The /26 prefix means the first 26 bits of the address identify the network and the remaining 6 identify the host. Written out, the mask is 255.255.255.192, in binary 11111111.11111111.11111111.11000000, and its Cisco wildcard or inverse form is 0.0.0.63. It covers 64 addresses, of which 62 can be given to hosts.
| CIDR prefix | /26 |
|---|---|
| Subnet mask | 255.255.255.192 |
| Mask in binary | 11111111.11111111.11111111.11000000 |
| Wildcard (inverse) mask | 0.0.0.63 |
| Host bits | 6 |
| Total addresses | 64 |
| Usable hosts | 62 |
| Block size (magic number) | 64 in octet 4 |
A 192.168.1.0/24 splits into exactly 4 subnets of this size.
| Network | First host | Last host | Broadcast |
|---|---|---|---|
| 192.168.1.0/26 | 192.168.1.1 | 192.168.1.62 | 192.168.1.63 |
| 192.168.1.64/26 | 192.168.1.65 | 192.168.1.126 | 192.168.1.127 |
| 192.168.1.128/26 | 192.168.1.129 | 192.168.1.190 | 192.168.1.191 |
| 192.168.1.192/26 | 192.168.1.193 | 192.168.1.254 | 192.168.1.255 |
Take the interesting octet of the mask, the one that is neither 255 nor 0. For /26 that is 192 in octet 4. Subtract it from 256:
256 - 192 = 64
That is the block size. Every /26 network address is a multiple of 64 in octet 4, so you can list them by counting: 0, 64, 128, 192, and so on. No binary needed once you know the number.
A /26 gives 62 usable addresses, four to a /24. It is the workhorse of departmental addressing: one floor, one team, one small office. Big enough that nobody complains, small enough that a /24 covers four of them.
A /26 holds 64 addresses in total. After reserving the network and broadcast addresses, 62 are usable by hosts.
The /26 subnet mask is 255.255.255.192 in dotted-decimal notation.
The wildcard mask, also called the inverse mask, is 0.0.0.63. It is the bitwise inverse of 255.255.255.192 and is what Cisco access lists and OSPF network statements expect.
The /26 mask written out bit by bit is 11111111.11111111.11111111.11000000: 26 ones followed by 6 zeros.
A /24 splits into 4 subnets of /26.