A common problem faced by dashboard administrators is communication between hosts in different parts of the network. The troubleshooting process for this sort of issue typically involves following the path of communication between the two hosts and verifying that each interconnecting switchport in the network topology is configured to use the required VLANs.
Meraki switches will automatically display an alert if mismatched VLAN settings are detected between connected switchports. This document describes the appearance and behavior of these alerts, as well as how to correct the VLAN mismatch.
What is a VLAN Mismatch?
A VLAN mismatch occurs when two connected switchports have different VLAN configurations. For example, switch 1 port 1 is configured for native VLAN: 1, allowed VLANs: all. This port connects to switch 2 port 48 which is configured for native VLAN: 1, allowed VLANs: 1 and 2 only. In this scenario, a host in VLAN 3 on switch 1 would not be able to communicate with a host on switch 2 in the same VLAN.
How a VLAN Mismatch is Detected
This feature utilizes CDP and LLDP packets from the past 3 hours to determine which switchports are connected. If any two connected switch ports belong to Meraki switches in the same dashboard organization, the switchport VLAN configurations are compared.
If any mismatch is found in native, allowed, or access VLANs, both switches will display an alert in the dashboard. The switches will continue displaying the alert until the VLAN mismatch is resolved.
Currently, VLAN mismatch detection is supported on Meraki switches in the same organization. VLAN mismatch detection for other Meraki devices (MRs, MXs, etc.) and non-Meraki devices is not supported.
Correcting a VLAN Mismatch
Once a VLAN mismatch is detected, the switch status will change to ‘Alerting’ and yellow in the dashboard. An overview of switch statuses in a network can be seen from the Switch > Switches page in dashboard. Select the alerting switch to view the switch’s overview page.
As seen below, an alert is displayed under the switch’s name at the top left of the switch overview page. Multiple alerts will show up if there are multiple ports on the switch with mismatches detected. Displayed alerts are automatically checked and generated about once every 40 minutes. However, updating a port's VLAN configuration will immediately update the alert.
In this case, the switch detects port 1 is not using the same VLAN settings as its connected switchport. To see more detail about the detected mismatch, select the port from the port view.
After selecting the switchport, scroll down to the Status section. Hover over the CDP/LLDP section’s VLAN mismatch warning for a comparison of the currently selected port’s VLAN settings and the connected port’s settings.
The CDP/LLDP section provides a link to the dashboard page of the switch connected to this switchport. Follow this link to view the connected switch. The connected switch’s overview page will also display an alert indicating which port detects a VLAN mismatch. Configure the switchport VLAN settings to match as appropriate. The VLAN configurations must match exactly in order for the mismatch alert to clear. To learn how to configure switchport VLAN membership, check out our Switch Ports article.
If multiple ports on the connected switch are alerting for VLAN mismatches, select the raw link in the CDP/LLDP section. The raw data will include the port on the connected switch to which this switch connects. In this case, the MS220 port 1 CDP/LLDP data shows that it connects to “MS250” on port 11.