Can you subnet a subnet?

danny069danny069 Member Posts: 1,025 ■■■■□□□□□□
This was a true/false question on my networking final exam this morning. I put down false. What do you guys and girls say?
I am a Jack of all trades, Master of None


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    gespensterngespenstern Member Posts: 1,243 ■■■■■■■■□□
    Why not? Why can't you take a subnet and subnet it into two /25? And subnet them further into even smaller subnets?
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    clarsonclarson Member Posts: 903 ■■■■□□□□□□
    Subnetting is the process of breaking down an IP network into smaller sub-networks. So, true
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    TallDude7TallDude7 Member Posts: 61 ■■□□□□□□□□
    VLSM. borrow bits from a subnet to make another subnet. pretty easy
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    SimridSimrid Member Posts: 327
    As the OP post said, a /24 can be broken down into two /25's. This is known as Supernetting.
    Network Engineer | London, UK | Currently working on: CCIE Routing & Switching

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    danny069danny069 Member Posts: 1,025 ■■■■□□□□□□
    Supernetting, wow I never heard this before. Our professor certainly did not tell us this. So technically...a subnet could be supernetted?
    I am a Jack of all trades, Master of None
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    nman99nman99 Member Posts: 35 ■■□□□□□□□□
    danny069 wrote: »
    Supernetting, wow I never heard this before. Our professor certainly did not tell us this. So technically...a subnet could be supernetted?

    Right, so for example if your internal network at your Main Campus consists of 4 individual /24 subnets, lets say , , and, you can combine these together and create a supernet, which would be You can then use this suppernetted network to maybe advertise your 4 Main Campus networks to a Secondary Site but by only using the supernet address ( instead of 4 individual network advertisements.

    Hope this helps
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    aschenbecheraschenbecher Member Posts: 27 ■■□□□□□□□□
    Thats soo cool. I am loving networking.
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    toasterboy1toasterboy1 Member Posts: 50 ■■□□□□□□□□
    Isn't that what Variable Length Subnet Masking (VLSM) is all about. Having a /24 network and breaking down into small and also uneven groups to not waste addresses. Like /30 for WAN or Serial links and large ones for actual users.
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    TWXTWX Member Posts: 275 ■■■□□□□□□□

    I do not remember the term being used as 'supernetting' for this. I know this concept as 'route summarization'.
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    networker050184networker050184 Mod Posts: 11,962 Mod
    It's all semantics. These days just approach everything from a bits perspective. In the real world anyway. For a test, do what the material says!
    An expert is a man who has made all the mistakes which can be made.
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    bigdogzbigdogz Member Posts: 881 ■■■■■■■■□□

    We have a winner!!!

    To the OP:
    Your professor should know Networking inside and out before he/she teaches the subject. I guess this is proof that it does not happen in all cases. Sometimes people just use the book or powerpoint slides to teach and do not take the time to learn more.

    Good Luck!
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    fuz1onfuz1on Member Posts: 961 ■■■■□□□□□□
    You guys never heard of supernetting?! Easier than VLSM/route summarization to say... icon_cool.gif

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    theodoxatheodoxa Member Posts: 1,340 ■■■■□□□□□□
    This is a bad question. While, you can take a subnet and break it into multiple smaller subnets, are you "subnetting the subnets" or just making smaller subnets from the original classful network?

    BTW, supernetting is just subnetting in reverse. For example, I could take 2 /24 networks and supernet them into 1 /23 network.

    It works the same as summarization.
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    xnxxnx Member Posts: 464 ■■■□□□□□□□
    This, it can be a method used to aggregate routes on a router too
    Getting There ...

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