erraneous connect with short-slot-time fails

erraneous connect with short-slot-time fails

[Holger Schurig]

Hi !

Background: ath5k-based card, wireless-testing
v2.6.32-rc6-41576-g4408b3b, wpa_supplicant hostap_0_6_7-581-geb999fe


I just got disconnected all the time to some AP and I wondered what
the issue was. That's the output from "iw event:"

wlan0 (phy #4): auth 00:1b:d4:44:35:90 -> 00:15:e9:84:1a:54 status: 0: Successful
wlan0 (phy #4): assoc 00:1b:d4:44:35:90 -> 00:15:e9:84:1a:54 status: 25: Association request rejected due to requesting station not supporting the short slot time option
wlan0 (phy #4): failed to connect to 00:1b:d4:44:35:90, status: 25: Association request rejected due to requesting station not supporting the short slot time option

First thing: the error message is confused. I turned off
short-slot-time on the AP, so it's the AP that does not support it.

However, the real question remains: why does the station
(ath5k+mac80211) tries to use short-slot-time in the first place? In
the probe response, the AP says clearly that he doesn't support this.


Here's the (partial) assoc request, followed by a (partial) assoc
response. And to shed evidence on the turned-off-status of the AP, at
the end is also a probe response from the AP:



IEEE 802.11
    Type/Subtype: Association Request (0)
    Frame Control: 0x0000 (Normal)
        Version: 0
        Type: Management frame (0)
        Subtype: 0
        Flags: 0x0
            DS status: Not leaving DS or network is operating in AD-HOC mode (To DS: 0 From DS: 0) (0x00)
            .... .0.. = More Fragments: This is the last fragment
            .... 0... = Retry: Frame is not being retransmitted
            ...0 .... = PWR MGT: STA will stay up
            ..0. .... = More Data: No data buffered
            .0.. .... = Protected flag: Data is not protected
            0... .... = Order flag: Not strictly ordered
    Duration: 314
    Destination address: 00:1b:d4:44:35:90 (00:1b:d4:44:35:90)
    Source address: 00:15:e9:84:1a:54 (00:15:e9:84:1a:54)
    BSS Id: 00:1b:d4:44:35:90 (00:1b:d4:44:35:90)
    Fragment number: 0
    Sequence number: 15
IEEE 802.11 wireless LAN management frame
    Fixed parameters (4 bytes)
        Capability Information: 0x0431
            .... .... .... ...1 = ESS capabilities: Transmitter is an AP
            .... .... .... ..0. = IBSS status: Transmitter belongs to a BSS
            .... ..0. .... 00.. = CFP participation capabilities: No point coordinator at AP (0x0000)
            .... .... ...1 .... = Privacy: AP/STA can support WEP
            .... .... ..1. .... = Short Preamble: Short preamble allowed
            .... .... .0.. .... = PBCC: PBCC modulation not allowed
            .... .... 0... .... = Channel Agility: Channel agility not in use
            .... ...0 .... .... = Spectrum Management: dot11SpectrumManagementRequired FALSE
            .... .1.. .... .... = Short Slot Time: Short slot time in use
            .... 0... .... .... = Automatic Power Save Delivery: apsd not implemented
            ..0. .... .... .... = DSSS-OFDM: DSSS-OFDM modulation not allowed
            .0.. .... .... .... = Delayed Block Ack: delayed block ack not implented
            0... .... .... .... = Immediate Block Ack: immediate block ack not implented
        Listen Interval: 0x0001
...


CONCLUSION: mac80211 tries to use short-slot time.







IEEE 802.11
    Type/Subtype: Association Response (1)
    Frame Control: 0x0010 (Normal)
        Version: 0
        Type: Management frame (0)
        Subtype: 1
        Flags: 0x0
            DS status: Not leaving DS or network is operating in AD-HOC mode (To DS: 0 From DS: 0) (0x00)
            .... .0.. = More Fragments: This is the last fragment
            .... 0... = Retry: Frame is not being retransmitted
            ...0 .... = PWR MGT: STA will stay up
            ..0. .... = More Data: No data buffered
            .0.. .... = Protected flag: Data is not protected
            0... .... = Order flag: Not strictly ordered
    Duration: 314
    Destination address: 00:15:e9:84:1a:54 (00:15:e9:84:1a:54)
    Source address: 00:1b:d4:44:35:90 (00:1b:d4:44:35:90)
    BSS Id: 00:1b:d4:44:35:90 (00:1b:d4:44:35:90)
    Fragment number: 0
    Sequence number: 1014
IEEE 802.11 wireless LAN management frame
    Fixed parameters (6 bytes)
        Capability Information: 0x0000
            .... .... .... ...0 = ESS capabilities: Transmitter is a STA
            .... .... .... ..0. = IBSS status: Transmitter belongs to a BSS
            .... ..0. .... 00.. = CFP participation capabilities: Station is not CF-Pollable (0x0000)
            .... .... ...0 .... = Privacy: AP/STA cannot support WEP
            .... .... ..0. .... = Short Preamble: Short preamble not allowed
            .... .... .0.. .... = PBCC: PBCC modulation not allowed
            .... .... 0... .... = Channel Agility: Channel agility not in use
            .... ...0 .... .... = Spectrum Management: dot11SpectrumManagementRequired FALSE
            .... .0.. .... .... = Short Slot Time: Short slot time not in use
            .... 0... .... .... = Automatic Power Save Delivery: apsd not implemented
            ..0. .... .... .... = DSSS-OFDM: DSSS-OFDM modulation not allowed
            .0.. .... .... .... = Delayed Block Ack: delayed block ack not implented
            0... .... .... .... = Immediate Block Ack: immediate block ack not implented
        Status code: Association denied due to requesting station not supporting short slot operation (0x0019)
        Association ID: 0x0000
    Tagged parameters (0 bytes)
...


CONCLUSION: the AP doesn't like that. And the textual representation
from tshark for this error as also confused about the roles of AP and
station :-)






IEEE 802.11
    Type/Subtype: Probe Response (5)
    Frame Control: 0x0050 (Normal)
        Version: 0
        Type: Management frame (0)
        Subtype: 5
        Flags: 0x0
            DS status: Not leaving DS or network is operating in AD-HOC mode (To DS: 0 From DS: 0) (0x00)
            .... .0.. = More Fragments: This is the last fragment
            .... 0... = Retry: Frame is not being retransmitted
            ...0 .... = PWR MGT: STA will stay up
            ..0. .... = More Data: No data buffered
            .0.. .... = Protected flag: Data is not protected
            0... .... = Order flag: Not strictly ordered
    Duration: 314
    Destination address: 00:20:a6:a0:56:1b (00:20:a6:a0:56:1b)
    Source address: 00:1b:d4:44:35:90 (00:1b:d4:44:35:90)
    BSS Id: 00:1b:d4:44:35:90 (00:1b:d4:44:35:90)
    Fragment number: 0
    Sequence number: 1845
IEEE 802.11 wireless LAN management frame
    Fixed parameters (12 bytes)
        Timestamp: 0x0000004DA3BDE1FA
        Beacon Interval: 0.102400 [Seconds]
        Capability Information: 0x0011
            .... .... .... ...1 = ESS capabilities: Transmitter is an AP
            .... .... .... ..0. = IBSS status: Transmitter belongs to a BSS
            .... ..0. .... 00.. = CFP participation capabilities: No point coordinator at AP (0x0000)
            .... .... ...1 .... = Privacy: AP/STA can support WEP
            .... .... ..0. .... = Short Preamble: Short preamble not allowed
            .... .... .0.. .... = PBCC: PBCC modulation not allowed
            .... .... 0... .... = Channel Agility: Channel agility not in use
            .... ...0 .... .... = Spectrum Management: dot11SpectrumManagementRequired FALSE
            .... .0.. .... .... = Short Slot Time: Short slot time not in use
            .... 0... .... .... = Automatic Power Save Delivery: apsd not implemented
            ..0. .... .... .... = DSSS-OFDM: DSSS-OFDM modulation not allowed
            .0.. .... .... .... = Delayed Block Ack: delayed block ack not implented
            0... .... .... .... = Immediate Block Ack: immediate block ack not implented
...




Who's the culprit, mac80211 or wpa_supplicant?

--
http://www.holgerschurig.de

Re: erraneous connect with short-slot-time fails

[Jouni Malinen]

On Mon, Nov 09, 2009 at 11:39:16AM +0100, Holger Schurig wrote:

> wlan0 (phy #4): assoc 00:1b:d4:44:35:90 -> 00:15:e9:84:1a:54 status: 25: Association request rejected due to requesting station not supporting the short slot time option

> First thing: the error message is confused. I turned off
> short-slot-time on the AP, so it's the AP that does not support it.

However, that text is correct as far as the proper use of status 25 is
concerned. Which AP is this?

> However, the real question remains: why does the station
> (ath5k+mac80211) tries to use short-slot-time in the first place? In
> the probe response, the AP says clearly that he doesn't support this.

IEEE 802.11-2007 states that the station indicates its support for short
slot time in (re)association request. This does not depend what the BSS
is currently using (slot time subfield inbeacon/probe
response/(re)association response frames).

> CONCLUSION: mac80211 tries to use short-slot time.

No.. It only indicates that it supports short slot time. It is up to the
AP to decide whether short slot time is used in the BSS.

> CONCLUSION: the AP doesn't like that. And the textual representation
> from tshark for this error as also confused about the roles of AP and
> station :-)

The "AP doesn't like that" part seems correct. The textual
representation may be confusing, but it is correct. The AP behavior is
not.

> Who's the culprit, mac80211 or wpa_supplicant?

Neither, the AP is. Have you verified whether you can work around this
by hardcoding mac80211 to send out zero as the short slot time?

-- 
Jouni Malinen                                            PGP id EFC895FA

Re: erraneous connect with short-slot-time fails

[Johannes Berg]

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On Mon, 2009-11-09 at 12:54 +0200, Jouni Malinen wrote:

> > CONCLUSION: the AP doesn't like that. And the textual representation
> > from tshark for this error as also confused about the roles of AP and
> > station :-)
> 
> The "AP doesn't like that" part seems correct. The textual
> representation may be confusing, but it is correct. The AP behavior is
> not.

It's not really a confusing textual representation either ... if you
consider that this code is supposed to be used only when the AP
_requires_ short-slot from the station, and the station advertises not
having it.

johannes

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Re: erraneous connect with short-slot-time fails

[Holger Schurig]

> However, that text is correct as far as the proper use of status 25
> is concerned. 

BTW, my note about the text was a side-mark.


> Which AP is this?

A Cisco 1231, firmware c1200-k9w7-tar.123-8.JEA (as firmware versions usually
make a huge difference to Cisco's)

This firmware was once marked as general deployment from Cisco (they
also have usally lot's of Early Adaptor firmware downloadable).
However, this was some years ago, not sure what currently is "GD" for
this AP.



And, as a side note: neither a Hermes II based card nor the libertas
firmware has problems associating to this AP.

--
http://www.holgerschurig.de

Re: erraneous connect with short-slot-time fails

[Holger Schurig]

The AP had a bogus configuration. An erraneous "mobility group 21"
statement was in it's config.

The issue had nothing to do short or long slot time at all.


Sigh. Sorry for wasting your time.

--
http://www.holgerschurig.de

Re: erraneous connect with short-slot-time fails

[Holger Schurig]

Side node:

> wlan0 (phy #4): auth 00:1b:d4:44:35:90 -> 00:15:e9:84:1a:54 status: 0: Successful
> wlan0 (phy #4): assoc 00:1b:d4:44:35:90 -> 00:15:e9:84:1a:54 status: 25: Association request rejected due to requesting station not supporting the short slot time option
> wlan0 (phy #4): failed to connect to 00:1b:d4:44:35:90, status: 25: Association request rejected due to requesting station not supporting the short slot time option

in this case, I had a case where the AP did send an authorization
response with success status, but an association response with an
error condition.

You once asked if I tested that.

Now I did, and it looked like mac80211+wpa_supplicant did the right
thing in this case.

--
http://www.holgerschurig.de

Re: erraneous connect with short-slot-time fails

[Johannes Berg]

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On Tue, 2009-11-10 at 09:00 +0100, Holger Schurig wrote:
> Side node:
> 
> > wlan0 (phy #4): auth 00:1b:d4:44:35:90 -> 00:15:e9:84:1a:54 status: 0: Successful
> > wlan0 (phy #4): assoc 00:1b:d4:44:35:90 -> 00:15:e9:84:1a:54 status: 25: Association request rejected due to requesting station not supporting the short slot time option
> > wlan0 (phy #4): failed to connect to 00:1b:d4:44:35:90, status: 25: Association request rejected due to requesting station not supporting the short slot time option
> 
> in this case, I had a case where the AP did send an authorization
> response with success status, but an association response with an
> error condition.
> 
> You once asked if I tested that.
> 
> Now I did, and it looked like mac80211+wpa_supplicant did the right
> thing in this case.

Heh yeah, but we fixed that in the meantime :)

johannes

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