Why can't some machines/devices connect?

[GavinBKK]

Every morning, I go to my local coffee shop of choice and do my morning email, read the paper, etc.

Sometimes the iPad connects. Sometimes it doesn't.

My iPhone nearly always connects, as does my MBA, but not always.

Other users have the same issue.

As noted in another thread, Android devices don't seem to have this issue.

Today, my iPad could not connect, but after an extended period with wifi turned off, it connected happily??

Is this a software bug?

Any ideas/fixes?

[agentx]

Yes overall Apple Equipment and/or MacOS/iOS do have issues with Wi-FI and DNS it has been going on for years IMHO. They have only just sorted an Atheros iMac Wi-FI driver bug a few days ago which my users have been living with since moving to Lion. http://support.apple.com/kb/DL1501

As far as connecting with iOS there is a bit of a trick to "forget network" then reconnect fresh. There are also issues with the mighty crappy mDNS mechanism on OS X which is also in use by iOS. Generally the mDNS mechanism does not always forget its list of DNS servers during network transition leading to DNS resolution issues until the process is restarted.
Basically the lights are on but no browsing or very slow browsing as it trys every DNS server it has cached.

Overall it is so dependant on chipset in use by routers/access points/and your own hardware and what OS you are running etc. I hope iOS 5.1 puts all this right as i have issues at many sites with iPads being able to connect fine then next day will not connect without forgetting and restarting.

[GavinBKK]

Interesting. My old 2007 MBPS has been shocking on wifi since Lion. When the new Hdd arrives, it's going back to SL.

Also, my old 24" iMac on SL is crap on wifi and never remembers passwords for it either. New SL install two months ago. New HDD coming for that one too.

So, could this be why the iPad connected ok after thirty minutes with the wifi switched off? iPad-wise, restarting rarely helps, but maybe I should do the Forget thing and try again.

Thanks very much for the input, very useful stuff to be aware of.
Gavin

[agentx]

"shocking on wifi" now is this connecting to Wi-Fi network or browsing just stops now and again with web pages hanging (DNS issues)?

Also another thing i have to do to fix issues is to remove the relevant network passwords from Keychain access and then re-eneter passwords. I also advise using WPA2 (AES) encryption on your network for some reason this is more reliable with MacOS X and iOS.

When things get really bad and network problems persist you could be looking at hardware issues too. Bad Airport card in your Macbook pro/iMac or a router/access point issue.

There are a few more tricks of the trade as well when browsing or DNS resolution goes astray.

sudo launchctl unload /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
sudo launchctl load /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

This will effectively restart DNS resolution mechanism. I tend to script this process and have in the past had it run every hour using launchd in "extreme" situations.

best of luck.

[agentx]

Also with a fixed network machine such as an iMac we almost always manually enter the ISP/or your chosen DNS servers manually into your Network interface preferences DNS tab rather than relying on the router passing the DNS.

Turn off IPv6 on your network interface.
On Lion you have to use a terminal command but Snow you can do this in the GUI (TCP/IP tab)

sudo networksetup –setv6off Wi-Fi

If you are using Ethernet then

sudo networksetup –setv6off Ethernet

[GavinBKK]

Sorry, been up in the Mango for meetings...

No, it is simply trying to connect, where they fail. OK, bin the pwd in Keychain. Can't do that on iOS though, correct?

I am not good enough to script, but, may I ask, is there a simple (like me) way to implement the script above?

Many thanks, once again agentx. It's people like you who make this forum special.

All the best,

gavin

[agentx]

Forget Network on iOS effectively clears the password and network information from configuration.

Here is a unix script as a .command which you can make executable and just click it if you have issues with DNS resolution.

#!/bin/sh
#Script to unload and reload mDNS as it is a bit crappy
sudo launchctl unload /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
echo "mDNS unloaded"
sleep 5
sudo launchctl load /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
echo "mDNS loaded"
sleep 5
echo "Hopefully you can get on with browsing again"
exit