/6 subnet mask (252.0.0.0)

A /6 network has 26 host bits, 67,108,864 addresses and 67,108,862 usable hosts. It is 262,144 /24 networks.

/6 at a glance

Netmask: 252.0.0.0
Wildcard mask: 3.255.255.255
Hex mask: 0xFC000000
Binary mask: 11111100.00000000.00000000.00000000
Host bits: 26
Total addresses: 67,108,864
Usable hosts: 67,108,862 (minus network and broadcast)
Compared with a /24: 262,144 /24 networks

Typical uses of a /6

A /6 (four /8s) appears in route aggregation and in reports of large legacy allocations; it is not used for host networks.

Example /6 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /6
0.0.0.0/6	0.0.0.0	0.0.0.1	3.255.255.254	3.255.255.255	4.0.0.0/6	calculate

The /6 boundary falls in the first octet, so /6 networks start every 4 in that octet (64 per address space): 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, 60, ....

What a /6 contains

Smaller block	How many
/16	1,024
/24	262,144
/26	1,048,576
/28	4,194,304
/29	8,388,608
/30	16,777,216
/32	67,108,864

Splitting a /6

Into	Subnets	Usable hosts each
/7	2	33,554,430
/8	4	16,777,214
/9	8	8,388,606
/10	16	4,194,302

/6 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/6 allowed?	Usable after reservation
AWS VPC	/16 to /28	No	-
Azure VNet	/2 to /29	Yes	67,108,859 (5 reserved)
Google Cloud VPC	/4 to /29	Yes	67,108,860 (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.