H3C Technologies H3C S10500 Series Switches - Manual (Page 106)

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Smart Link is a feature developed to address the slow convergence issue with STP. It provides link
redundancy as well as fast convergence in a dual uplink network, allowing the backup link to take over
quickly when the primary link fails. To sum up, Smart Link has the following features:
• Dedicated to dual uplink networks
• Subsecond convergence
• Easy to configure
Terminology
Smart link group
A smart link group consists of only two member ports: the master and the slave ports. At a time, only one
port is active for forwarding, and the other port is blocked and in the standby state. When link failure
occurs on the active port due to port shutdown or presence of unidirectional link for example, the standby
port becomes active to take over and the original active port transits to the blocked state.
As shown in
Figure
25 , Port1 and Port2 of Device C and Port1 and Port2 of Device D each form a smart
link group, with Port1 being active and Port2 being standby.
Master/slave port
Master port and slave port are two port roles in a smart link group. When both ports in a smart link
group are up, the master port preferentially transits to the forwarding state, and the slave port stays in the
standby state. Once the master port fails, the slave port takes over to forward traffic. As shown in
Figure
25 , you can configure Port1 of Device C and Port1 of Device D as master ports, and Port2 of Device C
and Port2 of Device D slave ports.
Master/slave link
The link that connects the master port in a smart link group is the master link. The link that connects the
slave port is the slave link.
Flush message
Flush messages are used by a smart link group to notify other devices to refresh their MAC address
forwarding entries and ARP/ND entries when link switchover occurs in the smart link group. Flush
messages are common multicast data packets, and will be dropped by a blocked receiving port.
Protected VLAN
A smart link group controls the forwarding state of some data VLANs (protected VLANs). Different smart
link groups on a port control different protected VLANs. The state of the port in a protected VLAN is
determined by the state of the port in the smart link group.
Transmit control VLAN
The transmit control VLAN is used for transmitting flush messages. When link switchover occurs, the
devices (such as Device C and Device D in
Figure
25 ) broadcast flush messages within the transmit
control VLAN.
Receive control VLAN
The receive control VLAN is used for receiving and processing flush messages. When link switchover
occurs, the devices (such as Device A, Device B, and Device E in
Figure
25 ) receive and process flush
messages in the receive control VLAN and refresh their MAC address forwarding entries and ARP/ND
entries.