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Configuring Flex Links
This chapter describes how to configure Flex Links, a pair of interfaces on the Cisco ME 3400 switch
that are used to provide a mutual backup. This feature is available only when the switch is running the
metro IP access or metro access image.
For complete syntax and usage information for the commands used in this chapter, see the command
Note
reference for this release.
The chapter consists of these sections:
•
•
•
Understanding Flex Links
Flex Links are a pair of a Layer 2 interfaces (switchports 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), allowing users to turn off STP and still provide 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, it is not necessary to configure Flex Links because STP
already provides link-level redundancy or backup.
Note
STP is available only on network node interfaces (NNIs)
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. 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
78-17058-01
Understanding Flex Links, page 17-1
Configuring Flex Links, page 17-2
Monitoring Flex Links, page 17-4
17-1, ports 1 and 2 on switch A are connected to uplink switches B and C. Because they are
C H A P T E R
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
17
17-1
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