Cisco Catalyst 2960 Command Reference Manual page 571

Chapter 2 Catalyst 2960 Switch Cisco IOS Commands
Command History Release
12.2(25)FX
12.2(25)SEE
12.2(37)SE
12.2(44)SE
Usage Guidelines With Flex Links configured, one link acts as the primary interface and forwards traffic, while the other
interface is in standby mode, ready to begin forwarding traffic if the primary link shuts down. The
interface being configured is referred to as the active link; the specified interface is identified as the
backup link. The feature provides an alternative to the Spanning Tree Protocol (STP), allowing users to
turn off STP and still retain basic link redundancy.
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Examples This example shows how to configure two interfaces as Flex Links:
Switch# configure terminal
Switch(conf)# interface fastethernet0/1
Switch(conf-if)# switchport backup interface fastethernet0/2
Switch(conf-if)# end
This example shows how to configure the Fast Ethernet interface to always preempt the backup:
Switch# configure terminal
Switch(conf)# interface fastethernet0/1
Switch(conf-if)# switchport backup interface fastethernet0/2 preemption forced
Switch(conf-if)# end
This example shows how to configure the Fast Ethernet interface preemption delay time:
Switch# configure terminal
Switch(conf)# interface fastethernet0/1
Switch(conf-if)# switchport backup interface fastethernet0/2 preemption delay 150
Switch(conf-if)# end
OL-8604-04
Modification
This command was introduced.
Added preemption, mode, forced, bandwidth, off, and delay keywords.
Added prefer vlan keyword.
The multicast, fast-convergence, delay, mode, prefer, and vlan keywords
were added.
This command is available only for Layer 2 interfaces.
You can configure only one Flex Link backup link for any active link, and it must be a different
interface from the active interface.
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.
A backup link does not have to be the same type (Fast Ethernet or Gigabit Ethernet, for instance) 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.
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.
If STP is configured on the switch, Flex Links do not participate in STP in all valid VLANs. If STP
is not running, be sure that there are no loops in the configured topology.
switchport backup interface
Catalyst 2960 Switch Command Reference
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