Networks
by bfilmfan
You need to watch this on-line presentation for a beginner's overview of TCP/IP. It's free and if you pay attention, you should be able to subnet networks afterwards:
Learn To Subnet
http://www.learntosubnet.com/
Also I would recommend the rest of the presentations called Learn TCP/IP, which covers DNS and How the OSI model works:
Another great way to get into beginner networking is to get the Sybex CCNA book. It's written for the beginner and provides some great info.
A trick to subnet masking is that the masks always fall on the same numbers.
If you can memorize these numbers...
4 8 16 32 64 128 192 224 240 248 252
You can figure out any mask in your head.
128 192 224 240 248 252 are your masks for a class c address.
128 = 25 bit mask or 255.255.255.128
This means that your network address is divided by 128 bits. so 0 to 127 is one network and 128 to 255 is the second.
192 = 26 bit mask or 255.255.255.192
192 - 128 = 64
This means that your network address is divided by 64 bits. so 0 to 63 is one network, 64 to 127 is the second, 128 to 191 is the third and 192 to 255 is the forth.
Do you see a pattern here?
the next mask is 224. 244 = 27 bit mask or 255.255.255.224
224 - 192 = 32. Your networks are seperated by 32 bits.
*Note* you need a deeper understanding of your boradcast address and such before you go out making VLANs and assigning Gateways but this should show you that the math that most people seem to get hung up on is really quite simple. In fact you really never have to change the hexidecmal address to binary if you don't want to.
Also if you notice in a 25 bit mask (255.255.255.128) the last useable network is 128 - 255. in a 27 bit mask (255.255.255.224) the last is 224.
Hints like these should make VLSM easy. Post any questions you have and good luck!
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