Flex links are layer-2 interfaces manually configuredin primary/failover
pairs. The Spanning Tree Protocol normally provides primary/failover
functionality, but it was designed for the sole purpose of preventing
loops.Flex links are used to ensure that there are backup links for
primary links.Only one of the links in a flex-link pair will be forwarding
traffic at any time.Flex links are designed for switches where you do
not wish to run spanning tree, and should be usedonly on switches
that do not run spanning tree. Should flex links be configured on a
switch running spanning tree ? The flex links will not participate in
STP.Flex links are configured on the primary interface by specifying
the backup interface with the switchport backup interface command
interface GigabitEthernet1/0/20
switchport access vlan 10
switchport backup interface Gi1/0/21
!
interface GigabitEthernet1/0/21
switchport access vlan 10
No configuration is necessary on the backup interface.
Neither of the links can be an interface that is a member of an
EtherChannel.An EtherChannel can be a flex-link backup for another
port channel.A single physical interface can be a backup to an Ether
Channel as well.The backup link does not need to be the same type
of interface as the primary. For example, a 100 Mbps interface can
be a backup for a 1 Gbps interface.
Monitoring flex links is done with the show interface switchport backup
command:
3750# sh int switchport backup
Switch Backup Interface Pairs:
Active Interface Backup Interface State
------------------------------------------------------------------------
GigabitEthernet1/0/20 GigabitEthernet1/0/21 Active Down/Backup Down
Best Regards,
Deepak Arora
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