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Hi all, can anyone tell me how we work out what the wildcard mask is ?

cheers

3 REPLIES
Green

A simple method would be to subtract the subnet mask from 255.255.255.255

eg. if you need to know the wildcard mask for 255.255.255.240 then you can do

255.255.255.255 - 255.255.255.240 = 0.0.0.15

HTH, rate if it does

Narayan

Green

hi Carl,

Wildcard mask is a bit matcher which is the inverse logic of the subnet mask (a subnet mask of 255.255.255.252 corresponds to a wildcard of 0.0.0.3, just inverse the binary 1s to 0s and vice versa) -> 0 = match and 1 = ignore, accordingly a wildcard of 0.0.0.0 = host, since all bits must match , and 255.255.255.255 = any, since we don't care what any bit is.

HTH,

Mohammed Mahmoud.

Silver

Hi,

The wildcard mask is an "inverse mask", that is: bit 0 means "care" and bit 1 means "don't care".

An example of application is an access list:

access-list 100 deny 192.168.1.0 0.0.0.15

Conversion in binary

0.0.0.15 -> 00000000.00000000.00000000.00001111

192.168.1.0 -> 11000000.10101000.00000001.0000000

The interval of denied addresses is:

From 11000000.10101000.00000001.00000000 to 11000000.10101000.00000001.00001111

In decimal

From 192.168.1.0 to 192.168.1.15

That is all addresses from 192.168.1.0 to 192.168.1.15 are denied.

I hope this helps.

Best regards.

Massimiliano.

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