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Should i do CCNA?

Discussion in 'General Cisco Certifications' started by MrNerdy, Jun 2, 2007.

  1. MrNerdy

    MrNerdy Megabyte Poster

    OK, not due to start CCNA until September, But i'm finding it very difficult learning Hex & Binary and Subnetting.
    Maths was never by strong point & after not doing much in over 20 years i'm starting to panic a bit!!!!

    I had thought of instead doing MCP then CCNA at a later date may be in 2008/09.
    I'm i panicking over nothing?
    Any advice most welcome.
    Certifications: ECDL, CiscoIT1 & A+
    WIP: Girlfriend & Network+
  2. dmarsh

    dmarsh Terabyte Poster

    I would say you are panicking over nothing.

    Hex and Binary conversions and arithmetic is taught in GCSE computer science. I admit it takes a little practice and I myself have had my dumb moments, you should be able to pick it up with a couple of good basic computer science books and a few weeks of study. Its really the eqivalent of normal arithmetic which we all seem to manage and is hardly advanced math.

    If you get stuck post a question on this forum !
  3. dmarsh

    dmarsh Terabyte Poster

    Many people create mental blocks for themselves that prevent them from learning.
    Just forget its math for a moment.

    When I was at primary school they explained basic number concepts, ie what is a unit, what is tens, what is hundreds, they
    had these wooden blocks designed to show what that many units looked like. This was a pictorial demonstration of the decimal number system.
    The groupings which are all factors of 10 mapped to the columns of your number representation. ie 201 means two hundred and one because theres a 2 in the hundreds column and a 1 in the units column.

    Well when you move to a different number system alot of the same rules still apply, just now the columns go up in a different factor, 2 in the case of binary, 8 in the case of octal, 16 in the case of hexidecimal. Because we only have 10 arabic numerals to represent the decimal system we use a-f to represent 11-15 in hexidecimal.

    There will be alot of resources on the internet explaing all this, wikipedias always good as a start.

    What exactly would you say you are stuggling with most at the moment ?
  4. Headache

    Headache Gigabyte Poster

    I believe this was mentioned to you before:


    Go there, order the platinum pack - option 3 (costs less that 15 quid) watch the video and you'll be subnetting quite happily within a week.

    Certainly worked for me.
    Certifications: CCNA
  5. zimbo
    Honorary Member

    zimbo Petabyte Poster

    right there is nothing to it so here we go:

    binary as you im sure have figured can either be a 1 or 0 or in computing terms ON or OFF. Binary can only be 1s and 0s.


    Decimal Binary
    1 01
    2 10
    3 11
    4 100
    5 101
    6 110
    7 111
    8 1111

    now the secret from converting from decimal to binary is this

    128 64 32 16 8 4 2 1

    Its called sum of weights. Lets assume you want the decimal number 70 in binary:

    looking at our series we say whats the largest number we have that can go into 70? 64 so we put a 1 under the 64. We then subtract 64 from 70 and we left with 6. We say thats the next biggest number that can go into 6? 4! so we put a 1 under the 4 and subtract 4 from 6 and we left with 2. 2 is the number that does into 2 so a 1 under the 2 and we left with nothing when you subtract. So add them up 64+4+2=70
    We then put 0 under all the other numbers

    128 64 32 16 8 4 2 1
    1 1 1

    So number 70 in bnary is: 01000110


    is basically 0-9 and then the letters A-F

    Converting from binary to HEX is easy this way:

    I give you the number 01111011 and say convert it to HEX for me. This is what you do:

    You take the 8 bit number and split the number into 2 4-bit blocks (no matter how big the number in binary you should always have 4 bit numbers)

    So: 0111 and 1011

    Now like the binary there is a secret range for this: 8 4 2 1

    What you do is put the binary under these numbers so:

    8 4 2 1
    0 1 1 1
    What you do is where there is a 1 you add those numbers together so we have 7

    8 4 2 1
    1 0 1 1
    We have 11 here

    So our two numbers are 7 and 11.

    7 is a valid HEX number so 7 is the first number BUT 11 isnt because its 0-9 and then A-F so 11 is prepresented by the letter B

    So our above number is 7B

    Hope this helps! :biggrin
    Certifications: B.Sc, MCDST & MCSA
    WIP: M.Sc - Computer Forensics
  6. dmarsh

    dmarsh Terabyte Poster

    Like I said the colums are powers :

    therefore the coulmns base 2 will be :-

    column 1 - 2pow0 = 1
    column 2 - 2pow1 = 2
    column 3 - 2pow2 = 4
    column 4 - 2pow3 = 8

    get it its all going up in powers of 2, 2 squared, 2 cubed etc..

    So for four columns it goes 8, 4, 2, 1 a zero or one in that column indicates if we have that number just like in the decimal example.

    1 0001 = 1 in 1s column = 1
    2 0010 = 1 in 2s column = 2
    3 0011 = 1 and a 2(see above) 1+2 = 3
    4 0100 = 1 in 4s column = 4
    5 0101 = 4 + 1 = 5
    6 0110 = 4 + 2 = 6
    7 0111 = 4 + 2 + 1 = 7
    8 1000 = 1 in 8s column
    9 1001
    10 1010 thats as far as we need to go for basic decimal to binary conversion
    ... however
    15 1111 = 8+4+2+1 = 15 (not eight as described earlier !)

    Thats where the sum of weights comes from its the powers of two. For a binary 8 bit number we'd need these columns :-

    128 64 32 16 8 4 2 1

    Its like a big sieve. We wrote two hundred and one as 201 because when 'sieving' the number the biggest component we can take out first in decimal is two 100's, next component is one unit.

    The colums in decimal are factors of 10 eg. 1000, 100, 10, 1.

    Theres various tricks you can use in the various number systems, like crossing the nines in decimal etc.

    Well the example above (from zimbo) uses a shorthand octal arithmetic to perform the conversion then converts octal to hex, because the binary, octal, hex number systems all have a common factor of 2 these tricks work. In this case octal base 8 and hex base 16, so two octal digits are always one hexidecimal digit.

    Theres other factors around this topic you may like to learn like basic logic operations (NOT, AND, OR, XOR) as the subnetting uses bit masks I believe. We haven't covered many of the conversions possible, nor have we covered the actual arithmetic. We've only dealt with positive numbers, theres also signed numbers, fixed point numbers and floating point numbers. All this like I said I would expect a computer literate school leaver to know so it should be well within the limits of a networking professional although perhaps not used on a daily basis !
  7. dmarsh

    dmarsh Terabyte Poster

  8. tripwire45
    Honorary Member

    tripwire45 Zettabyte Poster

    Certifications: A+ and Network+
  9. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

    Blinding post Zimbo! - even i understood all that 8)
    Certifications: C&G Electronics - MCSA (W2K) MCSE (W2K)
  10. MrNerdy

    MrNerdy Megabyte Poster

    OK panic over, a few beers & back on track.
    Thanks for all the advice.:D
    Certifications: ECDL, CiscoIT1 & A+
    WIP: Girlfriend & Network+

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