A /30 subnet mask is 255.255.255.252, with 4 addresses and 2 usable hosts.
| CIDR prefix | /30 |
|---|---|
| Subnet mask | 255.255.255.252 |
| Subnet mask (binary) | 11111111.11111111.11111111.11111100 |
| Wildcard mask | 0.0.0.3 |
| Network bits / host bits | 30 / 2 |
| Total addresses | 4 |
| Usable hosts | 2 |
| /30 subnets in a /8 | 4,194,304 |
| /30 subnets in a /16 | 16,384 |
| /30 subnets in a /24 | 64 |
The mask ends 6 bits into octet 4, so blocks step in increments of 4 in that octet. Two usable hosts: the traditional size for a point-to-point link between two routers.
| Network | First usable host | Last usable host | Broadcast |
|---|---|---|---|
| 192.168.1.0/30 | 192.168.1.1 | 192.168.1.2 | 192.168.1.3 |
| 192.168.1.4/30 | 192.168.1.5 | 192.168.1.6 | 192.168.1.7 |
| 192.168.1.8/30 | 192.168.1.9 | 192.168.1.10 | 192.168.1.11 |
| 192.168.1.12/30 | 192.168.1.13 | 192.168.1.14 | 192.168.1.15 |
| 192.168.1.16/30 | 192.168.1.17 | 192.168.1.18 | 192.168.1.19 |
| 192.168.1.20/30 | 192.168.1.21 | 192.168.1.22 | 192.168.1.23 |
| 192.168.1.24/30 | 192.168.1.25 | 192.168.1.26 | 192.168.1.27 |
| 192.168.1.28/30 | 192.168.1.29 | 192.168.1.30 | 192.168.1.31 |
A /30 subnet mask is 255.255.255.252. In binary that is 11111111.11111111.11111111.11111100: 30 network bits followed by 2 host bits. The wildcard mask is 0.0.0.3.
A /30 holds 4 addresses in total. Subtracting the network and broadcast addresses leaves 2 usable hosts.
A /24 divides into 64 subnets of size /30, because each extra mask bit doubles the number of subnets.
Calculate this over HTTP: curl https://networkcalc.com/api/ip/192.168.1.0/30.
See the Subnet Calculator API.