successfully send a frame at any point in time

50
Q

Ethernet shared media

A

Refer to designs that use hubs, require CSMA/CD, and therefore share the bandwidth

51
Q

Ethernet point-to-point

A

In a network built with switches, each (point-to-point) link works independently of the others