/0 subnet mask (0.0.0.0)

A /0 network has 32 host bits, 4,294,967,296 addresses and 4,294,967,294 usable hosts. It is 16,777,216 /24 networks.

/0 at a glance

Netmask: 0.0.0.0
Wildcard mask: 255.255.255.255
Hex mask: 0x00000000
Binary mask: 00000000.00000000.00000000.00000000
Host bits: 32
Total addresses: 4,294,967,296
Usable hosts: 4,294,967,294 (minus network and broadcast)
Compared with a /24: 16,777,216 /24 networks

The calculator accepts /1 to /32; pick a prefix there.

Typical uses of a /0

A /0 is not a subnet you assign: it is the whole IPv4 space. You meet it as the default route (0.0.0.0/0 via the gateway), as "anywhere" in AWS security groups, Azure NSGs and firewall rules, and in WireGuard AllowedIPs to send all traffic through the tunnel. An inbound rule with 0.0.0.0/0 exposes a port to the entire internet, so audit those first.

Well-known /0 blocks

0.0.0.0/0: Default route: matches every IPv4 address

Example /0 ranges

Network	Network address	First usable	Last usable	Broadcast	Next /0
0.0.0.0/0	0.0.0.0	0.0.0.1	255.255.255.254	255.255.255.255	(end of IPv4)

What a /0 contains

Smaller block	How many
/16	65,536
/24	16,777,216
/26	67,108,864
/28	268,435,456
/29	536,870,912
/30	1,073,741,824
/32	4,294,967,296

Splitting a /0

Into	Subnets	Usable hosts each
/1	2	2,147,483,646
/2	4	1,073,741,822
/3	8	536,870,910
/4	16	268,435,454

/0 in AWS, Azure and Google Cloud

Platform	Allowed subnet sizes	/0 allowed?	Usable after reservation
AWS VPC	/16 to /28	No	-
Azure VNet	/2 to /29	No	-
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.