Track 1 • Module G2 of 4 • IP Addressing & CIDR

IP Addresses, CIDR Notation (/24) & Subnetting Visualized

What does 192.168.1.0/24 or /26 actually mean? And how does a computer use its Subnet Mask to decide whether to send a packet straight to a neighbor via a Switch or to the Default Gateway Router?

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Street Name vs. House Number: An IPv4 address is 32 bits long (written as 4 numbers from 0 to 255, like 192.168.1.10). The CIDR slash number (like /24) simply says: "The first 24 bits (192.168.1) are the Street Name, and the remaining 8 bits (.10) are the House Number!" If two computers have the exact same Street Name bits, they are in the same subnet and talk via a Switch. If their Street Name bits differ even by 1 bit, they MUST use a Router!
Next: Module G3 (NAT & Firewalls) → ← Prev: Module G1 (Switches & Routers)
Interactive CIDR Subnet Slicer — Currently /24 (255.255.255.0)
📏 Visual IP Address Ruler for 192.168.1.0 → 192.168.1.255 (How Your CIDR Prefix Slices the Block) 🧭 L3 Default Gateway Router Used ONLY when Sender & Target are in DIFFERENT CIDR Subnet Slices! 🔌 L2 Local Switch Direct L2 delivery inside the SAME Subnet Slice 💻 Host A (Sender) IP: 192.168.1.10/24 Lives in Subnet: 192.168.1.0/24 Range: .0 to .255 🖥️ Host B (.50) IP: 192.168.1.50/24 Lives in Subnet: 192.168.1.0/24 ✓ SAME Subnet as Host A! 🗄️ Host C (.200) IP: 192.168.1.200/24 Lives in Subnet: 192.168.1.0/24 ✓ SAME Subnet as Host A!
Same CIDR Subnet = Direct L2 Switch Different CIDR Subnet = Must hop through L3 Router!
Try switching from /24 to /26 above, then click "Test 2: Host A (.10) → Host C (.200)"!
← Step G1: Switches (L2) & Routers (L3) Next Step G3: NAT, PAT & Firewalls →