To avoid single-point failures and guarantee network reliability, downstream devices are usually dual-homed to upstream devices, as shown in Figure 1.

Figure 1 Diagram for a dual uplink network

To remove network loops on a dual-homed network, you can use a spanning tree protocol or the Rapid Ring Protection Protocol (RRPP). The problem with STP, however, is that STP convergence time is long, which makes it not suitable for users who have high demand on convergence speed. RRPP can meet users’ demand on convergence speed, but it involves complicated networking and configurations and therefore is mainly used in ring-shaped networks.

NOTE:

For more information about STP and RRPP, see Layer 2—LAN Switching Configuration Guide and the chapter “Configuring RRPP.”

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 delivers the following benefits:

· 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. At a time, only one port is active for forwarding, and the other port is blocked, in other words, in 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 while the original active port transits to the blocked state.

As shown in Figure 1, GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 of Switch C and GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 of Switch D each form a smart link group, with GigabitEthernet 4/0/1 being active and GigabitEthernet 4/0/2 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, while the slave port stays in standby state. Once the master port fails, the slave port takes over to forward traffic. As shown in Figure 1, you can configure GigabitEthernet 4/0/1 of Switch C and that of Switch D as master ports, and GigabitEthernet 4/0/2 of Switch C and that of Switch 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 switches 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, which are referred to as 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 switches (such as Switch C and Switch D in Figure 1) 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 switches (such as Switch A, Switch B, and Switch E in Figure 1) receive and process flush messages in the receive control VLAN and refresh their MAC address forwarding entries and ARP/ND entries.

How Smart Link works

Link backup mechanism

As shown in Figure 1, 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. Normally, 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 1, 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 may 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).

Smart Link configuration task list

Complete the following tasks to configure Smart Link:

Task		Remarks
Configuring a Smart Link switch	Configuring protected VLANs for a Smart Link group	Required
	Configuring member ports for a Smart Link group	Required
	Configuring role preemption for a Smart Link group	Optional
	Enabling the sending of flush messages	Optional
Configuring an associated switch	Enabling the receiving of flush messages	Required

NOTE:

· A smart link switch is a switch that supports Smart Link and is configured with a smart link group and a transmit control VLAN for flush message transmission. Switch C and Switch D in Figure 1 are two smart link switches.

· An associated switch is a switch that supports Smart Link, and receives flush messages sent from the specified control VLAN. Switch A, Switch B, and Switch E in Figure 1 are examples of associated switches.

Configuring a Smart Link switch

Configuration prerequisites

Before configuring smart link, perform the following configurations:

· Shut down a port to prevent loops before configuring a port as a smart link group member. You can bring up the port only after completing the smart link group configuration.

· Disable the spanning tree feature and RRPP on the ports you want to add to the smart link group, and make sure that the ports are not member ports of any aggregation group.

NOTE:

A loop may occur on the network during the time when the spanning tree feature is disabled but Smart Link has not yet taken effect on a port.

Configuring protected VLANs for a Smart Link group

Protected VLANs for a smart link group are configured by referencing MSTIs. Before configuring the protected VLANs, configure the mappings between MSTIs and the VLANs to be protected.

To configure the protected VLANs for a smart link group:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter MST region view.	stp region-configuration	N/A
3. Configure the VLAN-to-instance mapping table.	· Approach 1: instance instance-id vlan vlan-list · Approach 2: vlan-mapping modulo modulo	Optional. Use either approach. All VLANs in an MST region are mapped to MSTI 0 by default.
4. Activate MST region configuration manually.	active region-configuration	N/A
5. Display the currently activated configuration information of the MST region.	display stp region-configuration [ \| { begin \| exclude \| include } regular-expression ]	Optional. This command is available in any view.
6. Return to system view.	quit	N/A
7. Create a smart link group and enter smart link group view.	smart-link group group-id	N/A
8. Configure protected VLANs for the smart link group.	protected-vlan reference-instance instance-id-list	By default, no protected VLAN is configured for a smart link group.

NOTE:

For more information about the stp region-configuration, instance, vlan-mapping modulo, active region-configuration, and display stp region-configuration commands, see Layer 2—LAN Switching Command Reference.

Configuring member ports for a Smart Link group

You can configure member ports for a smart link group either in smart link group view or in interface view. The configurations made in these two views have the same effect.

In smart link group view

To configure member ports for a smart link group in smart link group view:

Step	Command
1. Enter system view.	system-view
2. Create a smart link group and enter smart link group view.	smart-link group group-id
3. Configure member ports for a smart link group.	port interface-type interface-number { master \| slave }

In interface view

To configure member ports for a smart link group in interface view:

Step	Command
1. Enter system view.	system-view
2. Enter Ethernet interface view or layer 2 aggregate interface view.	interface interface-type interface-number
3. Configure member ports for a smart link group.	port smart-link group group-id { master \| slave }

Configuring role preemption for a Smart Link group

To configure role preemption for a smart link group:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Create a smart link group and enter smart link group view.	smart-link group group-id	N/A
3. Enable role preemption.	preemption mode role	Disabled by default
4. Configure the preemption delay.	preemption delay delay-time	Optional 1 second by default

NOTE:

The preemption delay setting takes effect only after role preemption is enabled.

Enabling the sending of flush messages

To enable the sending of flush messages:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Create a smart link group and enter smart link group view.	smart-link group group-id	N/A
3. Enable flush update in the specified control VLAN.	flush enable [ control-vlan vlan-id ]	Optional. By default, flush update is enabled, and VLAN 1 is the control VLAN.

CAUTION:

· The control VLAN configured for a smart link group must be different from that configured for any other smart link group.

· Make sure that the configured control VLAN already exists, and assign the smart link group member ports to the control VLAN.

· The control VLAN of a smart link group should also be one of its protected VLANs. Do not remove the control VLAN. Otherwise, flush messages cannot be sent properly.

Configuring an associated switch

Configuration prerequisites

Disable the spanning tree feature on the associated device’s ports that connect to the member ports of the smart link group; otherwise, the ports will discard flush messages when they are not in forwarding state in case of a topology change.

Enabling the receiving of flush messages

You do not need to enable all ports on the associated switches to receive flush messages sent from the transmit control VLAN, only those on the master and slave links between the smart link switch and the destination switch.

To enable the receiving of flush messages:

Step	Command	Remarks
1. Enter system view.	system-view	N/A
2. Enter Ethernet interface view or Layer 2 aggregate interface view.	interface interface-type interface-number	N/A
3. Configure the control VLAN for receiving flush messages.	smart-link flush enable [ control-vlan vlan-id-list ]	No control VLAN exists for receiving flush messages of Smart Link by default.

CAUTION:

· Configure all the control VLANs to receive flush messages.

· If no control VLAN is specified for processing flush messages, the switch forwards the received flush messages without processing them.

· Make sure that the receive control VLAN is the same as the transmit control VLAN configured on the Smart Link switch. If they are not the same, the associated switch will forward the received flush messages without any processing.

· Do not remove the control VLANs. Otherwise, flush messages cannot be sent properly.

· Make sure that the control VLANs are existing VLANs, and assign the port capable of receiving flush messages to the control VLANs.

Displaying and maintaining Smart Link

Task	Command	Remarks
Display smart link group information.	display smart-link group { group-id \| all } [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Display information about the received flush messages.	display smart-link flush [ \| { begin \| exclude \| include } regular-expression ]	Available in any view
Clear the statistics about flush messages.	reset smart-link statistics	Available in user view

Smart Link configuration examples

NOTE:

By default, Ethernet, VLAN, and aggregate interfaces are in DOWN state. Before configuring these interfaces, use the undo shutdown command to bring them up.

Single Smart Link group configuration example

Network requirements

As shown in Figure 2, Switch C and Switch D are smart link devices, and Switch A, Switch B, and Switch E are associated devices. Traffic of VLANs 1 through 30 on Switch C and Switch D are dually uplinked to Switch A.

Configure Smart Link on Switch C and Switch D for dual uplink backup.

Figure 2 Network diagram

Configuration procedure

1. Configure Switch C.

# Create VLANs 1 through 30, map these VLANs to MSTI 1, and activate the MST region configuration.

<SwitchC> system-view

[SwitchC] vlan 1 to 30

[SwitchC] stp region-configuration

[SwitchC-mst-region] instance 1 vlan 1 to 30

[SwitchC-mst-region] active region-configuration

[SwitchC-mst-region] quit

# Shut down GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2, disable the spanning tree feature on GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 separately, and configure them as trunk ports that permit VLANs 1 through 30.

[SwitchC] interface gigabitethernet 4/0/1

[SwitchC-GigabitEthernet4/0/1] shutdown

[SwitchC-GigabitEthernet4/0/1] undo stp enable

[SwitchC-GigabitEthernet4/0/1] port link-type trunk

[SwitchC-GigabitEthernet4/0/1] port trunk permit vlan 1 to 30

[SwitchC-GigabitEthernet4/0/1] quit

[SwitchC] interface gigabitethernet 4/0/2

[SwitchC-GigabitEthernet4/0/2] shutdown

[SwitchC-GigabitEthernet4/0/2] undo stp enable

[SwitchC-GigabitEthernet4/0/2] port link-type trunk

[SwitchC-GigabitEthernet4/0/2] port trunk permit vlan 1 to 30

[SwitchC-GigabitEthernet4/0/2] quit

# Create smart link group 1, and configure all VLANs mapped to MSTI 1 as the protected VLANs.

[SwitchC] smart-link group 1

[SwitchC-smlk-group1] protected-vlan reference-instance 1

# Configure GigabitEthernet 4/0/1 as the master port and GigabitEthernet 4/0/2 as the slave port for smart link group 1.

[SwitchC-smlk-group1] port gigabitethernet4/0/1 master

[SwitchC-smlk-group1] port gigabitethernet4/0/2 slave

# Enable flush message sending in smart link group 1, and configure VLAN 10 as the transmit control VLAN.

[SwitchC-smlk-group1] flush enable control-vlan 10

[SwitchC-smlk-group1] quit

# Bring up GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 again.

[SwitchC] interface gigabitethernet 4/0/1

[SwitchC-GigabitEthernet4/0/1] undo shutdown

[SwitchC-GigabitEthernet4/0/1] quit

[SwitchC] interface gigabitethernet 4/0/2

[SwitchC-GigabitEthernet4/0/2] undo shutdown

[SwitchC-GigabitEthernet4/0/2] quit

2. Configure Switch D.

# Create VLANs 1 through 30, map these VLANs to MSTI 1, and activate the MST region configuration.

<SwitchD> system-view

[SwitchD] vlan 1 to 30

[SwitchD] stp region-configuration

[SwitchD-mst-region] instance 1 vlan 1 to 30

[SwitchD-mst-region] active region-configuration

[SwitchD-mst-region] quit

[SwitchD] interface gigabitethernet 4/0/1

[SwitchD-GigabitEthernet4/0/1] shutdown

[SwitchD-GigabitEthernet4/0/1] undo stp enable

[SwitchD-GigabitEthernet4/0/1] port link-type trunk

[SwitchD-GigabitEthernet4/0/1] port trunk permit vlan 1 to 30

[SwitchD-GigabitEthernet4/0/1] quit

[SwitchD] interface gigabitethernet 4/0/2

[SwitchD-GigabitEthernet4/0/2] shutdown

[SwitchD-GigabitEthernet4/0/2] undo stp enable

[SwitchD-GigabitEthernet4/0/2] port link-type trunk

[SwitchD-GigabitEthernet4/0/2] port trunk permit vlan 1 to 30

[SwitchD-GigabitEthernet4/0/2] quit

# Create smart link group 1, and configure all VLANs mapped to MSTI 1 as the protected VLANs.

[SwitchD] smart-link group 1

[SwitchD-smlk-group1] protected-vlan reference-instance 1

# Configure GigabitEthernet 4/0/1 as the master port and GigabitEthernet 4/0/2 as the slave port for smart link group 1.

[SwitchD-smlk-group1] port gigabitethernet4/0/1 master

[SwitchD-smlk-group1] port gigabitethernet4/0/2 slave

# Enable flush message sending in smart link group 1, and configure VLAN 20 as the transmit control VLAN.

[SwitchD-smlk-group1] flush enable control-vlan 20

[SwitchD-smlk-group1] quit

# Bring up GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 again.

[SwitchD] interface gigabitethernet 4/0/1

[SwitchD-GigabitEthernet4/0/1] undo shutdown

[SwitchD-GigabitEthernet4/0/1] quit

[SwitchD] interface gigabitethernet 4/0/2

[SwitchD-GigabitEthernet4/0/2] undo shutdown

[SwitchD-GigabitEthernet4/0/2] quit

3. Configure Switch B.

# Create VLANs 1 through 30.

<SwitchB> system-view

[SwitchB] vlan 1 to 30

# Configure GigabitEthernet 4/0/1 as a trunk port, and assign it to VLANs 1 through 30. Enable flush message receiving on it, and configure VLAN 10 and VLAN 20 as the receive control VLANs.

[SwitchB] interface gigabitethernet 4/0/1

[SwitchB-GigabitEthernet4/0/1] port link-type trunk

[SwitchB-GigabitEthernet4/0/1] port trunk permit vlan 1 to 30

[SwitchB-GigabitEthernet4/0/1] smart-link flush enable control-vlan 10 20

[SwitchB-GigabitEthernet4/0/1] quit

# Configure GigabitEthernet 4/0/2 as a trunk port, and assign it to VLANs 1 through 30. Disable the spanning tree feature and enable flush message receiving on it, and configure VLAN 20 as the receive control VLAN.

[SwitchB] interface gigabitethernet 4/0/2

[SwitchB-GigabitEthernet4/0/2] port link-type trunk

[SwitchB-GigabitEthernet4/0/2] port trunk permit vlan 1 to 30

[SwitchB-GigabitEthernet4/0/2] undo stp enable

[SwitchB-GigabitEthernet4/0/2] smart-link flush enable control-vlan 20

[SwitchB-GigabitEthernet4/0/2] quit

# Configure GigabitEthernet 4/0/3 as a trunk port, and assign it to VLANs 1 through 30. Disable the spanning tree feature and enable flush message receiving on it, and configure VLAN 10 as the receive control VLAN.

[SwitchB] interface gigabitethernet 4/0/3

[SwitchB-GigabitEthernet4/0/3] port link-type trunk

[SwitchB-GigabitEthernet4/0/3] port trunk permit vlan 1 to 30

[SwitchB-GigabitEthernet4/0/3] undo stp enable

[SwitchB-GigabitEthernet4/0/3] smart-link flush enable control-vlan 10

[SwitchB-GigabitEthernet4/0/3] quit

4. Configure Switch E.

# Create VLANs 1 through 30.

<SwitchE> system-view

[SwitchE] vlan 1 to 30

# Configure GigabitEthernet 4/0/1 as a trunk port, and assign it to VLANs 1 through 30. Enable flush message receiving on it, and configure VLAN 10 and VLAN 20 as the receive control VLANs.

[SwitchE] interface gigabitethernet 4/0/1

[SwitchE-GigabitEthernet4/0/1] port link-type trunk

[SwitchE-GigabitEthernet4/0/1] port trunk permit vlan 1 to 30

[SwitchE-GigabitEthernet4/0/1] smart-link flush enable control-vlan 10 20

[SwitchE-GigabitEthernet4/0/1] quit

[SwitchE] interface gigabitethernet 4/0/2

[SwitchE-GigabitEthernet4/0/2] port link-type trunk

[SwitchE-GigabitEthernet4/0/2] port trunk permit vlan 1 to 30

[SwitchE-GigabitEthernet4/0/2] undo stp enable

[SwitchE-GigabitEthernet4/0/2] smart-link flush enable control-vlan 10

[SwitchE-GigabitEthernet4/0/2] quit

[SwitchE] interface gigabitethernet 4/0/3

[SwitchE-GigabitEthernet4/0/3] port link-type trunk

[SwitchE-GigabitEthernet4/0/3] port trunk permit vlan 1 to 30

[SwitchE-GigabitEthernet4/0/3] undo stp enable

[SwitchE-GigabitEthernet4/0/3] smart-link flush enable control-vlan 20

[SwitchE-GigabitEthernet4/0/3] quit

5. Configure Switch A.

# Create VLANs 1 through 30.

<SwitchA> system-view

[SwitchA] vlan 1 to 30

# Configure GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 as trunk ports that permit VLANs 1 through 30. Enable flush message receiving on them, and configure VLAN 10 and VLAN 20 as the receive control VLANs.

[SwitchA] interface gigabitethernet 4/0/1

[SwitchA-GigabitEthernet4/0/1] port link-type trunk

[SwitchA-GigabitEthernet4/0/1] port trunk permit vlan 1 to 30

[SwitchA-GigabitEthernet4/0/1] smart-link flush enable control-vlan 10 20

[SwitchA-GigabitEthernet4/0/1] quit

[SwitchA] interface gigabitethernet 4/0/2

[SwitchA-GigabitEthernet4/0/2] port link-type trunk

[SwitchA-GigabitEthernet4/0/2] port trunk permit vlan 1 to 30

[SwitchA-GigabitEthernet4/0/2] smart-link flush enable control-vlan 10 20

[SwitchA-GigabitEthernet4/0/2] quit

6. Verify the configuration.

You can use the display smart-link group command to display the smart link group configuration on a switch.

# Display the smart link group configuration on Switch C.

<SwitchC> display smart-link group 1

Smart link group 1 information:

Device ID: 000f-e23d-5af0

Preemption mode: NONE

Preemption delay: 1(s)

Control VLAN: 10

Protected VLAN: Reference Instance 1

Member Role State Flush-count Last-flush-time

-----------------------------------------------------------------------------

GigabitEthernet4/0/1 MASTER ACTVIE 5 16:37:20 2010/02/21

GigabitEthernet4/0/2 SLAVE STANDBY 1 17:45:20 2010/02/21

You can use the display smart-link flush command to display the flush messages received on a switch.

# Display the flush messages received on Switch B.

<SwitchB> display smart-link flush

Received flush packets : 5

Receiving interface of the last flush packet : GigabitEthernet4/0/3

Receiving time of the last flush packet : 16:25:21 2009/02/21

Device ID of the last flush packet : 000f-e23d-5af0

Control VLAN of the last flush packet : 1

Multiple Smart Link groups load sharing configuration example

Network requirements

As shown in Figure 3, Switch C is a smart link device, and Switch A, Switch B, and Switch D are associated devices. Traffic of VLANs 1 through 200 on Switch C are dually uplinked to Switch A by Switch B and Switch D.

Implement dual uplink backup and load sharing on Switch C: traffic of VLANs 1 through 100 is uplinked to Switch A by Switch B; traffic of VLANs 101 through 200 is uplinked to Switch A by Switch D.

Figure 3 Network diagram

Configuration procedure

1. Configure Device C.

# Create VLAN 1 through VLAN 200, map VLANs 1 through 100 to MSTI 1, and VLANs 101 through 200 to MSTI 2, and activate MST region configuration.

<SwitchC> system-view

[SwitchC] vlan 1 to 200

[SwitchC] stp region-configuration

[SwitchC-mst-region] instance 1 vlan 1 to 100

[SwitchC-mst-region] instance 2 vlan 101 to 200

[SwitchC-mst-region] active region-configuration

[SwitchC-mst-region] quit

# Shut down GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2, disable the spanning tree feature on GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 separately, configure the ports as trunk ports, and assign them to VLAN 1 through VLAN 200.

[SwitchC] interface gigabitethernet 4/0/1

[SwitchC-GigabitEthernet4/0/1] shutdown

[SwitchC-GigabitEthernet4/0/1] undo stp enable

[SwitchC-GigabitEthernet4/0/1] port link-type trunk

[SwitchC-GigabitEthernet4/0/1] port trunk permit vlan 1 to 200

[SwitchC-GigabitEthernet4/0/1] quit

[SwitchC] interface gigabitethernet 4/0/2

[SwitchC-GigabitEthernet4/0/2] shutdown

[SwitchC-GigabitEthernet4/0/2] undo stp enable

[SwitchC-GigabitEthernet4/0/2] port link-type trunk

[SwitchC-GigabitEthernet4/0/2] port trunk permit vlan 1 to 200

[SwitchC-GigabitEthernet4/0/2] quit

# Create smart link group 1, and configure all VLANs mapped to MSTI 1 as the protected VLANs for smart link group 1.

[SwitchC] smart-link group 1

[SwitchC-smlk-group1] protected-vlan reference-instance 1

# Configure GigabitEthernet 4/0/1 as the master port and GigabitEthernet 4/0/2 as the slave port for smart link group 1.

[SwitchC-smlk-group1] port gigabitethernet4/0/1 master

[SwitchC-smlk-group1] port gigabitethernet4/0/2 slave

# Enable role preemption in smart link group 1, enable flush message sending, and configure VLAN 10 as the transmit control VLAN.

[SwitchC-smlk-group1] preemption mode role

[SwitchC-smlk-group-1] flush enable control-vlan 10

[SwitchC-smlk-group-1] quit

# Create smart link group 2, and configure all VLANs mapped to MSTI 2 as the protected VLANs for smart link group 2.

[SwitchC] smart-link group 2

[SwitchC-smlk-group2] protected-vlan reference-instance 2

# Configure GigabitEthernet 4/0/1 as the slave port and GigabitEthernet 4/0/2 as the master port for smart link group 2.

[SwitchC-smlk-group2] port gigabitethernet4/0/2 master

[SwitchC-smlk-group2] port gigabitethernet4/0/1 slave

# Enable role preemption in smart link group 2, enable flush message sending, and configure VLAN 110 as the transmit control VLAN.

[SwitchC-smlk-group2] preemption mode role

[SwitchC-smlk-group2] flush enable control-vlan 110

[SwitchC-smlk-group2] quit

# Bring up GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 again.

[SwitchC] interface gigabitethernet 4/0/1

[SwitchC-GigabitEthernet4/0/1] undo shutdown

[SwitchC-GigabitEthernet4/0/1] quit

[SwitchC] interface gigabitethernet 4/0/2

[SwitchC-GigabitEthernet4/0/2] undo shutdown

[SwitchC-GigabitEthernet4/0/2] quit

2. Configure Switch B.

# Create VLAN 1 through VLAN 200.

<SwitchB> system-view

[SwitchB] vlan 1 to 200

# Configure GigabitEthernet 4/0/1 as a trunk port and assign it to VLANs 1 through 200. Enable flush message receiving and configure VLAN 10 and VLAN 110 as the receive control VLANs on GigabitEthernet 4/0/1.

[SwitchB] interface gigabitethernet 4/0/1

[SwitchB-GigabitEthernet4/0/1] port link-type trunk

[SwitchB-GigabitEthernet4/0/1] port trunk permit vlan 1 to 200

[SwitchB-GigabitEthernet4/0/1] smart-link flush enable control-vlan 10 110

[SwitchB-GigabitEthernet4/0/1] quit

# Configure GigabitEthernet 4/0/2 as a trunk port and assign it to VLANs 1 through 200. Disable the spanning tree feature and enable flush message receiving on it, and configure VLAN 10 and VLAN 110 as the receive control VLANs.

[SwitchB] interface gigabitethernet 4/0/2

[SwitchB-GigabitEthernet4/0/2] port link-type trunk

[SwitchB-GigabitEthernet4/0/2] port trunk permit vlan 1 to 200

[SwitchB-GigabitEthernet4/0/2] undo stp enable

[SwitchB-GigabitEthernet4/0/2] smart-link flush enable control-vlan 10 110

[SwitchB-GigabitEthernet4/0/2] quit

3. Configure Switch D.

# Create VLAN 1 through VLAN 200.

<SwitchD> system-view

[SwitchD] vlan 1 to 200

[SwitchD] interface gigabitethernet 4/0/1

[SwitchD-GigabitEthernet4/0/1] port link-type trunk

[SwitchD-GigabitEthernet4/0/1] port trunk permit vlan 1 to 200

[SwitchD-GigabitEthernet4/0/1] smart-link flush enable control-vlan 10 110

[SwitchD-GigabitEthernet4/0/1] quit

[SwitchD] interface gigabitethernet 4/0/2

[SwitchD-GigabitEthernet4/0/2] port link-type trunk

[SwitchD-GigabitEthernet4/0/2] port trunk permit vlan 1 to 200

[SwitchD-GigabitEthernet4/0/2] undo stp enable

[SwitchD-GigabitEthernet4/0/2] smart-link flush enable control-vlan 10 110

[SwitchD-GigabitEthernet4/0/2] quit

4. Configure Switch A.

# Create VLAN 1 through VLAN 200.

<SwitchA> system-view

[SwitchA] vlan 1 to 200

# Configure GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2 as trunk ports and assign them to VLANs 1 through 200. Enable flush message receiving and configure VLAN 10 and VLAN 110 as the receive control VLANs on GigabitEthernet 4/0/1 and GigabitEthernet 4/0/2.

[SwitchA] interface gigabitethernet 4/0/1

[SwitchA-GigabitEthernet4/0/1] port link-type trunk

[SwitchA-GigabitEthernet4/0/1] port trunk permit vlan 1 to 200

[SwitchA-GigabitEthernet4/0/1] smart-link flush enable control-vlan 10 110

[SwitchA-GigabitEthernet4/0/1] quit

[SwitchA] interface gigabitethernet 4/0/2

[SwitchA-GigabitEthernet4/0/2] port link-type trunk

[SwitchA-GigabitEthernet4/0/2] port trunk permit vlan 1 to 200

[SwitchA-GigabitEthernet4/0/2] smart-link flush enable control-vlan 10 110

[SwitchA-GigabitEthernet4/0/2] quit

5. Verify the configuration.

You can use the display smart-link group command to display the smart link group configuration on a switch.

# Display the smart link group configuration on Switch C.

<SwitchC> display smart-link group all

Smart link group 1 information:

Device ID: 000f-e23d-5af0

Preemption mode: ROLE

Preemption delay: 1(s)

Control VLAN: 10

Protected VLAN: Reference Instance 1

Member Role State Flush-count Last-flush-time

-----------------------------------------------------------------------------

GigabitEthernet4/0/1 MASTER ACTVIE 5 16:37:20 2010/02/21

GigabitEthernet4/0/2 SLAVE STANDBY 1 17:45:20 2010/02/21

Smart link group 2 information:

Device ID: 000f-e23d-5af0

Preemption mode: ROLE

Preemption delay: 1(s)

Control VLAN: 110

Protected VLAN: Reference Instance 2

Member Role State Flush-count Last-flush-time

-----------------------------------------------------------------------------

GigabitEthernet4/0/2 MASTER ACTVIE 5 16:37:20 2010/02/21

GigabitEthernet4/0/1 SLAVE STANDBY 1 17:45:20 2010/02/21

You can use the display smart-link flush command to display the flush messages received on a switch.

# Display the flush messages received on Switch B.

<SwitchB> display smart-link flush

Received flush packets : 5

Receiving interface of the last flush packet : GigabitEthernet4/0/2

Receiving time of the last flush packet : 16:25:21 2010/02/21

Device ID of the last flush packet : 000f-e23d-5af0

Control VLAN of the last flush packet : 10

12-High Availability Configuration Guide

Configuring Smart Link

Smart link group

Master/slave port

Master/slave link

Flush message

Protected VLAN

Transmit control VLAN

Receive control VLAN

How Smart Link works

Link backup mechanism

Topology change mechanism

Load sharing mechanism

Configuring a Smart Link switch

In smart link group view

In interface view

Configuring an associated switch

Displaying and maintaining Smart Link

Smart Link configuration examples

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Configuration procedure

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