Lab:05 CIDR and IP Subnetting with MXToolbox

CIDR

CIDR (Classless Inter-Domain Routing) is a modern way of assigning IP addresses using flexible network prefixes instead of fixed classes. CIDR allows any size of network, not restricted to fixed blocks.

Formate:IP_Address / Prefix

Example: 192.168.1.0/24 /24 → first 24 bits = network ID Remaining bits → hosts ID

Calculation:

Block=Net ID + Host ID

Hosts = 2^(32 - prefix/Net )

For 192.168.1.0/24 → Hosts = 2^(32−24) = 256 IPs

For 10.0.0.0/26 → Hosts = 2^(32−26) = 64 IPs

Additional Info:

Smaller number after / → bigger network Bigger number after / → smaller network

👉 Example:

/16 → large network

/24 → medium

/30 → very small

---

IP Subnetting

IP Subnetting is the process of dividing a large network into smaller, manageable networks (subnets).

Below are the benifits:

• Improve security
• Better performance
• Easy management
• Efficient IP usage

Step 1: Start with a Network

192.168.1.0/24 Total IPs = 256 Usable IPs = 254

Step 2: Need 2 Subnets

We borrow 1 bit from host part:

192.168.1.0/25 192.168.1.128/25

Step 3: Result

Example: 02

Example: 03

---

---

🧾 Final One-Line Summary

👉 CIDR defines IP range

Subnetting splits that range into smaller networks

MXToolbox helps you check and validate them

---

MXToolbox

MXToolbox is a web-based toolset used by network engineers and cloud architects to:

Check DNS records Analyze IP addresses Troubleshoot email (MX records) Detect blacklisting issues Test network connectivity

MS TOOL BOX

Usages: 1. DNS Troubleshooting Check A, MX, TXT, SPF records Verify domain configuration

👉 Example:

Your website not loading → check DNS mapping

📧 2. Email (MX Record) Testing Verifies mail server configuration Helps fix email delivery issues

👉 Example:

Emails going to spam → check SPF/DKIM

🚫 3. Blacklist Monitoring Checks if your server IP is blacklisted

👉 Important for:

Email servers Public-facing apps

🌐 4. IP & Network Analysis Shows: IP details Reverse DNS Host information ⚡ 5. Connectivity Tests Ping SMTP test Port checks

👉 Helps debug:

Server not reachable Port blocked

---

👉 In short: It helps you quickly diagnose network & DNS problems from a single place