CIDR ranges & subnet sizes, explained
Curated reference pages for the IP ranges and prefix lengths that actually come up in practice — private addressing, special-use ranges, router defaults, and the math behind every common subnet size. Need a block that isn't listed? Run it through the CIDR calculator.
Private ranges (RFC 1918)
The three blocks anyone can use internally — never routed on the public Internet.
Special-use ranges
Loopback, link-local, CGNAT, multicast and friends — reserved for one specific job each.
100.64.0.0/10
100.64.0.0/10 — the CGNAT range
0.0.0.0/0
0.0.0.0/0 — the route that matches everything
0.0.0.0/8
0.0.0.0/8 — "this network", source only
127.0.0.0/8
127.0.0.0/8 — the whole loopback /8
169.254.0.0/16
169.254.0.0/16 — link-local, APIPA, and one very famous IP
198.18.0.0/15
198.18.0.0/15 — the lab-only benchmarking range
192.0.2.0/24
192.0.2.0/24 — the address you write in docs
224.0.0.0/4
224.0.0.0/4 — multicast, where addresses are groups
240.0.0.0/4
240.0.0.0/4 — the forever-reserved Class E
The subnets everyone actually googles
Router defaults, Docker bridges and other blocks you'll meet in the wild.
192.168.1.0/24
192.168.1.0/24 — the default home subnet
192.168.0.0/24
192.168.0.0/24 — the other default home subnet
10.0.0.0/24
10.0.0.0/24 — the top slice of 10/8
172.17.0.0/16
172.17.0.0/16 — Docker's default bridge
192.168.50.0/24
192.168.50.0/24 — the ASUS default LAN
192.168.8.0/24
192.168.8.0/24 — the Huawei hotspot subnet
192.168.100.0/24
192.168.100.0/24 — the cable modem's front porch
Prefix lengths
How many addresses in a /28? Why does a /31 have no broadcast? Every common prefix, decoded.
/24
The /24 prefix: 256 addresses, 254 usable
/8
The /8 prefix: 16,777,216 addresses in one block
/16
The /16 prefix: 65,536 addresses, the classic Class B
/20
The /20 prefix: 4,096 addresses for serious cloud networks
/22
The /22 prefix: 1,024 addresses, four /24s wide
/23
The /23 prefix: 512 addresses, two /24s merged
/25
The /25 prefix: 128 addresses, half of a /24
/26
The /26 prefix: 64 addresses, a quarter of a /24
/27
The /27 prefix: 32 addresses, the small-VLAN standard
/28
The /28 prefix: 16 addresses, 14 to actually use
/29
The /29 prefix: 8 addresses, 6 usable
/30
The /30 prefix: 4 addresses and a 50% tax
/31
The /31 prefix: 2 addresses, zero waste
/32
The /32 prefix: one address, one host