The /30 subnet, explained
Everything about a /30 CIDR block — mask, address count, usable hosts and where a /30 fits in real network plans.
| Prefix length | /30 — 30 network bits, 2 host bits |
| Subnet mask | 255.255.255.252 |
| Wildcard (ACL) mask | 0.0.0.3 |
| Binary mask | 11111111.11111111.11111111.11111100 |
| Total addresses | 2^2 = 4 |
| Usable hosts | 2 (total − network − broadcast) |
| A /16 holds | 16,384 × /30 subnets |
| Example block | 192.168.1.0/30 |
Notes
A /30 prefix means the first 30 bits of the 32-bit IPv4 address identify the network and the remaining 2 bits identify hosts — giving 2^2 = 4 addresses. The first address (network) and the last (broadcast) are not assignable in a standard subnet.
Cloud sizing: too small for an AWS VPC (minimum /28 per VPC, /29 allowed for GCP subnets).
Adjacent sizes: /8 · /9 · /10 · /11 · /12 · /13 · /14 · /15 · /16 · /17 · /18 · /19 · /20 · /21 · /22 · /23 · /24 · /25 · /26 · /27 · /28 · /29 · /31 · /32
Frequently asked questions
How many IP addresses are in a /30?
4 total addresses, of which 2 are usable hosts (network and broadcast addresses are reserved).
What is the subnet mask for /30?
255.255.255.252 (wildcard mask 0.0.0.3).
What does /30 mean in an IP address?
The /30 suffix is CIDR notation: the first 30 bits are the network part, the last 2 bits are the host part.