08-26-2016 09:05 AM - edited 03-08-2019 07:10 AM
The Cisco Flex links is a great idea to provide layer 2 redundancy. But the fact that spanning-tree is disabled over Flex links makes it almost not practicable.
I really don't understand why spanning-tree have to be disabled on Flex links? I believe by the nature Flex links should have no issues to work with spanning-tree.
08-26-2016 12:02 PM
Hello
my understanding there would be no requirement for it. That's why by default its disabled when flex links are enabled.
you have two alternate ports to a destination and only one of those ports will be active when flex link is applied the other will be in a standby state. ( not load sharing)
Unlike stp which would have both port in an active state with the less preferred port/ path being blocked and is subject to convergence
For load sharing it also applicable to pass specific vlans over both ports at the same time 's in a deterministic fashion unlike stp
I guess you could say in certain circumstances is an alternative to running stp on two port to the same destination
res
paul
08-26-2016 12:20 PM
Well. Even you have only one physical link between 2 switches, most of the time you still need spanning-tree on it. Unless these 2 switches are your whole network and you also don't need to worry about someone else will run another link between them later on.
In some cases you don't need spanning-tree to run on Flex links, but disable it and there is no way you can enable it is totally different story.
The backup interface of the Flex links just have no MAC addresses so not forwarding traffic, Cisco should allow spanning-tree and always put it in the same spanning-tree status as the active one. This will make this feature a whole different use cases.
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