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subnetting question

Discussion in 'Routing & Switching' started by azrael2000, Sep 11, 2008.

  1. azrael2000

    azrael2000 New Member

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    Hi All.

    Have a little question about subnetting.

    I understand how to subnet an address to get the number of hosts or networks required.

    That is not a problem; however, if I have subnetted an IP, then want to subnet one of the subnets (hope that makes sense) how do I do it?

    I've tried a couple of different books but nothing is making sense...

    Regards
     
  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Just take the subnet range and run it through again? Unless there are other constraints I would have thought this would be the way to do it.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  3. azrael2000

    azrael2000 New Member

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    Ok, so if I take, for example 192.168.10.0 and make it a /28... that would leave me with subnets like

    192.168.10.0, 192.168.10.16, 192.168.10.32 and so on...

    If I want to take the 192.168.10.32 and make it into a /30, then what would the new subnets be and why?

    That's where I get a little confused.

    Regards
     
  4. BosonMichael
    Highly Decorated Member Award

    BosonMichael Yottabyte Poster

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    Just subnet it into /30-sized chunks. How many addresses are within a /30 subnet? Four, right? Two host addresses, a network address, and a broadcast address. So, split up a /28-sized chunk (of 16 addresses) into multiple /30-sized chunks:

    192.168.10.32/30
    192.168.10.36/30
    192.168.10.40/30
    192.168.10.44/30
     
    Certifications: CISSP, MCSE+I, MCSE: Security, MCSE: Messaging, MCDST, MCDBA, MCTS, OCP, CCNP, CCDP, CCNA Security, CCNA Voice, CNE, SCSA, Security+, Linux+, Server+, Network+, A+
    WIP: Just about everything!
  5. gamava

    gamava New Member

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    Try Variable length subnet mask(VLSM)
     
  6. albertc30

    albertc30 Kilobyte Poster

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    Any more doubts mate?
    Need any more help?

    Lets just hope that I can make it easier for you.

    Class C IP address = 192.168.28.0/24
    IP addresses range from 192.168.28.1 to 192.168.28.254
    Network ID = 192.168.28.0 Broadcast IP 192.168.28.255
    Gateway = 255.255.255.0 (default class C subnetmask)

    Lets subnet it to a 192.168.28.0/26

    Network IP ---------------- Range -------------- Broadcast IP
    192.168.28.0 - 192.168.28.1 / 192.168.28.62 - 192.168.28.63
    192.168.28.64 - 192.168.28.65 / 192.168.28.126 - 192.168.28.127
    192.168.28.128 - 192.168.28.129 / 192.168.28.190 - 192.168.28.191
    192.168.28.192 - 192.168.28.193 / 192.168.28.254 - 192.168.28.255

    So by subnetting it using 2 bits from the host portion of the address you got 4 networks and 62 available IPs peer network.

    Lets say that you used the first range 192.168.28.0/26 and now you need to ad another network to the existing network and you need just 28 hosts in that new network.

    How many bits do we need to take from the host portion of the address to allow at least 28 hosts?
    Not 1 as the first bit gets you 126 hosts peer network, not the first 2 as you'd get 62 hosts peer network but the first 3 as you'd get 30 available IPs peer network, more then enough for your new network of 28 hosts.
    One minor detail here that plenty of people seem to forget. Whatever many pcs are in a network they will almost certainly be conected to a router and that router's interface will also need an IP address, even worst if you are dealling with VLANS where the router's interface mitght need one IP address peer VLAN and all that need to be taken into account. So in this example if you'd be using 4 VLans having this network sub subneted to 192.168.28.64/27 you wouldn't have enough available IPs to acomodate this lan, so you'd need it to be sub subneted to a 192.168.28.64/26.

    Back in track, the next available and unsuable subnetwork is the 192.168.28.64/26 so lets change it to a 192.168.28.64/27. So we have;

    192.168.28.64 - 192.168.28.65 / 192.168.28.94 - 192.168.28.95
    192.168.28.96 - 192.168.28.97 / 192.168.28.126 - 192.168.28.127

    And that would be that subnetwork sub subneted into another subnetwork.

    Remember you can only sub subnet unused subnets and be aware not to overlapping.

    Hope it helps and not have complicated it to much.
     
    Certifications: CCNA
    WIP: 220-701 - A+

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