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Thread: Subnet question

  1. #1

    Subnet question

    Hello all, I'm new to the forum and want to ask a question with regards to subnets.

    I'm attempting to set up two Class C sub networks on the same class C network.

    I want both of my subnets to be capable of supporting 28 hosts and I have determined that as it is a class C network my subnetwork mask should be

    I also want all of my host addresses to be able to send packets to one another and both to be able to access the WAN (internet).

    So far I've determined that I'll need two routers to pull this one off (correct me if i'm wrong!).

    The way I was thinking of having it set up is as follows:

    Router 1:
    Wan Address 1:
    Subnet Mask:

    Wan Address 2:
    Subnet Mask:

    Network Address:
    Lan Address:
    Subnetwork Mask:
    Assignable IP address range:
    Broadcast Address:

    Router 2:
    Wan Address:
    Subnet Mask:

    Network Address:
    Lan Address:
    Assignable IP address range:
    Broadcast Address:

    I've tried this particular setup as it seemed after researching subnets. However none of the host computers are able to ping any computers on the other subnet. Where exactly am I going wrong?

    Also I really just wanted to keep it down to 2 subnets rather than having three (one extra for the lan link).

    Oh, I'm a tad sleep deprived too so maybe I'm not thinking too clearly hehe.
    Anyway any input would be greatly appreciated!

  2. #2


    What kind of router are you using? Most decent routers have multiple interfaces, all of which can be configured with seperate networks/subnets.

    The above is a simple topology that will work, for the networks to be able to talk to each other, you'll have to configure a routing protocol on the router, and/or NAT (if you want to explore a little deeper)
    Last edited by Bazza84; 04-14-10 at 07:04 AM. Reason: pic

  3. #3
    I don't actually have a specific router. I'm trying to get it running properly first in GNS3. I suppose for the purposes of testing it's a cisco 7200 router.

  4. #4
    O.k so I sorted the class C network out and I've just been playing around with making other networks just out of curiosity. Anyway I've succesfully made a few networks and now I was hoping to get them all cross communicating with each other. I want get host 1 to be able to communicate with Host 3, etc...

    I'm just completely clueless on how to connect the networks together so that they can all communicate with one another.

    Any ideas?

    Here's my topology:

  5. #5


    First thing you need is to configure the addresses on the serial interfaces, or whatever interface is connecting the routers together.

    To get them all talking, you can do one of these options

    Create static routes for each interface (It's a pain in the ass)

    Configure a routing protocol on each router to advertise the routes each router knows about. RIP, RIPv2, and OSPF are worth looking into.

    After you've done this, you should have everything talking away :-)

    Take a look at this

    btw GNS3 is great, but when you get into switching, you'll need packet tracer :-(

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