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Connecting two hosts with the same IP address but different subnet masks

Is it possible to communicate two hosts with the same IP address but different subnet mask without adding a router?

Is it possible to communicate two hosts with the same IP address but different subnet mask without adding a router? If so, what is the configuration?

Generally speaking, no two devices should have the same IP address unless they are behind a NAT device. Computers need routers to communicate with devices that are not on their same logical subnet. When one computer prepares to communicate with another, it basically goes through three steps to determine if the communication is local or gets addressed to the router. This routing information can be seen by issuing the "route print" command from the cmd prompt. These three steps include:

  1. Are both addresses the same class?

    Source 200 120 3 72
    Target 200 120 3 41

    YES

  2. Do both share the same network address?

    Source 200 120 3 72
    Mask 255 255 255 224
    Target 200 120 3 41
    Mask 255 255 255 224
    Binary = 11100000

    YES

  3. Are both on the same logical subnet?

    Source 1st Address 72 = 01001000
    Mask 224 = 11100000
    Target 2nd Address 41= 00101001

    NO

Since the first three bits listed above do not match, the sending computer now knows that the computer it wishes to communicate with is not local, therefore the router will receive the data and is responsible for delivery. I hope this helps you better understand the routing process.

This was last published in September 2004

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