Free networking tool

Subnetting, visualized

An IP address is like a street address. The network part says which street, the host part says which house. Move the mask and watch where that line falls.

1

Pick an address and a mask

Every IPv4 address is 32 ones and zeros. The mask decides where to cut them: the network part says which street, the host part says which house.

Tip: paste CIDR like 10.0.0.5/26 to set both.

/24

24 network bits + 8 host bits = 32

Same thing as the prefix, written as 4 numbers.

IP address
Tap a bit to flip it
1286432168421
192.
1286432168421
168.
1286432168421
10.
1286432168421
77
Subnet mask
Tap to move the line
255.
255.
255.
0
Network address
IP AND mask: host bits become 0
11000000
192.
10101000
168.
00001010
10.
00000000
0
Network bits: which street (mask = 1)Host bits: which house (mask = 0)The split line
2

What that mask gives you

192.168.10.0/24 is one network (one street). Here is what lives on it.

8 host bits28 = 256 addresses− 2(network + broadcast)254 usable hosts
Start of the blockEnd of the block
Network192.168.10.0
254 hosts192.168.10.1 – 192.168.10.254
Broadcast192.168.10.255
Network address
192.168.10.0
The street name. First address, not given to a device.
Broadcast address
192.168.10.255
Talks to every house on the street at once. Last address.
First usable host
192.168.10.1
The first address you can give a device.
Last usable host
192.168.10.254
The last address you can give a device.
Subnet mask
255.255.255.0
/24 written as 4 numbers.
Wildcard mask
0.0.0.255
The mask flipped: 255 minus each number. Used in ACLs and OSPF.

PrivateRFC 1918 — used inside homes and offices, not routed on the internet.

3

Cut the network into smaller networks

Subnetting means taking one big network and cutting it into equal pieces. To do it, you borrow bits from the host part. Each borrowed bit doubles the number of pieces and halves the size of each one.

Cut 192.168.10.0/24 into:
borrow 2 bits22 = 4 subnets of /26each: 26 = 64 addresses, 62 usable
Your IP, re-cut
Now a /26
11000000
192.
10101000
168.
00001010
10.
01001101
77
24 network bits: same for every piece2 borrowed bits: picks the piece (yours is 01 = #1)6 host bits: picks the device
The whole /24, as a map
Each square = 1 address (256 total). Tap one to move your IP there.
One colour = one subnetYour subnetYour IPStriped = network and broadcast (can't be given to a device)
All 4 subnets
Ready to use it on real gear?

Assign these addresses on a simulated switch, or learn networking step by step.

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