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Systems

CPU

arm or amd

3 proccesses of CPU: fetch decode execute

ALU : Arithmetic Logic Unit: does the real process of CPU

Expansion Cards

  • Graphic cards - GPU
  • Network card
  • Sound card

Logic Gates

NO AND OR NOR XOR NAND

Motherboard components

  • cpu
  • chipset
  • memory slot
  • expansion card slot
  • power connectors
  • SATA / NVMe connectors
  • fans connectors

BIOS / UEFI

Motherboard links all the components.

CPU structure

  • CU - Control Unit
  • ALU - Arithmetic logic unit
  • AGU - Address generation unit
  • MMU - Memory management unit
  • Cache
  • Clock rate

Hypervisor

On servers, it's between hardware and VMs.

You don't necessarily need a Host OS for Hypervisor to run on a hardware.

Hyper-V is of Microsoft's.

Networking

Network Protocols

  • IP (Internet protocol) : a postal system for internet, delivers data packets from one computer to another across a network

  • TCP (Transmission Control Protocol) : it's a reliable courier service on the internet, makes sure that data packets are delivered in order and without errors / like web browsing and email

  • TCP/IP : is the foundation of the internet, provides sets of rules and standards of how the data is transmitted and received across networks and devices

  • UDP (User Datagram Protocol) : UDP is like a speed delivery system, sends data packets quickly but not very reliable, no guarantee of the delivery even. Usually used for media streaming and for DNS because of it's speed.

  • HTTP : It's a language used by web browsers & Servers to communicate and exchange information, like loading webpages.

  • FTP (File Transfer Protocol) : a dedicated file sharing service on the internet, upload/download between computers/servers

  • SMTP : Postal service for emails only, sends email btw mail servers.

  • SSH (Secure Shell) : A secure tunnel to remotely access to computers, enables encrypted communication and you can execute command lines over a network.

  • DNS (Domain Name System) : It's a phone book/yellow pages for the internet, translates domain names into IP addresses that computers can understand. Humanly to computerly translation.

IP Protocol

  • Sends packets
  • Source IP address and destination IP address
  • A packet can be max 65mb
  • 32bit

TCP Protocol

  • Each data, 2 packages are sent. 1 for sending, 2 for the acknowledgement of the receipt

UDP Protocol

  • Lighter header, no need for confirmation from the acquirer. Faster, lighter communication.
  • Online games, videos, meetings. Media generally.

Broadcast Address

  • Highest address in a subnetwork.
  • ip address / 24 means there are 2^8 addresses on this subnetwork. Meaning that there are 256 addresses in the subnet, and 254 maximum number of devices.

DHCP

  • DHCP attributes IP addresses automatically to hosts on a network.
  • They can renew based on time or other parameters.
  • How the IP is distributed? With the DORA technic. Discover (host to server) Offer (server to host) Request (host to server) Acknowledge (server to host)

DNS

  • Domain Name System is the humanly versions of IP addresses.
  • When you choose Public DNS, it's like choosing a different phonebook.
  • ISP normally attributes us to a DNS automatically.

tracert [ip address] to see the details of the ip address.

Firewall

  • Firewall stands between the router and the internet, can be physical or virtual. Can control the incoming/outgoing packets.

Gateway

  • Gateway provides the connection between different VLANs or external networks. It's like a small tunnel between different virtual subnetworks.

IP Address

  • A num label to locate a host on a network.
  • nums btw 0-255 only.
  • There are static IP and dynamic IP.

MAC Address

  • Physical address of a device.

NAT

  • Network address translation.
  • Converts private IP addresses to a single public IP address (like the public IP address of the ISP or of the router)

PAT

  • Port address translation.
  • Provides connection from a local device to internet with a label called "virtual port" or simply "port".

Network Address

  • It's the first address in a subnetwork.
  • Broadcast address is the last address in a subnetwork.

Network Architecture

![[Pasted image 20240324153244.png]]

  • How many IP addresses needed for this network?
  • 2 for each router. 2x3 = 6
  • 400 end devices, 400
  • 1 for the Mail Server, 1
  • 407 in total

Class A : 1-126 Class B : 128 - 191 Class C : 192-223 Class D : 224 - 239 Class E : 240 - 255

Network Card

  • Has 2 interfaces, ethernet and wifi. Each interface has a MAC address, which is like the ID number of the interface/port.

OSI Model

  • Open Systems Interconnection

  • Has 7 layer for sending the packets between devices on a network.

    1. Physical layer: binary, cables, prises, hub, etc.
    1. Liaison layer: MAC address, switch vs
    1. Network layer: Router, IP addresses
    1. Transport layer: TCP or UDP header
    1. Session layer: login, a session could also be on SQL or DB or AD
    1. Presentation layer: VNC and RDP, Teamviewer, SSH, GUI, SSL, TLS, etc.
    1. Application layer: FTP (Filezilla), HTTP (Chrome), SMTP (Mail apps), IMAP and all network protocols

SQL Protocols

  • 21 : FTP Control
  • 22 : FTP Data
  • 23 : Telnet
  • 25 : SMTP
  • 53 : DNS
  • 80 : HTTP
  • 110 : POP3
  • 143 : IMAP
  • 443 : HTTPS

Telnet

  • Terminal on a network. We can connect to a server/switch or a computer's terminal with telnet.

pfSense

  • It's a virtual firewall OS.
  • We can connect to it's interface from the web browser.
  • We can block or allow connections and make many other configurations.

ICMP

  • Uses ping or traceroute/tracert to check the healthy connections on the internet.

Point-to-Point

  • How many IP addresses needed for a connection btw 2 devices?
  • At least 4 IP addresses needed because in a network we have the network address and broadcast address by default, apart from those 2 address for the devices are needed.

PuTTy

  • Putty is the app to connect to terminal of a switch or a router.
  • It uses SSH to connect to the router.
  • It uses Telnet to connect to the switch.

Routing

  • It finds the shortest route btw the switches and devices.
  • It uses the default gateway which is 0.0.0.0 usually.

Switch

  • Switch distributes the connection coming from the routers to the hosts.
  • At least 2 switches should be used in a network in case one goes down.

VLAN

  • Local virtual network.
  • Separates a group of devices on a different network logically.
  • steps to create VLAN
  • enter CLI of the switch; enable configure terminal vlan 192.168.1.0 vlan [NAME of the VLAN] interface fa0/1 switchport mode access switchport access vlan 192.168.1.0 end write memory

Wireshark

  • A packet analsys tool, checks the incoming and outgoing packets, give all the details on them.
  • We can see the steps of a DHCP request.

Subnetworks

  • All IP addresses are found in subnet mask, usually like 255.255.255.0;
  • 1111 1111 . 1111 1111 . 1111 1111 . 0000 0000 : equals to something like this.
  • Subnet address is found by IP Address + subnet mask (with the AND logic). If there's a zero, result is zero.
  • If multiple devices are on the same subnetwork address, they can intercommunicate.
  • Let's say that an ip address and it's subnet mask is displayed as following;
    • 192.168.1.0 / 28
    • Means that there are 4 zeros. 2^4 IP addresses can be contained on the network. 16 addresses in total but 14 devices maximum.
    • Addresses start from 192.168.1.0 (the network address), 192.168.1.1, 192.168.1.2, 192.168.1.3 .......... 192.168.1.14, 192.168.1.15 (broadcast address) making it 16 addresses in total.

Excercise:

PC A: 192.168.100.4 / 28

PC B: 192.168.100.17 / 28

PC C: 192.168.100.30 / 28

How many devices? Can they communicate?