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Editorial Team
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Asked: 2026-05-14T08:29:44+00:00

Some background first. I have a .net client agent installed on each of the

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Some background first. I have a .net client agent installed on each of the machines in the lan. They are interacting with my central server [website] also on the same lan.

It is important for my website to figure out which of the machines can talk to each other. For example, machines of one subnet cannot directly talk to machines of another subnet without configuring the routers and such. But machines in the same subnet should be able to talk to each other directly.

The problem I am facing is when the lan setup is like in Figure 1.

Figure 1

Because Comp1, Comp2 and Comp3 are behind a router, they have got the ipaddress 192.168.1.2 till 192.168.1.4. My client agent on these machines report the same ipaddress back to the server. However, machines Comp4, Comp5 also have the same ipaddresses.

Thus, as far as my server is concerned, there are 2 machines with the same ipaddress. Not just that, because the subnet mask is 255.255.255.0 for all machines, my server is fooled into thinking that Comp1 can directly talk to Comp5, which is not possible.

So, how do I solve this? What do I need to change in my client or in my server, so that I can support this scenario. These two are the only things in my control.

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1 Answer

  1. Editorial Team

    EDIT: Seems that the network diagram
    is over simplified and there could be
    multiple router/subnet levels. My
    original answer will not handle this
    scenario. Also, with the restriction
    of modifying only the client app or server
    app and not tampering with the
    routers and firewalls makes
    it more difficult.

    EDIT2: Using ‘arp -a’ you can extract
    the MAC address of the router. If the
    client apps can manage to do this then
    the puzzle is solved!

    The client app knows the local machine address and passes it to the server app.

    The server app knows the remote address when a connection comes in. This would be machine address or a router address.

    From these two values you can work out what you ask.

    For example:

    Server app receives connection from 10.10.10.2 with client supplying 192.168.1.2

Server app receives connection from 10.10.10.3 with client supplying 192.168.1.3

    The ‘remote address’ distinguishes the subnets.

    So, all you need to figure out is how to extract the remote address of a client connection. If you are using any of the popular web technologies for your server app then this is very easy.

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