What kind of device could solve the following dilemma and how?

Given: 2 networks A and B with the same IP range: mask

Find: how to translate addresses from one of the networks(A or B) and combine them with the second network to get merged network mask on one patch-cord? enter image description here

  • You can use routers with NAT to translate between the two networks, but I don't know what you mean by combining them for a merged network. They are two separate networks; a drawing may help. Companies with overlapping network addresses merge, and they use NAT routers as a temporary measure until one or the other, or both, can be readdressed.
    – Ron Maupin
    Jul 14, 2016 at 21:31
  • picture added, please also see a comment below Jul 15, 2016 at 7:29
  • 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 14, 2017 at 21:12

2 Answers 2


This is a common issue when companies merge. The correct answer is to renumber one (or both) networks. However, in the short term, src and/or dst NAT can make each network appear to be a different range. There will have to be intermediary gear as one router cannot have two interfaces with overlapping subnets.

[Update: one could use VRF to simulate multiple devices, but that's an Advanced Level technique.]

  • A problem with NAT is that you can't assign to router ports addresses with overlapping networks(mask on the picture cannot be changed to 21), thus you won't be able to communicate with both networks simultaneously. What I was thinking of is a specific device(e.g. FPGA based) allowing ip header modification(address and mask) for packets. Are those exist or schematics is developed by someone? Jul 15, 2016 at 7:28
  • That's what I said... intermediary gear You cannot connect a router to lan A and lan B at the same time (overlap), but you can connect a router in lan A to a router in lan B.
    – Ricky
    Jul 15, 2016 at 7:53

Just a suggestion, as I don't understand at this level too much but could you not create virtual interfaces on those routers, assign them alternate IP addresses that are not the same and then do some funky IP-routing/NAT-ing to get them to communicate?

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