90TerminologySmart Link groupA Smart Link group consists of only two member ports: the master and the subordinate. At a time,only one port is active for forwarding, and the other port is blocked, that is, in the standby state.When link failure occurs on the active port due to port shutdown or presence of unidirectional linkfor example, the standby port becomes active to take over while the original active port transits tothe blocked state.As shown in Figure 18 on page 89, GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 ofSwitch C form a Smart Link group, with GigabitEthernet 4/0/1 being active and GigabitEthernet4/0/2 being standby. GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 of Switch E formanother Smart Link group, with GigabitEthernet 4/0/2 being active and GigabitEthernet 4/0/1being standby.Master portMaster port is a port role in a Smart Link group. When both ports in a Smart Link group are up,the master port preferentially transits to the forwarding state. Once the master port fails, thesubordinate port takes over to forward traffic. During this period, if the Smart Link group is notconfigured with role preemption, the master port stays in standby state until the next linkswitchover even if it has recovered.As shown in Figure 18 on page 89, you can configure GigabitEthernet 4/0/1 of Switch C andGigabitEthernet 4/0/2 of Switch E as master ports.Subordinate (slave) portSubordinate port (also known as slave port) is another port role in a Smart Link group. Whenboth ports in a Smart Link group are up, the subordinate port is placed in the standby state.When the master port fails, the subordinate port takes over to forward traffic.As shown in Figure 18 on page 89, you can configure GigabitEthernet 4/0/2 of Switch C andGigabitEthernet 4/0/1 of Switch E as subordinate ports.Flush messageFlush messages are used by a Smart Link group to notify other switches to refresh their MACaddress forwarding entries and ARP/ND entries when link switchover occurs in the Smart Linkgroup. Flush messages are common unicast data packets, and will be dropped by a blockedreceiving port.Transmit control VLANThe transmit control VLAN is used for transmitting flush messages. When link switchover occurs,the switches (such as Switch C and E in Figure 18 on page 89) broadcast flush messages withinthe transmit control VLAN.Receive control VLANThe receive control VLAN is used for receiving and processing flush messages. When linkswitchover occurs, the switches (such as Switch A, B, and D in Figure 18) receive and process
