Dual internet connection automatic failover?

Question

Hello,
we have two internet connections at home, and both are not very reliable, so i tought about configuring them for automatic failover.
I'm using them on my W520 and both connections are coming from separate routers, which are always running.
One is conected to w520 via ethernet cable, second via wifi.
Both are on different subnets and normally both routers IPs are set as default gateway.
The problem is, that the routers are always on, so the w520 has usually still connectivity to both routers (i.e. ping to both 192.168.100.252 and 192.168.1.1 is always working).
If one internet connection drops, this is on router side and w520 and its windows doesn't notice this as the connection from w520 to router is still OK.
So if the active connection fails (on router side) i have to manually disconnect it on w520, otherwise i get no internet (as the traffic is still routed via same network interface which reaches only the router [that without internet]).
I read something to use different metric for interfaces, but this is already configured "automatically" and this seem not to have any effect in case that connection to routers still work.
C:\>route print
IPv4 Route Table
===========================================================================
Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0  192.168.100.252    192.168.100.9     20
          0.0.0.0          0.0.0.0      192.168.1.1      192.168.1.5     30
I tried also to configure "Access Connections" for both connections simultaneously hoping it will choose the second in case of failure, but this doesn't work too:
(it maybe works in case the one connection fails to connect on w520 (e.g. router down), but this is not my case)
Is there any way how to configure this failover within OS (windows 7) only, without some dual wan router?
Thanks

Answer 1

As long as Windows have a working connection (interface link) either lan or wlan Windows don't know that one of the routers do not have a working internet connection. As far as i know there is no such functionality in Windows to make this work automatically. There might be some software available that can help you out, but not sure how this software should be aware of the missing internet access from one of the routers. That software will have to change the metric in the routing table (route print) on your Windows machine when one link is down.
With regards to the metric and default gateway, you can use several interfaces all configured with a default gateway, but only the one with the lowest metric will be used. The default gateway is the last resort and normally this is the only one used on a client computer even if it's possible to add more specific static routes. Two interfaces with a default gateway and same metric won't work and don't think it's even possible to set in Windows. In that case how should Windows know what default gateway to use. So basically set more than one default gateway in Windows is pointless unless you want Windows to switch when the link goes down (link to the PC).
I think the best option is to do this on the router and buy the required equipment for such functionality and maybe it's the only working options as well. You can also create two batchfiles, one that change the metric and default to use connection 1 and the other to use connection 2. That way you can switch manually just by a doubleclick on a icon. You use "route add...", "route delete..." and "route change..." to add, change and delete routes like the default gateway. It's still not automatic though.
-gan