Hi Alexey,
I think flex link preemption was not supported on 7600 and 6500. It was on radar for a while and I guess not yet released (but can be wrong here as did not track it for a while).
Once it is supported it will work like this:
Functional Behavior
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When the original Active interface goes down, the configured Backup interface takes over and starts forwarding traffic. Later, when the original Active interface comes back up, it may preempt the Backup interface depending upon the preemption scheme configured by the user:
- If the configured preemption mode is Off, original Active interface then starts backing up the Backup interface by not forwarding traffic, and is ready to take over when the Backup goes down.
- If the configured preemption mode is Forced, original Active interface will then preempt the current Backup interface after a user-specified preemption delay. The preemption delay value for a backup interface pair is used to accommodate the STP forwarding delay time on the neighbor switch interface. By default, this value is 35 seconds.
- If the configured preemption mode is Bandwidth and the available bandwidth of the original Active interface is more than that of Backup interface, original Active interface will then preempt the Backup interface after a user-specified preemption delay.
- If the configured preemption mode is Bandwidth and the available bandwidth of the original Active interface is less than or same as that of Backup interface, original Active interface then starts backing up the Backup interface by not forwarding traffic, and is ready to take over when the Backup goes down.
Nik
HTH,
Niko
