Tips for subnetting quickly on exam day
NivSa · posted · 124 views
I can do subnetting but it takes me way too long. On the exam I'll have limited time. What shortcuts or methods do you use to subnet fast? I've heard of the "magic number" method but haven't tried it yet. Any tips for memorizing the common subnet sizes?
- The magic number method saved me. Subtract the interesting octet from 256, that's your block size. For a /26 (mask 255.255.255.192), the magic number is 256-192=64. So subnets start at .0, .64, .128, .192. Done in seconds. — 22maya2n2,
- I also memorize the powers of 2 table: /24=256 hosts, /25=128, /26=64, /27=32, /28=16, /29=8, /30=4, /31=2. Once you know that, you instantly know how many hosts and what the block size is. Makes everything way faster. — ben31833,
- Practice with the subnet calculator here on NetForge, then try without it. After doing 20-30 subnets with the calculator checking your work, you'll be fast enough for any exam. That's how I got comfortable with it. — Yaron,
- Just tried the magic number method on a few practice problems and it's SO much faster. 256 minus the subnet octet, count up in blocks. I was doing it the long binary way before, no wonder it took forever. Thank you! — NivSa,
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