Smart Link provides link redundancy using dual uplinks between different layers of the network, such as between the access layer and the distribution layer as shown in the figure below.
In this type of scenario Smart Link can be used in place of STP for faster convergence. Normally only the primary connection is active. When the primary connection is down, the backup connection will carry the traffic. This arrangement can be used for load sharing as well, in which case one link is configured as primary for a group of VLANs and the other link as primary for another group of VLANs (similar to MTSP instances).
Below is an example on how to configure Smart Link with VLAN load sharing. VLANs 1-10 are mapped to Smart Link group 1, while VLANs 11-20 are mapped to Smart Link group 2. The "role" option that follows "preemptive-mode" indicates that a Master port will take over as Master (for a group) after it comes back up from a failure.
smart-link group 1 master a1 slave a2
smart-link group 1 protected-vlans 1-10
smart-link group 1 send-control-vlan 1
smart-link group 1 preemption-mode role
smart-link group 1 preemption-delay 10
smart-link group 2 master a2 slave a1
smart-link group 2 protected-vlans 11-20
smart-link group 2 send-control-vlan 11
smart-link group 2 preemption-mode role
smart-link group 2 preemption-delay 10
To view Smart Link configuration and status, use the show smart-link commands.