aaa is mostly done on the access switch, if your 6300M will be your access switch, then those ports should be configured for aaa. Similar to qos, but that can be done at multiple layers.
It's quite common to replicate the existing switch configuration to new switches, then link the new switches to your existing network (trunk/tagged VLANs), and start moving over clients. In that way you have a nice & smooth migration and you can even move back if needed.
If it's just APs on the new switches, and the APs are on non-authenticated ports, then it's even easier. But if you are not sure about this, work with your Aruba partner to get proper advice.
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Herman Robers
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If you have urgent issues, always contact your Aruba partner, distributor, or Aruba TAC Support. Check
https://www.arubanetworks.com/support-services/contact-support/ for how to contact Aruba TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
In case your problem is solved, please invest the time to post a follow-up with the information on how you solved it. Others can benefit from that.
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