A subnet mask is always 32 bits long, just like an IP address. Its binary representation is unique because it always consists of a sequence of continuous 1s followed by a sequence of continuous 0s.
In the experiment you are currently performing, you are using a /26 subnet mask. Here is how that looks in binary:
1. The CIDR Notation (/26)
The number 26 simply tells you there are twenty-six 1s in a row.
2. The Binary Breakdown
If we write out 32 bits and make the first 26 of them 1 and the rest 0, we get:
11111111.11111111.11111111.11000000
3. Converting to Decimal (Dotted Quad)
To get the decimal version (255.255.255.192) used in your Python script, we convert each 8-bit group (octet):
11111111= 25511111111= 25511111111= 25511000000= 192 (128 + 64)
Common Examples:
| CIDR | Binary Representation | Decimal Mask |
|---|---|---|
| /8 | 11111111.00000000.00000000.00000000 |
255.0.0.0 |
| /16 | 11111111.11111111.00000000.00000000 |
255.255.0.0 |
| /24 | 11111111.11111111.11111111.00000000 |
255.255.255.0 |
| /26 | 11111111.11111111.11111111.11000000 |
255.255.255.192 |
Why binary matters:
The computer performs the bitwise AND operation bit-by-bit. Wherever there is a 1 in the mask, the computer "keeps" the original IP bit (Network portion). Wherever there is a 0, the computer "ignores" the bit by turning it into a 0 (Host portion).
You can see this in action by running your network_calc.py script; it calculates the result of this binary interaction for you
