Draytek Vigor2120n-plus User Manual page 335

5. Open Wireless LAN (2.4GHz)>>Security and Wireless LAN (5GHz)>>Security.
Configure Security as 12345678 for both pages. Click OK to save the settings.
Same value
for 2.4GHz
and 5GHz
6. Now, Vigor router will let the wireless clients connect to less congested wireless LAN,
such as 5GHz to prevent from network congestion.
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Vigor2120 Series User's Guide