Subnetting Homework

JeetusJeetus Member Posts: 7 ■■□□□□□□□□
Good Morning,

My network admin at work has set me some homework. I don't want the answer, but what I am looking for is a push in the right direction and also to check if my method is correct. Here is the scenario -
You work in a small office and have been asked to re-design the network to best practices, the building has two floors and each floor has 490 ports that need to all be working.

You need two subnet for voice and data using the 192.168.x.x network and you also need to allow 6 ip addresses for your comms room devices.

Design the network using best practices and the least number of ip address.

This is where I am up to so far -

192.168.x.x - CLASS C IP
Subnet Mask:
Therefore - 192.168.x.x/24

Considering we only need two subnets I only borrowed the 1 bit from the subnet mask giving me the following subnets -


Subnet Mask:



First of all - is my above working correct? If not please can you advise where but not why.
Second - I am not sure where to go from here. Any advice would be much appreciated.

Thanks in advance :)


  • yoba222yoba222 Senior Member Member Posts: 1,233 ■■■■■■■■□□
    The way this question is worded gives me the impression that it is a bit of a trick question, designed to give you enough rope to hang yourself with.
    Which may have happened.

    You made two /25 networks; so by your math, that's 126 and 126 available hosts. How's that going to fit 490 hosts?
    A+, Network+, CCNA, LFCS,
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  • JeetusJeetus Member Posts: 7 ■■□□□□□□□□
    Aarrgghh!! Youre right. Ok back to the drawing board.
  • JeetusJeetus Member Posts: 7 ■■□□□□□□□□
    Thing is, the 192.168.x.x is a class C address which if I'm not mistaken gives us a subnet mask. In which case we really only have 7 bits to play with and the various power of 2 permutations wont give us the right number of hosts to accommodate the 490 port/host requirement unless........we assume that there is to be a limited IP pool available via a DHCP server that needs to be implemented under the "best practice" part of the scenario?
  • JeetusJeetus Member Posts: 7 ■■□□□□□□□□
    Spoke to my network admin this morning and he slapped himself saying he should have mentioned to use VLSM but then he also admonished me saying that I should have jumped to VLSM myself since I managed to work out that the classful setup wont work. In any case I managed to work it out, when I get a sec Ill put up my calculations :)
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