Terminology
Smart link group
A smart link group consists of only two member ports: the primary and the secondary ports. Only one port is active for forwarding at a time, and the other port is blocked and in standby state. When link failure occurs on the active port due to port shutdown or the presence of unidirectional link, the standby port becomes active and takes over. The original active port transits to the blocked state.
As shown in Figure 37, Port C1 and Port C2 of Device C form a smart link group. Port C1 is active, and Port C2 is standby. Port D1 and Port D2 of Device D form another smart link group. Port D1 is active, and Port D2 is standby.
Primary/secondary port
Primary port and secondary port are two port types in a smart link group. When both ports in a smart link group are up, the primary port preferentially transits to the forwarding state. The secondary port stays in standby state. When the primary port fails, the secondary port takes over to forward traffic.
As shown in Figure 37, Port C1 of Device C and Port D1 of Device D are primary ports. Port C2 of Device C and Port D2 of Device D are secondary ports.
Primary/secondary link
The link that connects the primary port in a smart link group is the primary link. The link that connects the secondary port is the secondary link.
Flush message
When link switchover occurs, the smart link group uses flush messages to notify other devices to refresh their MAC address entries and ARP/ND entries. Flush messages are common multicast data packets, and will be dropped by a blocked receiving port.
Protected VLAN
A smart link group controls the forwarding state of protected VLANs. Each smart link group on a port controls a different protected VLAN. The state of the port in a protected VLAN is determined by the state of the port in the smart link group.
Transmit control VLAN
The transmit control VLAN is used for transmitting flush messages. When link switchover occurs, the devices (such as Device C and Device D in Figure 37) send flush messages within the transmit control VLAN.
Receive control VLAN
The receive control VLAN is used for receiving and processing flush messages. When link switchover occurs, the devices (such as Device A, Device B, and Device E in Figure 37) receive and process flush messages in the receive control VLAN. In addition, they refresh their MAC address entries and ARP/ND entries.