Configuring FlexLinks and the MAC Address-Table Move Update Feature
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Configuring FlexLinks and the MAC Address-Table Move Update Feature

This chapter contains the following topics:

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Related References

Restrictions for Configuring FlexLinks and MAC Address-Table Move Update

The following are restrictions for configuring FlexLinks and the MAC Address-Table Move Update feature:

  • FlexLinks are supported only on Layer 2 ports and port channels, not on VLANs or on Layer 3 ports.
  • You can configure up to 16 backup links.
  • You can configure only one FlexLinks backup link for any active link, and it must be a different interface from the active interface.
  • An interface can belong to only one FlexLinks pair. An interface can be a backup link for only one active link. An active link cannot belong to another FlexLinks pair.
  • Neither of the links can be a port that belongs to an EtherChannel. However, you can configure two port channels (EtherChannel logical interfaces) as FlexLinks, and you can configure a port channel and a physical interface as FlexLinks, with either the port channel or the physical interface as the active link.
  • A backup link does not have to be the same type (Gigabit Ethernet or port channel) as the active link. However, you should configure both FlexLinks with similar characteristics so that there are no loops or changes in behavior if the standby link begins to forward traffic.
  • STP is disabled on FlexLinks ports. A FlexLinks port does not participate in STP, even if the VLANs present on the port are configured for STP. When STP is not enabled, be sure that there are no loops in the configured topology.
Related Tasks
Related References

Information About FlexLinks and the MAC Address-Table Move Update

This chapter describes how to configure FlexLinks, a pair of interfaces on the switch that provide a mutual backup. It also describes how to configure the MAC address-table move update feature, also referred to as the FlexLinks bidirectional fast convergence feature.

FlexLinks

FlexLinks are a pair of a Layer 2 interfaces (switch ports or port channels) where one interface is configured to act as a backup to the other. The feature provides an alternative solution to the Spanning Tree Protocol (STP). Users can disable STP and still retain basic link redundancy. FlexLinks are typically configured in service provider or enterprise networks where customers do not want to run STP on the switch. If the switch is running STP, FlexLinks are not necessary because STP already provides link-level redundancy or backup.

You configure FlexLinks on one Layer 2 interface (the active link) by assigning another Layer 2 interface as the FlexLinks or backup link. On switches, the FlexLinks can be on the same switch or on another switch in the stack. When one of the links is up and forwarding traffic, the other link is in standby mode, ready to begin forwarding traffic if the other link shuts down. At any given time, only one of the interfaces is in the linkup state and forwarding traffic. If the primary link shuts down, the standby link starts forwarding traffic. When the active link comes back up, it goes into standby mode and does not forward traffic. STP is disabled on FlexLinks interfaces.

Related Tasks
Related References

FlexLinks Configuration

In the following figure, ports 1 and 2 on switch A are connected to uplink switches B and C. Because they are configured as FlexLinks, only one of the interfaces is forwarding traffic; the other is in standby mode. If port 1 is the active link, it begins forwarding traffic between port 1 and switch B; the link between port 2 (the backup link) and switch C is not forwarding traffic. If port 1 goes down, port 2 comes up and starts forwarding traffic to switch C. When port 1 comes back up, it goes into standby mode and does not forward traffic; port 2 continues forwarding traffic.

You can also configure a preemption function, specifying the preferred port for forwarding traffic. For example, you can configure the FlexLinks pair with preemption mode. In the scenario shown, when port 1 comes back up and has more bandwidth than port 2, port 1 begins forwarding traffic after 60 seconds. Port 2 becomes the standby port. You do this by entering the switchport backup interface preemption mode bandwidth and switchport backup interface preemption delay interface configuration commands.

Figure 1. FlexLinks Configuration Example

If a primary (forwarding) link goes down, a trap notifies the network management stations. If the standby link goes down, a trap notifies the users.

FlexLinks are supported only on Layer 2 ports and port channels, not on VLANs or on Layer 3 ports.

Related Tasks

VLAN FlexLinks Load Balancing and Support

VLAN FlexLinks load balancing allows users to configure a FlexLinks pair so that both ports simultaneously forward the traffic for some mutually exclusive VLANs. For example, if FlexLinks ports are configured for 1 to 100 VLANs, the traffic of the first 50 VLANs can be forwarded on one port and the rest on the other port. If one of the ports fail, the other active port forwards all the traffic. When the failed port comes back up, it resumes forwarding traffic in the preferred VLANs. In addition to providing the redundancy, this FlexLinks pair can be used for load balancing. FlexLinks VLAN load balancing does not impose any restrictions on uplink switches.

Figure 2. VLAN Flex Links Load-Balancing Configuration Example. The following figure displays a VLAN FlexLinks load-balancing configuration.

MAC Address-Table Move Update

The MAC address-table move update feature allows the switch to provide rapid bidirectional convergence when a primary (forwarding) link goes down and the standby link begins forwarding traffic.

Figure 3. MAC Address-Table Move Update Example. In the following figure, switch A is an access switch, and ports 1 and 2 on switch A are connected to uplink switches B and D through a FlexLinks pair. Port 1 is forwarding traffic, and port 2 is in the backup state. Traffic from the PC to the server is forwarded from port 1 to port 3. The MAC address of the PC has been learned on port 3 of switch C. Traffic from the server to the PC is forwarded from port 3 to port 1.

If the MAC address-table move update feature is not configured and port 1 goes down, port 2 starts forwarding traffic. However, for a short time, switch C keeps forwarding traffic from the server to the PC through port 3, and the PC does not get the traffic because port 1 is down. If switch C removes the MAC address of the PC on port 3 and relearns it on port 4, traffic can then be forwarded from the server to the PC through port 2.

If the MAC address-table move update feature is configured and enabled on the switches, and port 1 goes down, port 2 starts forwarding traffic from the PC to the server. The switch sends a MAC address-table move update packet from port 2. Switch C gets this packet on port 4 and immediately learns the MAC address of the PC on port 4, which reduces the reconvergence time.

You can configure the access switch, switch A, to send MAC address-table move update messages. You can also configure the uplink switches B, C, and D to get and process the MAC address-table move update messages. When switch C gets a MAC address-table move update message from switch A, switch C learns the MAC address of the PC on port 4. Switch C updates the MAC address table, including the forwarding table entry for the PC.

Switch A does not need to wait for the MAC address-table update. The switch detects a failure on port 1 and immediately starts forwarding server traffic from port 2, the new forwarding port. This change occurs in 100 milliseconds (ms). The PC is directly connected to switch A, and the connection status does not change. Switch A does not need to update the PC entry in the MAC address table.

Related Tasks
Related References

VLAN Load Balancing Configuration Guidelines

Follow these guidelines to configure VLAN load balancing on the FlexLinks feature:

  • For FlexLinks, VLAN load balancing, you must choose the preferred VLANs on the backup interface.
  • You cannot configure a preemption mechanism and VLAN load balancing for the same FlexLinks pair.

Follow these guidelines to configure MAC address-table move update feature:

  • You can enable and configure this feature on the access switch to send the MAC address-table move updates.
  • You can enable and configure this feature on the uplink switches to get the MAC address-table move updates.
Related Tasks
Related References

Default FlexLinks and MAC Address-Table Move Update Configuration

  • FlexLinks is not configured, and there are no backup interfaces defined.
  • The preemption mode is off.
  • The preemption delay is 35 seconds.
  • The MAC address-table move update feature is not configured on the switch
Related Tasks
Related References

How to Configure FlexLinks and the MAC Address-Table Move Update Feature

Configuring FlexLinks

SUMMARY STEPS

    1.    configure terminal

    2.    interface interface-id

    3.    switchport backup interface interface-id

    4.    end


DETAILED STEPS
     Command or ActionPurpose
    Step 1configure terminal


    Example:
    
Switch# configure terminal
     

    Enters global configuration mode.

     
    Step 2interface interface-id


    Example:
    
Switch(conf)# interface gigabitethernet1/0/1
     

    Specifies the interface, and enter interface configuration mode. The interface can be a physical Layer 2 interface or a port channel (logical interface). The port-channel range is 1 to 48.

     
    Step 3switchport backup interface interface-id


    Example:
    
Switch(conf-if)# switchport backup interface 
gigabitethernet1/0/2
     

    Configures a physical Layer 2 interface (or port channel) as part of a FlexLinks pair with the interface. When one link is forwarding traffic, the other interface is in standby mode.

     
    Step 4end


    Example:
    
Switch(conf-if)# end
     

    Returns to privileged EXEC mode.

     
    Related Concepts
    Related References

    Configuring a Preemption Scheme for a Pair of FlexLinks

    SUMMARY STEPS

      1.    configure terminal

      2.    interface interface-id

      3.    switchport backup interface interface-id

      4.    switchport backup interface interface-id preemption mode [forced | bandwidth | off]

      5.    switchport backup interface interface-id preemption delay delay-time

      6.    end

      7.    show interface [interface-id] switchport backup

      8.    copy running-config startup config


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 configure terminal


      Example: 
      Switch# configure terminal
       

      Enters global configuration mode

       
      Step 2interface interface-id


      Example:
      Switch(conf)# interface gigabitethernet1/0/1
       

      Specifies the interface, and enter interface configuration mode. The interface can be a physical Layer 2 interface or a port channel (logical interface). The port-channel range is 1 to 48.

       
      Step 3switchport backup interface interface-id


      Example:
      Switch(conf-if)# switchport backup interface gigabitethernet1/0/2
       

      Configures a physical Layer 2 interface (or port channel) as part of a FlexLinks pair with the interface. When one link is forwarding traffic, the other interface is in standby mode.

       
      Step 4switchport backup interface interface-id preemption mode [forced | bandwidth | off]


      Example:
      Switch(conf-if)# switchport backup interface gigabitethernet1/0/2 preemption mode forced
       

      Configures a preemption mechanism and delay for a FlexLinks interface pair. You can configure the preemption as:

      • forced—(Optional) The active interface always preempts the backup.
      • bandwidth—(Optional) The interface with the higher bandwidth always acts as the active interface.
      • off—(Optional) No preemption occurs from active to backup.

       
      Step 5switchport backup interface interface-id preemption delay delay-time


      Example:
      Switch(conf-if)# switchport backup interface gigabitethernet1/0/2 preemption delay 50
       

      Configures the time delay until a port preempts another port.

      Note   

      Setting a delay time only works with forced and bandwidth modes.

       
      Step 6end


      Example:
      Switch(conf-if)# end
       

      Returns to privileged EXEC mode.

       
      Step 7show interface [interface-id] switchport backup


      Example:
      Switch# show interface gigabitethernet1/0/2 switchport backup
       

      Verifies the configuration.

       
      Step 8copy running-config startup config


      Example:
      Switch# copy running-config startup config
       

      (Optional) Saves your entries in the switch startup configuration file.

       
      Related Concepts
      Related References

      Configuring VLAN Load Balancing on FlexLinks

      SUMMARY STEPS

        1.    configure terminal

        2.    interface interface-id

        3.    switchport backup interface interface-id prefer vlan vlan-range

        4.    end


      DETAILED STEPS
         Command or ActionPurpose
        Step 1configure terminal


        Example:
        
Switch# configure terminal
         

        Enters global configuration mode.

         
        Step 2interface interface-id


        Example:
        
Switch (config)# interface gigabitethernet2/0/6
         

        Specifies the interface, and enters interface configuration mode. The interface can be a physical Layer 2 interface or a port channel (logical interface). The port-channel range is 1 to 48.

         
        Step 3switchport backup interface interface-id prefer vlan vlan-range


        Example:
        
Switch (config-if)# switchport backup interface 
gigabitethernet2/0/8 prefer vlan 2
         

        Configures a physical Layer 2 interface (or port channel) as part of a FlexLinks pair with the interface and specifies the VLANs carried on the interface. The VLAN ID range is 1 to 4094.

         
        Step 4end


        Example:
        
Switch (config-if)# end
         

        Returns to privileged EXEC mode.

         
        Related References

        Configuring MAC Address-Table Move Update

        SUMMARY STEPS

          1.    configure terminal

          2.    interface interface-id

          3.    Use one of the following:

          • switchport backup interface interface-id
          • switchport backup interface interface-id mmu primary vlan vlan-id

          4.    end

          5.    mac address-table move update transmit

          6.    end


        DETAILED STEPS
           Command or ActionPurpose
          Step 1configure terminal


          Example:
          
Switch# configure terminal
           

          Enters global configuration mode.

           
          Step 2interface interface-id


          Example:
          
Switch (config)# interface gigabitethernet1/0/1
           

          Specifies the interface, and enter interface configuration mode. The interface can be a physical Layer 2 interface or a port channel (logical interface). The port-channel range is 1 to 48.

           
          Step 3 Use one of the following:
          • switchport backup interface interface-id
          • switchport backup interface interface-id mmu primary vlan vlan-id


          Example:
          
Switch(config-if)# switchport backup interface 
gigabitethernet0/2 mmu primary vlan 2
           

          Configures a physical Layer 2 interface (or port channel), as part of a FlexLinks pair with the interface. The MAC address-table move update VLAN is the lowest VLAN ID on the interface.

          Configure a physical Layer 2 interface (or port channel) and specifies the VLAN ID on the interface, which is used for sending the MAC address-table move update.

          When one link is forwarding traffic, the other interface is in standby mode.

           
          Step 4end


          Example:
          
Switch(config-if)# end
           

          Returns to global configuration mode.

           
          Step 5mac address-table move update transmit


          Example:
          Switch(config)# 
mac address-table move update 
transmit
           

          Enables the access switch to send MAC address-table move updates to other switches in the network if the primary link goes down and the switch starts forwarding traffic through the standby link.

           
          Step 6end


          Example:
          
Switch (config)# end
           

          Returns to privileged EXEC mode.

           
          Related Concepts
          Related References

          Configuring a Switch to Obtain and Process MAC Address-Table Move Update Messages

          SUMMARY STEPS

            1.    configure terminal

            2.    mac address-table move update receive

            3.    end


          DETAILED STEPS
             Command or ActionPurpose
            Step 1 configure terminal


            Example: 
            Switch# configure terminal
             

            Enters global configuration mode

             
            Step 2mac address-table move update receive


            Example:
            Switch (config)# mac address-table move update receive
             

            Enables the switch to obtain and process the MAC address-table move updates.

             
            Step 3end


            Example:
            Switch (config)# end
             

            Returns to privileged EXEC mode.

             
            Related Concepts
            Related References

            Monitoring FlexLinks and the MAC Address-Table Move Update

            Command

            Purpose

            show interface [interface-id] switchport backup

            Displays the FlexLinks backup interface configured for an interface or all the configured FlexLinks and the state of each active and backup interface (up or standby mode).

            show mac address-table move update

            Displays the MAC address-table move update information on the switch
            Related Tasks

            Configuration Examples for FlexLinks

            Configuring FlexLinks: Examples

            This example shows how to verify the configuration after you configure an interface with a backup interface:

            
Switch# show interface switchport backup

Switch Backup Interface Pairs:
Active Interface Backup Interface State
------------------------------------------------------------------------
GigabitEthernet1/0/1 GigabitEthernet1/0/2 Active Up/Backup Standby

            This example shows how to verify the configuration after you configure the preemption mode as forced for a backup interface pair:

            
Switch# show interface switchport backup detail

Active Interface Backup Interface State
------------------------------------------------------------------------
GigabitEthernet1/0/211 GigabitEthernet1/0/2 Active Up/Backup Standby
Interface Pair : Gi1/0/1, Gi1/0/2
Preemption Mode : forced
Preemption Delay : 50 seconds
Bandwidth : 100000 Kbit (Gi1/0/1), 100000 Kbit (Gi1/0/2)
Mac Address Move Update Vlan : auto
            Related Concepts
            Related Tasks
            Related References

            Configuring VLAN Load Balancing on FlexLinks: Examples

            In the following example, VLANs 1 to 50, 60, and 100 to 120 are configured on the switch:

            
Switch(config)# interface gigabitethernet 2/0/6
Switch(config-if)# switchport backup interface gigabitethernet 2/0/8 prefer vlan 60,100-120

            When both interfaces are up, Gi2/0/8 forwards traffic for VLANs 60 and 100 to 120 and Gi2/0/6 forwards traffic for VLANs 1 to 50.

            
Switch# show interfaces switchport backup

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State
------------------------------------------------------------------------
GigabitEthernet2/0/6    GigabitEthernet2/0/8    Active Up/Backup Standby

Vlans Preferred on Active Interface: 1-50
Vlans Preferred on Backup Interface: 60, 100-120

            When a FlexLinks interface goes down (LINK_DOWN), VLANs preferred on this interface are moved to the peer interface of the FlexLinks pair. In this example, if interface Gi2/0/6 goes down, Gi2/0/8 carries all VLANs of the FlexLinks pair.

            
Switch# show interfaces switchport backup

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State
------------------------------------------------------------------------
GigabitEthernet2/0/6    GigabitEthernet2/0/8    Active Down/Backup Up

Vlans Preferred on Active Interface: 1-50
Vlans Preferred on Backup Interface: 60, 100-120

            When a FlexLinks interface comes up, VLANs preferred on this interface are blocked on the peer interface and moved to the forwarding state on the interface that has just come up. In this example, if interface Gi2/0/6 comes up, VLANs preferred on this interface are blocked on the peer interface Gi2/0/8 and forwarded on Gi2/0/6.

            
Switch# show interfaces switchport backup

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State
------------------------------------------------------------------------
GigabitEthernet2/0/6    GigabitEthernet2/0/8    Active Up/Backup Standby

Vlans Preferred on Active Interface: 1-50
Vlans Preferred on Backup Interface: 60, 100-120

Switch# show interfaces switchport backup detail

Switch Backup Interface Pairs:

Active Interface        Backup Interface        State
------------------------------------------------------------------------
FastEthernet1/0/3       FastEthernet1/0/4       Active Down/Backup Up

Vlans Preferred on Active Interface: 1-2,5-4094
Vlans Preferred on Backup Interface: 3-4
Preemption Mode  : off
Bandwidth : 10000 Kbit (Fa1/0/3), 100000 Kbit (Fa1/0/4)
Mac Address Move Update Vlan : auto
            Related Tasks
            Related References

            Configuring the MAC Address-Table Move Update: Examples

            This example shows how to verify the configuration after you configure an access switch to send MAC address-table move updates:

            
Switch# show mac-address-table move update

Switch-ID : 010b.4630.1780
Dst mac-address : 0180.c200.0010
Vlans/Macs supported : 1023/8320
Default/Current settings: Rcv Off/On, Xmt Off/On
Max packets per min : Rcv 40, Xmt 60
Rcv packet count : 5
Rcv conforming packet count : 5
Rcv invalid packet count : 0
Rcv packet count this min : 0
Rcv threshold exceed count : 0
Rcv last sequence# this min : 0
Rcv last interface : Po2
Rcv last src-mac-address : 000b.462d.c502
Rcv last switch-ID : 0403.fd6a.8700
Xmt packet count : 0
Xmt packet count this min : 0
Xmt threshold exceed count : 0
Xmt pak buf unavail cnt : 0
Xmt last interface : None
            Related Concepts
            Related Tasks
            Related References

            Additional References for FlexLinks and MAC Address-Table Move Update

            Related Documents

            Related Topic Document Title

            Layer 2 command reference

            Layer 2/3 Command Reference (Catalyst 3850 Switches)

            Standards and RFCs

            Standard/RFC Title

            None

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            Feature Information for Flex Links and MAC Address-Table Move Update

            Releases Feature Information

            Cisco IOS XE 3.2SE

            This feature was introduced.