/11 Subnet Mask
A /11 prefix means the subnet mask is 255.224.0.0. It has 21 host bits, giving 2,097,152 total addresses and 2,097,150 usable hosts.
/11 at a glance
| Property | Value |
|---|---|
| CIDR prefix | /11 |
| Subnet mask | 255.224.0.0 |
| Wildcard mask | 0.31.255.255 |
| Total addresses | 2,097,152 |
| Usable hosts | 2,097,150 |
| Host bits | 21 |
How it is calculated
A /11 sets the first 11 bits to 1 (network) and the remaining 21 bits to 0 (host). Usable hosts = 221 − 2 = 2,097,150.
The wildcard mask 0.31.255.255 is the inverse — used in Cisco ACLs and OSPF network statements.
Frequently asked questions
What is a /11 subnet mask?
A /11 equals 255.224.0.0 in dotted decimal (wildcard 0.31.255.255). It provides 2,097,152 total addresses and 2,097,150 usable hosts.
How many hosts are in a /11?
A /11 has 21 host bits, so it supports 2,097,150 usable hosts.
What is the wildcard mask for /11?
The wildcard (inverse) mask for /11 is 0.31.255.255, used in Cisco ACLs and OSPF statements.
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