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basic VLSM Subnetting Help

Discussion in 'General Cisco Certifications' started by Chris H, Apr 6, 2012.

  1. Chris H

    Chris H New Member

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    Hi,

    I have been given a scenario to work through by my university. I have been asked to design a network for a small school. there are 5 rooms, 3 for students and 2 for admin/staff these networks need to be kept separate (on a different subnet) for security reasons. We have been told to use a class c IP Address of 192.168.1.0

    This is what I have done:

    Room 1 (student) Subnet mask: 255.255.255.224, Subnet address: 192.168.1.0, 1st Host Address: 192.168.1.1, Last Host Address: 192.168.1.30, Broadcast Address: 192.168.1.31

    Room 2 (student) Subnet mask: 255.255.255.224, Subnet address: 192.168.1.32, 1st Host Address: 192.168.1.33, Last Host Address: 192.168.1.62, Broadcast Address: 192.168.1.63

    Room 3 (student) Subnet mask: 255.255.255.224, Subnet address: 192.168.1.64, 1st Host Address: 192.168.1.65, Last Host Address: 192.168.1.94, Broadcast Address: 192.168.1.95

    Room 4 (Admin/Staff) Subnet mask: 255.255.255.240, Subnet address: 192.168.1.96, 1st Host Address: 192.168.1.97, Last Host Address: 192.168.1.110, Broadcast Address: 192.168.1.111

    Room 5 (Admin/Staff) Subnet mask: 255.255.255.240, Subnet address: 192.168.1.112, 1st Host Address: 192.168.1.113, Last Host Address: 192.168.1.126, Broadcast Address: 192.168.1.126


    Each room has a switch which all the hosts connect to, these switches then go into anther switch in the comms room which in turn connects to the router (default gateway of: 192.168.0.254)

    My problem is that when this design is configured in packet tracer I am not able to ping each room (i.e. Host 1 in room 1 to host 2 in room 3) also none of the hosts can ping the router.

    That's where I'm a little lost, I thought this would work. We have been told we are not allowed to use DHCP but we must use VLSM.

    Any help would be much appreciated.

    Regards
    Chris
     
    Last edited: Apr 6, 2012
  2. soundian

    soundian Gigabyte Poster

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    I'm no network guru but that question would make more sense (to me) if it was VLAN and not VLSM that you were required to use.
    If it were VLANs you could hook up the comms room switch to the router and allow them to communicate with each other that way, while maintaining separation for security purposes. I don't see how hooking up 5 different subnets (6 if you count the default gateway) to a switch is going to work.

    Hopefully one of the proper networkers will be passing by soon and spot what we've both missed.
     
    Certifications: A+, N+,MCDST,MCTS(680), MCP(270, 271, 272), ITILv3F, CCENT
    WIP: Knuckling down at my new job
  3. danielno8

    danielno8 Gigabyte Poster

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    Soundian,

    For each VLAN, you need a different subnet, as each VLAN is in turn a single broadcast domain.

    Chris,

    You need a default gateway per subnet.....not one for all. Just to highlight exactly why it is not working, when your hosts (in different rooms) currently try to ping each other, they note that they are not in the same subnet, and therefore need to send the packet to their default gateway. When they try to do this, they cannot, as their default gateway is ALSO outside their subnet.

    In order to complete this there are a number of steps, involving creating VLAN's on the switches, and trunk links between the switch in each room and the switch where the router connects. You will also need to configure the router to do the inter-VLAN routing. This is called 'router on a stick' if you want to look up more info around this.

    Cheers

    EDIT: your subnetting all looks good, just need to get the rest hooked together to make it work :)
     
    Last edited: Apr 6, 2012
    Certifications: CCENT, CCNA
    WIP: CCNP
  4. Chris H

    Chris H New Member

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    Hi, thanks for the quick response, I get what you mean about the different default gateways for each subnet, don't know why I didn't think about that. I will have a play around with it later after work and let you know. Again that's very much.

    Chris.
     
  5. Chris H

    Chris H New Member

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    Ok sorry for the late reply, everything is working well now, thank you so much for your help guys.

    Chris.
     

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