Chapter 18: Essentials of Networking (A+ Study Notes)

A+

Study Notebook

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You can find my complete study notes in Google Docs format below: https://docs.google.com/document/d/1zcKLWfsns1tqzmXtVRJbcd9NqfaEcjifgIo-oJIbEgc/edit?usp=sharing

References:
M. MEYERS, 2019.  CompTIA A+ All-in-One Exam Guide. 10th ed.

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Chapter 18: Essentials of Networking

• host
• Local host
• Remote host
• Web Server
• E.g. Apache HTTP Server, Microsoft Internet Information Services (IIS)
• Client
• Print Server
• File server
• Mail server
• NIC (Network Interface Controller) - it breaks files into smaller data units to be sent other the network and then puts them back together to create whole files - frames. NIC processes frames. 
• Frames
• Packets - included within a frame 
• PDU (Protocol Data Usage) - that's how we organise packet.  Certain chunks of data from within the packet.
• Ethernet Frame (e.g. switches & mac addresses) 
• IP Packet 
• TCP segment/UDP datagram (Data (TCP, UDP, ICMP))
• MAC address - every NIC has a MAC (media access control address)
• MAC address is binary number. 
• Binary - it's a string of ones and zeros. Each one and zero is 1 bit. 
• MAC address is 12-hexadecimal numbers. 48 bits long.
• Hexadecimals - base 16 counting system - converts 4 Binary values  into shorter and easier to read strings: 

0000 = 0
0001 = 1
0010 = 2
0011 = 3
0100 = 4
0101 = 5
0110 = 6
0111 = 7
1000 = 8
1001 = 9
1010 = A
1011 = B
1100 = C
1101 = D
1110 = E
1111 = F

• 248 - 248 (over 281 trillion) possible MAC addresses

• Both sending NIC and receiving NIC Mac address is stored within the Frame.
• Data itself 
• Data check - CRC (cyclic redundancy check) - mathematical algorithm

• `ipconfig /all` (Windows - find MAC address)
• ` ifconfig /NICname/ | '/ether/{print $2}' ` (macOS - find MAC address)

• Ethernet (10/100/1000BaseT or simply Ethernet)  
• Uses star bus topology - e.g. that all computers connect to one box such as switch/hub etc. 
• Hub will share all the available bandwidth. 
• Switch - will pair only those machines which need the file
• E.g. Match Sending MAC address with receiving MAC address (every network card has a unique MAC address consisting of 12 hexadecimal characters, 48 bits) 
• Connects through cable called unshielded twisted pair (UTP)
• Consists of AWG 22-26 gauge wire twisted together into color-coded pairs. Each wire is individually insulated and encased as a group in a common jacket.
• UTP (Cat) categories: 

• Telecommunication Industry Association (TIA) establishes UTP cats. Which fall under ANSI/TIA 568 specifications. 
• Shielded Twisted Pair (STP) - same as above only shielded with extra layer of shielding to protect from electromagnetic interference 
• RJ-11 connector  - connects phone line. 
• RJ-45 connector (RJ = registered jack) - standard for UTP connectors. And is much larger than RJ-11. 
• RJ-45 connector has to be of the same CAT as the UTP cable!
• PVC vs  Plenum-grade cabling 
• PVC - produces noxious fumes when burned  
• Plenum-grade cable - is with fire-retardant jacket. 
• ANSI/TIA has 2 standards for connecting RJ-45 connector to the UTP cable: T568A and T568B
• Diagram of how to connect RJ-45 according to these standards:

• Crossover cable - when connecting 2 computers directly  
• It is a standard UTP cable with RJ-45 connector, but one end is T568A and another T568B. What as the result reverses sending and receiving wires and thus does the job of switch/hub. 

• Ethernet Connector alternatives:

• Fiber optic Cable - uses light, instead of electricity 
• Immune to lightning, short circuits, static. 
• Signal travels much farther, 2000 meters (vs 100m of UTP) 
• Usually uses 62.5/125 multimode fiber optic cable (which requires 2 cables) 
• Light types: multimode vs single-mode.
• Light can be sent as regular light (multimode) or laser light (single-mode) . But each light type require different fiber optic cables. 
• Multimode Fiber Optic Cabling- most often uses LEDs. transmits multiple light signals at the same time, each reflecting at a different angle within the core of the cable. Due to the reflection the light strength reduces.  As such, such cables are used for shorter distances. Speeds are usually around 10, 100, 1000, 10.000 Mbps.
• Single-mode Fiber Optic Cabling  - uses laser light. Allows light to travel much larger distances. Over 100miles@ 100 Terabites per second. But rarely used nowadays.
  
• Half-duplex - data flows only one way. That's why fiber optic needs 2 cables.
• Fiber Optic common connector types:

Older (require 2 connectors on every fiber connection):
ST connector - looks round

SC connector - square-shaped

Newer (support two fiber cables in one connector):

LC connector - 

• Coaxial Cable - commonly used to connect cable modems, TVs and satellites 
• Rated based on RG rating. To know: RG-59 and RG-6.
• Rated by impedance which is measured in oHms
• Impedance - is the effective resistance to the flow of an alternating current electrical signal through cable
• RG-59 and RG-6 - have impedance of 75-ohm
• RG-59 is thinner and doesn't carry data as far as RG-6
• Types of connectors: 
• BNC connector - quarter twist connector. Rarely used.  

• F-type connector  - uses screw connector. Commonly used in TVs. 

• LAN (local area network) - small network. Group of computers located physically close to each other. 

• LAN is almost always a Broadcast domain - a group of computers connected to one or more switches. 
• SOHO environment (Small Office/Home Office)
• Ethernet over Power
• Solid Core UTP - better conductor, but stiff and will break if handled too often
• Stranded Core UTP - not as good conductor, but will survive substantial handling without breaking
• Horizontal Cabling - cabling which goes from one room into e.g. server room. 
• Equipment racks
• Patch panels -  box with a row of female connectors (ports) in the front and permanent connections in the back, to which you connect the horizontal cabling
• Most common patch panel uses type of connector called: 110 block or 110-punchdown block.
• Although, patch panels support various connection types: UTP, STP, fiber.
• UTP patch panels also come with relevant CAT ratings. And they are backward compatible. 
• Patch cables - short stranded (not solid) UTP cables. To allow more abuse. 

• HUB vs Switches
• HUB will share all the available bandwidth. 
• SWITCHEs will pair only those machines which need the file
• E.g. Match Sending MAC address with receiving MAC address (every network card has a unique MAC address consisting of 12 hexadecimal characters, 48 bits) 

WAN - larger network where e.g. multiple LANs need to be connected together 

• Router - LAN connected to WAN through router
• Biggest WAN is the Internet. 

• IP Addressing

MAN - is a WAN over the municipal city