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Question about cascading routers

By ICUB4UCME
Jul 5, 2008
  1. hi guys,
    i'm working on setting up a network with a version of the 3-router approach to seperate the network into 2 mutually exclusive segments. i'm actually using 2 routers and experiencing some things that seem odd to me. i've uploaded a diagram of the current configuration.

    my understanding is that when you place a router in place it seperates the networks lan and wan sides so direct communication is not possible. what i'm seeing happen is that there are 2 ranges of ip address (one from each router) that are easily visible from either side of router B. at the very least B should see A and A not see B but router B seems almost transparent in this case. i can actually connect to the WAN port on router B from the Lan side of router B.

    anyway. my question is that for the results i'm desiring is it required that i have 3 routers or is it possible to configure things with only 2 routers? thanks
     
  2. jobeard

    jobeard TS Ambassador Posts: 9,343   +622

    routing depends upon the actual subnet addresses AND the subnet mask.
    for discussion, assume router A has address 192.168.1.1.
    The address and subnet mask of router B is now the issue.

    If B has any address other than 192.168.1.x, then segment A should NOT see
    segment B, BUT segment B users should be able to see segment A.
    This is due to all traffic flowing thru router A

    On the other hand, if router A and B share the first three parts of the address
    (A=192.168.1.1 and B=192.168.1.128 or similar), then both segments A and B
    will see each other.

    To totally isolate segments A and B, a common router above would be a solution
    Code:
                      Modem
                         +
                     router-C (192.168.1.1 ) 
                    +      +
             router-A    router-B
    192.168.2.1          192.168.3.1
         +                   +
    isolated(A)         isolated(B)
    
    the WAN side of A and B will have addresses associated with 192.168.1.x
     
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