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/21 subnet mask
A /21 block has 2,048 addresses with the netmask 255.255.248.0.
255.255.248.0| CIDR notation | /21 |
| Netmask | 255.255.248.0 |
| Wildcard mask | 0.0.7.255 |
| Total addresses | 2,048 |
| Usable hosts | 2,046 |
| Usable in an AWS subnet | 2,043 |
| Example range | 10.0.0.0/21: 10.0.0.0 to 10.0.7.255 |
How /21 fits with other sizes
- A /8 holds 8,192 subnets of /21.
- A /16 holds 32 subnets of /21.
- A /20 holds 2 subnets of /21.
- It splits into 2 subnets of /22.
- It splits into 4 subnets of /23.
- It splits into 16 subnets of /25.