How to troubleshoot why ath0 can't connect to a passwordless wireless network?

[Sam Leffler]

Yuri wrote:
> I have a several wireless networks without password that my linux box 
> easily connects to.
>
> On FreeBSD 'ifconfig ath0 up scan' command shows it. 'ifconfig ath0 
> ssid <my-ssid> up' brings interface to 'associated' state. But 
> dhclient fails to set it up.
>
> I have another device on the same system: ral0. It sometimes connects 
> to these networks ok, sometimes has the same problem.
>
> What can I do to understand what may be a problem with ath0 in my case?
>
> I tried to use tcpdump. It shows outbound DHCP packets and nothing is 
> inbound.
>
> I asked similar question here before, somebody asked me to downgrade 
> atheros driver to one particular lower version. But this didn't help.
>
> Relevant dmesg lines are:
> ath_hal: 0.9.30.13 (AR5210, AR5211, AR5212, AR5216, RF5111, RF5112, 
> RF2413, RF5413, RF2133)
> ath0: <Atheros 5212> mem 0xcffe0000-0xcffeffff irq 16 at device 5.0 on 
> pci0
> ath0: mac 7.8 phy 4.5 radio 5.6
>
> I use 71-PRERELEASE

You seem to say your network is open (no security).  If not you need to 
show your network configuration.

wlanstats shows statistics collected by the 802.11 layer.  athstats show 
stats collected by the ath driver.  Both are important tools for 
diagnosing problems.

tcpdump can be used to tap traffic at 3 layers: 802.3, 802.11, and 
driver.  It can be used to identify where packets are lost in the 
hierarchy (if at all).

Assuming packets are going out but not coming back you can sniff from a 
3rd station to look for traffic in the air but not received.

Given how little info you posted it's virtually impossible to advise you 
what is wrong.  When in doubt c&p real output; describing a problem 
often causes useful info to be left out.

BTW hal version 0.9.30.13 was a test build; RELENG_7 has 0.9.20.3 and 
HEAD has source code for a much newer version.

    Sam