In case you have the same (B)SSID for 2.4 and 5GHz but you want to force your Mac to one of them it can be easily done with Terminal. First scan the network then using sudo join the selected BSSID followed by the channel. You must have joined the network and saved the secret to your keychain previously.
/System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport -s
SSID BSSID RSSI CHANNEL HT CC SECURITY (auth/unicast/group)
Fios-B5YRw b8:f8:53:2d:c9:63 -66 132 Y US WPA2(PSK/AES/AES)
SINGH c8:a7:0a:9f:33:fa -88 132 Y US WPA2(PSK/AES/AES)
BandidoBoricua 24:f5:a2:f0:3a:03 -87 100 Y US WPA(PSK/AES,TKIP/TKIP) WPA2(PSK/AES,TKIP/TKIP)
3WV73 f8:e4:fb:0c:f8:db -72 11 Y US WPA2(PSK/AES/AES)
FiOS-QT6C6 c8:a7:0a:9f:33:fc -70 8 Y US WPA2(PSK/AES/AES)
xfinitywifi 16:4e:5a:1f:be:b8 -73 6 Y US NONE
JWASH 04:4e:5a:1f:be:b8 -74 6 Y US WPA(PSK/AES,TKIP/TKIP) WPA2(PSK/AES,TKIP/TKIP)
Fios-B5YRw b8:f8:53:2d:c9:62 -49 6 Y US WPA2(PSK/AES/AES)
BandidoBoricua 24:f5:a2:f0:3a:01 -67 5 Y US WPA(PSK/AES,TKIP/TKIP) WPA2(PSK/AES,TKIP/TKIP)
sudo /System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport --channel=Fios-B5YRw132Update: 2020-10-24
Unfortunately this change is not persistent
thanks, not persistant, but we can do it repeatedly
@hris, I’m glad it works. Yeah, as of now you must do it all the time, maybe Apple will do something about this in the future.
This does not work in Bug Sur. I have SSIDs the same for 2.4/5Ghz. This method does not allow me to choose which to connect to. The –channel parameter is SSID. If I could use BSSID, then that may work, but the –channel parameter does not accept BSSID/mac addr.
I haven’t tried it in Big Sur yet. Did you have any luck so far?