/28 subnet mask (255.255.255.240)

A /28 network has 4 host bits, 16 addresses and 14 usable hosts. It is 1/16 of a /24.

/28 at a glance

Netmask: 255.255.255.240
Wildcard mask: 0.0.0.15
Hex mask: 0xFFFFFFF0
Binary mask: 11111111.11111111.11111111.11110000
Host bits: 4
Total addresses: 16
Usable hosts: 14 (minus network and broadcast)
Compared with a /24: 1/16 of a /24

Calculate a /28 in the subnet calculator

Typical uses of a /28

A /28 has 14 usable hosts: 16 addresses minus network and broadcast. It is the smallest subnet AWS allows, and AWS reserves 5 of the 16 addresses, leaving 11. EC2 prefix delegation also hands out /28 blocks to a network interface. ISPs sell /28 static blocks to businesses.

Example /28 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /28
10.0.0.0/28	10.0.0.0	10.0.0.1	10.0.0.14	10.0.0.15	10.0.0.16/28	calculate
172.16.0.0/28	172.16.0.0	172.16.0.1	172.16.0.14	172.16.0.15	172.16.0.16/28	calculate
192.168.1.0/28	192.168.1.0	192.168.1.1	192.168.1.14	192.168.1.15	192.168.1.16/28	calculate
203.0.113.0/28	203.0.113.0	203.0.113.1	203.0.113.14	203.0.113.15	203.0.113.16/28	calculate

The /28 boundary falls in the fourth octet, so /28 networks start every 16 in that octet (16 per /24): 0, 16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, 240.

How many /28s fit

In a	Number of /28 subnets
/8	1,048,576
/16	4,096
/20	256
/24	16

What a /28 contains

Smaller block	How many
/29	2
/30	4
/32	16

Splitting a /28

Into	Subnets	Usable hosts each
/29	2	6
/30	4	2
/31	8	2
/32	16	1

/28 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/28 allowed?	Usable after reservation
AWS VPC	/16 to /28	Yes	11 (5 reserved)
Azure VNet	/2 to /29	Yes	11 (5 reserved)
Google Cloud VPC	/4 to /29	Yes	12 (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.