Chapter 3 - Ethernet Basics Flashcards
Frames
Operate at Layer 2 and use MAC addresses for destination and source
Packets
Operate at Layer 3 and use IP addresses for destination and source
The five fields of a basic ethernet frame
Destination Address
Source Address
Type
Data
Frame Check Sequence (FCS)
Preamble
Added to frame by sending NIC
Gives receiving NIC time to realize a frame is coming and to know exactly where it starts
7 byte series of alt. 1s and 0s
Size of MAC Address
48-bit (6 byte)
Type field
Helps receiving computer interpret the frame contents at a very basic level (IPv4 or IPv6 for example)
Does NOT tell you if the frame carries higher level data such as an email message or web page
Data field
Contains whatever payload the frame carries
Minimum ethernet frame size
64 bytes
Pad
Extra data added to ethernet frame if it contains less than the minimum requirement of 64 bytes
FCS
Frame Check Sequence
Used to “recognize when bad things happen to good data”
Creating using Cyclic Redundancy Check (CRC) to ensure data arrives correctly
CRC
Cyclic Redundancy Check
When ethernet frame sent, sending machine runs this math formula and attaches the result as the Frame Check Sequence (FCS)
The receiving computer then performs the same math and if the answers don’t match, the frame is dropped
NICs that can only communicate in one direction at a time run in ___
Half-duplex mode
NICs that can send and receive at the same time run in ___
Full-duplex mode
RJ-45 Connector
Plastic connector with 8 pins. Each pin connects to a single wire inside the cable
Enables devices to put voltage on the individual wires within the cable
An RJ-45 connector is sometimes called a ___, and the act of installing it on the end of UTP cable is called ___
Crimp
Crimping
CSMA/CD
Carrier-Sense Multiple Access with Collision Detection
Was used on Ethernet networks to determine which computer should use a shared cable at a given moment to attempt to avoid collisions
Carrier Sense
Each node using a network examines cable before sending data frame. If another machine is using network, waits a few milliseconds, rechecks, and if it detected no traffic sent out its frame
Multiple Access
All machines have equal access to the wire
Reasons to use more than one switch
More nodes than available ports
Physical distance requirements
Fault tolerance
Uplink Ports
Enable you to connect two switches using a straight-through cable
Older switches had a dedicated uplink port, modern switches autosense when another switch is plugged in
MDI-X
Auto-Medium-Dependent Interface Crossover
Technical term for an uplink port and the autosensing feature of ports in modern switches
Crossover Cable
Reverses the sending and receiving pairs on one end of the cable allowing switches to hear each other
Not necessary in modern switches
Spanning Tree Protocol
Adopted to eliminate the problem of accidental switching loops
Uses special frames called BPDUs and a Root Bridge to prevent loops from happening in the first place
BPDU
Bridge Protocol Data Unit
Frames used in Spanning Tree Protocol to communicate with other switches to prevent loops from happening
Root Bridge
One switch is elected as Root Bridge which acts as the center of the Spanning Tree Protocol universe
Each switch then uses the root bridge as a reference point to maintain a loop-free topology
(TCN) BPDU
Topology Change Notification BPDU
Go into effect if a link or device goes down so that switches can reroute around the failed device/interface
