Network Engineer
Subnetting for network engineers: CIDR cheat sheet for VPC and LAN design
Memorize the four CIDR values you use weekly: /24 (254 hosts), /22 (1022), /28 (14), /30 (2). Derive the rest from 2^(32-prefix) minus 2 for the network and broadcast addresses.
Network engineers do CIDR math daily when designing VPCs, sizing VLANs, and writing firewall rules. The key numbers to memorize: /24 = 254 usable hosts, /22 = 1022, /28 = 14, /30 = 2 (point-to-point links). Everything else is derivable from the 2^(32-prefix) formula.
Why this matters for you
In AWS VPC design, a /16 gives 65,536 IPs split across subnets. A typical 3-tier web app uses a /24 public subnet (ALB), a /24 private app subnet, and a /24 data subnet, leaving room for a /28 management subnet. In on-prem VLAN design, a /24 per floor or department is the default, but dense IoT deployments may need a /22 to avoid running out of DHCP leases.
Verdict
Memorize the four CIDR values you use weekly: /24 (254 hosts), /22 (1022), /28 (14), /30 (2). Derive the rest from 2^(32-prefix) minus 2 for the network and broadcast addresses.
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