# Networking Refresher

## Introduction

* IP Addresses
* MAC Addresses
* TCP, UDP, and the Three-Way Handshake
* Common Ports and Protocols
* The OSI Model
* Subnetting

## IP Addresses

**Layer 3 - Network**

IP (Internet Protocol) addresses, IPv4 and IPv6 - core internet addressing protocols, operating on layer 3 of OSI model.

* IPv4: `192.168.0.1` - decimal notation
  * 4 octets of 8 bits = 32 bits
  * Total IPv4 addresses:

$$
2^{32} = 4,294,967,296
$$

* IPv6: `2001:0db8:85a3:0000:0000:8a2e:0370:7334` - hexadecimal notation
  * 8 groups of 16 bits = 128 bits
  * Total IPv6 addresses:

$$
2^{128} ≈ 3.4 × 10^{38}
$$

**Key IPv6 improvements:**

* Enhanced security
* Simplified network configuration
* More efficient routing

**Transition challenges:**

* IPv4 and IPv6 not directly compatible
* Ongoing global shift from IPv4 to IPv6
* Critical for sustaining internet growth and accommodating future devices

<figure><img src="https://2377137241-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FyNXjlRfAJA38cZuMdmG3%2Fuploads%2FDUIH3uJDaNmhzctTGZqM%2Fimage.png?alt=media&#x26;token=272d915c-b085-4347-993e-806b0c77548b" alt="Private IP Address"><figcaption></figcaption></figure>

Displays the network interface configuration and status:

{% tabs %}
{% tab title="Unix" %}

```sh
ifconfig
```

{% endtab %}

{% tab title="Windows" %}

```batch
ipconfig
```

{% endtab %}
{% endtabs %}

## MAC Addresses

**Layer 2 - Data Link**

MAC (Media Access Control) address - unique identifier assigned to network interface controllers (NICs) of network devices.

* MAC Address: `00:1A:2B:3C:4D:5E` - hexadecimal notation
  * 6 pairs of hexadecimal digits = 48 bits:
    * First 3 pairs: Manufacturer identifier
    * Last 3 pairs: Unique device identifier

Lookup devices using the first 3 pairs: [https://www.macvendorlookup.com](https://www.macvendorlookup.com/)

<figure><img src="https://2377137241-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FyNXjlRfAJA38cZuMdmG3%2Fuploads%2FTYQcDr2N39Rspwt1IQvM%2Fimage.png?alt=media&#x26;token=496263cc-f81f-4277-8917-308958714828" alt="Check the Vendor details using the first 3 pairs: https://www.macvendorlookup.com"><figcaption></figcaption></figure>

## TCP, UDP, and the Three-Way Handshake

**Layer 4 - Transport**

TCP (Transmission Control Protocol) and UPD (User Datagram Protocol) - transport layer protocols in computer networks.

* TCP:
  * Connection-oriented
  * Reliable, ordered, error-checked delivery
  * Uses acknowledgment, retransmission, and flow control
  * Breaks data into packets with sequence numbers
  * Suitable for: web browsing, email, file transfer, remote login
* UDP:
  * Connectionless
  * Simpler and lightweight
  * No guaranteed delivery or packet order
  * Suitable for: streaming media, online gaming, DNS, VoIP

Three-Way Handshake - establishes TCP connections:

1. `SYN`: Client sends SYN packet with initial sequence number
2. `SYN-ACK`: Server responds with SYN-ACK packet, own sequence number
3. `ACK`: Client acknowledges with ACK packet, incremented sequence number

Capture Packet Data using Wireshark:

```sh
wireshark&
```

<figure><img src="https://2377137241-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FyNXjlRfAJA38cZuMdmG3%2Fuploads%2FLHmaJjyeM19W5f5XMnxy%2Fimage.png?alt=media&#x26;token=e8fc6d79-a784-4364-9910-8f1e7c76d82e" alt="wireshark&#x26;"><figcaption></figcaption></figure>

## Common Ports and Protocols

TCP Protocols:

<table><thead><tr><th width="417">Protocol</th><th width="87">Port</th></tr></thead><tbody><tr><td>FTP (File Transfer Protocol)</td><td>21</td></tr><tr><td>SSH (Secure Shell)</td><td>22</td></tr><tr><td>Telnet</td><td>23</td></tr><tr><td>SMTP (Simple Mail Transfer Protocol)</td><td>25</td></tr><tr><td>HTTP (Hypertext Transfer Protocol)</td><td>80</td></tr><tr><td>HTTPS (Hypertext Transfer Protocol Secure)</td><td>443</td></tr><tr><td>POP3 (Post Office Protocol version 3)</td><td>110</td></tr><tr><td>IMAP (Internet Message Access Protocol)</td><td>143</td></tr><tr><td>RDP (Remote Desktop Protocol)</td><td>3389</td></tr><tr><td>SMB (Server Message Block)</td><td>445</td></tr><tr><td>FTPS (FTP over SSL/TLS)</td><td>990</td></tr><tr><td>MySQL</td><td>3306</td></tr></tbody></table>

UDP Protocols:

<table><thead><tr><th width="417">Protocol</th><th width="88">Port</th></tr></thead><tbody><tr><td>DHCP (Dynamic Host Configuration Protocol)</td><td>67, 68</td></tr><tr><td>SNMP (Simple Network Management Protocol)</td><td>161</td></tr><tr><td>NTP (Network Time Protocol)</td><td>123</td></tr><tr><td>TFTP (Trivial File Transfer Protocol)</td><td>69</td></tr></tbody></table>

Protocols using both TCP and UDP:

<table><thead><tr><th width="416">Protocol</th><th width="90">Port</th></tr></thead><tbody><tr><td>DNS (Domain Name System)</td><td>53</td></tr><tr><td>LDAP (Lightweight Directory Access Protocol)</td><td>389</td></tr></tbody></table>

## The OSI Model

OSI (Open Systems Interconnection) model - conceptual framework standardizing communication system functions into seven distinct layers.

<figure><img src="https://2377137241-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FyNXjlRfAJA38cZuMdmG3%2Fuploads%2FgF4r8XnJXXy3JTnpeRJk%2Fimage.png?alt=media&#x26;token=dde93a55-a5b8-4b6e-bcdd-422af9f28d1a" alt="The OSI model"><figcaption></figcaption></figure>

key aspects:

* Separates complex network communication into manageable layers
* Facilitates interoperability and troubleshooting
* Conceptual model, not always reflecting exact implementations
* Useful reference for understanding network communication

## Subnetting

Subnetting - Process of dividing a network into smaller subnetworks

CIDR (Classless Inter-Domain Routing) - Method to represent IP addresses and subnet masks

Concepts:

* Borrows bits from host portion to create subnet identifier
* Allows efficient use of IP addresses
* Facilitates network management and routing

CIDR Notation:

* Format: IP address/prefix length
* Example: 192.168.0.0/24
  * First 24 bits: Network portion
  * Remaining 8 bits: Host portion

Subnetting example:

<table><thead><tr><th width="174">Original Network</th><th width="163">192.168.0.0/24</th></tr></thead><tbody><tr><td>Subnet Mask</td><td>255.255.255.0</td></tr></tbody></table>

Subnetting (borrowing 2 bits):

<table><thead><tr><th width="106">Subnet</th><th width="246">Network Range</th><th width="180">CIDR Notation</th></tr></thead><tbody><tr><td>1</td><td>192.168.0.0 - 192.168.0.63</td><td>192.168.0.0/26</td></tr><tr><td>2</td><td>192.168.0.64 - 192.168.0.127</td><td>192.168.0.64/26</td></tr><tr><td>3</td><td>192.168.0.128 - 192.168.0.191</td><td>192.168.0.128/26</td></tr><tr><td>4</td><td>192.168.0.192 - 192.168.0.255</td><td>192.168.0.192/26</td></tr></tbody></table>

New Subnet Mask: `255.255.255.192`

Benefits:

* Flexible network boundaries
* Efficient address allocation
* Enhanced network organization

Subnetting Sheet:

<figure><img src="https://2377137241-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FyNXjlRfAJA38cZuMdmG3%2Fuploads%2F5rXdd83wATWjrcibmOqD%2Fimage.png?alt=media&#x26;token=f9c86e3f-bfe9-4eb8-b1bb-fb52407e1677" alt="Subnetting Sheet"><figcaption><p>Source: The Cyber Mentor</p></figcaption></figure>

Bits Sheet:

<figure><img src="https://2377137241-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FyNXjlRfAJA38cZuMdmG3%2Fuploads%2Fk9HYdx5QXstcp79oLlsy%2Fimage.png?alt=media&#x26;token=91396f79-0605-4d79-bf4f-8d45000f9a9f" alt="Bits Sheet"><figcaption><p>Source: The Cyber Mentor</p></figcaption></figure>

How to calculate the Subnet:

<figure><img src="https://2377137241-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FyNXjlRfAJA38cZuMdmG3%2Fuploads%2FWznfMbSbitSZjDN5ku2H%2Fimage.png?alt=media&#x26;token=e95be043-da33-4d5c-b8d2-e7fc2379234a" alt="How to calculate the Subnet"><figcaption></figcaption></figure>