Subnetting Questions

[dales]

Hi all,

Just thought I'd share with you this site I stumbled on. Its a subnetting quiz and I've gone through at least 20 questions. Its been a great help in teaching me to subnet correctly as you can keep going though the questions until you get it right constantly. I dont know how many questions there are in total.

stinky linky

[Finkenstein]

That's pretty cool, thanks. I had a fun little bit of practice with doing these in my head. I'm getting better!

[christ69]

Nice find.....great for practice.....definately need to refresh from time to time.

[kevicho]

Thanks for this, useful to keep the old brain ticking, for me i do practice tests to stop me making silly mistakes on the proper exams.

Bit of note here

clicked the advanced subnetting bit, and it gived cidr numbers and hex netmasks as well.

CIDR is pretty simple, that is how many 1's you have in your netmask (starting from the left obviously)

The hex netmask is different and will try to explain as follows (for those not in the know)#

hexadecimal is a base 16 system, humans work in base 10 (read it was to do with how many fingers we have and thats how we started to count) and computers in base 2 (1s and 0s - or could be considered yes / no), so this sytem goes from 1 to 9, when it gets to 9 it can still continue, but uses letters instead of numbers, basically from a to f
where
a=10
b=11
c=12
d=13
e=14
f=15

Once we count 16, we say it is 10 (=16) 11 is 17 and so on), then we o through the letters, so 1F for example is 31.
So in binary these values are
8=8 1000
9=9 1001
a=10 1010
b=11 1011
c=12 1100
d=13 1101
e=14 1110
f=15 1111


However this is not what is important, what we need to do with is the following:

We now there are 8 bits in a an octet, and for each octet, 2 letters/numbers are used to represent it.

We also know that the binary for 15 is 1111

so f2 is 11110010
and
fe is 11111110

Can you see the pattern yet?

So for these questions we break the netmask into 4 sections, and then convert the hex to binary (via decimal if you need to), so for (h)example

0xff000000

we break into twos

0x ff 00 00 00

ff is 255, so we get 11111111

or simpler

f is 1111 so we double it

and all the rest are 0's, so i picked an easy one there, but the subnet mask is 255.0.0.0

is we had

0xfffffffc we could

0x ff ff ff fc
1111 1111 1111 1111 1111 1111 1111 1010 = 255.255.255.248

and so on

Hope this helps someone, took me a short while to figure out.

[Tinus1959]

Nice find, Thanks!