Subnet trick...

PCHoldmannPCHoldmann Member Posts: 450
This is good for Cisco exams, and work, if you ever need to figure out subnets on paper.

To figure out the valid addresses in a subnet:
Take the octet that is not 0 or 255 and subtract that value from 256 - i.e. 256 - 224 = 32. Now make a chart starting at 0, and adding the value from that last step with each line (the note board I got for the CCNA had gridlines, which made it even easier)

Now, leaving room in between, write on each line the value of the line below, minus 1
  0		31
 32		63
 64		95
 96		127
128		159
160		191
192		223
224		255
The values on the left are the valid subnet addresses, and the right is the broadcast address.

If you want, now fill in the valid ranges in between
  0	1-30		31
 32	33-62		63
 64	63-94		95
 96	97-126		127
128	127-158		159
160	161-190		191
192	192-222		223
224	225-254		255
There you go, all your addresses, with subnet and broadcast addresses.

(Sorry for the formatting) :)
There's no place like ^$
Visit me at Route, Switch, Blog


  • Fu LoserFu Loser Member Posts: 123
    Thats the most simple explanation for that trick I have seen!

  • ThanatosKnightThanatosKnight Member Posts: 33 ■■□□□□□□□□
    Can I ask you what kind of practice tests you did for the exam ?

    I'm currently doing the netsim labs included in the cisco press books(wendell odom) , I also did the cisco press simulation exams (intro cd e icnd cd) and some questions on the trascender demo .

    Thanks a lot
  • PCHoldmannPCHoldmann Member Posts: 450
    I used the same Cisco press tests, and also the PrepLogic tests that came with the ExamCram2 book, along with the practices on CCNA test is based on the last version, but still help). And used the practices on this site, of course! I also looked around on the internet for demo, but I don't remeber which ones I found. I like the Cisco Press ones, but I warn you the sims are more involved on the test!


    There's no place like ^$
    Visit me at Route, Switch, Blog
  • Sulblk27Sulblk27 Member Posts: 148
    Thanks for the new way of lookking at subnetting....just when I think I had it down cold- I wind up stumbling over the process of getting the right subnets! icon_redface.gif

    I am looking to purchase the cisco press learning kit, are there any other simulators I can get that would be comparable to the test sims?
    Thanks in advance
    Someone asked me when will my studying be over......
  • ThanatosKnightThanatosKnight Member Posts: 33 ■■□□□□□□□□
    Infact , I'm doin' the boson router netsim labs (learnig edition), because the sims on the cisco press tests are not difficult .

    The labs are well done ... Infact , It's possible to do some troubleshooting
    and the configurations are related to different network devices ... So you have to do the things with all in your mind and when everything works it gives you a lot of satisfaction... Isn't It ?

    Thanatos :D
  • rconsolerconsole Member Posts: 2 ■□□□□□□□□□
    You may also try RouterConsole simulator; I believe the free version can be useful for any CCNA candidate.

    Good luck!
  • RigsVilleRigsVille Member Posts: 2 ■□□□□□□□□□
    Thankd for the info - I've been told this technique before but never fully understood it, now I do!

    Thanks for the posting.

    -- Rig
  • Promedia-77Promedia-77 Member Posts: 4 ■□□□□□□□□□
    That is a nice trick , although it is very old to be honest, with all due respect. You guys should check your cds you get with your ccna books. And for the CCNA exam, you need to be really fast on your IP questions. Know all the magic numbers as well, you only have about 1 minute and 30 seconds for each question.
  • medicmedic CCNA, A+, Network+, Security+, Project+ Member Posts: 116 ■■■□□□□□□□
    Magic numbers?
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