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/31 subnet mask
A /31 block has 2 addresses with the netmask 255.255.255.254. Used for point-to-point links (RFC 3021), where both addresses are usable.
255.255.255.254| CIDR notation | /31 |
| Netmask | 255.255.255.254 |
| Wildcard mask | 0.0.0.1 |
| Total addresses | 2 |
| Usable hosts | 2 |
| Usable in an AWS subnet | n/a (AWS allows /16 to /28) |
| Example range | 10.0.0.0/31: 10.0.0.0 to 10.0.0.1 |
How /31 fits with other sizes
- A /8 holds 8,388,608 subnets of /31.
- A /16 holds 32,768 subnets of /31.
- A /20 holds 2,048 subnets of /31.
- A /24 holds 128 subnets of /31.
- It splits into 2 subnets of /32.