I am a little confused with subnetting. Looking for a proper explanation.

Suppose I have 3 routers A, B and C.

Int 1: <-- Router A
Int 1: <-- Router B

Int 2: <-- Router B
Int 1: <-- Router C

Now my confusion is that Int 1 of Router C ( has network of and on the other routers there is same network as well.

How can packets transfer between two same networks with router? Because they are on different subnets? Looking for a proper answer.


EDIT Overlapping will occur for this scenario. But what happens if I add 2 more additional routers and still give subnetted ip to one of the routers which is not directly connected to above 3 routers?

  • Hi an welcome to network Engineering. I would expect that Router B would refuse this configuration, as it will have overlapping subnets on its Int1 and Int2. If Router B's Int1 and Int2 are part of the same routing instance ("VRF"), then their IP networks must not overlap. Mar 1 '19 at 10:24
  • 1
    Possible duplicate of How do you calculate the prefix, network, subnet, and host numbers?
    – user36472
    Mar 1 '19 at 10:25
  • @Marc'netztier'Luethi what if there are more than 10 routers and similar subnetted IP is given to 2 farthest routers from each other. Since they are not directly connected, it will not give overlapping.
    – Waleed
    Mar 1 '19 at 11:04
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    @Waleed overlapping subnets on different routers are configurable, but it is literally asking for trouble. If these subnets are to be part of the same routing domain (or become active in the same dynamic routing protocol), it will give hosts in the larger subnet unreachability of hosts in the remote (smaller) subnet, since they will believe that they are all on the local subnet, too. Hosts on the smaller subnet cannot reach their peers in the overlapping part of the remote subnet, and all sorts of connectivity hilarity ensues. Overlapping subnets are a thing to avoid™. Mar 1 '19 at 11:10
  • 2
    Generally, you cannot overlap IP addresses, no matter what subnet mask is used. An IP address should be unique as the subnet mask is only the length of the routing prefix. As Marc has pointed out, it isn't entirely impossible but it's a bad idea and most often there's a much better solution, and much easier in the long term.
    – Zac67
    Mar 1 '19 at 16:13

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