TRILL Hellos are sent on all ports in a VLAN that have TRILL enabled and on all ports of a native Ethernet VLAN that has a VLAN ID that is operationally an Access VLAN for the TRILL network. Each RBridge learns and maintains an RBridge-VLAN-Port association in its neighbor table based on received TRILL Hello packets. If multiple RBridges are attached to the same VLAN interface, TRILL pseudonodes are used to simplify management of the link state database and each pseudonode is implicitly mapped to a single RBridge that is connected to a single port in the VLAN.
TRILL Hellos sent on TRILL VLANs will have the access port (AC) flag set to zero. If there are only only two TRILL ports on a link and they are configured as broadcast, then Hellos are sent with the Bypass (BY) pseudonode flag set to one. If there are less than two ports on a broadcast link, then a pseudonode is created. If multiple RBridges are detected on the port, subsequent TRILL Hellos are sent with the BY flag cleared. TRILL Hellos sent on Access VLANs will have the AC flag set to one. This instructs TRILL neighbors not to include this link in the TRILL link path and tree computations. A DRB is elected on the Access VLAN RBridge links for the purpose of assigning appointed forwarding status to each RBridge connected to the Access VLAN.
VLAN Mapping is not supported in the initial release, so the VLAN Mapping (VM) flag is always cleared. If a TRILL Hello is received with the VM flag set, VLAN Pruning is operationally disabled.
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