Smart Link is dedicated to dual-uplink networks as shown in Figure 1-1 to provide link redundancy with subsecond convergence. It allows the backup link to take over quickly when the primary link fails. In addition to fast convergence, Smart Link is easy to configure.

Terminology

Figure 1-1 Smart Link application scenario

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, that is, 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 while the original active port transits to the blocked state.

As shown in Figure 1-1, GigabitEthernet 2/0/1 and GigabitEthernet 2/0/2 of Device C form a smart link group, with GigabitEthernet 2/0/1 being active and GigabitEthernet 2/0/2 being standby. GigabitEthernet 2/0/1 and GigabitEthernet 2/0/2 of Device E form another smart link group, with GigabitEthernet 2/0/2 being active and GigabitEthernet 2/0/1 being standby.

Master port

Master 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, the slave port takes over to forward traffic. During this period, if the smart link group is not configured with role preemption, the master port stays in standby state until the next link switchover even if it has recovered.

As shown in Figure 1-1, you can configure GigabitEthernet 2/0/1 of Device C and GigabitEthernet 2/0/2 of Device E as master ports.

Slave port

Slave port is a port role in a smart link group. When both ports in a smart link group are up, the slave port is placed in the standby state. When the master port fails, the slave port takes over to forward traffic.

As shown in Figure 1-1, you can configure GigabitEthernet 2/0/2 of Device C and GigabitEthernet 2/0/1 of Device E as slave ports.

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.

Transmit control VLAN

The transmit control VLAN is used for transmitting flush messages. When link switchover occurs, the devices (such as Device C and E in Figure 1-1) 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 devices (such as Device A, B, and D in Figure 1-1) receive and process flush messages in the receive control VLAN and refresh their MAC address forwarding entries and ARP/ND entries.

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.

Operating Mechanism of Smart Link

Link backup mechanism

As shown in Figure 1-1, the link on GigabitEthernet 2/0/1 of Device C is the active link, and the link on GigabitEthernet 2/0/2 of Device C is the standby link. Normally, GigabitEthernet 2/0/1 is in the forwarding state, while GigabitEthernet 2/0/2 is in the standby state. When the link on GigabitEthernet 2/0/1 fails, GigabitEthernet 2/0/2 takes over to forward traffic while GigabitEthernet 2/0/1 is blocked and placed in the standby state.

When a port switches to the forwarding state, the system outputs log information to notify the user of the port state change.

As link switchover can outdate the MAC address forwarding entries and ARP/ND entries on all devices, you need a forwarding entry update mechanism to ensure proper transmission. By far, the following two update mechanisms are provided:

l Uplink traffic-triggered MAC address learning, where update is triggered by uplink traffic. This mechanism is applicable to environments with devices not supporting smart link, including devices of other vendors’.

l Flush update where 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 its MAC address forwarding entries and ARP/ND entries.

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.

Role preemption mechanism

As shown in Figure 1-1, the link on GigabitEthernet 2/0/1 of Device C is the active link, and the link on GigabitEthernet 2/0/2 of Device C is the standby link. Once GigabitEthernet 2/0/1 fails, GigabitEthernet 2/0/2 takes over to forward traffic. During this period, if the smart link group is configured with role preemption, GigabitEthernet 2/0/1 takes over to forward traffic as soon as it recovers.

Load sharing mechanism

A ring network may carry traffic of multiple VLANs. Smart link can forward traffic of different VLANs in different smart link groups, thus implementing 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 MSTIs.

Configuring a Smart Link Device

To use Smart Link on a device, you must configure the device with a smart link group and transmit control VLAN for flush message transmission. Device C and Device E in Figure 1-1 are two examples of Smart Link devices.

Configuration Prerequisites

l Before configuring a port as a smart link group member, shut down the port to prevent loops. You can bring up the port only after completing the smart link group configuration.

l Disable STP 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 or service loopback group.

Configuring a Smart Link Device

Follow these steps to configure a smart link device:

To do…		Use the command…	Remarks
Enter system view		system-view	—
Create a smart link group and enter smart link group view		smart-link group group-id	Required
Configure protected VLANs for the smart link group		protected-vlan reference-instance instance-id-list	Required By default, no protected VLAN is configured for a smart link group.
Specify the master port for the smart link group	In smart link group view	port interface-type interface-number master	Required Use either approach.
Specify the master port for the smart link group	In Ethernet interface view or Layer-2 aggregate interface view	port smart-link group group-id master	Required Use either approach.
Specify the slave port for the smart link group	In smart link group view	port interface-type interface-number slave	Required Use either approach.
Specify the slave port for the smart link group	In Ethernet interface view or Layer-2 aggregate interface view	port smart-link group group-id slave	Required Use either approach.
Enable role preemption		preemption mode role	Optional Disabled by default.
Enable flush update in the specified control VLAN		flush enable [ control-vlan vlan-id ]	Optional By default, VLAN 1 is used for flush update.

l The protected-vlan command configures protected VLANs for a smart link group by referencing MSTIs. To view VLAN-to-MSTI mappings, use the display stp region-configuration command. For VLAN-to-MSTI mapping configuration, refer to MSTP Configuration in the Access Volume.

l The protected VLANs configured for a smart link group must be different from those configured for any other smart link group.

l Make sure that the configured control VLANs are existing VLANs, and you must assign the smart link group member ports to the control VLANs.

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

Smart Link Device Configuration Example

Network requirements

l Create smart link group 1.

l The protected VLANs of smart link group 1 are mapped to MSTI 0 through 8.

l Configure GigabitEthernet 2/0/1 as the master port of the smart link group, and GigabitEthernet 2/0/2 as the slave port.

l Configure VLAN 20 for flush update.

Configuration procedure

<Sysname> system-view

[Sysname] vlan 20

[Sysname-vlan20] quit

[Sysname] interface GigabitEthernet 2/0/1

[Sysname-GigabitEthernet2/0/1] stp disable

[Sysname-GigabitEthernet2/0/1] port link-type trunk

[Sysname-GigabitEthernet2/0/1] port trunk permit vlan 20

[Sysname-GigabitEthernet2/0/1] quit

[Sysname] interface GigabitEthernet 2/0/2

[Sysname-GigabitEthernet2/0/2] stp disable

[Sysname-GigabitEthernet2/0/2] port link-type trunk

[Sysname-GigabitEthernet2/0/2] port trunk permit vlan 20

[Sysname-GigabitEthernet2/0/2] quit

[Sysname] smart-link group 1

[Sysname-smlk-group1] protected-vlan reference-instance 0 to 8

[Sysname-smlk-group1] port GigabitEthernet2/0/1 master

[Sysname-smlk-group1] port GigabitEthernet2/0/2 slave

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

Configuring an Associated Device

The active and standby links in a smart link group may traverse multiple devices between the Smart Link device and the destination device. For Smart Link to work, you need to enable all the ports on the way to the destination to process the flush messages sent from the smart link device.

For example, as all the numbered ports on Device A, B, and D in Figure 1-1 are on the way of the active and standby links from Device C and E to Device A, you need to enable the ports to process flush messages received from the control VLAN configured on Device C and E.

Configuring an Associated Device

Follow these steps to configure an associated device:

To do…	Use the command…	Remarks
Enter system view	system-view	—
Enter Ethernet interface view or Layer-2 aggregate interface view	interface interface-type interface-number	—
Configure the control VLAN for receiving flush messages	smart-link flush enable [ control-vlan vlan-id-list ]	Required No control VLAN exists for receiving flush messages of Smart Link by default.

l Configure all the control VLANs to receive flush messages.

l If no control VLAN is specified for processing flush messages, the device forwards the received flush messages directly without processing them.

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

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

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

Associated Device Configuration Example

Network requirements

Configure GigabitEthernet 2/0/1 to receive and process flush messages in VLAN 20.

Configuration procedure

<Sysname> system-view

[Sysname] vlan 20

[Sysname-vlan20] quit

[Sysname] interface GigabitEthernet2/0/1

[Sysname-GigabitEthernet2/0/1] port link-type trunk

[Sysname-GigabitEthernet2/0/1] port trunk permit vlan 20

[Sysname-GigabitEthernet2/0/1] smart-link flush enable control-vlan 20

Displaying and Maintaining Smart Link

To do...	Use the command…	Remarks
Display smart link group information	display smart-link group { group-id \| all }	Available in any view
Display information about the received flush messages	display smart-link flush	Available in any view
Clear the statistics about flush messages	reset smart-link statistics	Available in user view

Smart Link Configuration Examples

Single Smart Link Group Configuration Example

Network requirements

Both Device C and Device E are dually uplinked to Device A.

Configure Smart Link on the devices for uplink backup, adopting VLAN 1 (the default) for flush update.

Network diagram

Figure 1-2 Network diagram for smart link configuration

Configuration procedure

1) Configuration on Device C

# Disable STP on GigabitEthernet 2/0/1 and GigabitEthernet 2/0/2 separately.

<DeviceC> system-view

[DeviceC] interface GigabitEthernet 2/0/1

[DeviceC-GigabitEthernet2/0/1] stp disable

[DeviceC-GigabitEthernet2/0/1] quit

[DeviceC] interface GigabitEthernet 2/0/2

[DeviceC-GigabitEthernet2/0/2] stp disable

[DeviceC-GigabitEthernet2/0/2] quit

# Create smart link group 1 and configure all VLANs mapped to MSTIs 0 through 31 as the protected VLANs.

[DeviceC] smart-link group 1

[DeviceC-smlk-group1] protected-vlan reference-instance 0 to 31

# Configure GigabitEthernet 2/0/1 as the master port and GigabitEthernet 2/0/2 as the slave port.

[DeviceC-smlk-group1] port GigabitEthernet2/0/1 master

[DeviceC-smlk-group1] port GigabitEthernet2/0/2 slave

# Enable flush message sending in smart link group 1.

[DeviceC-smlk-group1] flush enable

[DeviceC-smlk-group1] quit

2) Configuration on Device E

# Disable STP on GigabitEthernet 2/0/1 and GigabitEthernet 2/0/2 separately.

<DeviceE> system-view

[DeviceE] interface GigabitEthernet 2/0/1

[DeviceE-GigabitEthernet2/0/1] stp disable

[DeviceE-GigabitEthernet2/0/1] quit

[DeviceE] interface GigabitEthernet 2/0/2

[DeviceE-GigabitEthernet2/0/2] stp disable

[DeviceE-GigabitEthernet2/0/2] quit

# Create smart link group 1 and configure all VLANs mapped to MSTIs 0 through 31 as the protected VLANs.

[DeviceE] smart-link group 1

[DeviceC-smlk-group1] protected-vlan reference-instance 0 to 31

# Configure GigabitEthernet 2/0/2 as the master port and GigabitEthernet 2/0/1 as the slave port.

[DeviceE-smlk-group1] port GigabitEthernet2/0/2 master

[DeviceE-smlk-group1] port GigabitEthernet2/0/1 slave

# Enable flush message sending in smart link group 1.

[DeviceE-smlk-group1] flush enable

[DeviceE-smlk-group1] quit

3) Configuration on Device B

# Configure VLAN 1 as the receive control VLAN for GigabitEthernet 2/0/1, GigabitEthernet 2/0/2, and GigabitEthernet 2/0/3.

<DeviceB> system-view

[DeviceB] interface GigabitEthernet 2/0/1

[DeviceB-GigabitEthernet2/0/1] smart-link flush enable

[DeviceB-GigabitEthernet2/0/1] quit

[DeviceB] interface GigabitEthernet 2/0/2

[DeviceB-GigabitEthernet2/0/2] smart-link flush enable

[DeviceB-GigabitEthernet2/0/2] quit

[DeviceB] interface GigabitEthernet 2/0/3

[DeviceB-GigabitEthernet2/0/3] smart-link flush enable

[DeviceB-GigabitEthernet2/0/3] quit

4) Configuration on Device D

# Configure VLAN 1 as the receive control VLAN for GigabitEthernet 2/0/1, GigabitEthernet 2/0/2, and GigabitEthernet 2/0/3.

<DeviceD> system-view

[DeviceD] interface GigabitEthernet 2/0/1

[DeviceD-GigabitEthernet2/0/1] smart-link flush enable

[DeviceD-GigabitEthernet2/0/1] quit

[DeviceD] interface GigabitEthernet 2/0/2

[DeviceD-GigabitEthernet2/0/2] smart-link flush enable

[DeviceD-GigabitEthernet2/0/2] quit

[DeviceD] interface GigabitEthernet 2/0/3

[DeviceD-GigabitEthernet2/0/3] smart-link flush enable

[DeviceD-GigabitEthernet2/0/3] quit

5) Configuration on Device A

# Configure VLAN 1 as the receive control VLAN for GigabitEthernet 2/0/1 and GigabitEthernet 2/0/2.

<DeviceA> system-view

[DeviceA] interface GigabitEthernet 2/0/1

[DeviceA-GigabitEthernet2/0/1] smart-link flush enable

[DeviceA-GigabitEthernet2/0/1] quit

[DeviceA] interface GigabitEthernet 2/0/2

[DeviceA-GigabitEthernet2/0/2] smart-link flush enable

[DeviceA-GigabitEthernet2/0/2] quit

6) Verifying the configurations

You can use the display smart-link group command to display the smart link group configuration on each device. For example:

# Display the smart link group configuration on Device C.

[DeviceC] display smart-link group 1

Smart link group 1 information:

Device ID: 000f-e23d-5af0

Preemption mode: NONE

Control VLAN: 1

Protected VLAN: Reference Instance 0 to 31

Member Role State Flush-count Last-flush-time

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

GigabitEthernet2/0/1 MASTER ACTVIE 5 16:37:20 2009/02/21

GigabitEthernet2/0/2 SLAVE STANDBY 1 17:45:20 2009/02/21

You can use the display smart-link flush command to display the flush messages received on each device. For example:

# Display the flush messages received on Device B.

[DeviceB] display smart-link flush

Received flush packets : 5

Receiving interface of the last flush packet : GigabitEthernet2/0/3

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

l The traffic of VLAN 1 through VLAN 200 on Device C are dually uplinked to Device A by Device B and Device D. Implement load sharing to uplink the traffic of VLAN 1 through VLAN 100 and the traffic of VLAN 101 through VLAN 200 over different links to Device A.

l Implement dual link backup on Device C: the traffic of VLANs 1 through 100 (mapped to MSTI 0) is uplinked to Device A by Device B; the traffic of VLANs 101 through 200 (mapped to MSTI 2) is uplinked to Device A by Device D. Smart link group 1 references MSTI 0, and smart link group 2 references MSTI 2.

l The control VLAN of smart link group 1 is VLAN 10 and that of smart link group 2 is VLAN 101.

Network diagram

Figure 1-3 Network diagram for multi-instance load sharing configuration

Configuration procedure

1) Configuration on Device C

# Create VLAN 1 through VLAN 200, map VLAN 1 through VLAN 100 to MSTI 0 and VLAN 101 through VLAN 200 to MSTI 2, and activate MST region configuration.

<DeviceC> system-view

[DeviceC] vlan 1 to 200

[DeviceC] stp region-configuration

[DeviceC-mst-region] instance 0 vlan 1 to 100

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

[DeviceC-mst-region] active region-configuration

[DeviceC-mst-region] quit

# Disable STP on GigabitEthernet 2/0/1 and GigabitEthernet 2/0/2 separately, configure the ports as trunk ports, and assign them to VLAN 1 through VLAN 200.

[DeviceC] interface GigabitEthernet 2/0/1

[DeviceC-GigabitEthernet2/0/1] stp disable

[DeviceC-GigabitEthernet2/0/1] port link-type trunk

[DeviceC-GigabitEthernet2/0/1] port trunk permit vlan 1 to 200

[DeviceC-GigabitEthernet2/0/1] quit

[DeviceC] interface GigabitEthernet 2/0/2

[DeviceC-GigabitEthernet2/0/2] stp disable

[DeviceC-GigabitEthernet2/0/2] port link-type trunk

[DeviceC-GigabitEthernet2/0/2] port trunk permit vlan 1 to 200

[DeviceC-GigabitEthernet2/0/2] quit

# Create smart link group 1.

[DeviceC] smart-link group 1

# Configure protected VLANs for smart link group 1.

[DeviceC-smlk-group1] protected-vlan reference-instance 0

# Configure GigabitEthernet 2/0/1 as the master port and GigabitEthernet 2/0/2 as the slave port.

[DeviceC-smlk-group1] port GigabitEthernet2/0/1 master

[DeviceC-smlk-group1] port GigabitEthernet2/0/2 slave

# Enable role preemption.

[DeviceC-smlk-group1] preemption mode role

# Configure VLAN 10 as the transmit control VLAN of smart link group 1.

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

[DeviceC-smlk-group-1] quit

# Create smart link group 2.

[DeviceC] smart-link group 2

# Configure protected VLANs for smart link group 2.

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

# Configure GigabitEthernet 2/0/1 as the slave port and GigabitEthernet 2/0/2 as the master port.

[DeviceC-smlk-group2] port GigabitEthernet2/0/1 slave

[DeviceC-smlk-group2] port GigabitEthernet2/0/2 master

# Enable role preemption.

[DeviceC-smlk-group2] preemption mode role

# Configure VLAN 101 as the transmit control VLAN of smart link group 2.

[DeviceC-smlk-group2] flush enable control-vlan 101

[DeviceC-smlk-group2] quit

2) Configuration on Device B

# Create VLAN 1 through VLAN 200.

<DeviceB> system-view

[DeviceB] vlan 1 to 200

# Configure GigabitEthernet 2/0/1 and GigabitEthernet 2/0/2 as trunk ports, and assign them to VLAN 1 through 200; enable flush message receiving on GigabitEthernet 2/0/1 and GigabitEthernet 2/0/2 and configure VLAN 10 and VLAN 101 as the receive control VLANs.

[DeviceB] interface GigabitEthernet 2/0/1

[DeviceB-GigabitEthernet2/0/1] port link-type trunk

[DeviceB-GigabitEthernet2/0/1] port trunk permit vlan 1 to 200

[DeviceB-GigabitEthernet2/0/1] smart-link flush enable control-vlan 10 101

[DeviceB-GigabitEthernet2/0/1] quit

[DeviceB] interface GigabitEthernet 2/0/2

[DeviceB-GigabitEthernet2/0/2] port link-type trunk

[DeviceB-GigabitEthernet2/0/2] port trunk permit vlan 1 to 200

[DeviceB-GigabitEthernet2/0/2] smart-link flush enable control-vlan 10 101

[DeviceB-GigabitEthernet2/0/2] quit

3) Configuration on Device D

# Create VLAN 1 through VLAN 200.

<DeviceD> system-view

[DeviceD] vlan 1 to 200

[DeviceD] interface GigabitEthernet 2/0/1

[DeviceD-GigabitEthernet2/0/1] port link-type trunk

[DeviceD-GigabitEthernet2/0/1] port trunk permit vlan 1 to 200

[DeviceD-GigabitEthernet2/0/1] smart-link flush enable control-vlan 10 101

[DeviceD-GigabitEthernet2/0/1] quit

[DeviceD] interface GigabitEthernet 2/0/2

[DeviceD-GigabitEthernet2/0/2] port link-type trunk

[DeviceD-GigabitEthernet2/0/2] port trunk permit vlan 1 to 200

[DeviceD-GigabitEthernet2/0/2] smart-link flush enable control-vlan 10 101

[DeviceD-GigabitEthernet2/0/2] quit

4) Configuration on Device A

# Create VLAN 1 through VLAN 200.

<DeviceA> system-view

[DeviceA] vlan 1 to 200

[DeviceA] interface GigabitEthernet 2/0/1

[DeviceA-GigabitEthernet2/0/1] port link-type trunk

[DeviceA-GigabitEthernet2/0/1] port trunk permit vlan 1 to 200

[DeviceA-GigabitEthernet2/0/1] smart-link flush enable control-vlan 10 101

[DeviceA-GigabitEthernet2/0/1] quit

[DeviceA] interface GigabitEthernet 2/0/2

[DeviceA-GigabitEthernet2/0/2] port link-type trunk

[DeviceA-GigabitEthernet2/0/2] port trunk permit vlan 1 to 200

[DeviceA-GigabitEthernet2/0/2] smart-link flush enable control-vlan 10 101

[DeviceA-GigabitEthernet2/0/2] quit

5) Verifying the configurations

You can use the display smart-link group command to display the smart link group configuration on each device. For example:

# Display the smart link group configuration on Device C.

[DeviceC] display smart-link group all

Smart link group 1 information:

Device ID: 000f-e23d-5af0

Preemption mode: ROLE

Control VLAN: 10

Protected VLAN: Reference Instance 0

Member Role State Flush-count Last-flush-time

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

GigabitEthernet2/0/1 MASTER ACTVIE 5 16:37:20 2009/02/21

GigabitEthernet2/0/2 SLAVE STANDBY 1 17:45:20 2009/02/21

Smart link group 2 information:

Device ID: 000f-e23d-5af0

Preemption mode: ROLE

Control VLAN: 101

Protected VLAN: Reference Instance 2

Member Role State Flush-count Last-flush-time

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

GigabitEthernet2/0/2 MASTER ACTVIE 5 16:37:20 2009/02/21

GigabitEthernet2/0/1 SLAVE STANDBY 1 17:45:20 2009/02/21

You can use the display smart-link flush command to display the flush messages received on each device. For example:

# Display the flush messages received on Device B.

[DeviceB] display smart-link flush

Received flush packets : 5

Receiving interface of the last flush packet : GigabitEthernet2/0/2

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 : 10

01-Access Volume

1 Smart Link Configuration

Smart link group

Master port

Slave port

Flush message

Transmit control VLAN

Receive control VLAN

Protected VLAN

Link backup mechanism

Role preemption mechanism

Load sharing mechanism

Network requirements

Configuration procedure

Configuring an Associated Device

Network requirements

Configuration procedure

Displaying and Maintaining Smart Link

Smart Link Configuration Examples

Network requirements

Network diagram

Configuration procedure

Network requirements

Network diagram

Configuration procedure

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