• What Is TCP/IP?
• Terminology
• What TCP/IP Can be Used For?
• A Brief Look at TCP/IP Model
• OSI Model
  • Physical Layer - Transporting Bits
  • Data Link Layer - Hop to Hop
  • Network Layer - End to End
    • IP Addresses and MAC addresses
  • Transport Layer - Service to Service
  • Overview Of The OSI Model
• IPv4 Subnetting
  • What is subnetting
  • How To Write A CheatSheet?
  • How To Find The 7 Attributes of a Given IP Address?
  • Tips For Solving The 7 Attributes Faster
  • Subnetting In /17 - /24 Range
  • Subnetting In /1 - /16 Range
• Network Devices
  • How Data Flows Through The Internet
    • Hosts
    • Ip Addresses
    • Network
    • Repeater
    • Hub
    • Bridge
    • Switch
    • Router
    • Other Network Devices
    • For More About Networking and Subnetting

⭐ The Transmission Control Protocol/Internet Protocol is a set of protocols (communication standards) that describe how two or more computers can communicate over a network.

• Datagrams: A packet of data passed across a network
• Routing: is the process of selecting a path for traffic in a network or between or across multiple networks
• Encapsulation: Arranging data into packets to be transmitted over computer networks
• Deencapsulation: is the reverse computer-networking process
• Client: a computer or a process that accesses data, resources, or services of another computer on the network
• Host: a computer that can communicate with other Internet hosts over the Internet network. Its Internet address and name identify it.
  • Local host: the computer at which the user is working
  • Foreign host: any other hostname on the network
• Network: A network is a collection of interconnected devices, systems, or components that can communicate and exchange data with each other (WAN, LAN...)
  • Physical network: the hardware that makes up the network (cables, servers, routers, switches...). The physical network must support the implementation of the logical network for proper functioning
  • Logical network: is the virtual design, functional aspect of the network based on the organization's needs, in other words, it's the blueprint for implementing the physical network infrastructure (how systems are interconnected, routing protocols, IP addressing, logical network segmentation...)
• Packet: a block of data used by the process to receive and send data in one transaction between the host and its network
• Port: A logical endpoint that allows network protocols and services to communicate (send and receive data)
• Protocol: A set of rules for handling communications at the physical or logical level. A protocol can use another protocol to accomplish its mission

• Log in remotely
• Transfer emails
• Transfer files
• Manage Network

The following table shows the protocols used at each layer of the TCP/IP Model

• ⭐ Connection-oriented Protocol (TCP, SCTP...):

  • requires both devices to be able to communicate with each other
  • TCP successfully makes the connection reliable by :
    • data arrives in-order
    • data has minimal errors (i.e., correctness)
    • No duplicate data
    • lost or discarded packets are resent
    • includes traffic congestion control

• ⭐ Connectionless Protocol (UDP, HTTP, ICMP, IP...):

  • A message is sent from one endpoint to another without a prior arrangement
  • Used for broadcast

⭐ Networking Goal is to allow two hosts to share data between them

• Transporting bits by using an L1 technology

• Interact with the wire (i.e., L1)

  • NIC Network Interface Cards / Wi-Fi Access Cards

  • 🧮 Addressing Scheme - MAC addresses

  • 48 bits, represented as 12 hex digits

  • 94-65-4c-3d-65-e5 (Windows) / 94:65:4c:3d:65:e5 (Linux) / 9465.4c3d.65e5 (CISCO)

💡 Every NIC has a unique MAC address

💡 ARP: Address Resolution Protocol Links a L3 address to a L2 address

• 🧮 Addressing scheme - IP Addresses

💡 Takeaway: L2 and L3 work together to move data across the internet

⭐ Distinguish data streams. This layer ensures that data is received by the right process in your host (multiple tabs in the browser)

• 🧮 Addressing Scheme - Ports
  • [0 - 65535] -- TCP -- favors reliability
• Servers listen for requests to predefined Ports
• Clients select a random Port for each connection

⭐ Takeaway: Network Devices and Protocols operate on specific layers, but these are not strict rules [Exceptions: routers, Address Resotluion Protocol (ARP)...]. It is just a model

⭐ Subnetting means dividing a network into sub-networks.

➡️ Subnetting Attributes:

• Network ID: The first IP address in the sub-network
• Broadcast IP: The last IP address in the sub-network
• First host: The first IP address after the sub-network ID
• Last host: The first IP address before the broadcast IP
• Next Network: The first IP address after the broadcast IP
• # IP addresses: Number of all available IP addresses in a sub-network
• CIDR/Subnet: Converting between CIDR/Subnet Mask

Row 1️⃣: Start with 1, double until you reach 128 (right to left)

Row 2️⃣: Subtract the top row from 256 (256-1 = 255 ...)

Row 3️⃣: From /32, list CIDR notation (decrement by 1 from right to left)

1️⃣ : Use the given CIDR/Mask and find

• CIDR/subnet map to each other
• Groupe size ==> IP Address
• Start at .0 in the relevant octet
• Increase by group size until you PASS target IP

2️⃣ : get Net ID ➡️ Next Network ➡️ BC IP ➡️ First Host ➡️ Last Host ➡️ IP addresses (Group Size)

🎯: Group size can be multiplied to get quickly to the subnet of the targeted IP address

🎯: Every group size lands on 128 at some point

🎯: Each group size aligns with the subnet value in the corresponding column with each subsequent column to the left.

🎯: Start higher, and subtract

• To get the CIDR notation of the 3rd octet

  💡: Start over from the right side and keep decrementing

  💡: Total of IP Addresses = 2 ^ (32 - CIDR)

• To get the CIDR notation of the 3rd octet

  💡: Start over from the right side and keep decrementing

  💡: Total of IP Addresses = 2 ^ (32 - CIDR)

💡: 0.0.0.0 /0 is commonly used in the routing table as the default route or default gateway

💡: In reality most of the last /2 addresses are unassignable as host addresses

⭐ Any system that sends or receives traffic.

• phone
• computer
• laptop
• servers
• cloud servers
• Internet of Things (IoT) (speaker, refrigerator...)

⭐ Client: initiates request. Servers respond. (Relative to specific communication)

⭐ IP Address is the identity of each host

• IPv4 is 32bit
• Hierarchically assigned

💡 : all of those hosts above exist in a network

⭐ Network is what transports traffic between hosts

• Logical grouping of hosts which require similar connectivity
• Subnetworks, subnet
• 💡 Networks connect to other networks (The Internet is simply an inter-connected network)

💡: A wire between two hosts is considered a network, the downside is that the signal decays as it travels long distances

⭐: A repeater simply regenerate the signal that it receives

• it's very useful to connect two hosts in different buildings, so the signal won't decay

⭐ A hub is simply a multi-port repeater

• Facilitates adding another host

💡 Problem: everyone receives everyone's else data

⭐ Bridges sits in between Hub-connected hosts

• Bridges only have two port
• Bridge learn which hosts are on each side

⭐ Switches facilitate communication between hosts within the same network

• Switches are a combination of Hubs and Bridges
  • Multi ports
  • Learns which hosts are on each port

⭐ Routers facilitate communication between networks

• Provides a traffic control point (security, filtering, redirecting)
  • In the past, Switches could not perform such filtering
  • Routers are considered the logical separation of devices
• Routers learn which network they are attached to
  • Known as Routes - Sorted in Routing Table

💡 - Routing Table - all known networks for a Router

⭐ Routing is the process of moving data between networks

• Primary purpose of a Router is Routing

⭐ Switching is the process of moving data within networks

• Primary purpose of a switch is Switching

Any network device performs weather Routing and/or Switching

• Access Points
• Firewalls
• Proxies
• Virtual Routers
• Layer 3 Switches

• Wikipedia
• IBM
• Requirements for Internet Hosts -- Communication Layers -- RFC-1123
• List of IP protocol numbers
• 📺 Video series by Practical Networking on Youtube