/30 Subnet Mask: How Many IPs?
4 addresses, 2 usable, mask 255.255.255.252.
A /30 has 4 addresses and 2 usable, the traditional size for a point-to-point link between two routers. Modern links often use /31 instead (RFC 3021).
Subnet mask for /30
The /30 subnet mask is 255.255.255.252: 30 bits for the network and 2 for hosts.
| Subnet mask | 255.255.255.252 |
|---|---|
| Mask in binary | 11111111.11111111.11111111.11111100 |
| Wildcard mask | 0.0.0.3 |
| Total addresses | 4 |
| Usable hosts | 2 |
| In /24 terms | 64 of them fit in one /24. |
| Example (10.0.0.0/30) | 10.0.0.0 - 10.0.0.3 |
Usable addresses in cloud subnets
Cloud providers reserve extra addresses in every subnet, so fewer than 2 are available to your machines.
| AWS | not allowed (smallest is /28) |
|---|---|
| Azure | not allowed (smallest is /29) |
| Google Cloud | not allowed (smallest is /29) |
| Oracle Cloud | 1 usable |
Limits and reserved counts are commonly documented values; check your provider's current documentation before you plan around them.
Other sizes
/16 | /22 | /23 | /24 | /25 | /26 | /27 | /28 | /29 | /30
Split a block into /30 subnets with the subnet splitter, or calculate any block with the CIDR calculator.
FAQ
How many usable IP addresses are in a /30?
2 usable addresses out of 4. The network and broadcast addresses are reserved.
What is the subnet mask for /30?
255.255.255.252, with wildcard mask 0.0.0.3.
How many usable addresses does a /30 have in AWS?
None: AWS does not allow a subnet smaller than /28.