Subnetting - a few bits and bobs i dont understand

[Bigjakkstaffa]

I'm not asking for help with homework here, namely because this isnt strictly homework, however im currently in the process of learning about Subnetting, workign through a few workbooks and things and i've hit a couple of stumbling blocks:

1) How can you calculate a hosts network address using its IP Address and Subnet mask? I know how to do this myself, but im having real difficulty explaining it to someone else, and was wondering if theres some kind of formula to it?

2) If all 0 and all 1 subnet-network addresses are invalid, what boundary would be used ot subnet a class C network, giving the maximum number of hosts?

I havent got the foggiest on how to work that one out, and help woudl be much appreciated

Cheers

--Jakk:t

[Baddog]

http://articles.techrepublic.com.com/5100-1035_11-5778292.html :t

[bruceb]

Use this free utility

http://www.wildpackets.com/products/free_utilities/ipsubnetcalc/overview

[bruceb]

Attached is a program from Wildpackets.com
Network Calculator .. very versatile .. read text file

It is freeware, but they normally ask you to fill out
a small form to download it

[Midknyte]

the NM separates the networks and hosts. you basically count how many bits are allocated for networks versus hosts. 255 = 2^7 + 2^6 + ..... + 2^0.

let's say you have a 255.255.255.240 SM.

240 = 2^7 + 2^6 + 2^5 + 2^4, so that's 4 bits for networks and 4 for hosts. the number of networks is 2^nbits. so 2^4 is 16 networks. hosts are 2^hbits-2 because you have to take out the network id and broadcast id. So each network has (2^4)-2 hosts, which is 14.

you can use this online calculator: http://www.cotse.com/networkcalculator.html