Is it possible to have two identical IP adresses in two different subnets such as PC1 and PC4?

Network 1


Simply configuring PC1 with that address will not work. If a packet is destined for PC1, the router would look for the destination address in its routing table, and it would find that it should send the packet out the interface with the address.

The original premise of IP is that every host is assigned a unique IP address, and this allows end-to-end IP connectivity. What you have breaks that, and it can cause problems.

There are some complex ways that you may be able to make this work, e.g. NAT, but this is something that you really want to avoid if at all possible.

  • Doesn't the router only look at the subnet adress to determin the interface so that it's possible to differentiate the two IP adresses?
    – elFreak
    Aug 6 '17 at 19:40
  • 1
    No, IP packets have no subnet field, just a destination address. An address has to uniquely identify the destination. Configuring overlapping subnets like you do in your diagram won't work. Aug 6 '17 at 19:44
  • And why would the packet be sent to PC4 rather than PC1?
    – elFreak
    Aug 6 '17 at 19:48
  • @elFreak, routing happens on the layer-3 address, and each packet is individually routed, regardless of its source or what packets have come before it. A packet will have a destination IP address, which is the only thing a router will consider when routing a packet. The router will look for the destination IP address in its routing table, and it will send the packet to the interface with the longest match Your router will find a match on the interface, so any packet destined to the address will be sent out that interface.
    – Ron Maupin
    Aug 6 '17 at 19:53
  • @elFreak, any packets destined to the address that originate on the network will never be sent to the router because the source host knows how to reach the destination address on its own network. Any packets sent to the address that originate on the network will be sent to the router because the source host recognizes that the address is on a different network.
    – Ron Maupin
    Aug 6 '17 at 19:55

It's not feasible to configure identicàl ipaddress in different subnets because ip conflict will occur . Routing issue will occur .

But still you can use identical IP address in different subnets . if both are different networks in this scenario use source NAT IP addresss .so that orginal ip address is hided by nat translations to avoid ip conflicts .


It's possible using VRFs on Router1. The rotuer can have each interface in a different virtual L3 domain with its own separate routing table. This way you can even set identical IP addresses on the router's interfaces. However, you still won't be able to send traffic from PC4 to PC1 because PC4 will just reply to itself (likewise the other direction).

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