H3C Technologies H3C S12500 Series Switches - Manual (Page 117)

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How Smart Link works
Link backup mechanism
As shown in Figure 23 , the link on GigabitEthernet 4/0/1 of Switch C is the master link, and the link on
GigabitEthernet 4/0/2 of Switch C is the slave link. Typically, GigabitEthernet 4/0/1 is in forwarding
state, while GigabitEthernet 4/0/2 is in standby state. When the link on GigabitEthernet 4/0/1 fails,
GigabitEthernet 4/0/2 takes over to forward traffic while GigabitEthernet 4/0/1 is blocked and placed
in 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.
• To keep traffic forwarding stable, the master port that has been blocked due to link failure does not take
over immediately upon its recovery. Instead, link switchover will occur at next link switchover.
Topology change mechanism
Because link switchover can outdate the MAC address forwarding entries and ARP/ND entries on all
switches, 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 switches not supporting smart link, including
switches of other vendors.
• Flush update where a Smart Link-enabled switch updates its information by transmitting flush
messages over the backup link to its upstream switches. This mechanism requires the upstream
switches to be capable of recognizing smart link flush messages to update their MAC address
forwarding entries and ARP/ND entries.
Role preemption mechanism
As shown in Figure 23 , the link on GigabitEthernet 4/0/1 of Switch C is the master link, and the link on
GigabitEthernet 4/0/2 of Switch C is the slave link. Once the master link fails, GigabitEthernet 4/0/1
is automatically blocked and placed in standby state, while GigabitEthernet 4/0/2 takes over to
forward traffic. When the master link recovers,
• If the smart link group is not configured with role preemption, to keep traffic forwarding stable,
GigabitEthernet 4/0/1 that has been blocked due to link failure does not immediately take over to
forward traffic. Rather, it stays blocked until the next link switchover.
• If the smart link group is configured with role preemption, GigabitEthernet 4/0/1 takes over to
forward traffic as soon as its link recovers, while GigabitEthernet 4/0/2 is automatically blocked
and placed in standby state.
Load sharing mechanism
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 (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 Multiple Spanning Tree
Instances (MSTIs).