How Smart Link works
Link backup
As shown in Figure 37, the link on Port C1 of Device C is the primary link. The link on Port C2 of Device C is the secondary link. Port C1 is in forwarding state, and Port C2 is in standby state. When the primary link fails, Port C2 takes over to forward traffic and Port C1 is blocked and placed in standby state.
When a port switches to the forwarding state, the system outputs log information to notify the user of the port state change.
Topology change
Link switchover might outdate the MAC address entries and ARP/ND entries on all devices. A flush update mechanism is provided to ensure correct packet transmission. With this mechanism, a Smart Link-enabled device updates its information by transmitting flush messages over the backup link to its upstream devices. This mechanism requires the upstream devices to be capable of recognizing Smart Link flush messages to update their MAC address forwarding entries and ARP/ND entries.
Preemption mode
As shown in Figure 37, the link on Port C1 of Device C is the primary link. The link on Port C2 of Device C is the secondary link. When the primary link fails, Port C1 is automatically blocked and placed in standby state, and Port C2 takes over to forward traffic. When the primary link recovers, one of the following actions occurs:
If the smart link group is not configured with a preemption mode, Port C1 stays blocked to keep traffic forwarding stable. Port C1 does not take over to forward traffic until the next link switchover.
If the smart link group is configured with a preemption mode and the preemption conditions are met, Port C1 takes over to forward traffic as soon as its link recovers. Port C2 is automatically blocked and placed in standby state.
Load sharing
A ring network might carry traffic of multiple VLANs. Smart Link can forward traffic from different VLANs in different smart link groups for load sharing.
To implement load sharing, you can assign a port to multiple smart link groups. Configure each group with a different protected VLAN. Make sure the state of the port is different in these smart link groups, so traffic from different VLANs can be forwarded along different paths.
You can configure protected VLANs for a smart link group by referencing Multiple Spanning Tree Instances (MSTIs). For more information about MSTIs, see Layer 2—LAN Switching Configuration Guide.