/2 subnet mask (192.0.0.0)

A /2 network has 30 host bits, 1,073,741,824 addresses and 1,073,741,822 usable hosts. It is 4,194,304 /24 networks.

/2 at a glance

Netmask: 192.0.0.0
Wildcard mask: 63.255.255.255
Hex mask: 0xC0000000
Binary mask: 11000000.00000000.00000000.00000000
Host bits: 30
Total addresses: 1,073,741,824
Usable hosts: 1,073,741,822 (minus network and broadcast)
Compared with a /24: 4,194,304 /24 networks

Typical uses of a /2

A /2 is a quarter of the IPv4 internet. Nobody numbers hosts out of one; it shows up in route summaries and as the largest subnet Azure lets you create inside a virtual network.

Example /2 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /2
0.0.0.0/2	0.0.0.0	0.0.0.1	63.255.255.254	63.255.255.255	64.0.0.0/2	calculate

The /2 boundary falls in the first octet, so /2 networks start every 64 in that octet (4 per address space): 0, 64, 128, 192.

What a /2 contains

Smaller block	How many
/16	16,384
/24	4,194,304
/26	16,777,216
/28	67,108,864
/29	134,217,728
/30	268,435,456
/32	1,073,741,824

Splitting a /2

Into	Subnets	Usable hosts each
/3	2	536,870,910
/4	4	268,435,454
/5	8	134,217,726
/6	16	67,108,862

/2 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/2 allowed?	Usable after reservation
AWS VPC	/16 to /28	No	-
Azure VNet	/2 to /29	Yes	1,073,741,819 (5 reserved)
Google Cloud VPC	/4 to /29	No	-

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.