Subnetting Question

tech12

I have been practicing a few of these different questions and I got stuck on this one. I'm not exactly sure how the valid host starts at 57.


What valid host range is the ip address 192.168.219.62
SNM: 255.255.255.248 a part of?

answer: 192.168.219.57 - 192.168.219.62

Can someone explain how we got to .57? greatly appreciated.

spd3432

Magic number is 8 ( 256 - 248 ). (Sub)Network numbers will be on multiples of 8 (0 8 16 24 32 40 48 56 64 ...) .62 will fall onto the .56 subnet, therefore the first usable number is .57 with the last usable number .62 with .63 being the broadcast address.

miller811

Check out this thread.... which should be a sticky

http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html

tech12

thanks for the response! I will have a look at the thread. i really want to get my head around this.

I know this might vary from person to person but how long should it take someone to do these type of questions?

jtdk985

less than a minute each should be fine, but you will start to get them in about 30 seconds after doing them.

subnettingquestions.com - Free Subnetting Questions and Answers Randomly Generated Online

give yourself 30minutes a day for about a week on that website doing questions, even time yourself if you can, and you will get better. its really more memorization than calculation when you start getting fast. you will see repeating numbers and be able to call them out very fast

tech12

Thanks Jtdk985! Yeah I have been looking at that site. In fact that's where my question came from Guess I have quite a bit of work to do!

mella060

tech12 wrote: »

i really want to get my head around this.

I know this might vary from person to person but how long should it take someone to do these type of questions?

Remember, subnetting takes time. It took me around 3-4 weeks of solid practice to really master it. Once you can work out problems in your head in less then 30 seconds then you are on the right track.

Remember to write it all down on paper to start with. Really helps to make it stick in your brain. I went through the subnetting chapter in Todd Lammles CCNA book and did the exercises again and again until i got it. Key is to write it all down on paper, bit by bit. Do that until you can just work it out in your head.

I would focus more on the formulas and how it all works before just doing random questions. Learn the math and how and why you get certain numbers. In the beginning it should be more about calculation then memorization.

ccnxjr

Almost daily for about 3-4 weeks I'd write out all the networks for various subnet masks, mostly 4th octect masks /24 through /30
you can stare at the tables, but i think you will remember it faster (and more reliably) if you do the calculations, that way if you do have a brain freeze, you can bank on your "muscle memory" to calculate out the right subnet #'s and networks.

Your training materials should provide techniques for making this easier however it all boils down to the binary operations.

Back to your original question, lets look at the mask 255.255.255.248 , the interesting number is 248, lets take a look at the binary
255.255.255.1111 1000
The mask tells us which portion of the IPv4 address will be used for identifying the network.
Based on the mask, we observe that there are 3 bits available for hosts, or 8 possible values: 000 through 111.
The null value in the "host" portion will leave us with the network number, whereas all 1's in the host portion will give us the broadcast number for that particular network. Therefore we do not use those numbers in the VALID host range, so we subtract 2 (the broadcast value and null value) from the possible value of 8 to give us 6 valid hosts, 001 through 110


now the ip address
192.168.219.62 , lets convert the fourth octect to binary:
192.168.219. 0011 1110
so lets AND the mask and ip address to get the network#
255.255.255.1111 1000 AND
192.168.219.0011 1110
will give us
192.168.219.0011 1000
in decimal: 192.168.219.56
So we have the network 192.168.219.56
Back to binary,
The network we're looking at now is 192.168.219.0011 1000 or 192.168.219.56
So the first host will be 192.168.219.0011 1001 or 192.168.219.57
The broadcast address is 192.168.219.0011 1111 or 192.168.219.63
Therefore the last valid host address is 192.168.219.0011 1110 or 192.168.219.62

It's easier to see the relationships in binary, but as techies we need to find a simpler way of expressing it in people speak :P

tech12

Thank you so ccnxjr, I truely appreciate that explanation as I now understand how that value was in the answer. Trust me, right about now i need all of the explaining i can get when it comes to this. The concept is coming slowly but surely. I have all of my masks and binary equivelents memorized but moreso i understand why they are the way they are. Thanks to everyone for your help!

sentimetal

tech12 wrote: »

Thank you so ccnxjr, I truely appreciate that explanation as I now understand how that value was in the answer. Trust me, right about now i need all of the explaining i can get when it comes to this. The concept is coming slowly but surely. I have all of my masks and binary equivelents memorized but moreso i understand why they are the way they are. Thanks to everyone for your help!

I was where you are now three months ago - you'll get it, believe me. Don't give up and subnetting will click as long as you keep at it. I can do it in my head so easily now.

tech12

Thank you, sentimetal for your encouragement. It's pretty frustrating when your learning on your own with all this material and some of it you get some of it you don't. Im to the point where its like what is it going to take for me to understand (i know practice but i feel like im doing everything wrong) all of the types of subnetting questions. Well, back to the drawing board it is.

gouki2005

miller811 wrote: »

Check out this thread.... which should be a sticky

http://www.techexams.net/forums/ccna-ccent/38772-subnetting-made-easy.html

yes i know this the method i use .