Subnetting Notes


Boolean Logic

0 AND 0 = 0
0 AND 1 = 0
1 AND 0 = 0
1 AND 1 = 1

0 OR 0 = 0
0 OR 1 = 1
1 OR 0 = 1
1 OR 1 = 1

Useful Graph

This graph helps me reduce the number of errors I make while answering subnettting questions on exams. I typically draw it as I sit down to an exam and then use it as a reference while checking my work before submitting an answer.

Find the column with the corresponding prefix bits as the practice question you are working on and then pay attention to how that correlates to the “Magic number” and “Subnet mask” rows.

Magic number 128 64 32 16 8 4 2 1
Prefix bits 1 2 3 4 5 6 7 8
Prefix bits 9 10 11 12 13 14 15 16
Prefix bits 17 18 19 20 21 22 23 24
Prefix bits 25 26 27 28 29 30 31 32
Subnet mask 128 192 224 240 248 252 254 255

Thanks to Steve on networking-forum.com

One thought on “Subnetting Notes

  1. Pingback: Subneting practice | Syr21

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