IP Subnetting Quick Reference for IT Technicians

Understanding subnetting is essential for configuring networks. A subnet mask defines which part of an IP address is the network and which is the host. Common notation uses CIDR: /24 means 255.255.255.0, which gives 254 usable host addresses (256 minus network and broadcast addresses). Common subnets for small business: /24 (254 hosts) for most office LANs, /25 (126 hosts) to split a /24 in half, /28 (14 hosts) for small server VLANs, /30 (2 hosts) for point-to-point router links. For larger networks: /22 gives 1022 hosts, /21 gives 2046 hosts. Key addresses in a subnet: the first address is the network address (not assignable), the last is the broadcast address (not assignable), all others are usable hosts. Example: 192.168.1.0/24 — network address is 192.168.1.0, broadcast is 192.168.1.255, usable range is 192.168.1.1–192.168.1.254. Use a subnet calculator (e.g., subnet-calculator.com) when planning — no need to memorize all values.