I have 2 home networks. one internet, and the other is just a test network in one room. The computer I'm using connects to both networks. internet via USB WIFI, the room network by cat 5E. For simplicity I made them both with identical network IDs, with standard class C net mask. the internet LAN uses DHCP from Wi-Fi router set to a small range like 2-15. the wired network in the room uses 100-150. the original setup was all done statically and I had no issues, but after adding DHCP from an old router. and going DHCP on my system it failed to connect to the internet. even after release and renew with the other network then shut off. thinking maybe something to do with same network id on 2 interface maybe it's trying wrong network. disable the LAN interface it works, re-enable it still works. I think the I.P on the lan may not have released during release/ renew.
so what I'm wondering is there anyway to make this work with out changing one network I.D? would think it would work and try both till get response, or one then the other. so it should still work.
anybody know of anyway I can change a setting on the computer to tell what network to use first, or how to alter the routing table so that the address ranges point to different interfaces if this is possible. since normal routing tables don't usually go beyond network id for criteria.
not a big deal to change ID, but this got me curios.

 

You can't have two networks with the same subnets. Which one should be the default gateway?

It IS possible, but for what you are trying to do, I'd suggest this:

Change one network, doesn't matter which, to be 192.168.1.0/24, this gives you IP addresses 192.168.1.1 to 192.168.1.254 usable, netmask is 255.255.255.0

Set the nameservers to be your ISP (these can be the same for both networks).

Set one router to be the network 192.168.1.1, with the router address being 192.168.1.1 Routers are typically the first address in a subnet, doesn't have to be that way, but it's easier to remember.

Set the IP address on your windows NIC connected to the 192.168.1.x network to be 192.168.1.100, with the default gateway as 192.168.1.1

You should now have two networks, one in the free class A area of 10.0.0.0/8, and one in the free class C network of 192.168.1.0/24 (These are not routeable on the internet).

If both routers are connected to the internet, enable network address translation on both routers, so more than one device behind the router can access the net. If there isn't an internet connection for the second network, no need to enable NAT.

In windows, a "Default Route" needs to be used, this is the routing entry for 0.0.0.0, it should point to the router address with the fastest internet connection.

Hope this helps, post if you have issues. It helps to have a notebook to configure the second router while changing settings in Windows, otherwise you end up at a state in the middle where you don't have connectivity if you don't do it in a precise order.