Subnet Masking

[Scarecrow Man]

I need help with Subnetting. If anyone has good links to info for Subnetting, VLSM (Variable Length Subnet Masking) or any other subnet info please post. It would be very much appreciated.

P.S. CIDR (Classless Inter-Domain Routing) Subnetting preferred but I also would like some Classfull info.

[homecomputeraid]

Hi Scarecrow Man,

You can download a free subnet calculator here:

http://www.solarwinds.net/Tools/Free_tools/Subnet_Calc/

Here's a subnetting tutoial:

http://www.ralphb.net/IPSubnet/

May I ask what your interest in subnetting is? I may be able to provide further resources if you're studying for a Cisco exam or something.

[Scarecrow Man]

Thanks Ted,

I am currently enrolled in Cisco CCNA semester 3, and studying in School.

I am still a bit fuzzy on the subnetting. I have read the tutorial from ralphb.net and while it had some good info, it was not quite in depth enough for the level I am at now.

Basically I am working through problems that require me to take an IP address, such as 140.16.0.0 /20 and subnet it into 4 subnets, and then make subnets inside those subnets.

I am OK with it in the classroom and can follow along with the professor, but when it comes time to take it home and continue from where I left off for some reason I am completely lost.

http://www.subnetmask.info is also a useful network calculator.

[Scarecrow Man]

Here is an example of my first assignment.

Oh, and the Advanced Subnet Calculator is amazing! Thanks a lot Ted.

VLSM_Activity_1_1.doc

[homecomputeraid]

You're welcome for the calculator Scarecrow Man.

I'm not sure how to explain it. I know for the CCNA Exam, and in the classroom, you'll probably be prohibited from using a subnet calculator. It sounds like you're trying to learn how to use route aggregation and summarization to keep the size of the routing tables down. You'll have a campus that has an entire subnet, then a building that has a number of bits, then a floor in that building that has a number of bits, etc. You'll have to take care to have give each building enough bits to account for all its floors and hosts, and to have all the subnets for the floors 'inside' its own subnet.

Do you understand AND'ing, and how to tell how many subnets per mask, and hosts per subnet will result from using a given number of bits?

Unfortunately, although I know how to do it, I don't find it easy to explain to others. I'll see what I can find on the Internet. In studying for your CCNA exam, it's well worth it in my opinion to get a practice exam like those available from Boson: http://www.boson.com/. I also use Sybex and Cisco Press books in studying.

[Scarecrow Man]

Thanks HCA.

That is good info, and yes I know about AND'ing.

I also use Boson software.

I will just keep plugging away at it, thanks for the info. It helped more than you know! :P