I have a Windows PC with 2 NICs; one NIC connects this machine to the local LAN while the other NIC connects this machine directly to an X-ray machine (which I'll call the RayLAN).

So my question is this: Is it possible that an IP address on the local LAN would conflict with the statically assigned IPs on the RayLan? I'll rephrase with more specificity: If the RayLAN NIC was assigned and some other PC on the local LAN happened to have that same IP, would that be a problem? My gut says no as these are two separate networks that are not bridged.

Thanks! Barry

  • 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 can provide and accept your own answer. – Ron Maupin Dec 15 '19 at 3:54

Both your PC's links need to use distinct IP subnets without overlap. If the RayLAN NIC uses then you can't use any address from anywhere else in your network without causing problems. You don't even need an IP address collision, a subnet address collision already is a problem.

Specifically, your PC wouldn't know where to route packets destined for but not to the RayLAN. Since is directly connected it would attempt to contact any destination directly via ARP and without using a gateway.

When both NICs' subnets are supposed to be separate each one needs a distinct, non-overlapping subnet address that is not used elsewhere.

There are ways to (somewhat) make everything work despite the collisions (like using longer subnet masks/prefixes, specific low-metric routes, or even NAT) but your life will be much easier if you sort out the address problem once and for all.

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  • I'm afraid you lost me with the "". I understand the first part but don't understand the significance of the "/24" part of it. I do understand the subnet part. I need to make sure the two subnets are different. If the LAN network is using, may I use (for the private RayLAN) something like Is that enough of a difference -and- is that "" okay if I make both the X-ray machine and the PC's NIC (for the private RayLan) that same – rumplestiltskin Jun 12 '19 at 4:09
  • I'll add that there is no Internet access for the X-ray machine nor the PC (when using that private NIC); that PC -can- access the Internet with the other NIC (and, in fact, that NIC is used when other machines on the LAN need to copy files on the PC to those other machines. – rumplestiltskin Jun 12 '19 at 4:13
  • Check out networkengineering.stackexchange.com/questions/7106/… for the relevance of subnet masks; making the mask shorter increases the problem. Whether Internet access is possible doesn't matter, you can't have duplicate host or subnet addresses in your network. – Zac67 Jun 12 '19 at 4:56
  • @rumplestiltskin means the IP address in a /24 subnet (or with the network mask). You cannot re-use IP addresses in any case, even when you change the network mask somewhere. IP addresses need to be unique, no matter the subnet size. – Zac67 Jul 12 '19 at 10:54

It won't cause any conflict if they are connected to different network switches.

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    That is an overly broad statement that is wrong under many circumstances. It could certainly be a problem, even if they are connected to two different switches, if the switch interfaces are part of the same VLAN. – Ron Maupin Jul 12 '19 at 13:29

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