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Some notes about networking, TCP/IP Model, OSI Model, Network devices, Subnetting, and Network Devices

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# NetPractice
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![ReadMe](https://img.shields.io/badge/ReadMe-018EF5?logo=readme&logoColor=fff&style=flat-square)

## Content
- [What Is TCP/IP?](https://github.com/LeakedByteBuster/NetPractice#what-is-tcpip)
- [Terminology](https://github.com/LeakedByteBuster/NetPractice/tree/main#terminology)
- [What TCP/IP Can be Used For?](https://github.com/LeakedByteBuster/NetPractice/tree/main#what-tcpip-can-be-used-for-non-exhaustive-list)
- [A Brief Look at TCP/IP Model](https://github.com/LeakedByteBuster/NetPractice/tree/main#a-brief-look-at-tcpip-model)
- [OSI Model](https://github.com/LeakedByteBuster/NetPractice/tree/main#osi-model)
  - [Physical Layer - Transporting Bits](https://github.com/LeakedByteBuster/NetPractice/tree/main#physical-layer---transporting-bits)
  - [Data Link Layer - Hop to Hop](https://github.com/LeakedByteBuster/NetPractice/tree/main#data-link-layer---hop-to-hop)
  - [Network Layer - End to End](https://github.com/LeakedByteBuster/NetPractice/tree/main#data-link-layer---hop-to-hop)
    - [IP Addresses and MAC addresses](https://github.com/LeakedByteBuster/NetPractice/tree/main#ip-addresses-and-mac-addresses)
  - [Transport Layer - Service to Service](https://github.com/LeakedByteBuster/NetPractice/tree/main#transport-layer---service-to-service)
  - [Overview Of The OSI Model](https://github.com/LeakedByteBuster/NetPractice/tree/main#overview-of-osi-model)
- [IPv4 Subnetting](https://github.com/LeakedByteBuster/NetPractice/tree/main#ipv4-subnetting)
  - [What is subnetting](https://github.com/LeakedByteBuster/NetPractice/tree/main#what-is-subnetting) 
  - [How To Write A CheatSheet?](https://github.com/LeakedByteBuster/NetPractice/tree/main#how-to-write-a-cheatsheet)
  - [How To Find The 7 Attributes of a Given IP Address?](https://github.com/LeakedByteBuster/NetPractice/tree/main#how-to-find-the-7-attributes-of-a-given-ip-address)
  - [Tips For Solving The 7 Attributes Faster](https://github.com/LeakedByteBuster/NetPractice/tree/main#tips-for-solving-the-7-attributes-faster)
  - [Subnetting In /17 - /24 Range](https://github.com/LeakedByteBuster/NetPractice/tree/main#subnetting-in-17---24-range)
  - [Subnetting In /1 - /16 Range](https://github.com/LeakedByteBuster/NetPractice/tree/main#subnetting-in-1---16-range)
- [Network Devices](https://github.com/LeakedByteBuster/NetPractice/tree/main#Network-Devices)
  - [How Data Flows Through The Internet](https://github.com/LeakedByteBuster/NetPractice/tree/main#How-Data-Flows-Through-The-Internet)
    - [Hosts](https://github.com/LeakedByteBuster/NetPractice/tree/main#hosts-)
    - [Ip Addresses](https://github.com/LeakedByteBuster/NetPractice/tree/main#ip-addresses-)
    - [Network](https://github.com/LeakedByteBuster/NetPractice/tree/main#network-)
    - [Repeater](https://github.com/LeakedByteBuster/NetPractice/tree/main#repeater)
    - [Hub](https://github.com/LeakedByteBuster/NetPractice/tree/main#hub)
    - [Bridge](https://github.com/LeakedByteBuster/NetPractice/tree/main#bridge)
    - [Switch](https://github.com/LeakedByteBuster/NetPractice/tree/main#switch)
    - [Router](https://github.com/LeakedByteBuster/NetPractice/tree/main#router)
    - [Other Network Devices](https://github.com/LeakedByteBuster/NetPractice/tree/main#other-network-devices)
    - [For More About Networking and Subnetting](https://github.com/LeakedByteBuster/NetPractice/tree/main#for-more-information)

## What Is TCP/IP?
⭐ ***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**.*

## Terminology
- **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
  
### What TCP/IP Can be Used For? (Non-Exhaustive List)
- Log in remotely
- Transfer emails
- Transfer files
- Manage Network

## A Brief Look at TCP/IP Model

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

Layers                  | Protocols Used         |
------------------------|---------------------|
Application layer       | SMTP, SSH, FTP, HTTPS, HTTP, DHCP...|
Transport layer         | TCP (connection-oriented), UDP (connectionless), SCTP (connection-oriented)...|
Internet layer          | IP(IPv4, IPv6), ICMP, IGMP...|
Link + Physical layer   | Mac Address, Fiber, Wireless, Ethernet Cables... |

- ⭐ **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

## OSI Model
⭐ ***Networking Goal** is to allow two hosts to share data between them*

### Physical Layer - Transporting Bits
- Transporting bits by using an L1 technology

### Data Link Layer - Hop to Hop
- 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**

### Network Layer - End to End
- 🧮 Addressing scheme - **IP Addresses**

#### IP Addresses and MAC addresses
💡 *Takeaway: **L2 and L3 work together** to move **data across the internet***

### Transport Layer - Service to Service

⭐ ***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**

![transport layer in networking](https://github.com/Mushigarou/NetPractice/blob/main/Images/Transport%20Layer.png)

### Overview of OSI Model

⭐ *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***

## IPv4 Subnetting

### What Is Subnetting?

⭐ **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

### How To Write A CheatSheet?
**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)

<div align="center">
  
| 128 | 64  | 32  | 16  | 8   | 4   | 2   | 1   | **Groupe Size** |
------|-----|-----|-----|-----|-----|-----|-----|------------------
| 128 | 192 | 224 | 240 | 248 | 252 | 254 | 255 | **Subnet**      |
| /25 | /26 | /27 | /28 | /29 | /30 | /31 | /32 | **CIDR**        |

</div>

### How To Find The 7 Attributes of a Given IP Address?
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)
  
![Solving subnetting for a target IP](https://github.com/Mushigarou/NetPractice/blob/main/Images/Subnetting_Attribute.png)

### Tips For Solving The 7 Attributes Faster

🎯: 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

### Subnetting In /17 - /24 Range
- **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)***

<div align="center">
  
| 128 | 64  | 32  | 16  | 8   | 4   | 2   | 1   | **Groupe Size** |
------|-----|-----|-----|-----|-----|-----|-----|------------------
| 128 | 192 | 224 | 240 | 248 | 252 | 254 | 255 | **Subnet**      |
| /25 | /26 | /27 | /28 | /29 | /30 | /31 | /32 | **CIDR**        |
| /17 | /18 | /19 | /20 | /21 | /22 | /23 | /24 | **3rd Octet**  |

</div>

#### Example:

<div align="center">
  
|  **Subnetting Attributes** |➡️ **of 10.4.235.99 /21:**            | ➡️ ** of 10.4.211.66 /18:** |
-----------------------------|--------------------------------------|----------------------------  |
**Network ID:** |   10.4.232.0 [3rd Octet => .224 => .232]  | 10.4.192.0 [3rd Octet : .128 => .192 => .0]  |
**Broadcast IP:**| 10.4.239.255                                      | 10.4.255.255                                   |
**First host:** |  10.4.232.1                                        |  10.4.192.1                                      |
**Last host:** |  10.4.239.254                                       |  10.4.255.254                                    |
**Next Network:** | 10.4.240.0                                       |  10.5.0.0                                     |
**# Total IP addresses:** | 2048     [32 - 21 = 11 & 2 ^ 11]  |   16,384         [32-18 = 14 & 2 ^ 14 = ]      |
**CIDR/Subnet:** |   255.255.248.0                                   |  255.255.192.0  |

</div>

### Subnetting In /1 - /16 Range

- **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)***

| 128 | 64  | 32  | 16  | 8   | 4   | 2   | 1   | **Groupe Size** |
------|-----|-----|-----|-----|-----|-----|-----|------------------
| 128 | 192 | 224 | 240 | 248 | 252 | 254 | 255 | **Subnet**      |
| /25 | /26 | /27 | /28 | /29 | /30 | /31 | /32 | **4th Octet**   |
| /17 | /18 | /19 | /20 | /21 | /22 | /23 | /24 | **3rd Octet**   |
| /9 | /10  | /11 | /12 | /13 | /14 | /15 | /16 | **2nd Octet**   |
| /1 | /2   | /3  | /4  | /5  | /6  | /7  | /8  | **1st Octet**   |

</div>

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

#### Example:

<div align="center">
  
|  **Subnetting Attributes** |➡️ **of 10.50.111.222 /12:**   | ➡️ ** of 10.50.111.222 /7:** | ➡️ ** of 213.50.111.222 /2:**    |
-----------------------------|-------------------------------|----------------------------  |---------------------------------|
**Network ID:**              | 10.48.0.0 [.48 => .64 ]       | 10.0.0.0 [.8 => .10 => .12]  | 192.0.0.0 [.128 => .192 => .0]  |
**Broadcast IP:**            | 10.63.255.255                 | 11.255.255.255               | 255.255.255.255                 |
**First host:**              | 10.48.0.1                     | 10.0.0.1                     | 192.0.0.1                       | 
**Last host:**               | 10.64.255.254                 | 11.255.255.254               | 255.255.255.254                 |
**Next Network:**            | 10.64.0.0                     | 12.0.0.0                     | **n/a**                                                                                                                [No leading octet, we're at end of IPv4 addresses]|
**# Total IP addresses:**    | 1,048,576    [2 ^ (32-12)]    | 33,554,432  [2^(32-7)]       | 1,073,741,824                   |
**CIDR/Subnet:**             | 255.240.0.0                   |  254.0.0.0                   | 192.0.0.0                       |

</div>

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

## Network Devices
### How Data Flows Through The Internet
#### Hosts :
⭐ *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 Addresses :

⭐ *IP Address is the identity of each host*
  - IPv4 is 32bit
  - Hierarchically assigned

![IP addresses](https://github.com/Mushigarou/NetPractice/blob/main/Images/ip_addresses.png)

💡 : all of those hosts above exist in a network

#### 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)

#### Repeater

💡: 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**

#### Hub
⭐ *A hub is simply a **multi-port repeater***
  - Facilitates adding another host

💡 **Problem**: everyone receives everyone's else data

#### Bridge

⭐ Bridges sits in between Hub-connected hosts
  - Bridges only have two port
  - Bridge learn which hosts are on each side

#### Switch

⭐ *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**

#### Router

⭐ *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*

</div>
<div align="right">
  <b><a href="#top">↥ back to top</a></b>
</div>

#### Other Network Devices
Any network device performs weather Routing and/or Switching
- Access Points
- Firewalls
- Proxies
- Virtual Routers
- Layer 3 Switches

</div>
<div align="right">
  <b><a href="#top">↥ back to top</a></b>
</div>

## For More Information:
- [Wikipedia](https://en.wikipedia.org/wiki/Internet_protocol_suite)
- [IBM](https://www.ibm.com/docs/en/aix/7.2?topic=management-transmission-control-protocolinternet-protocol)
- [Requirements for Internet Hosts -- Communication Layers -- RFC-1123](https://datatracker.ietf.org/doc/html/rfc1122)
- [List of IP protocol numbers](https://en.wikipedia.org/wiki/List_of_IP_protocol_numbers)
- 📺 [**Video series by Practical Networking on Youtube**](https://subnetipv4.com/)

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