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:
```powershell
# 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! 🛠️