Changing native VLAN causes vms to no longer be able to talk

[loopsatan4894]

I have a Cisco 3850, and everything between my two vlans is just happy with ports being trunk and having a vlan of 30 with a native VLAN of 1. Inter VM communication stops working if I change the native VLAN to 30. I have the vswitch in esxi properly tagged as 30 as well.

But if I don't change the native VLAN, the Cisco that I'm trying to add to the network complains about a mismatched native VLAN on my original switch.

I'm newish to networking so I'm just kind of at a loss as to why this is being difficult

edit: Changed duplicate to mismatched.

[mlund]

Hi

In cisco, native vlan means that the native vlan is untagged, and also by default this is vlan1, and this is per interface, so you can have different native vlans on different interfaces. If you change the native vlan from 1 to 30, means that on this interface vlan 30 is now untagged, and that will not match your VM.

For your new switch if you are doing a trunk port between them the native vlan should be the same, otherwise you got the mismatch.

If you are connecting two switches together with ports in access-mode, then you will get mismatch if the ports are on different vlans.

There may be situations where you are forced to have different native vlans, and in that case you can disable cdp on the interface, because it is the cdp protocol that warns about the native mismatch.

There are also a possibility to force the switch to tag the native vlan, but that is a global command, so it will take effect for all ports on the switch.

/Mikael

[miandrew]

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@loopsatan4894 wrote:

I have a Cisco 3850, and everything between my two vlans is just happy with ports being trunk and having a vlan of 30 with a native VLAN of 1. Inter VM communication stops working if I change the native VLAN to 30. I have the vswitch in esxi properly tagged as 30 as well.

But if I don't change the native VLAN, the Cisco that I'm trying to add to the network complains about a mismatched native VLAN on my original switch.

I'm newish to networking so I'm just kind of at a loss as to why this is being difficult

edit: Changed duplicate to mismatched.

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It sounds like you're experiencing a VLAN mismatch issue when you try to change the native VLAN to 30. The fact that your inter-VLAN communication stops working when you make this change is likely due to the mismatch in VLAN configuration between your Cisco switch and your ESXi vSwitch.

The reason your Cisco switch is complaining about a mismatched native VLAN when you don't make the change is because the default native VLAN on Cisco switches is VLAN 1, and if your ESXi vSwitch is tagged as VLAN 30, it creates a conflict.

To resolve this, you should ensure consistency in your VLAN configurations:

1. On your Cisco switch, set the native VLAN back to 1 (the default). This aligns with the default native VLAN on ESXi.

2. On your ESXi vSwitch, make sure it's configured to use VLAN 30 as you mentioned. Ensure that all VMs and ports connected to this vSwitch are also configured for VLAN 30.

By having the same native VLAN (VLAN 1) on your Cisco switch and your ESXi vSwitch, and properly tagging VLAN 30 where needed, you should be able to maintain inter-VLAN communication without issues. Remember that VLAN configuration consistency is crucial for proper communication between devices on different VLANs. If you have further questions or run into any problems, feel free to ask for more assistanc or check this website.