Subnetting??

zenlakin

Just curious where a good place to start to learn subnetting would be? I have done a little but get stuck on some relatively easy stuff at time and want to get this weakness ironed out so it isn't an issue when I get to the point of taking the test. As far as what I am looking for, I figure I should just go back to the beginning and start from there. Thanks guys.

Webmaster

www.techexams.net/forums/viewtopic.php?t=7268

www.learntosubnet.com

rakem

also


www.subnettingquestions.com has some good questions.

Kaminsky

I've have just finished studying all of this and after many months visiting and revisiting subnetting I think I have finally cracked it and it should stick this time.

Five things that helped me to finally crack it:

1) Always keep in mind the class you are working with. Always!.. thats the key to remembering which octet the mask starts and how your subnets start to roll out.

2) Think in binary in the subnetting octets. It really is quicker funnily enough. Forget the tables and tricks.

3) Remember the "256-" rule.. You use it a lot. Remember the class and write down the mask in the class format. IE for a 172 address with mask of 255.255.240.0 you write [16.0] 172.x.16.0 to 172.x.31.255 (the 3rd octect increases by 16 for each subnet boundary) for 255.255.255.240 you write [0.16] 172.x.0.16 to 172.x.0.31 (the last octect increases by 16 for each subnet boundary). I found doing this stopped me getting confused with the boundary increments as they go up

4) Spend lots and lots of time on subnettingquestions.com working out why when you get a question wrong.

5) Forget about the binary "AND" nonesense. At the moment I think it is only used to calculate the beginning of the subnet the question's subnetted IP address is on. It's actually a lot quicker just to work it out with the "256-" rule and then do multiplication to where you need to get to in the subnet boundaries.

One final thing I am planning to do when I take my test to help me save as much time as possible on subnetting questions during the exam is do some quick maths as the start of the exam, quickly write down the following 3 tables for later lookup.

1) The subnet boundaries.. 128, 192, 224, 240, 248, 252, 254, 255

2) 2^ table (2, 4, 8 ... 32768,65536) numbered 1-16 to calculate subnets/hosts quicker.

3) 16 times table upto 256 to help with calculating boundaries. This will include 32, 64, etc boundaries.

These tables take less than a minute to write down and could be done during the exam intro I hope.

After subnetting classful addresses you lead straight into VLSM which I found to be tricky and the practice questions on it very time consuming and very very sneaky!

Biggest tip I can give you for this , bearing in mind I've only just finished it myself, is to have another little table you prepare before your exam starts that shows the ranges for the masks /25 .. /30 (/31 and /32 wouldn't give usable host addresses). EG /30 gives subnet, broadcast and 2 usable host addresses... perfect for either side of a WAN link...

VLSM looks really confusing but it does work out if you write down the actual ip addresses used and see where they are spread out across the devices you have assigned them too.

With VLSM though, I did keep having a niggling thought in the back of my mind when doing this which was "use NAT and use a 10 range address inside the whole private network.. just to stop all the mucking about" ... of course, your routing tables wouldn't thank you for it!

Hope that helps