Variable Length Subnet Masks... I'm having a breakdown lol.

mattipler

Just started semester 3 and the first module is variable length subnet masks. To say I'm struggling with it is an understatement. I just don't seem able to get it clear in my head. I struggled greatly with subnet masking but that's straight forward now. I just don't pick up anything that's remotely mathematic quickly. When I read on cisco-netacad.net the explanation within the module for them it seems to me that a degree in advanced mathematics is required to even stand a chance of understanding them fully. Anyway, being tested on it in a few days and I feel as though I'm screwed.
Don't know how putting a post on here is going to change anything but if someone has any advice I can't begin to express how grateful I'd be.

mp3spy

mattipler wrote:

Just started semester 3 and the first module is variable length subnet masks. To say I'm struggling with it is an understatement. I just don't seem able to get it clear in my head. I struggled greatly with subnet masking but that's straight forward now. I just don't pick up anything that's remotely mathematic quickly. When I read on cisco-netacad.net the explanation within the module for them it seems to me that a degree in advanced mathematics is required to even stand a chance of understanding them fully. Anyway, being tested on it in a few days and I feel as though I'm screwed.
Don't know how putting a post on here is going to change anything but if someone has any advice I can't begin to express how grateful I'd be.

I was in the same boat as you...Check out Todd Lammle's CCNA Fast Pass book...Check out Chapter 2. I read that chapter about three times and I know it pretty well now. Its not easy..you just need to practice!! Lammle gives excellent examples and I'm sure people will try and explain it to you the same way he wrote the chapter...I am sure one of the CCNAs or CCNPs will explain it better to you....

Good Luck...

DirtySouth

If you're a visual person, this diagram might help you understand VLSM better. It helped me to learn VLSM by writing all the subnets out on paper.
http://www.more.net/technical/netserv/tcpip/IP-VLSM-Diagram.html

kadshah

I read that chapter about three times

i read the chapter 5 times before understanding it. Don't beat yourself up it will sink in sooner or later.

steve-o87

mattipler wrote:
Just started semester 3 and the first module is variable length subnet masks. icon_cry.gif To say I'm struggling with it is an understatement. I just don't seem able to get it clear in my head. I struggled greatly with subnet masking but that's straight forward now. I just don't pick up anything that's remotely mathematic quickly. When I read on cisco-netacad.net the explanation within the module for them it seems to me that a degree in advanced mathematics is required to even stand a chance of understanding them fully. Anyway, being tested on it in a few days and I feel as though I'm screwed.
Don't know how putting a post on here is going to change anything but if someone has any advice I can't begin to express how grateful I'd be.


I was in the same boat as you...Check out Todd Lammle's CCNA Fast Pass book...Check out Chapter 2. I read that chapter about three times and I know it pretty well now. Its not easy..you just need to practice!! Lammle gives excellent examples and I'm sure people will try and explain it to you the same way he wrote the chapter...I am sure one of the CCNAs or CCNPs will explain it better to you....

Good Luck...

I agree! I didn't understand subnetting at all before picking up his book. At first you'll start writing them out on paper and eventually you can start doing them in your head

Hope all goes well

mattipler

Thanks for the replies guys. Don't suppose anyone knows anywhere I can get some VLSM questions to practice. Seen quite a few websites on here but they all seem to be subnetting and my subnetting is ok. I just don't understand logical side of VLSM... I understand the theory.

EdTheLad

mattipler wrote:

Thanks for the replies guys. Don't suppose anyone knows anywhere I can get some VLSM questions to practice. Seen quite a few websites on here but they all seem to be subnetting and my subnetting is ok. I just don't understand logical side of VLSM... I understand the theory.

If you understand subnetting you understand vlsm.Subneting is a way of dividing an ip major network number.So if i have an address space
10.5.5.0/24, this means i can use numbers 10.5.5.0 -> 10.5.5.255
If you subnet this to have imagine 14 hosts per subnet you will use 4 bits of subnetting, so the mask will be 255.255.255.240.
If you look at the subnetting you will have
10.5.5.0,16.32.48.....240

If you have a single ptp link between 2 routers it a shame to use the addresses 10.5.5.1/28 and 10.5.5.2/28 on both sides because the other 12 addresses that could be used on that subnet are wasted.
i.e 10.5.5.3 - > 10.5.5.14, if you used vlsm you could subnet the subnet
so instead of using the 10.5.5.1/28 you could break this subnet using a mask of /30 which will give subnets 10.5.5.0/30,10.5.5.4/30,10.5.5.8/30,10.5.5.12/30 all these new subnets fall inside the 10.5.5.0/28 range so they keep the address intergity.
Now on the ptp links you could use these /30 networks and on the lan segments you can use /28 subnets.As you can see the mask has varied from /28 to /30.What benifits have you received? On all ptp links you use only 4 numbers instead of 16, you have saved ip addresses.

mattipler

Thanks for your help guys! It clicked in the end! I think I was "over-thinking" about it all if that makes sense. Got 100% in the module exam.

We're doing OSPF routing protocol this week, module 2... read the full online chapter from start to finish today... took me 4 hours along with viewing the graphics etc. It's a hell of a lot to take in. But then I suppose they wouldn't pay people with CCNA's so well if it was a piece of piss now would they?

DirtySouth

mattipler wrote:

Thanks for your help guys! It clicked in the end! I think I was "over-thinking" about it all if that makes sense. Got 100% in the module exam.

We're doing OSPF routing protocol this week, module 2... read the full online chapter from start to finish today... took me 4 hours along with viewing the graphics etc. It's a hell of a lot to take in. But then I suppose they wouldn't pay people with CCNA's so well if it was a piece of piss now would they?

You must be right in line with what I'm doing. I'm in my 3rd semester on module three. We just finished up OSPF and are doing EIGRP now. Good Luck!

rakem

mattipler wrote:

Thanks for the replies guys. Don't suppose anyone knows anywhere I can get some VLSM questions to practice. Seen quite a few websites on here but they all seem to be subnetting and my subnetting is ok. I just don't understand logical side of VLSM... I understand the theory.

http://www.subnettingquestions.com/

NetworkGod

http://www.learntosubnet.com/ try that.. very good site

Danman32

It's like carving the roast beast. Some want thin slices, some want thicker ones. All of the slices, no matter how thin or thick, is a particular part of the whole roast.