Subnet Mask
/30 Subnet Mask
A /30 prefix means the subnet mask is 255.255.255.252. It has 2 host bits, giving 4 total addresses and 2 usable hosts.
/30 at a glance
| Property | Value |
|---|---|
| CIDR prefix | /30 |
| Subnet mask | 255.255.255.252 |
| Wildcard mask | 0.0.0.3 |
| Total addresses | 4 |
| Usable hosts | 2 |
| Host bits | 2 |
How it is calculated
A /30 sets the first 30 bits to 1 (network) and the remaining 2 bits to 0 (host). Usable hosts = 22 − 2 = 2.
The wildcard mask 0.0.0.3 is the inverse — used in Cisco ACLs and OSPF network statements.
Frequently asked questions
What is a /30 subnet mask?
A /30 equals 255.255.255.252 in dotted decimal (wildcard 0.0.0.3). It provides 4 total addresses and 2 usable hosts.
How many hosts are in a /30?
A /30 has 2 host bits, so it supports 2 usable hosts.
What is the wildcard mask for /30?
The wildcard (inverse) mask for /30 is 0.0.0.3, used in Cisco ACLs and OSPF statements.
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