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Amazone
Learn Wildcard Mask In 10 Minutes
2 posters
Page 1 of 1
Learn Wildcard Mask In 10 Minutes
For some people, Subnet Calculation is real horror.
After some time of learning and training, they find out that Subnetting is very easy.
Then these people come in touch with the "Wildcard Mask Tragedy". WHAT IS THIS?
Well, did we say Subnetting is easy?
Wildcard Mask Calculation is EASIER!
Lets say...
We have network 100.0.0.0 with Subnetmask 255.255.255.240.
We want to create an ACL for this network. THis WHOLE network should be denied something.
For the acl, we need the proper Wildcard Mask for that Subnet.
The Subnetmask is binary
11111111.11111111.11111111.11110000=255.255.255.240
For Wildcard Masks, only the ZEROS are interesting.
So make a simple addition (watch the last oktett!)
8+4+2+1=15
So the wildcard mask will be
0.0.0.15
---------------------------------------------
Other example
We have network
100.0.0.0 with Subnetmask 255.255.248.0
255.255.248.0=11111111.11111111.11111000.00000000
4+2+1.128+64+32+16+8+4+2+1
That is Wildcard Mask
0.0.7.255
---------------------------------------------
another easy way is :
subtract the octets from 255
255.255.240.0
255-255=0
255-255=0
255-240=15
255-0=255
so the wildcard mask is 0.0.15.255
After some time of learning and training, they find out that Subnetting is very easy.
Then these people come in touch with the "Wildcard Mask Tragedy". WHAT IS THIS?
Well, did we say Subnetting is easy?
Wildcard Mask Calculation is EASIER!
Lets say...
We have network 100.0.0.0 with Subnetmask 255.255.255.240.
We want to create an ACL for this network. THis WHOLE network should be denied something.
For the acl, we need the proper Wildcard Mask for that Subnet.
The Subnetmask is binary
11111111.11111111.11111111.11110000=255.255.255.240
For Wildcard Masks, only the ZEROS are interesting.
So make a simple addition (watch the last oktett!)
8+4+2+1=15
So the wildcard mask will be
0.0.0.15
---------------------------------------------
Other example
We have network
100.0.0.0 with Subnetmask 255.255.248.0
255.255.248.0=11111111.11111111.11111000.00000000
4+2+1.128+64+32+16+8+4+2+1
That is Wildcard Mask
0.0.7.255
---------------------------------------------
another easy way is :
subtract the octets from 255
255.255.240.0
255-255=0
255-255=0
255-240=15
255-0=255
so the wildcard mask is 0.0.15.255
Page 1 of 1
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