Cisco Catalyst 2960 Series, Configuration Manual

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Configuring Flex Links , on page 380
Configuring Flex Links: Examples, on page 387
Flex Links Configuration
In the following figure, ports 1 and 2 on switch A are connected to uplink switches B and C. Because they
are 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 configure a preemption function, specifying the preferred port for forwarding traffic. For example,
you can configure the Flex Links 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
switchport backup interface preemption mode bandwidth and
switchport backup interface preemption delay interface configuration commands.
Figure 39: Flex Links Configuration Example
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.
Related Topics
Configuring a Preemption Scheme for a Pair of Flex Links , on page 381
Configuring Flex Links , on page 380
VLAN Flex Links Load Balancing and Support
VLAN Flex Links load balancing allows users to configure a Flex Links pair so that both ports simultaneously
forward the traffic for some mutually exclusive VLANs. For example, if Flex Links ports are configured for
1 to 100 VLANs, the traffic of the first 50 VLANs can be forwarded on one port and the rest on the other
port. If one of the ports fail, the other active port forwards all the traffic. When the failed port comes back up,
it resumes forwarding traffic in the preferred VLANs. In addition to providing the redundancy, this Flex Links
pair can be used for load balancing. Flex Links VLAN load balancing does not impose any restrictions on
uplink switches.
Consolidated Platform Configuration Guide, Cisco IOS Release 15.2(4)E (Catalyst 2960-X Switches)
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Information About Flex Links and MAC Address-Table Move Update