Guidelines And Limitations For Flex Link - Cisco nexus 5000 series Configuration Manual

Guidelines and Limitations for Flex Link

Flex Links are supported only on Layer 2 ports and port channels, not on VLANs or on Layer 3 ports.
Figure 25: Flex Links Configuration Example
Preemption
You can optionally configure a preemption mechanism to specify the preferred port for forwarding traffic.
For example, you can configure a Flex Link pair with preemption mode so that when a port comes back up,
if it has greater bandwidth than the peer port, then it will begin forwarding after 35 seconds (default preemption
delay) and the peer port will be on standby. This is done by entering the preemption mode bandwidth and
delay commands.
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.
You can configure preemption in the following three modes:
• Forced—The active interface always preempts the backup.
• Bandwidth—The interface with the higher bandwidth always acts as the active interface.
• Off—There is no preemption; the first interface that is up is put in forwarding mode.
You can also configure the preemption delay as a specified amount of time (in seconds) before preempting a
working interface for another. This ensures that the counterpart in the upstream switch has transitioned to an
STP forwarding state before the switch over.
Multicast Fast-Convergence
When a Flex Link interface is learned as an mrouter port, the standby (non-forwarding) interface is also
co-learned as an mrouter port if the link is up. This co-learning is for internal software state maintenance and
has no relevance with respect to IGMP operations or hardware forwarding unless multicast fast-convergence
is enabled. With multicast fast-convergence configured, the co-learned mrouter port is immediately added to
the hardware. Flex Link supports multicast fast convergence for IPv4 IGMP.
Guidelines and Limitations for Flex Link
Consider the following guidelines and limitations when configuring Flex Links:
• You can configure only one Flex Link backup link for any active link and it must be a different interface
• An interface can belong to only one Flex Link pair; it can be a backup link for only one active link.
Cisco Nexus 5000 Series NX-OS Layer 2 Switching Configuration Guide, Release 5.1(3)N1(1)
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from the active interface.
Configuring Flex Links
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