Router's ssid changes from infrastructure to ad-hoc

Question

For a period of time the router's ssid is shown (on various computers) as a normal infrastructure network - computers connect fine and everything works however after a few minutes / hours all computers see the same ssid as an ad-hoc network (not infrastructure). At this point a computer that was already connected continues to work - a computer that isn't cannot connect. Rebooting the router temporarily restores the visibility of the correct infrastructure ssid.

Is something interfering?

Connecting computers: macbook (2009), iphone 3g, windows vista desktop, windows xp desktop.

Details:

• D-Link DSL-2740B router set to WPA2-PSK (Personal)
• Enable Wireless : Yes
• Wireless Network Name (SSID) : ######
• Country : Australia
• Wireless Channel : 1
• 802.11 Mode : Mixed 802.11n, 802.11g and 802.11b
• Channel Width : Auto 20/40 MHz
• Transmission Rate : Best (automatic)
• Hide Wireless Network : No
• Group Key Update Interval : 0 (seconds) this is the default value

Update:

Firmware has been updated to the latest available: v4.15b363

Running airport -s: Before in the normal list:

SSID BSSID             RSSI CHANNEL HT CC SECURITY (auth/unicast/group)
caxxxxxx 00:24:01:56:##:## -42  1,+1    Y  -- WPA2(PSK/AES/AES) 

After (misbehaving), note bssid is identical & no longer in the 'normal' list:

1 IBSS network found:
SSID BSSID             RSSI CHANNEL HT CC SECURITY (auth/unicast/group)
caxxxxxx 00:24:01:56:##:## -42  1,+1    Y  -- WPA2(PSK/AES/AES)

Answer 1

I suppose it's possible that your router is still publishing its SSID correctly, but something else is publishing the same SSID as an ad-hoc network. But if that were the case, it seems strange that rebooting the router fixes it, and it also seems strange that nothing can connect after this problem crops up. If you had two networks with the same name in the same area, clients would be able to connect at the link-layer, they just might not be able to get anywhere if they happened to join the IBSS network instead of the infrastructure network.

Sounds most likely to be a bug in the D-Link router. Did you check the D-Link website to make sure you have the most recent firmware for your router? No use fighting a bug that's already been fixed.

An easy way to see if more than one device is publishing the same SSID is to do a scan with a low-level tool that reports each AP separately. Buried within Mac OS X is the "airport" command-line tool that'll let you do this:

/System/Library/PrivateFrameworks/Apple80211.framework/Resources/airport -s

By the way, why is your Group Key Update Interval 0 seconds? Does that mean "disabled"?

Update: Please update with the hardware revision and FCC ID (if it has one) of that router. The FCC ID will probably enable me to look up which vendor's wireless chipset D-Link used in that model, so I can avoid it. I'll update with what I find.

If that model router was never sold in the US, it might not have an FCC ID. I'm not sure if there are any equivalent regulatory certification IDs in other regions that might be useful in the same way.

At this point, though, it seems very likely this is just a router bug, and you'd probably have to buy a different router to fix it. You could try contacting D-Link to see if they know of this bug and have a workaround or if they have a firmware fix on the way.

Answer 2

Just to add that on my DSL-2740B rev C3, being active for the last... can't remember, must be 3+ years - and with the 3.01b484 EU firmware since the last 18 months or so, I had in the last couple of days this exact issue happening 3-4 times.

My freshly booted Linux wlan client doesn't connect, wpa_supplicant says authentication times out, and iwlist eth1 scan reports a very visible access point -- but in "ad-hoc" mode instead of "managed".

Rebooting the router fixes the issue.

I don't know whether 3.03b481 (which seems to be the latest) fixes the issue... not going to flash it unless the problem becomes more frequent.