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Port channel hangs

Hi. In our office we have a floor switch connected to core switches(vss). There are two up links from floor switch connected to the core. We bundled the two uplink as port channel 5.

My question is ,we did power maintenance and shut the floor switch for a while. When the floor switch booted it forms port channel wit the core. I could see the floor switch as cdp neighbors in my core switch.
However I could login the floor switch. No data traffic crossing the floor switch. All the server connected in that floor switch are unreachable.

To fix the issue my senior made the port channel shut and unshutted it. Then the port channel come up and traffic flows.

My doubt here is
1) do port channel hangs?
2) even if it hanged then how cdp traffic reaches the floor switch and core could have info about the floor switch
3) I made both the interface shut and unshut one by one. It didn't work. But when I shut port channel it worked?

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Re:Port channel hangs

is negociation enabled on either side of this etherchannel? also what type of link aggregation.protocol is enabled?


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