Subnet Mask
/27 Subnet Mask
A /27 prefix means the subnet mask is 255.255.255.224. It has 5 host bits, giving 32 total addresses and 30 usable hosts.
/27 at a glance
| Property | Value |
|---|---|
| CIDR prefix | /27 |
| Subnet mask | 255.255.255.224 |
| Wildcard mask | 0.0.0.31 |
| Total addresses | 32 |
| Usable hosts | 30 |
| Host bits | 5 |
How it is calculated
A /27 sets the first 27 bits to 1 (network) and the remaining 5 bits to 0 (host). Usable hosts = 25 − 2 = 30.
The wildcard mask 0.0.0.31 is the inverse — used in Cisco ACLs and OSPF network statements.
Frequently asked questions
What is a /27 subnet mask?
A /27 equals 255.255.255.224 in dotted decimal (wildcard 0.0.0.31). It provides 32 total addresses and 30 usable hosts.
How many hosts are in a /27?
A /27 has 5 host bits, so it supports 30 usable hosts.
What is the wildcard mask for /27?
The wildcard (inverse) mask for /27 is 0.0.0.31, used in Cisco ACLs and OSPF statements.
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