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I have the following topology:

Default Gateway1 <--> SWITCH1 <--> [ NIC2 - (Windows 10 PC) - NIC1 ] <--> SWITCH2 <--> Default Gateway2 --> Internet

NIC1 is DHCP configured, and connects to the internet successfully.

NIC2 has a static IP address/subnet mask/default gateway (They are correct as I tested them on another machine) but I can't ping its IP from switch1, even though they are directly connected.

I'm trying to isolate the issue to find if it's from the switch or PC, I can ping default gateway1 from switch1.

For NIC2, Wireshark shows that ARP can't resolve the MAC address for default gateway1, although this interface receives CDP/VTP Packets from switch1.

Is this a case of windows preferring to use the first interface and "implicitly" disabling the other one? Or do I need a specific configuration under the interface on switch1?

The interface configuration (authenticated using dot1x):

SW1-2960#show running-config interface g2/0/2
Building configuration...

Current configuration : 378 bytes
!
interface GigabitEthernet2/0/2
 switchport mode access
 authentication host-mode multi-auth
 authentication open
 authentication order dot1x mab
 authentication priority dot1x mab
 authentication port-control auto
 authentication periodic
 authentication timer reauthenticate 900
 authentication timer restart 2
 mab
 dot1x pae authenticator
 spanning-tree portfast edge
end

SW1-2960#
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  • This is more a comment than an answer, but I went beyond the length limit of what a comment can be. There are many unknowns in your setup. By the look of the provided config, this port is configured to use NAC/802.1X. VLAN may or may not get assigned based on authentication too. Based on the provided information we cannot tell why is the switch unable to ping the NIC2 interface, but if the authentication is not working, it should fail open & thus the interface will most likely get the default vlan assigned to the port. One thing I can suggest is to remove all the authentication configuration & Commented Jun 13, 2021 at 21:01
  • Most OSes are working fine with multiple NICs, including Windows 10. Your question is either about a host issue (off-topic) or it doesn't provide enough information to answer (also off-topic). Please check logs, status outputs etc to make sure that the PC's NIC is connected to the desired VLAN (it should show up on the VLAN's MAC table). Add the relevant information to your question.
    – Zac67
    Commented Jun 15, 2021 at 20:09

2 Answers 2

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Switch1 won't know jack about the network(s) on Switch2 unless you add an appropriate route. But as Win10 is not a router, one should not be routing foreign networks at it. (i.e. sw1's network cannot reach sw2's network through the PC.) The PC should be able to ping either switch, as it has directly connected interfaces in each network. The other devices in each network (i.e. the switches) cannot reach devices in the opposite network. (that's the job of a router.)

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  • I'm not trying to reach switch2 from sw1, I want the PC to be able to communicate with both switches, but it can only communicate with switch 2. Commented Jun 13, 2021 at 20:56
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    Then you have a host based issue (which is off-topic), or PEBKAC.
    – Ricky
    Commented Jun 14, 2021 at 14:09
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Your network is a really bad design. In order to route packets between networks, you use a router. In order to bridge frames on the same network, you use a bridge (a switch is a bridge). Your PC is neither a router nor a bridge, so traffic on each side of the PC is confined to that side of the PC.. It may be possible to run a routing or bridging application on your PC, but that is off-topic here.

Your switch would also need a layer-3 interface in the same network as your NIC for the switch to be able to ping the NIC.

If you are running separate networks on each NIC, then you should be able to use each network from your PC, although only one default route will be active in the PC.

If you are running the same network on both NICs, then you have other problems, and your symptoms will fit that scenario.

Unfortunately, questions about host/server configurations are off-topic here.

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