Native VLAN Mismatch Smart port enabled in Cisco switches CBS 350

Native VLAN Mismatch Smart port enabled in Cisco switches CBS 350: Smartport is a Cisco feature that automatically applies a set of preconfigured commands (called macros) to a switch port when it detects a specific type of device, such as an IP phone, printer, or wireless access point.

How it Works smartport in CBS 350

Detection: The switch uses protocols like CDP (Cisco Discovery Protocol) or LLDP to identify the connected device.

Macro Application: Once identified, it executes a macro (e.g., CISCO_PHONE_AUTO_SMARTPORT) to configure settings like VLANs, Quality of Service (QoS), and security.

Removal: When the device is disconnected (link-down), the switch typically removes those settings to return the port to a default state

Enabling and Disabling Smartports

Global Configuration

To turn the feature on or off for the entire switch:
Enable: macro auto global processing
Disable: no macro auto global processing

Per-Interface Configuration

You can control Smartports on a specific port even if it is enabled globally:

Enable on a port:
interface
macro auto smartport

Disable on a port:
interface
no macro auto smartport

Why Use (or Disable) Them?

Pros: It saves significant time in large deployments by ensuring devices like IP phones always get the correct voice VLAN and priority without manual work.

Cons: It can cause unexpected configuration changes or connectivity drops if a device is misidentified. In many environments where security is tight, admins prefer to disable Smartports to maintain strict manual control over port settings.

Note: On newer Cisco Business (CBS) switches, Smartport is often disabled by default in newer firmware versions because of these potential conflicts.

On the Cisco CBS350, a native VLAN mismatch often occurs because the Smartport feature automatically reconfigures ports when it detects a “neighbor” switch or device, overriding your manual settings.

Why Smartport causes this issues?

When Smartport is enabled, it uses protocols like CDP or LLDP to identify connected devices. If it detects another switch, it might automatically apply a “Switch” macro that resets the port’s native VLAN to VLAN 1 (default), even if you manually configured it to something else

How to fix it (CLI)

To stop the switch from fighting your manual configuration, you should globally disable Smartports:
Enter configuration mode:
configure

Disable Smartport globally:

no macro auto global processing (or macro auto disabled depending on firmware).
Manually set your trunk and native VLAN to match the other side:
interface
switchport mode trunk
switchport trunk native vlan

How to fix it (Web GUI)

Log in and switch the Display Mode (top right) to Advanced.
Navigate to Smartport > Properties.

Set Administrative Auto Smartport to Disable and click Apply.

Verify the native VLAN matches under VLAN Management > Port VLAN Membership or Port Config.

Verification

Use show interfaces trunk to see the operational native VLAN on the CBS350.

Use show cdp neighbors detail to see what the neighbor switch expects the native VLAN to be.

Note: If you are connecting a CBS350 to an older Sx350/550 or an IOS-based switch, a known bug (CSCwd91090) can cause false mismatch reports if the native VLAN is not explicitly “allowed” on the trunk

To resolve native VLAN mismatches while maintaining Voice VLAN functionality on a CBS350, you should disable the global Auto Smartport feature and switch to Telephony OUI for voice device detection.

Disable Smartports Globally

Disabling this stops the switch from overriding your native VLAN settings when it detects a neighbor.
CLI:

configure no macro auto global processing (or macro auto disabled).
Web GUI: Go to Smartport > Properties, select Disable for “Administrative Auto Smartport,” and click Apply.

Configure Voice VLAN Manually

Since “Auto Voice VLAN” depends on Smartports, you must use Telephony OUI (Organization Unique Identifier) to ensure phones are still placed in the correct VLAN based on their MAC address.

Step 1: Set the Voice VLAN ID

Go to VLAN Management > Voice VLAN > Properties. Enter your Voice VLAN ID and select Enable Telephony OUI.

Step 2: Enable on Interfaces

In VLAN Management > Voice VLAN > Interface Settings, select the ports connected to phones and set Voice VLAN State to Enable

Fix the Native VLAN Mismatch

With Smartports disabled, your manual trunk settings will now “stick”.

CLI Example:
interface
switchport mode trunk
switchport trunk native vlan .
Web GUI: Go to VLAN Management > Port VLAN Membership, select the port, click Join VLAN, and manually set the Native VLAN ID