/30 · 255.255.255.252
Open in the calculator
4 addresses, 2 usable. The traditional point-to-point link size between two routers: network, two hosts, broadcast. /31 does the same job with half the addresses.
Key numbers
| Prefix length | /30 (30 network bits, 2 host bits) |
| 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 (total minus network and broadcast) |
| Fits in a /24 | 64 times |
| Block size | Increments of 4 in octet 4 |
Example ranges
Private (RFC 1918) blocks of this size. Click one to open it in the calculator.
| Block | First address | Last address | Usable hosts |
|---|---|---|---|
| 10.0.0.0/30 | 10.0.0.0 | 10.0.0.3 | 10.0.0.1 – 10.0.0.2 |
| 172.16.0.0/30 | 172.16.0.0 | 172.16.0.3 | 172.16.0.1 – 172.16.0.2 |
| 192.168.0.0/30 | 192.168.0.0 | 192.168.0.3 | 192.168.0.1 – 192.168.0.2 |
Usable addresses in the cloud
Cloud providers reserve a few addresses in every subnet for the router, DNS and future use, so the usable count is lower than the formula gives.
| Provider | Usable in a /30 | Notes |
|---|---|---|
| AWS VPC subnet | n/a | Not allowed: AWS subnets must be between /16 and /28. |
| Azure virtual network subnet | n/a | Not allowed: /29 is the smallest Azure subnet. |
| Google Cloud subnet | n/a | Not allowed: /29 is the smallest primary range. |
How the numbers are derived
An IPv4 address has 32 bits. A /30 uses 30 of them for the network, leaving 2 host bits, so the block has 22 = 4 addresses. The first address (all host bits 0) is the network address and the last (all host bits 1) is the broadcast address, which leaves 2 for hosts. The subnet mask is 30 ones followed by 2 zeros, written in dotted decimal as 255.255.255.252; the wildcard mask 0.0.0.3 is its inverse, used in Cisco ACLs and OSPF configuration.
FAQ
How many hosts can a /30 have?
4 addresses in total, of which 2 are usable after removing the network and broadcast addresses. Cloud providers reserve a few more: -1 usable in AWS and Azure, 0 in Google Cloud.
How many /30 subnets fit in a /24?
64. A /24 has 256 addresses and a /30 has 4, so 256 ÷ 4 = 64 blocks.