IP Addressing Basics

• IPv4: 192.168.1.1 (32-bit, decimal)

  • Private Ranges:

    • 10.0.0.0/8

    • 172.16.0.0/12

    • 192.168.0.0/16

• IPv6: 2001:0db8:85a3::8a2e:0370:7334 (128-bit, hex)

  • Shorthand: Replace consecutive zeros with :: once.

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Subnetting Essentials

IPv4 Subnet Mask Shortcuts

CIDR	Subnet Mask	Hosts per Subnet
/24	255.255.255.0	254
/30	255.255.255.252	2

Formula:

• Hosts = 2(32−CIDR)−22(32−CIDR)−2

• Example: /26 = 64 - 2 = 62 hosts.

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Common Protocols & Ports

Protocol	Port	Use Case
HTTP	80	Unencrypted web traffic
HTTPS	443	Encrypted web traffic
SSH	22	Secure remote access
DNS	53	Domain name resolution
DHCP	67/68	Dynamic IP assignment

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Network Troubleshooting Commands

• ping <IP>: Test connectivity.

• tracert <IP> (Windows) / traceroute <IP> (Linux): Map path to destination.

• ipconfig (Windows) / ifconfig (Linux): View interface details.

• netstat -ano: List active connections and ports.

• nslookup <domain>: Query DNS records.

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Security Best Practices

1. Firewall Rules:

   • Block all inbound traffic by default.

   • Allow only necessary ports (e.g., 443 for HTTPS).

2. Use VLANs to segment traffic (e.g., separate guest and internal networks).

3. Disable unused ports on switches/routers.

4. Always use SSH instead of Telnet.

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Quick Reference Tables

OSI Model Layers

Layer	Name	Example
7	Application	HTTP, FTP
4	Transport	TCP, UDP
3	Network	IP, ICMP
2	Data Link	MAC addresses
1	Physical	Cables, signals

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Pro Tips

🔹 Use Wireshark to analyze traffic patterns. 🔹 Memorize private IP ranges to avoid conflicts. 🔹 For labs: /30 subnets = perfect for point-to-point links.

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Where to Learn More

• Cisco NetAcad: Free networking labs.

• TryHackMe: Hands-on network security rooms.

• RFC 1918: Private IP address standards.

• Cisco Packet Tracer

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Fun Fact: The first RFC (Request for Comments) was written in 1969 to define ARPANET protocols—the precursor to the modern internet!

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