notes/projects/gg/avahi_mdns-reflector/20250714-esxi-networking.md

You're absolutely correct. In VMware ESXi, the "VLAN ID" field in the "Add Port Group" wizard is only for Access VLANs (single VLAN). To configure a trunk port group (multiple VLANs), you need to manually edit the port group settings after creation. Here's the step-by-step guide to configure a trunk port group with multiple VLANs:

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Step-by-Step: Configure Trunk Port Group in ESXi

1. Create the Port Group (Access Mode)

1. Go to vSphere Client > Networking > Switches > vSwitches.
2. Select the vSwitch you want to use.
3. Click Add Port Group.
4. Enter a Name (e.g., MGMT_VLAN).
5. Select VLAN Type: Access (this is the default).
6. Enter the VLAN ID for the management VLAN (e.g., 10).
7. Click OK.

⚠️ Note: This creates an Access VLAN (single VLAN). To enable trunking, you must edit the port group manually.

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2. Edit the Port Group to Enable Trunking

1. Right-click the port group (e.g., MGMT_VLAN) and select Edit Settings.
2. Under VLAN Settings, change VLAN Type to Trunk.
3. In the Tagged VLANs field, enter the VLAN IDs you want to allow (e.g., 10,20,30).
   • Important: Separate VLAN IDs with commas (no spaces).
4. Click OK.

✅ Example: If your management VLAN is 10 and you need mDNS traffic on VLANs 20 and 30, enter 10,20,30 in the Tagged VLANs field.

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3. Assign the VM to the Port Group

1. Go to the VM's settings.
2. Under Network Adapter, select the port group you configured (MGMT_VLAN).
3. Ensure the VM is assigned to the correct VLANs (the port group will handle the tagging).

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Key Notes

• Trunking is not available in the "Add Port Group" wizard. You must manually edit the port group to enable trunking.
• Physical Switch Configuration: Ensure the physical switch port connected to the ESXi host is configured as a trunk with the same VLANs (e.g., 10,20,30).
• VM Configuration: The VM will receive an IP address from the untagged VLAN (e.g., VLAN 10) and will have access to the tagged VLANs (e.g., 20,30) via the trunk port group.

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Why This Works

• Trunking allows the VM to communicate on multiple VLANs via a single physical interface.
• The untagged VLAN (e.g., 10) is used for management or default traffic.
• The tagged VLANs (e.g., 20,30) are used for specific services (like mDNS).

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Alternative: Use Command Line (PowerCLI)

If you prefer using the command line, you can configure trunking with PowerCLI:

# Connect to vCenter
Connect-VIServer -Server vcenter.example.com

# Get the vSwitch and port group
$vs = Get-VirtualSwitch -Name "vSwitch0"
$pg = Get-VMHostNetworkAdapter -VMHost $vmhost -Name "MGMT_VLAN"

# Set the port group to Trunk with VLANs 10,20,30
Set-VMHostNetworkAdapter -VMHost $vmhost -NetworkAdapter $pg -VlanId 10,20,30

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Summary

• Trunk port groups in ESXi require manual editing after creation.
• Use the Tagged VLANs field to specify multiple VLANs (e.g., 10,20,30).
• Ensure the physical switch is also configured as a trunk with the same VLANs.

Let me know if you need help verifying the switch configuration or troubleshooting VLAN tagging! 🛠️