0

I am on a small office network that opted to use 192.168 private address ranges. I occasionally VPN into another network that uses a 10.X private IP range, since it requires a large number of hosts. What happens if the small office network I was on happened to be 10.X as well. If there were two hosts with the same private IP I am connected to, what are the repercussions?

Thanks!

4
  • Is the network behind the vpn 10.0.0.0/8 (mask 255.0.0.0) and the new planed an 10.x.x.x/24 (mask 255.255.255.0)? Dec 29, 2014 at 18:05
  • let's say that they are both /16
    – ppadru1
    Dec 29, 2014 at 18:12
  • 2
    Then you won't reach any host in the remote network. But: If there are special remote host (e.g. 10.12.14.100) you want to reach, you can set specific routes for them. But in this case, when you have an host with also 10.12.14.100 in your local lan, you won't be able to reach that host. Dec 29, 2014 at 18:17
  • Yes, they will conflict, and the one with the lower metric will typically be preferred.
    – davidgo
    Dec 29, 2014 at 18:17

2 Answers 2

1

If the networks start to overlap, they can come into conflict. Although it will not give you a "duplicate ip" error if both use DHCP and everything is configured properly, packages will stop arriving correctly.

For this to happen, the subnet has to allow for these ranges to overlap.

For example: 10.0.0.x with 255.255.255.0 and another one identical to that, even though the ip addresses handed out differ, will cause this.

This is also true for 10.0.x.x with a subnetmask of 255.255.0.0 which will overlap with 10.0.0.x with 255.255.255.0

But using 10.0.0.x with 255.255.255.0 and 10.0.100.x with 255.255.255.0 will work okay.

But a rule of thumb for any networking organisation: a 10.0.x.x range is a Class A network, which is only used when you expect to have a large network with vlan's etc. If you aim for a private home network, always stick wtih a Class C (192.168.x.x) network instead. This way, you can be ensured nothing will overlap and get in eachother's way.

4
  • Even with different subnets, if all hosts are used, isn't there still a small amount of overlap?
    – ppadru1
    Dec 29, 2014 at 18:55
  • A subnet determines which ip addresses belong to a network. If you set the subnet such that 2 different networks overlap, only then you will have problems that connections time out because a return packet was sent to a different ip address.
    – LPChip
    Dec 29, 2014 at 19:05
  • These networks are actually parts of two different companies, so there was no coordination in subnetting the class A private IP ranges to avoid routing conflicts
    – ppadru1
    Dec 29, 2014 at 19:46
  • Yes, and given that they have different subnets and ip ranges, there is no problem. Your question was: What if... and thats the answer. If a problem would have appeared, your network administrator would have to change the ip subnet for your network or not use VPN as technology. You can also use RDP to get similar results.
    – LPChip
    Dec 29, 2014 at 21:04
-2

They will not conflict as long as their Subnet Masks are different. IPv4 subnetting reference

3
  • The local host doesn't know anything about the subnettiong of a remote network. You can access google (173.194.39.23) without knowing the networkmask of it. Dec 29, 2014 at 18:12
  • 1
    Both these comments (ie @llo and @boboes) are only partially correct - The IP addresses can can conflict if subnet masks are different if the actuall IP's are in the same range, for example 10.0.0.0 netmask 255.255.255.0 and 10.0.0.0 netmask 255.255.0.0 will have a conflict for 10.0.0.1 - 10.0.0.254 where the smaller subet will win out. In the case of a VPN the VPN often sets routes which gives your PC information about the routes of the remote network.
    – davidgo
    Dec 29, 2014 at 18:17
  • @davidgo that is what I thought. If the subnet masks are different but all hosts are being used, there will at least be some conflict.
    – ppadru1
    Dec 29, 2014 at 18:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.