Switch Management VLAN

The Management VLAN plays a crucial role in how a Switch connects to the Internet and communicates with the cloud. In order to connect to the cloud, the Switch needs to obtain a network configuration via DHCP. The Switch sends out DHCP configuration requests on all ports to which the Management VLAN is assigned. Once a network configuration has been obtained via DHCP, the Switch will begin reporting statistic data to the cloud and receive configuration settings from the cloud. 

By default, the Management VLAN is pre-configured on every port, ensuring a seamless plug-and-play experience. This allows the Switch to function immediately upon connection to a network, without requiring configuration—regardless of which port is used.

Example

Consider an 8-port Switch where the Management VLAN is configured on all ports.

The ports are connected to various devices, including a router, another Switch, Access Points, and end devices. How does the Switch determine which port to use as the uplink?

If a router is connected to port 1 and responds to the Switch’s DHCP request, port 1 will be designated as the uplink port. The other connected devices on ports 4, 5, 7, and 8 will not respond to DHCP requests.

Use cases for modifying the Management VLAN

1. Re-purposing Default VLANs

You may want to assign a different default VLAN (other than the Management VLAN) to specific ports for different use cases. However, only one default VLAN can be assigned per port. Since the Management VLAN is only required on the uplink port, you have the flexibility to assign default VLANs to non-uplink ports without affecting the cloud connectivity.

2. Preventing rogue DHCP Servers

A Switch may be connected to multiple routers or devices with DHCP servers. However, only one DHCP server should provide an IP address to the Switch—this should be the router connected to the Internet.

To prevent rogue DHCP servers from assigning incorrect IP address configurations and disconnecting the Switch from the cloud, you can remove the Management VLAN from non-uplink ports. This ensures that only the proper upstream router provides DHCP to the Switch.

Allowed Management VLAN

As mentioned before, Switch ports are pre-configured with the Management VLAN as the default VLAN. However, the Management VLAN can also be set as an Allowed VLAN instead of the default VLAN. To learn more about default vs. allowed VLANs, refer to this article.

Benefits of using Management VLAN via allowed VLAN:

• Tagged Management VLAN traffic coming from the Switch allows upstream devices to distinguish management traffic from other traffic.
• Enables prioritization of management traffic over other network traffic (e.g., reserving full throughput for management while throttling other traffic).

The graphic below visualizes this use-case.

If the Management VLAN is set as Allowed VLAN, both the Switch uplink port and the connected port of the upstream device must be configured with the allowed Management VLAN (tag 4094). This ensures the upstream device properly recognizes management traffic.

What happens if the Management VLAN is removed from all Switch Ports?

As mentioned before, the Management VLAN is essential for the Switch to connect to the Internet and communicate with the cloud. If it is entirely removed from all ports, the Switch will continue to function but can no longer be monitored or managed remotely.

To restore cloud management, the Switch must be reset to factory settings, which will reinstate the default Management VLAN configuration.