Network routing behaviour

Question

The below image represents the high level configuration of a Windows 2019 Server that was recently built with 2 network adaptors. The 192.168.1.0/24 network circle shown below was not working. The network adaptors on the server were live and showed as connected within windows with a static IPs assigned. A config issue within VMware resulted in the network connection shown bellow as crossed out not working. The windows server shown was the only device connected to both of the respective networks. That however is not the issue I am asking about. Due to the config issue on that network causing that issue we noticed interesting behaviour of the Windows box with how it routed traffic.

If we initiated a ping to 192.168.1.1 from the server we indeed received a reply, although that IP resides on the same subnet as the network adaptor connected to the dead network. A tracert showed that the ping was sent via the other network adaptor using its default gateway. If we forced the ping out the 192.168.1.10 adaptor with the -S parameter the ping would fail.

Although the network object we were trying to reach existed on the same subnet as a network adaptor, which as far as Windows was concerned was in a connected state, it sent out the ping via the other network adaptor using the default gateway. It's almost like it failed over, as Windows detected the network it was connected to had nothing in it.

Is this standard behaviour of Windows?

Answer 1

Hello there,

Yes, the behavior you described is consistent with how Windows handles network connectivity and routing in certain scenarios. Windows operating systems use a feature called "Automatic Metric" to determine the best network interface to use for routing traffic. When multiple network interfaces are active, Windows assigns a metric value to each interface. The interface with the lowest metric becomes the default route for outbound traffic.

In the situation you described, where there are two network adapters (interfaces) present on the same subnet, Windows might assign a lower metric to one of them based on various factors such as link speed, connection quality, or manual configuration. The adapter with the lower metric would be preferred for routing traffic to devices on the same subnet.

Hope this resolves your Query !!

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