/21 Subnet
Subnet Mask
255.255.248.0
Wildcard Mask
0.0.7.255
Total IPs
2,048
Usable Hosts
2,046
Network Bits
21
Host Bits
11
About /21 Networks
Medium subnet — multi-floor office or building. A /21 subnet uses the mask 255.255.248.0 and provides 2,046 usable host addresses out of 2,048 total IPs.
Example /21 Networks
| Network | Broadcast | First Host | Last Host |
|---|---|---|---|
| 10.0.0.0/21 | 10.0.7.255 | 10.0.0.1 | 10.0.7.254 |
| 172.16.0.0/21 | 172.16.7.255 | 172.16.0.1 | 172.16.7.254 |
| 192.168.0.0/21 | 192.168.7.255 | 192.168.0.1 | 192.168.7.254 |
| 192.168.0.0/21 | 192.168.7.255 | 192.168.0.1 | 192.168.7.254 |
| 8.8.8.0/21 | 8.8.15.255 | 8.8.8.1 | 8.8.15.254 |
Adjacent CIDRs
Frequently Asked Questions
What is a /21 subnet?
A /21 subnet uses the subnet mask 255.255.248.0 with 2,046 usable host addresses and 2,048 total IP addresses. It has 21 network bits and 11 host bits.
How many hosts in a /21 network?
A /21 network supports 2,046 usable hosts out of 2,048 total IP addresses. The usable range excludes the network address and broadcast address.
What subnet mask does /21 use?
A /21 subnet uses the mask 255.255.248.0 (wildcard mask 0.0.7.255). This means the first 21 bits identify the network and the remaining 11 bits identify hosts.