I want to place my Asustor NAS between my PC and switch- but it doesn't work correctly?

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Your switch/router is probably not supporting 2.5GbE. The cheapest way to make it work is a USB3 to Ethernet adaptor which will connect your NAS to a 1GbE switch/router. Simple Amazon basics adaptor should work: USA https://amzn.to/39f6YJQUK https://amzn.to/2PCxcOBDE https://amzn.to/32FKoHMAlternatively you should consider getting a 10GbE switch which is backwards compatible with 5GbE and 2.5GbE and of course 1GbE. Netgear GS110MX (around $150) should work:UK https://amzn.to/2vwpHC1USA https://amzn.to/2IbOkH8DE https://amzn.to/32E0PVfI hope this helps.