Help with wildcard masks

Does anyone have any tips for find wildcard masks? This is giving some trouble, especially when dealing with multiple c-blocks or multiple b-blocks.

Could someone post a method and a few examples?

TIA

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Comments

blackninja

It's really easy to find the wild card mask, just flip the bits of the subnet mask;

subnet mask
255.255.255.0
11111111 11111111 11111111 00000000

wildcard mask
0.0.0.255
00000000 00000000 00000000 11111111

subnet mask
255.255.240.0
11111111 11111111 11110000 00000000

wildcard mask
0.0.15.255
00000000 00000000 00001111 11111111

or a trick is to minus the mask against 255:

255.255.240.0

255 - 255 = 0
255 - 255 = 0
255 - 240 = 15
255 - 0 = 255

0.0.15.255

Simples

peanutnoggin

blackninja wrote: »

or a trick is to minus the mask against 255:

255.255.240.0

255 - 255 = 0
255 - 255 = 0
255 - 240 = 15
255 - 0 = 255

0.0.15.255

Subtracting the mask from all 255's is the easiest way in my opinion. Good explanation blackninja.

abefroman

That's easy enough.

Thanks!

thehourman

What exactly is wildcard mask?
As far as I know it is a amount of bits between subnet bits and host bits. Am I right?

steve514

A wildcard mask is the number of bits that indicate what part of an ip address can automatically assume any value. A wildcard mask is really just the subnet mask with the ones and zeros inverted to create the wildcard mask. An example of this would be a wildcard mask of 0.0.0.255, which corresponds to the subnet mask of 255.255.255.0. Hope this helps!

thehourman

So it is like changing all 1s into 0s and all 0s into 1s?

steve514

For the most part - yes