breakitdown

What does /8 mean?

Answer

A /8 network keeps the first 8 bits (the first number) fixed and leaves 24 bits for hosts: 16,777,216 addresses, of which 16,777,214 are usable hosts. The netmask is 255.0.0.0.

Worked example: 10.0.0.0/8. Type any block to compare.

Try

10.0.0.0/8 is 16,777,216 addresses: 10.0.0.0 to 10.255.255.255. 16,777,214 usable for hosts (the first is the network address, the last is broadcast).

1000001010000000000000000000000000000
8 network bits 24 host bits
Network
10.0.0.0
First usable
10.0.0.1
Last usable
10.255.255.254
Broadcast
10.255.255.255
Addresses
16,777,216
Usable hosts
16,777,214
Netmask
255.0.0.0
Wildcard (ACL) mask
0.255.255.255
Historic class
A
Range type
Private network · not routed on the internet

Special-purpose range

Private network 10.0.0.0/8 RFC 1918
The largest of the three private IPv4 ranges: 16.7 million addresses for use inside homes and organisations. Not routed on the public internet.

Split it into subnets

or

4 subnets.

SubnetUsable rangeHostsBroadcast
10.0.0.0/1010.0.0.1 – 10.63.255.2544,194,30210.63.255.255
10.64.0.0/1010.64.0.1 – 10.127.255.2544,194,30210.127.255.255
10.128.0.0/1010.128.0.1 – 10.191.255.2544,194,30210.191.255.255
10.192.0.0/1010.192.0.1 – 10.255.255.2544,194,30210.255.255.255

Is this IP in the range?

Range to CIDR blocks

What to know

/8 is the size of the old Class A networks. On the public internet, IANA hands out IPv4 space to the regional registries in /8 blocks, and a few early organizations still hold an entire /8 (Apple's is 17.0.0.0/8).

Most people meet a /8 as 10.0.0.0/8, the largest private range. Nobody puts 16 million hosts on one subnet; organizations take 10.0.0.0/8 as their whole internal address plan and carve it into /16 or /24 subnets per site, VPC or VLAN.

Gotchas

Related explainers

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