Routing between two networks with same subnet.

March 7, 2012 at 13:32:40
Specs: Windows XP SP3
I am trying to see if the following scenario is possible:
Two networks. NetA: IP subnetID 10.101.x.x subnet 255.255.0.0. Devices have static-assigned IP's. Only DHCP runs on wireless AP for wireless client connection. IP addressing scheme set by hardware vendor, so not under my control. NetB: IP subnet 10.x.x.x subnet 255.0.0.0. Campus LAN and also not under my control. DHCP supplied addressing. Any ideas on how to get NetA devices to route to NetB? I would like to be able to provide Internet access (via NetB)to NetA devices. Let me know if I have missed any relevant details that could possibly make this happen. I am tending toward thinking it cant happen but thought I would ask some people smarter than me....

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#1
March 7, 2012 at 13:43:54
The networks are not in the same subnet.
You are not admin of either network

If the campus IT dept discovers you trying to route between their network and this other one you would get kicked out of school

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#2
March 7, 2012 at 13:58:58
thanks for the quick reply wanderer. I guess I did miss a couple of details. I am the admin of the NetA network. The IP scheme is determined by one of the hardware vendors and I have aligned the other devices to match their scheme for ease of use and troubleshooting. Changing all the IP's would be a major hassle, especially since they are all static. The network itself was designed for theatrical control systems (lighting consoles, dimmers, sound equipment monitoring, and audio streaming) used during live productions.
I am hoping to develop a proposal for the Campus IT department. This is my job, I am not a student and as such, I am not going to jeopardize my job on this. But I would like to see if a solution is possible and then present to them. They are a very small department and very impacted so I am trying to do some of the research ahead of time.

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#3
March 7, 2012 at 14:19:22
simply put a router in between the two subnets. assign each side of the router a static ip in its corresponding subnet.

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#4
March 7, 2012 at 14:36:48
yeah i thought of that but their DNS servers are in the 10.101.x.x range (actually all the campus servers are in the 10.101.x.x subnet). I could use 4.2.2.2 for DNS but then I lose DNS queries to on-campus resources.

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#5
March 7, 2012 at 14:54:48
campus has internet right? To do so the campus dns has to be set to forward reqeusts to the internet for internet name resolution.

A bigger question is does Net A presently have a gateway entry?
That will cause problems it if does.

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#6
March 7, 2012 at 15:20:17
Gateways on all Net A devices are set to device IP so device acts as own gateway. My understanding is that is the same as no gateway. Could be wrong? I can clear gateway on most devices, not sure if I can do all.
Campus does have internet and I understand that DNS has to forward. My concern is that DNS entries destined for 10.101.5.11 (for example) would get confusing since NetA would be the 10.101.x.x subnet but 10.101.5.11 resides on NetB.
These may have been more pertinent details to include original question but I didnt want to get too long winded in the post. My apologies.
To me, the larger issue is: Is it even possible to route between networks with subnet overlap? I.E. my NetA subnet lies completely within NetB's subnet.
I suppose, theoretically, I can make static routes on the router for outbound communication. Maybe even port based routes for HTTP, FTP, etc traffic to be forwarded to a specific interface on the router (the NetB interface). Sounds like a lot of configuration on the router but doable to make the project work.

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#7
March 7, 2012 at 16:42:57
"Gateways on all Net A devices are set to device IP so device acts as own gateway"

Say what? You mean if a device has 10.101.x.y it has the same for gateway?
Thats great. You can assign a gateway which will be the ip you assign the router.

NetB has internet right? Its pointed to the campus dns servers right?

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