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How Smart Link works
Link backup mechanism
As shown in Figure 23, the link on Port1 of Device C is the master link, and the link on Port2 of Device C
is the slave link. Typically, Port1 is in the forwarding state, and Port2 is in the standby state. When the
master link fails, Port2 takes over to forward traffic and Port1 is blocked and placed in the standby state.
NOTE:
When a port switches to the forwarding state, the system outputs log information to notify the user of
the port state change.
Topology change mechanism
Because link switchover can outdate the MAC address forwarding entries and ARP/ND entries on all
network devices, you need a forwarding entry update mechanism to ensure proper transmission. The
following update mechanisms are provided:
Uplink traffic-triggered MAC address learning, where update is triggered by uplink traffic. This
mechanism is applicable to environments with network devices that do not support Smart Link,
including devices of other vendors.
Flush update where 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 device
to be capable of recognizing Smart Link flush messages to update its MAC address forwarding
entries and ARP/ND entries.
Role preemption mechanism
As shown in Figure 23, the link on Port1 of Device C is the master link, and the link on Port2 of Device C
is the slave link. Once the master link fails, Port1 is automatically blocked and placed in the standby
state, and Port2 takes over to forward traffic.
When the master link recovers, one of the following occurs:
If the smart link group is not configured with role preemption, Port1 stays blocked, and no link
switchover occurs, ensuring traffic stability. Port1 does not transition to the forwarding state until the
next link switchover occurs.
If the smart link group is configured with role preemption, Port1 takes over to forward traffic as soon
as its link recovers, and Port2 is automatically blocked and placed in the standby state.
Load sharing mechanism
A ring network may carry traffic of multiple VLANs. Smart Link can forward traffic of different VLANs in
different smart link groups to implement load sharing.
To implement load sharing, you can assign a port to multiple smart link groups (each configured with
different protected VLANs), making sure that the state of the port is different in these smart link groups. In
this way, traffic of different VLANs can be forwarded along different paths.
You can configure protected VLANs for a smart link group by referencing MSTIs.
Smart Link collaboration mechanisms
Smart Link cannot sense by itself when faults occur on the uplink of the upstream devices, or when faults
are cleared. To monitor the uplink status of the upstream devices, you can configure the Monitor Link
function to monitor the uplink ports of the upstream devices. Monitor Link adapts the up/down state of
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