Subnetting question time

MAC_AddyMAC_Addy Member Posts: 1,740 ■■■■□□□□□□
I often find myself questioning my ability to subnet. However, when asking questions on - Free Subnetting Questions and Answers Randomly Generated Online I have found that I can calculate and answer (correctly) within about 2 - 3 minutes per question. I just took 20 questions and got them all correct (woot!). Just wondering if that's quick enough for the test?

What's funny is that I have taken ICND 1 & 2 before, and I still find myself questioning my time to answer these questions.

The thing that usually takes me the longest is calculating the block sizes. For example, block size of 8 - just writing down by hand the increments. What I did on ICND 1 is write down on the sheet my increment sizes before I even started the test. So 8 16 24 32 40, blah blah. That just takes a bit of time. Time that can be spend before even hitting "start". Plus, writing down the increments may get rid of the pre-test jitters.

Anyone else have anything they can chime in for myself, or any future test-takers?
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  • Jon_CiscoJon_Cisco Member Posts: 1,772 ■■■■■■■■□□
    I used that site a lot. Subnetting to me is all about practice.

    I also put filled out a little subnetting chart on my scrap paper. I didn't actually need to refer to it but if I got stuck it was there for quick confirmation. I also used Ciscos free binary game on my phone to practice converting quickly.
  • mikeybinecmikeybinec Member Posts: 484 ■■■□□□□□□□
    Using Mikey's block size method (you must memorize the block sizes) you should be able to subnet in 45 seconds (get the subnet id, get the broadcast, and the range)
    Cisco NetAcad Cuyamaca College
    A.S. LAN Management 2010 Grossmont College
    B.S. I.T. Management 2013 National University
  • dontstopdontstop Member Posts: 579 ■■■■□□□□□□
    Generally if it's a number that I don't know off the top of my head I'll just try and find the closest multiple by doing some quick math. For instance with an address 222 and a block size of 16, I'd try and find a multiple that would get me in the ballpark of 222 and then add on from there.

    16 * 4 = 64
    64 * 3 = 192
    192 + 16 = 208... and so on.

    Generally I find this the case only for block sizes of 8 or 16. Generally other block sizes I can do in my head. Does anyone have a faster method? I think for the exam I would write out my 8's and 16's and leave the rest as I can very quickly determine them.

    Found this old post from mikey and it's pretty much what I've explained above but he's done in a lot fewer words ;)
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