Subnetting in 10 Minutes

Subnetting is famously over-taught. Here's the version that covers 95% of real life: the /24 and what it tells you.

The notation

192.168.1.50/24

The /24 is the prefix length: the first 24 bits are the network part, the remaining 8 bits identify the host. Same network part = same local network = devices talk directly. Different network part = traffic goes through the router.

What /24 means in practice

An IPv4 address is 32 bits. /24 fixes the first three numbers:

192.168.1.50/24  →  network is 192.168.1.x, host is .50

So on a typical home network (192.168.1.0/24):

• Your devices: 192.168.1.2 through 192.168.1.254
• Your router: usually 192.168.1.1
• Another home using 192.168.2.0/24 is a different network — your laptop can't reach 192.168.2.50 without a router in between

That's it. That's the 95%.

The other prefix lengths you'll see

Prefix	Network size	Where you see it
/32	Exactly one address	Firewall rules ("only this IP")
/24	256 addresses	Home and small office networks
/16	65,536 addresses	Bigger orgs (10.1.0.0/16)
/8	16.7 million	10.0.0.0/8 — the whole private range
/31	2 addresses	Point-to-point links (routers talking to each other)

Each bit you add halves the network. You don't need to do binary math by hand — but know that /25 is half a /24, because someone will say it in a meeting.

Netmasks: the old notation

Before /24 notation, the same idea was written as a netmask:

192.168.1.50  netmask 255.255.255.0   (= /24)

255.255.255.0 in binary is twenty-four 1s followed by eight 0s — same information, clunkier format. You'll still see netmasks in old docs and some router UIs. When in doubt: 255s = network part, 0 = host part.

Why you can stop here

For home networks and small offices, everything is /24 and the router handles the rest. Learn the deeper binary math if you ever need to carve one network into smaller pieces (VLANs, cloud VPCs) — until then, "first three numbers match = same network" will serve you correctly every day.

Next: DNS