/10 Subnet Mask ReferenceIPv4
A /10 quarters a /8, giving 4,194,304 addresses behind mask <code>255.192.0.0</code>. One particular /10 is a celebrity: <code>100.64.0.0/10</code>, the carrier-grade NAT range on which much of the world's mobile and broadband traffic begins life.
/10 facts at a glance
- Subnet mask
- 255.192.0.0
- Wildcard mask
- 0.63.255.255
- Binary mask
- 11111111.11000000.00000000.00000000
- Total addresses
- 4,194,304
- Usable hosts
- 4,194,302 (excludes network & broadcast)
- Block size
- 4,194,304 addresses (222)
- Typical role
- Large enterprise and carrier aggregation
Example /10 networks
Three consecutive /10 blocks, starting at the /10 boundary that contains 198.51.100.0:
| Network | Usable range | Usable hosts |
|---|---|---|
| 198.0.0.0/10 | 198.0.0.1 – 198.63.255.254 | 4,194,302 |
| 198.64.0.0/10 | 198.64.0.1 – 198.127.255.254 | 4,194,302 |
| 198.128.0.0/10 | 198.128.0.1 – 198.191.255.254 | 4,194,302 |
How to calculate a /10 mask
A /10 mask sets the first 10 bits of a 32-bit number to 1 and leaves the remaining 22 bits as 0. In binary that reads 11111111.11000000.00000000.00000000, which converts to dotted decimal 255.192.0.0. Each block covers a contiguous run of 222 = 4,194,304 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 0.63.255.255.
Where /10 is used
- Carrier-grade NAT subscriber addressing (RFC 6598 shared address space).
- Consumer mesh and VPN products that deliberately pick the 100.64.0.0/10 region to avoid clashing with RFC 1918 home ranges.
- Large internal segmentation where a /8 is excessive but a /11 feels tight.
RFC 6598 assigns 100.64.0.0/10, running 100.64.0.0 through 100.127.255.255, to carrier-grade NAT. Thousands of subscribers share these addresses, so they must stay off the public Internet and out of enterprise addressing plans.
Frequently asked questions
What is 100.64.0.0/10?
Shared address space for carrier-grade NAT, standardized in RFC 6598. ISPs translate subscriber traffic from these addresses onto public IPs at the network edge.
What is the subnet mask for a /10?
<code>255.192.0.0</code>, wildcard <code>0.63.255.255</code>: ten fixed bits and twenty-two host bits.
How many addresses are in a /10?
4,194,304 total and 4,194,302 usable by convention.
Should I use 100.64.x.x addresses inside my company?
Best avoided. Standards reserve the range for ISP CGNAT, and remote users behind mobile carriers already source traffic from it, which invites confusing overlaps.
Open this block in a calculator
Open the /10 block in the subnet calculator