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Subnet Masking Binary?


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Alright, I'm taking my test in about two weeks and I'm half way done with my book and I wanted to get some help just to make sure I got it

Lets say we have a Class C IP (!92.168.0.x) /24 (

Gateway is

Comp A is

Comp B is

So Comp A gets AND'ed with SubnetMask to get the Result of a binary String lets call it BinA


Comp B gets AND'ed with SubnetMask to get the REsult of a binary String, Lets call that BinB

So then BinA & BinB is then Compared Correct??

And if I made the Subnet Mask /25 (1111111.11111111.1111111.10000000)

Does that mean CompA & B can not talk anymore due to Comp B's Ip being above 128? BUT! Is it still able to forward Information out to the gateway and to the internet? Is the gateway Exempt from the subnet Mask cuz norrmaly if it was a Host like CompA it wouldn't be able to see it right?

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Short answer is Comp B will not see the router or Comp A. Also Comp B will have an invalid IP, that is the network number, the first usable number will be 129.

In the real world, it can get really goofy, and this is why overlapping networks with similar numbers are BAD and you need to keep that stuff organized and vlan'd. If you only change the subnet mask of Comp B, the above statement is true from the perspective of Comp B. Comp A and the router will still have the /24 mask. That means that Comp B will see broadcasts because they go from 0-255 there. Comp B will try to answer those broadcasts and traffic will get mixed up.... I've seen this happen and it's hard as hell to troubleshoot. But for your exams and labs, ignore this rant, it shouldn't happen on paper! Moral of this story is get your subnet masks matching on everything!

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