Configuring Flex Links - Cisco nexus 5000 series Configuration Manual

Configuring Flex Links

This chapter contains the following sections:
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Information About 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). You 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 are 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 Links or backup link. The Flex Links interface can be on the same switch. 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. Flex Links are not configured by default and there are
no backup interfaces defined. STP is disabled on Flex Link interfaces.
In the Flex Links Configuration Example, 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.
OL-25842-01
Information About Flex Links, page 229
Guidelines and Limitations for Flex Link, page 230
Default Settings for Flex Link, page 231
Configuring Flex Links, page 232
Configuring Flex Link Preemption, page 233
Verifying Flex Link Configuration, page 235
Flex Link Configuration Examples, page 236
Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.1(3)N1(1)
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