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Because of how routers separate networks is it possible to say use the network 192.168.1.0/24 several times as long as you have enough networks to separate?

Example:

192.168.1.0/24 <--> 172.16.0.0/24 <--> 192.168.1.0/24

  • Is there any particular reason you are setting it up this way? I suppose, technically it would work, the source IP being included in the packet header. What lies in between the two routers? – A. Warrenfells Aug 13 '13 at 16:24
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    No reason. I was just curious as it came in to my head. I honestly wouldn't setup an office like this because it would be confusing but just curious as to if it would work, – Jason Aug 13 '13 at 17:33
  • It would not work very well unless you are using VRFs. How will the middle router know which of the subnets you want to send traffic to if it's available out both ports? – Daniel Dib Aug 13 '13 at 17:52
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    Your example seems to imply you have an intention to communicate between hosts in the first 192.168.1.0/24 and the second 192.168.1.0/24. Is that true? If yes, this can run into difficulty. OTOH, if no duplicates will exist between the two 192.168.1.0/24 networks, then you could make a bridge between them and run them as one network that is distributed. – Skaperen Aug 13 '13 at 21:02
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 7 '17 at 21:53
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I will only work if there is NAT between each of the networks (IP space re-use via VRF set aside). Otherwise each network has to be unique or routing will fail.

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Any given network that serves the public probably has a few thousand instances of 192.168.1.0/24 attached to it at any given moment, so it works. It would be somewhat insane to do so deliberately on networks managed by one company, so I'm glad to hear you wouldn't. In the case you provide where you are connecting two private networks to a third private network, there will also be some potential lack-of-joy from "double NAT" if a connection to the outside world (public IP address) is contemplated - perhaps even triple NAT depending where you connect to. Best to avoid that, IME.

After some lack of joy when setting up VPN, I have eliminated all instances of 192.168.0.0, 192.168.1.0, 192.168.2.0, 192.168.100.0, 10.0.0.0, 172.16.0.0 from any of my networks. Up until that point 192.168.1.0 was fine for many years, but having been through that, even networks I don't currently plan to connect to VPN get an address that's as non-default as I can manage, and none of them are the same. Picking a non-default section of the private address space greatly reduces issues when users are connecting from places that (nearly always) are using one of those defaults.

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  • I was assuming you meant with NAT. Otherwise the answer from Aziraphile is more correct. – Ecnerwal Aug 13 '13 at 18:01
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If you carefully set up the routing, configurations like that can be used for anycast addresses. E.g. 2 DNS servers each in the duplicate subnet with the same IP address - the closer one would respond to DNS requests from other subnets.

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2

Use cannot use same subnet in single network. If your network is segregated into various segment and if your are having source nat for address translation in between this network segments then your can use same networkl subnet.

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Simplest answer is, Yes. However, each "network" will have issues reaching the other two.

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If you are just attempting to transit these duplicate networks, it will work. However, without NAT, or some other kludge, one duplicate network will not be able to talk to another. In your example, each router directly connected to one of the 192.168.1.0/24 networks will have a single "connected" route to 192.168.1.0/24. Neither will have a route to the far-side 192.168.1.0/24. Don't do this, it's very bad design.

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With this kind of configuration, when you try to ping a 192.168.1.0/24 network from 172.16.0.0/24 network, one ping would be successful and the next ping will be dropped. You will see something like this !.!.!.!.! when you try to ping.

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