How can I tell if my wifi dongle has access-point capabilities?

Question

I have a Realtek 8191SU USB wifi dongle for use on my Raspberry Pi. I'm trying to set up a wifi access point using this tutorial. However, I'm running into a few errors, and I suspect it might be because my dongle does not support running as an access point. Is there a way to tell if this has access point capabilities?

EDIT

Is there a generic way, similar to lsusb or ifconfig, that can provide information on any wifi dongle?

Solution 1

I'm not 100% sure about this answer. It can confirm access-point capabilities in some situations, but also seems to throw an error with other wifi dongles.

With access-point wifi dongle attached (Ralink RT5370):

$ iw list
...
    Supported interface modes:
...
         * AP

With Realtek 8191SU dongle attached:

$ iw list
nl80211 not found.

Solution 2

For older cards that don't use the mac80211 framework:

$ iwconfig

lists network devices. Note the Mode in the second line:

$ sudo iwconfig
wlan0     unassociated  Nickname:"<WIFI@REALTEK>"
          Mode:Auto  Frequency=2.412 GHz  Access Point: Not-Associated   
          Sensitivity:0/0  
          Retry:off   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality:0  Signal level:0  Noise level:0
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

lo        no wireless extensions.

eth0      no wireless extensions.

The Ubuntu Documentation says "What we need for a wireless "base-station" or "access-point" is a wireless network card that does "master mode"" which can be set using iwconfig:

$ sudo iwconfig wlan0 mode master

Yields (assuming no errors):

$ sudo iwconfig
wlan0     unassociated  Nickname:"<WIFI@REALTEK>"
    *-->  Mode:Master  Frequency=2.412 GHz  Access Point: Not-Associated   
          Sensitivity:0/0  
          Retry:off   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality:0  Signal level:0  Noise level:0
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0

lo        no wireless extensions.

eth0      no wireless extensions.

The manual states, "If you don’t get an error you’re in business.", which I assume means that if it succeeds and shows "Mode:Master" in iwconfig, then your card can be used as an access-point. (It doesn't say anything about whether failing means you don't have an access-point-capable card. This is just one way to see if you do.)

For new drivers using the mac80211 framework and nl80211 interface, iwconfig does not work and you need to use $ iw list as you stated above. The opposite is true for the older devices. My device is also Realtek, and $ iw list doesn't work with it, because I don't think its driver is mac80211-compatible.

Comments

[Sparhawk]

Is "one transmit" the relevant part here? What does that mean exactly? Also, I was more searching for a generic solution similar to lsusb or ifconfig for analysing any wifi dongle. Information about my specific dongle is certainly useful, but I'll edit the question to be clearer about the generic implementations.

[Sparhawk]

(I won't accept my own answer until I'm sure that the second response is unequivocal proof that AP is not supported.)

[Marki555]

That "one trasmit" tells only about how many OFDM frequencies/channels it will be able to use while sending/receiving. So it tells only about speed, not about how many clients can connect to this chipset.

[MrUser]

Oh, and this link gives a good list of network device commands with sample output for some.

[derobert]

"Access Point: Not-Associated" isn't listing a capability. It's telling you its not associated with an access point, in normal client mode.

[Sparhawk]

@derobert is correct. I tested this on the one that works, and it came up "Not-Associated".

[MrUser]

@Sparhawk I didn't say that Access Point was the capability. If you look at my answer, I say that the second line shows capabilities, but I didn't say everything on that line is a capability. (I'll edit my answer to be more clear) So @derobert's comment is somewhat moot. Besides, the arrow in my answer shows that the Mode was changed to Master. The man page says, Master (the node is the synchronisation master or acts as an Access Point).

[Sparhawk]

@MrUser Ah okay, sorry, I misinterpreted your answer. However, I tested again with the access-point dongle and the non–access-point dongle. Both have "Mode:Managed".

[MrUser]

@Sparhawk, Is the access-point dongle the Ralink RT5370? Then iw list works for that and not iwconfig, as I explain in my answer. If the non-access-point dongle can't be put into Master Mode, this also makes sense, since it's a non-access-point dongle. I'm not an expert in this. I'm just trying to make sense of one method which worked for me.

[Sparhawk]

@MrUser Okay, this seems plausible now. Yes, my access-point dongle is the Ralink RT5370. I don't know much about the details, but it's about a year old. Thanks for the clarification and apologies for the confusion. I've changed my −1 to +1.