/8 subnet mask (255.0.0.0)

A /8 network has 24 host bits, 16,777,216 addresses and 16,777,214 usable hosts. It is 65,536 /24 networks.

/8 at a glance

Netmask: 255.0.0.0
Wildcard mask: 0.255.255.255
Hex mask: 0xFF000000
Binary mask: 11111111.00000000.00000000.00000000
Host bits: 24
Total addresses: 16,777,216
Usable hosts: 16,777,214 (minus network and broadcast)
Compared with a /24: 65,536 /24 networks
Classful equivalent: Class A

Typical uses of a /8

The /8 is the old Class A size and the unit IANA used when it handed IPv4 space to the regional registries. 10.0.0.0/8 is the biggest RFC 1918 private block, giving large enterprises and cloud landing zones room to carve out thousands of VPCs without overlap. 127.0.0.0/8 is reserved for loopback.

Well-known /8 blocks

10.0.0.0/8: Private network (RFC 1918)
127.0.0.0/8: Loopback (RFC 1122)
0.0.0.0/8: "This network" (RFC 791)

Example /8 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /8
10.0.0.0/8	10.0.0.0	10.0.0.1	10.255.255.254	10.255.255.255	11.0.0.0/8	calculate

What a /8 contains

Smaller block	How many
/16	256
/24	65,536
/26	262,144
/28	1,048,576
/29	2,097,152
/30	4,194,304
/32	16,777,216

Splitting a /8

Into	Subnets	Usable hosts each
/9	2	8,388,606
/10	4	4,194,302
/11	8	2,097,150
/12	16	1,048,574

/8 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/8 allowed?	Usable after reservation
AWS VPC	/16 to /28	No	-
Azure VNet	/2 to /29	Yes	16,777,211 (5 reserved)
Google Cloud VPC	/4 to /29	Yes	16,777,212 (4 reserved)

Cloud providers reserve addresses in every subnet (first four and the last address (network, VPC router, DNS, future use, broadcast) on AWS), so the usable count there differs from the classic 2^n - 2.