Chapter 21: The Internet (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 21: The Internet

• Internet is broken down into Tiers:

• Tier1 (small number of companies which own long distance, high-speed fiber optic networks called backbones. Backbones connect major cities. Interconnect at special locations called NAPs (Network Access Points))
• Peering Agreement 
• NOC (Network Operation Center)
• They sell connection to Tier2
• Tier 2 (smaller regional networks who connect to Tier 1) 
• Tier 3 (even smaller ISPs than Tier 2) 
• ISP’s
  
• TCP/ IP
• Main framework of the internet 
• Common language of the Internet.
• Addressing scheme for computers to communicate over the internet

As such, all the backbone routers, high-speed backbone lines, TCP/ IP all come together to create a massive interconnected network. It enables communications and services for building applications that enable humans and machines to interface across vast distances. 

• Connection concepts:
• ISPs require 2 things to work perfectly: 
• Hardware for connectivity (Modem, cables lines etc.)
• Software (Protocols to govern connection and  the data flow) and Application (to take advantage of TCP/ IP)
  
• To connect you to the internet ISPs use one of eight technologies that fall into 4 categories:

• Dial-up: Analog and ISDN
• Modem - enable computers to talk to each other over phone line.
• Convert analog to digital 
• Phone lines speed is calculated in baud
• 1 baud = 1 cycler per second
• Max 2400 bauds
• Modems pack multiple bits into each baud
• 56 Kb/s 
• RJ-11
• ISDN (Integrated Services Digital Network) - Terminal adapter (not Modem), as such signal is always digital 
• ISDN consists of two types of channels:
• Bearer (B) - data and voice info over 64 Kbps
• Delta (D) - setup and config info at 16 Kbps

• Dedicated DSL Cable and Fiber
• DSL (Digital Subscriber Line) 
• Asymmetric DSL (ADSL) - Fast download / slow upload
• Symmetric DSL (SDSL) - Download and upload are same    
• Speeds: UP (768 - 3MB/s ) / Down (1.5-7 Mb/s) 
• PPPoE (Point-to-Point Protocol Over Ethernet) - PPP is streaming protocol
• login to use internet 
• Cable
• RG-6 and RG-59 (D: 15-1000 Mbps Up: 5-35Mbps)
• Fiber
• FTTN (Fiber to the node) / FTTP (fiber to the premises)
• Coxial or Ethernet Cabling 
• 50Mbps - 1 Gbps
• DOCSIS (Data Over Cable Interface Specification)
• Wireless / Celular/ Mobile
• Satellite 
• Good for remote locations: Countryside/ Ocean etc. 
• Latency - as such might require large antennas

• Routers
• NAT (Network Address Translation) - all routers are NATs
• It presents all you network to the Internet as a single Machine 
• Multiple Ethernet ports
• Wifi (WAP)
• Firewall

• Firewall - port blocking 
• Router has open `Outgoing port` e.g 80  but closed `Incoming Port` e.g. 80 
• On the server side `Listening port` 80 has to be open 
• When the server sends it back, the port will be switched 

• Internet Application Protocols: 
• HTTP / HTTPS - provides graphic interface for the web
• Web servers use following ports: 

HTTPS = Port 443

HTTP = Port 80

• Email 
• Following ports need to be open:
• Sends data to the SMTP server
• SMTP (Simple Main Transfer Protocol) - Handles outgoing email
• Port 25
• Gets data from these:
• POP/ POP3 (Post Office Protocol) - handles incoming email
• Port 110
• IMAP / IMAP4  (Internet Message Access Protocol) - Port 143
• Folder synchronisation is good

• FTP (File Transfer Protocol) 
• Transfer Modes:
• Passive - (TCP port 21)
• Active (TCP port 20 - 21) 
• It is fast 
• But it changes ports ( E.g. if data was sent on port 21 it will try to comeback on port 20. As such this port might be blocked by the router) 
• Requires Port Triggering 
• Telnet and SSH
• Telnet - it is terminal emulator for TCP/IP networks and enables you to connect to a server/router and run commands on that machine. But the problem is that it sends passwords as clear text
• Port 23 
• SSH (Secure Shell) - works as Telnet but all connection is encrypted. It can also move files. 
• Port 22
• SFTP (Secure FTP) -  secure FTP network protocol which allows to transfer files over secure SSH connection 
• VoIP (Voice over IP) - allows to make voice calls over your computer network 
• Remote Desktop Protocol (RDP) or Virtual Network Computing (VNC)
• VPN (Virtual Private Network) - uses the internet to create a private connection to a remote network 
• PPTP (Point-toPoint Tunneling Protocol Virtual Private Network)(port 1723)
• Easy to decrypt, better use OpenVPN
• L2TP
• IPsec
• File Sharing
• Internet Utility Protocols
• LDAP (Lightweight Directory Access Protocol) - enables OSes and apps to access directories
• By default when working with Active Directory
• SNMP (Simple Network Management Protocol) - enables remote query and remote configuration of network. 
• SMB (Server Message Block) - Windows network file and print sharing protocol. CIFS. 
• AFP  (Apple Filing Protocol)
• SLP (Service Location Protocol) - devices use this protocol to show available services over local network and to discover those services. 

• IoT (Internet of Things) 
• 802.11
• ZigBee
• Z-wave 

• Proxy Server
• Filters out unwanted traffic, or blocks certain websites, etc. 
• Proxy server can do caching
• E.g. if there everyone accesses the same webpage all the time, proxy server could cache it - to speed things up 

• Port Numbers - to allow communication between applications. To get data to correct app.
• 0 - 65535
• 0 - 1023 - most well known/mostly used ports for applications 
• 21 - FTP
• 22 - SSH
• 23 - TELNET
• 25 - SMTP
• 53 - DNS
• 80 - HTTP
• 110 - POP3
• 143 - IMAP
• 443 - HTTPS
• 137- 139 - NETBIOS/NETBT
• 445 - SMB/CIFS
• 427 - SLP
• 548 -AFP

• 1024 - 49151 - registered ports 
• 3389 - RDP (Remote Desktop Protocol) 
• 49152 - 65535 - Dynamic/Ephemeral ports