IP addressing can anyone help!!??

tottstotts Member Posts: 117
Hello there. I'm a bit confused about a question in a book I have... Exam cram 2.

The question asks...

Identify three valid host addresses in the network with a subnet mask of (choose three).


The answer they is...

Answer: A, C and D. A subnet mask of divides the fourth octet into subnet part: the highest four bits and a host part (the lowest four bits). We simply check the fourth octet to check that all subnet and host parts are okay. The host bit portion cannot be 0000 or 1111. A, C and D are correct because 33 in decimal is 0010 0001, and 126 in decimal is
0111 1110.

My query is... why can't the host bit portion be 0000 or 1111??? I'd appreciate your input, cheers!!!

totts from essex


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    SlowhandSlowhand Mod Posts: 5,161 Mod
    I'm sure there are lots of Cisco gurus on here that can give you a more detailed explanation than I can, but the gist of it is this:

    You're looking for three valid host addresses. The bits can't be all zeroes or all ones because that would make them either a network address (all zeroes), or a broadcast address (all ones). The key to these kinds of questions (especially on the test), is to read the questions closely for those little "gotcha" phrases and keywords.

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    boyles23boyles23 Member Posts: 130
    I am studying subnetting at this very moment, here is the answer to your question. You would have 16 subnets (256-240 = 16) so you start at 0,16,32,48,64,80,96,112,128,144,160,176,192,208,224,240 and those are your subnets. So you can see that 112 and 208(answers b and f) would be subnets, so they are eliminated.

    When you are figuring out your available hosts, 175 is a broadcast address and the 33,119 and 126 are valid hosts. So there are your answers, sorry this is put together so short, I didnt feel like typing out a whole table. I would advise you buy Lammle's book, that is were I learned it from and it lives up to the hype about teaching you subnetting.

    Let me know if you have any other questions.

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