Newbie !! Subnets Very Confusing...

[HelpfromU]

Hi experts.

Read the rules about posting. I m sorry . I bought TCP/IP Unleashed to learn about TCP/IP. Printed some material from internet. From the last eight hours i m trying to get the subnets concept in my mind. I am fed up and will try again after a few days. Can someone point me some tips to help me calculate subnets outof a given IP address. Will sincerely appreciate every bit of information you will provide me .

Thanks

[Huckleberry]

RFC 791 (the definition of IP addressing) desired that any individual IP address would by definition, only reside in one IP network. To ensure this, they defined 1/2 of the IP address space would be class A addresses (~50%), 1/4 of the IP address space would be class B addresses (~25%), 1/8th of the IP address space would be class C addresses (~12.5%), and the remaining 1/8 (~12.5%) would be for miscellaneous uses like Multicast. This is how they chopped it up - using static-length subnet masks particular to each class. The resulting addresses ranges are roughly:
A: 1.0.0.0 - 126.0.0.0
B: 128.1.0.0 - 191.254.0.0
C: 192.0.1.0 - 223-255-254.0

Thus, given a particular IP address, you can determine the *original* network class the address belonged to.

This original method was nice and organized, but had one significant drawback: As an organization was forced to use a network of some particular size, there were many unused addresses, IOW lots of wasted IP address space. (for example, if my company had a need for 300 addresses, a class C network was too small. I could either get a second class C, or I could try to get a class B. In either case, there would be wasted [unused] addresses; either 208 wasted in the 2xC scenario, or 65,234 in the case of the class B scenario)

So, if somebody were to invent a more flexible way of allocating IP addresses, there would be less waste - hence the variable length subnet.

A variable length subnet allows you to take whatever network you have been given, and arbitrarily "chop it up." So, if your ISP had only 1 class C at its disposal, it could chop a little piece off of the end of its network and give to you.

For the specific methods of using the network mask and network address to determine the network base address and host number, I'll leave that up to your research.

Hope this helps.

[some of this material was taken from the following publication: "CCNA Exam Certification Guide," by Wendell Odom, Copyright 1999 Lacidar Unlimited, Inc.]

[HelpfromU]

thanks Huckleberry

[chuckerants]

This is why I dropped out of the TCP/IP class.

Good luck.

[engjohn]

read this page... it has really good info... You need to understand binary and network address to understand subnetting.


http://lantech.geekvenue.net/chucktips/jason/chuck/1022445898/index_html


Originally posted by HelpfromU
Hi experts.

Read the rules about posting. I m sorry . I bought TCP/IP Unleashed to learn about TCP/IP. Printed some material from internet. From the last eight hours i m trying to get the subnets concept in my mind. I am fed up and will try again after a few days. Can someone point me some tips to help me calculate subnets outof a given IP address. Will sincerely appreciate every bit of information you will provide me .

Thanks

[tbones1337]

Cicso class isnt that hard.. My buddies taking it.. and he still cant set-up a network correctly @ our lans.