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Thank you for the information you shared.
As per the case description, I could understand that your RUCKUS setup is not working after replacing the modem.
If your ISP modem is directly connected to the ICX-7150-C12P Switch, it doesn’t work only with Modem. The connection must be from a Router or Modem-Router combo device. Could you please confirm this once?
Please refer to the short guide link below about how to connect the devices as a reference: