Variable subnet mask addressing

radionic

Hi, I am new to this site and am not sure about the rules. I am a student preparing for the CCNA exam using the Sybex Study Guide. Am finding the book overal good but also found a huge gap with regards class B and A networks. The shows a very quick way to subnet class C networks by memorisisng the following table.


Prefix mask usable host block size
/26 192 62 64
/27 224 30 32
/28 240 14 16
/29 248 6 8
/30 252 2 4
/31 254 1 2
/32 255 0 1


But I need someone to help me extend this table for class B and A. I.e. mask for /24 prefix and block size.


I thank you in advance for your support.

SS

johnnynodough

Best way to extend your tables is to learn how to do it

Seriuosly, once you learn how to do it you will not forget it, tables that you have memorized can be easily forgotten, but the methods to do it are much harder to lose. Some people have had luck with www.learntosubnet.com ; I have not. Some got it from Wendell Odem's CCNA book: I didnt. Some got it from Todd Lamelle's Sybex CCNA book, I didnt. I payed 10 bucks and bought this PDF - http://www.thebryantadvantage.com/TheBryantAdvantageMasterySeries.html
And got it easily in days. Its the approach he uses that helped me, more of an eastern method, you achieve the results before you realize you got them, that way you get the intimidation out of the way.

Good Luck, its mostly downhill after VLSM, with a few peaks along the way.

johnnynodough

There really should be a sticky about VLSM on this board