Dell N3200-ON Networking N-Series Switches User Guide version 6.8.0 - Page 744

The operation of GVRP relies upon the services provided by the Generic Attribute Registration Protocol (GARP). GVRP can create up to 1024 VLANs. For information about GARP timers, see "What Are GARP and GMRP?" on page 926. Double-VLAN Tagging For trunk ports, which are ports that connect one switch to another switch, the Dell Networking N-Series switches support double-VLAN tagging as an option. This feature allows service providers to connect to Virtual Metropolitan Area Networks (VMANs). With double-VLAN tagging, service providers can pass VLAN traffic from one customer domain to another through a metro core in a simple and cost-effective manner. By using an additional tag on the traffic, the switch can differentiate between customers in the MAN while preserving an individual customer's VLAN identification when the traffic enters the customer's 802.1Q domain. With the introduction of this second tag, customers are no longer required to divide the 4-byte VLAN ID space to send traffic on a Ethernet-based MAN. In short, every frame that is transmitted from an interface has a double-VLAN tag attached, while every packet that is received from an interface has a tag removed (if one or more tags are present). In Figure 20-2, two customers share the same metro core. The service provider assigns each customer a unique ID so that the provider can distinguish between the two customers and apply different rules to each. When the configurable EtherType is assigned to something different than the 802.1Q (0x8100) EtherType, it allows the traffic to have added security from misconfiguration while exiting the metro core. For example, if the edge device on the other side of the metro core is not stripping the second tag, the packet would never be classified as a 802.1Q tag, so the packet would be dropped rather than forwarded in the incorrect VLAN. 744 VLANs