Flex Links - Cisco WS-CBS3032-DEL Software Configuration Manual

Understanding Flex Links and the MAC Address-Table Move Update

Flex Links

Flex Links 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. Flex Links 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, Flex Links is not necessary because STP already provides
link-level redundancy or backup.
You configure Flex Links on one Layer 2 interface (the active link) by assigning another Layer 2
interface as the Flex Link or backup link. On stacking-capable switches, the Flex Link 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 Flex Link interfaces.
In Figure
configured as Flex Links, 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
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.
Figure 21-1
Uplink
switch B
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.
Flex Links are supported only on Layer 2 ports and port channels, not on VLANs or on Layer 3 ports.
Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
21-2
Chapter 21
21-1, ports 1 and 2 on switch A are connected to uplink switches B and C. Because they are
Flex Links Configuration Example
Port 1
Switch A
Configuring Flex Links and the MAC Address-Table Move Update Feature
Figure 21-1, you can configure the Flex Links pair with
Uplink
switch C
Port 2
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