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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, and the original active port transits to the blocked state.
As shown in
Figure 23 , Port 1 and Port 2 of Device C form a smart link group and those of Device D form
another, with Port 1 being active and Port 2 being 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, and the secondary port
stays in standby state. Once the primary port fails, the secondary port takes over to forward traffic. As
shown in Figure 23 , you can configure Port 1 of Device C and that of Device D as primary ports, and Port
2 of Device C and that of Device D 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
Flush messages are used by a smart link group to notify other devices to refresh their MAC address
forwarding entries and ARP/ND entries when link switchover occurs in the smart link group. 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 23 ) 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 23 ) receive and process flush
messages in the receive control VLAN and refresh their MAC address forwarding entries and ARP/ND
entries.
How Smart Link works
Link backup
As shown in Figure 23 , the link on Port 1 of Device C is the primary link. The link on Port 2 of Device C
is the secondary link. Typically, Port 1 is in forwarding state, and Port 2 is in standby state. When the
primary link fails, Port 2 takes over to forward traffic and Port 1 is blocked and placed in standby state.