/4 subnet mask (240.0.0.0)

A /4 network has 28 host bits, 268,435,456 addresses and 268,435,454 usable hosts. It is 1,048,576 /24 networks.

/4 at a glance

Netmask: 240.0.0.0
Wildcard mask: 15.255.255.255
Hex mask: 0xF0000000
Binary mask: 11110000.00000000.00000000.00000000
Host bits: 28
Total addresses: 268,435,456
Usable hosts: 268,435,454 (minus network and broadcast)
Compared with a /24: 1,048,576 /24 networks

Typical uses of a /4

A /4 is the size of the multicast block 224.0.0.0/4 (old Class D) and the reserved 240.0.0.0/4 (old Class E). It is also the shortest mask Google Cloud accepts for a subnet primary range, though you would never need one that large.

Well-known /4 blocks

224.0.0.0/4: Multicast (RFC 5771), old Class D
240.0.0.0/4: Reserved, old Class E (RFC 1112)

Example /4 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /4
0.0.0.0/4	0.0.0.0	0.0.0.1	15.255.255.254	15.255.255.255	16.0.0.0/4	calculate

The /4 boundary falls in the first octet, so /4 networks start every 16 in that octet (16 per address space): 0, 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, 240.

What a /4 contains

Smaller block	How many
/16	4,096
/24	1,048,576
/26	4,194,304
/28	16,777,216
/29	33,554,432
/30	67,108,864
/32	268,435,456

Splitting a /4

Into	Subnets	Usable hosts each
/5	2	134,217,726
/6	4	67,108,862
/7	8	33,554,430
/8	16	16,777,214

/4 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/4 allowed?	Usable after reservation
AWS VPC	/16 to /28	No	-
Azure VNet	/2 to /29	Yes	268,435,451 (5 reserved)
Google Cloud VPC	/4 to /29	Yes	268,435,452 (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.