From an IPv4 CIDR input, computes network address, broadcast, first/last usable host, host count, subnet mask, and a binary breakdown. Classifies the address (RFC 1918, loopback, link-local).
networking · cidr · subnet · ipv4
Designing VPC subnets, writing firewall rules, debugging kubectl networking — you keep doing the same arithmetic. This lab pulls every value out of a single input.
192.168.1.0/24 = "a 256-address block starting at 192.168.1.0, with the first 24 bits as the network portion".
| Prefix | Host bits | Total addresses | Usable hosts |
|---|---|---|---|
| /24 | 8 | 256 | 254 |
| /23 | 9 | 512 | 510 |
| /16 | 16 | 65,536 | 65,534 |
| /28 | 4 | 16 | 14 |
| /30 | 2 | 4 | 2 (point-to-point) |
| /31 | 1 | 2 | 2 (RFC 3021) |
| /32 | 0 | 1 | 1 (host route) |
"Usable" subtracts the network address (first) and broadcast (last). /31 and /32 are exceptions — point-to-point links use both addresses.
Pre-CIDR "classful" architecture is dead in routers but worth knowing:
0.0.0.0 – 127.255.255.255 (/8 default mask)128.0.0.0 – 191.255.255.255 (/16)192.0.0.0 – 223.255.255.255 (/24)224.0.0.0 – 239.255.255.255)10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16