/10 subnet mask: 255.192.0.0

The /10 prefix means the first 10 bits of the address identify the network and the remaining 22 identify the host. Written out, the mask is 255.192.0.0, in binary 11111111.11000000.00000000.00000000, and its Cisco wildcard or inverse form is 0.63.255.255. It covers 4,194,304 addresses, of which 4,194,302 can be given to hosts.

/10 at a glance

Every /10 inside 10.0.0.0/8

A 10.0.0.0/8 splits into exactly 4 subnets of this size.

The magic number for /10

Take the interesting octet of the mask, the one that is neither 255 nor 0. For /10 that is 192 in octet 2. Subtract it from 256:

256 - 192 = 64

That is the block size. Every /10 network address is a multiple of 64 in octet 2, so you can list them by counting: 0, 64, 128, 192, and so on. No binary needed once you know the number.

Where a /10 shows up in practice

The /10 has one famous occupant: 100.64.0.0/10, the shared address space reserved by RFC 6598 for carrier-grade NAT. If you see a device with a 100.64.x.x address, it is behind a provider's NAT and not on a normal private network. That single fact is most of what a /10 is for.

Frequently asked questions

How many hosts are in a /10?

A /10 holds 4,194,304 addresses in total. After reserving the network and broadcast addresses, 4,194,302 are usable by hosts.

What is the subnet mask for /10?

The /10 subnet mask is 255.192.0.0 in dotted-decimal notation.

What is the wildcard mask for /10?

The wildcard mask, also called the inverse mask, is 0.63.255.255. It is the bitwise inverse of 255.192.0.0 and is what Cisco access lists and OSPF network statements expect.

What is /10 in binary?

The /10 mask written out bit by bit is 11111111.11000000.00000000.00000000: 10 ones followed by 22 zeros.