Technical Tip: How to fix the error: 'WARNING: VLAN interface for default vlan -id is missing'

[pprince]

Description	This article describes how to fix the error 'VLAN interface for default vlan-id is missing' while troubleshooting a case where a managed FortiSwitch shows offline on FortiGate.
Scope	FortiGate v6.4.x and above, FortiSwitch v6.4.x and above.
Solution	During FortiSwitch authorization, FortiGate by default creates certain VLANs. A default VLAN is created with VLAN ID 1 to be assigned to all switch ports upon discovery. If the VLAN ID 1 default configuration has been changed, delete it, or if it is not present as one of the VLANs in the FortiLink configuration, FortiSwitch will not show online after authorizing it. This scenario can be verified with the commands: execute switch-controller diagnose-connection WARNING: VLAN interface for default vlan-id is missing ... please check config Fortswith status will show as discovered/Down: execute switch-controller get-conn-status Managed-devices in current vdom root: FortiLink interface : fortilink SWITCH-ID         VERSION           STATUS         FLAG   ADDRESS        JOIN-TIME           SERIAL         S108DVLXXXXXXXXXX  N/A               Discovered/Down 2                     N/A           S108DVLXXXXXXXXXX To fix the issue, configure a default VLAN using the following CLI commands: For example: config system interface edit "<VLAN_NAME>" set interface "fortilink" set vlanid XX set switch-controller-feature default-vlan  <----- This setting declares this VLAN as the default VLAN for the switch-controller. next end Important Considerations: The 'set switch-controller-feature default-vlan' command cannot be applied to an existing VLAN interface.  If no VLAN with this setting is present, a new VLAN interface must be created specifically for this purpose. While any VLAN ID and name can be technically used as the default VLAN, it is recommended in most environments to use VLAN ID 1 with the default name as defined by the FortiOS version in use. These default VLANs are automatically created upon a new FortiLink configuration. They are created using the 'switch-controller initial-config template'.   config switch-controller initial-config template     edit "_default"         set vlanid 1     next     edit "quarantine"         set vlanid 4093         set dhcp-server enable     next     edit "rspan"         set vlanid 4092         set dhcp-server enable     next     edit "voice"         set vlanid 4091     next     edit "video"         set vlanid 4090     next     edit "onboarding"         set vlanid 4089     next     edit "nac_segment"         set vlanid 4088         set dhcp-server enable     next end The name for the default VLAN ID 1 is different depending on the FortiOS version: VLAN ID Name (v6x) Name (v6.4) Name (v7.0-v7.6) 1 vsw.fortilink default _default 4091 voice voice voice         4090 video        video   video        4092 rspan         rspan         rspan         4089 onboarding    onboarding    onboarding   The name of the VLAN in the initial-config template is hardcoded, but the VLAN ID values can be changed.  Recommended Approach: To fix the issue, and if aligning with the default VLAN Name and ID is desired (using VLAN 1 as the default VLAN with its default name), two options are available: Option 1: Delete and Recreate VLAN 1: Delete the current VLAN 1 interface and recreate it using the appropriate default name and the default-vlan setting. This is a suitable option if there are not many references for VLAN ID 1.  For example: config system interface     edit "_default"         set vdom "root"         set ip x.x.x.x/x         set allowaccess ping         set interface "fortilink"         set vlanid 1         set switch-controller-feature default-vlan     next end Option 2: Modify the VLAN name ID in the config file and restore the config: Export the full FortiGate configuration. Search and replace all references to VLAN ID 1 with the correct default name (e.g: default in v7.4). Restore the modified configuration to the FortiGate.