VLANs | 229Configuring a VLAN Tunnel (DVLAN or VLAN-Stack)VLAN stacking, also called Double VLAN (DVLAN) and QinQ, support VLAN tunneling. In more detail,with the VLAN-Stack feature, you can “stack” VLANs into one tunnel and switch them through thenetwork. This feature is a way to pass VLAN traffic from one customer domain to another through a metrocore in a simple, cost-effective manner.The additional tag on the traffic helps differentiate between customers in the MAN while preserving theVLAN identification of the individual customers when the traffic enters their own 802.1Q domains. The4-byte tag precedes the VLAN tag and carries:• Protocol ID (Ethertype field)• Customer ID (VLAN ID field)DVLAN Tagging Considerations• Frame size: If the port is enabled for DVLAN tagging and maximum length frames are expected,jumbo frame support should also be enabled (Use the mtu command in Interface Config mode).• Port types: DVLAN tagging may be enabled for a LAG, but not for LAG members, VLAN routingports, or probe ports.• Control frames: Control frames (e.g. GARP, LACPDUs) will be double-tagged.• Ethertypes for DVLAN tags (“DVLAN tag” is sometimes shortened to DVT):• 802.1Q tag (0x8100)• vMAN tag (0x88A8)• Custom tag (any valid value)• The tunnel port (core port; uplink port) cannot be a routed port.• After the outer tag is added, QoS on the inner tag is not supported.DVLAN Configuration SequenceIf you have created the required VLANs and you want to associate access and trunk ports with a particularDVLAN bridging instance, you must enable the system for double VLAN tagging, define the access andtrunk ports, and then enable tagging on the trunk (core) port.Note: VLAN stacking functionality existed in SFTOS prior to SFTOS 2.5.2.0, but it was nottested in SFTOS 2.5.2.0, so it is not supported in versions after SFTOS 2.5.1.13.Step Command Syntax Command Mode Purpose1 dvlan-tunnel ethertype {802.1Q |vman | custom 0-65535}Global Config Enables the system for double VLANtagging with selected tagging.2 interface unit/slot/port Global Config By default, all ports become trunk (core)ports. Select a port to configure as an accessport.
