R3303-HP HSR6800 Routers High Availability Configuration Guide

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How Smart Link works
Link backup mechanism
As shown in Figure 28, the link on GigabitEthernet 3/0/1 of Router C is the primary link, and the link
on GigabitEthernet 3/0/2 of Router C is the secondary link. Typically, GigabitEthernet 3/0/1 is in
forwarding state, and GigabitEthernet 3/0/2 is in standby state. When the primary link fails,
GigabitEthernet 3/0/2 takes over to forward traffic and GigabitEthernet 3/0/1 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 mechanism
Because link switchover can outdate the MAC address forwarding entries and ARP/ND entries on all
devices, a forwarding entry update mechanism is needed to ensure proper transmission. The following
two update mechanisms are provided:
• Uplink traffic-triggered MAC address learning—Update is triggered by uplink traffic. This
mechanism is applicable to environments with devices not supporting Smart Link, including devices
of other vendors.
• Flush update—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.
Role preemption mechanism
As shown in Figure 28, the link on GigabitEthernet 3/0/1 of Router C is the primary link, and the link
on GigabitEthernet 3/0/2 of Router C is the secondary link. Once the primary link fails, GigabitEthernet
3/0/1 is automatically blocked and placed in standby state, and GigabitEthernet 3/0/2 takes over to
forward traffic. When the primary link recovers, one of the following things happen:
• If the smart link group is not configured with role preemption, to keep traffic forwarding stable,
GigabitEthernet 3/0/1 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 3/0/1 takes over to
forward traffic as soon as its link recovers, and GigabitEthernet 3/0/2 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).