Can a Mac's airport card run 802.11 N, G, B or A only?

Question

Occasionally it's nice to hard code a wired connection network port to not auto negotiate and force things to be 100 half duplex even though a higher speed is configured and negotiable on the switch.

Can I similarly force airport software and thus the hardware to only run one flavor of 802.11? Can I use the airport command to prefer a higher / lower channel rather than join by signal strength? Might alternative drivers be available or some developer testing tool to exert this level of control over the WiFi chipsets in Macs.

I want to force this on the mac end for cases where I can't control the base stations or want to test a specific channel of a simultaneous dual band router that is live with other traffic.

mac:bin mike$ airport --scan
                            SSID BSSID             RSSI CHANNEL HT CC SECURITY (auth/unicast/group)
                     na ala hele 00:26:36:9c:32:23 -59  2       Y  US WPA(PSK/TKIP/TKIP) WPA2(PSK/AES,TKIP/TKIP) 
                     na ala hele 00:26:bb:79:23:1f -59  2       Y  US WPA(PSK/TKIP/TKIP) WPA2(PSK/AES,TKIP/TKIP) 
                fast na ala hele 00:26:bb:79:23:20 -74  149,+1  Y  US WPA(PSK/TKIP/TKIP) WPA2(PSK/AES,TKIP/TKIP) 
mac:bin mike$ airport --getinfo
     agrCtlRSSI: -75
     agrExtRSSI: 0
    agrCtlNoise: -86
    agrExtNoise: 0
          state: running
        op mode: station 
     lastTxRate: 81
        maxRate: 300
lastAssocStatus: 0
    802.11 auth: open
      link auth: wpa2-psk
          BSSID: 00:26:bb:79:23:20
           SSID: fast na ala hele
            MCS: 4
        channel: 149,1
mac:bin mike$ ls -l /usr/local/bin/airport 
lrwxr-xr-x  1 root  wheel  89 Sep 13 11:40 /usr/local/bin/airport -> /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport

Answer 1

Maybe this help, you can access to the airport command utility with

sudo ln -s /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport /usr/sbin/airport

Then, type

sudo airport en1 prefs JoinMode=Strongest JoinModeFallback=KeepLooking

JoinMode = Ranked and JoinModeFallback = Prompt are the defaults, if you want to switch back

Answer 2

If you just want to check whether the base station is sending on the right channel, Kismac may be of use to you. This will show all modes that your Airport card supports, including dual-band base stations. It's also great for checking wi-fi coverage with the built-in signal monitor, which can chart signal strength as you walk around with laptop in hand.

Answer 3

From my understanding, I think this is only possible at the router level. So that router's will only accept "X" traffic, and not at the broadcast level (your NIC). I suppose you could use ipfw to throttle bandwidth on certain machines, to do, um, your testing ;)

Answer 4

With the Wireless Diagnostic that Apple introduced in 10.8.4 - I now have the beginnings of a workable answer.

Running the tool (which is in /System/Library/Core Services) by option clicking the Airport icon in the menu bar - I can capture arbitrary frames on any allowable channel (but not actually join a base station on this specified channel or radio mode). This saves a standard tcpdump file that can be analyzed. The Info tab in the Utilities window and the associated tools for Logging, Frame Capture, Wi-Fi Scan and Performance allow me to troubleshoot most wireless situations.

I have also added an Aerohive AP121 router to my toolset and that allows near real time FFT graphical spectrum analysis of tricky radio situations, but that's a bit of overkill for wanting an OS X tool to begin to tease apart challenging wireless environments.

No answer seems to let me control the OS X / radio software stack to force a connection or operation on one of the frequency bands, though so the answer seems to be no at the moment (as well as for quite some time).