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RonNewYork
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Subnetting question

Wed Mar 22, 2017 1:13 pm

I've been studying subnetting, reading about it on various sites. I found one site, http://www.subnettingquestions.com/, which has been rather helpful in that there are just a lot of subnetting questions with the answer. I get nearly all of them. But not all:

What is the first valid host on the subnetwork that the node 172.21.100.223/23 belongs to?

This is a class B network and /23 means (to me) that there are 510 hosts per subnetwork (assuming fixed length). That part I understand because /23 means

11111110 00000000

in the 3rd and 4th octet and 2^9 is 512, etc. But I am completely lost about the subnetwork. It seems that there are just two networks available here (24-23)? Or 1?

It's not that I need the answer but I seem not to have a mechanism for decompiling this question, sort of a step-by-step to follow.

RON

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