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Cisco Systems, Inc. www.cisco.com
Configuring FlexLinks and the MAC
Address-Table Move Update
Restrictions for the FlexLinks and the MAC Address-Table Move
Update
To use this feature, the switch must be running the LAN Base image.
Information About Configuring the FlexLinks and the MAC
Address-Table Move Update
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 is 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. 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.
In Figure 57 on page 378, 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 choose to configure a preemption mechanism, specifying the preferred port for forwarding traffic. For
example, in the example in Figure 57 on page 378, 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 interface configuration switchport backup
interface preemption mode bandwidth and switchport backup interface preemption delay commands.
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