/7 subnet mask (254.0.0.0)

A /7 network has 25 host bits, 33,554,432 addresses and 33,554,430 usable hosts. It is 131,072 /24 networks.

/7 at a glance

Netmask: 254.0.0.0
Wildcard mask: 1.255.255.255
Hex mask: 0xFE000000
Binary mask: 11111110.00000000.00000000.00000000
Host bits: 25
Total addresses: 33,554,432
Usable hosts: 33,554,430 (minus network and broadcast)
Compared with a /24: 131,072 /24 networks

Typical uses of a /7

A /7 is two adjacent /8s. You see it in summarised routes and filter lists, not in LAN design.

Example /7 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /7
0.0.0.0/7	0.0.0.0	0.0.0.1	1.255.255.254	1.255.255.255	2.0.0.0/7	calculate

The /7 boundary falls in the first octet, so /7 networks start every 2 in that octet (128 per address space): 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, ....

What a /7 contains

Smaller block	How many
/16	512
/24	131,072
/26	524,288
/28	2,097,152
/29	4,194,304
/30	8,388,608
/32	33,554,432

Splitting a /7

Into	Subnets	Usable hosts each
/8	2	16,777,214
/9	4	8,388,606
/10	8	4,194,302
/11	16	2,097,150

/7 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/7 allowed?	Usable after reservation
AWS VPC	/16 to /28	No	-
Azure VNet	/2 to /29	Yes	33,554,427 (5 reserved)
Google Cloud VPC	/4 to /29	Yes	33,554,428 (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.