Hyper-v: NIC Issues

I'm having issues on VM running on Hyper-v with multiple NIC's. I have 3 NICs and they all have been binded individually. e.g. NIC 1 - Virtual Network 1, NIC 2 - Virtual Network 2, NIC 3 - Virtual Network 3.

With one of the guest OS, I have attached NIC 1 and 2. They are installed correctly and I do get response from them when pinging.

I'm getting issues with them when I'm unplugging cables to do test. When I unplug the cable from NIC 3, I get replies from the IP assigned on NIC 1 and no replies from the IP assigned to NIC 3. This is as expected.

However, when I unplug the cable from NIC 1, I get no reply from either IPs even though the cable is still plugged into the Nic 3.

How would I go about fixing this issue? Thank you
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Are you pinging from the Hyper-V machine or from a separate one?  How are subnets set up with these devices?
dave558Author Commented:
On a separate machine. Subnets are the same.

I noticed with Linux-based guest, when the networks are different, it behaves this way:
* unplugging NIC 3, the IP is not reachable for itself
* unplugging NIC 1, the IP is not reachable for itself
Behaviour when the subnet are the same:
* unplugging cable from NIC 3, I get replies from the IP assigned on NIC 1 and no replies from the IP assigned to NIC 3.
* unplugging cable from NIC 1, both devices aren't reachable

I'm thinking this issue would be related to traffic still being routed to the down interface. A fix to this would be to configure sourced based-routing.

However, I have a Windows-based guess that does the exact same thing as mentioned earlier regardless of whether the subnet is different or not. When NIC 1 is down, all other IPs assigned on the other NICs can't be reached.

I noticed that the Virtual Network Adapter never goes out in the "Network and Sharing Centre". I'm suspecting might be the reason as the system sill thinks the adapter is up on VMs.
Svet PaperovIT ManagerCommented:
You need to debug the routing table on the Windows host by using ROUTE command. For example, ROUTE PRINT displays the routing table.

The NIC on the virtual server doesn’t go off when unplugging the cable because the Virtual Adapter behaves as a Virtual switch not as a single adapter.
dave558Author Commented:
Yes, reason for NIC to run continuously is due to the virtual switch of hyper-v.

ROUTE doesn't appear to offer any routing decision based on policies and very limited to what it can do. I've looked at various virtual software but haven't found anything that do what is intended ie route traffic based on where the traffic was received.

Also after reviewing my needs, virtual routing solution isn't the most optimal and scalable solution. Due to limitation of hyper-v, alternatives such as XEN will be trialled instead.

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