A TRILL packet contains an inner and outer VLAN Tag. The inner 802.1Q tag represents the native Ethernet VLAN tag for the transport packet and must be present in the TRILL data packet. The inner frame must always have a VLAN ID of 1-4094. This is required to properly prune forwarding trees and reduce packet flooding. The outer 802.1Q tag represents the TRILL Designated VLAN and is determined by the Designated RBridge (DRB). All TRILL control traffic and data traffic is transmitted over the TRILL Designated VLAN, except for some TRILL Hello packets. The TRILL Designated VLAN Tag may or may not appear in the Ethernet header of the packet on the wire. This is determined by the Ethernet port configuration. By default, the priority bits in the outer 802.1Q tag should match the priority bits of the inner 802.1Q tag. Remapping of VLAN IDs and 802.1Q priority bits is permitted and is a local RBridge configuration option.
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