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Catalyst 3750-X and 3560-X Switch Software Configuration Guide
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Chapter 23 Configuring Flex Links and the MAC Address-Table Move Update Feature
Configuring Flex Links and MAC Address-Table Move Update
• An interface can belong to only one Flex Link pair. An interface can be a backup link for only one
active link. An active link cannot belong to another Flex Link 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 Flex Links, and you can configure a port channel
and a physical interface as Flex Links, 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 Flex Links 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 Flex Link ports. A Flex Link 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.
Follow these guideline to configure VLAN load balancing on the Flex Links feature:
• For Flex Link 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 Flex Links
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.
Default Configuration
The Flex Links are 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.
Configuring Flex Links
Beginning in privileged EXEC mode, follow these steps to configure a pair of Flex Links:
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 interface interface-id Specify 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 switchport backup interface interface-id Configure a physical Layer 2 interface (or port channel)
as part of a Flex Link pair with the interface. When one
link is forwarding traffic, the other interface is in standby
mode.