iphone 4s won't connect to airport extreme after yosemite install on iMac 2009

Please follow the steps in this Apple guide for troubleshooting connection issues on the iPhones to see if it might provide a solution your issue.

iOS: Troubleshooting Wi-Fi networks and connections - Apple Support

Can you verify your DNS servers? Please try a different browser, say, Firefox on your iMac. If you connect the iMac via a wired connection, does Safari (or any other browser work)? DNS issues (or your ISP's DNS may also be misbehaving).

How is Yosemite upgrade related to iPhone 4s/iPhone 5 wireless connectivity? Did you also upgrade to iOS8 recently?

The two may be unrelated. You may have several different issues.

Yosemite has a new protocol Apple Wireless Direct Link - AWDL. A lot of issues in Yosemite/WiFi are related to the implementation (a buggy one) which are causing grief for Yosemite users. If you have a wired connection, some of these problems go away. If there is a Yosemite machine which is 'live' in the network, it causes issues for other non-Yosemite devices which may be using WiFi, like iDevices, ATVs, etc.. It may explain what you observe. Do you have a non-Yosemite Mac available?

There are quite a few reports of Bluetooth/WiFi coexistence issues in Yosemite.

That is really helpful.. Loner T.

If we only knew about some of this before hand it would make our lives so much easier.

Here is an article about peer to peer wifi going on..

http://help.apple.com/deployment/ios/#/apd8fc751f59

So it is jumping off the wireless infrastructure and directly passing files between the clients.. using channel 6 in 2.4ghz and 149 + 153 in 5ghz.

Anyone using AC wireless in US or many other places will have to use 149 to get the full ability of the AC wireless.

Peer-to-Peer discovery is initiated using Bluetooth Low Energy (BTLE) when a user selects AirPlay on an iOS 8 or OS X Yosemite v/10.10 device. This causes the device and the Apple TV to visit Wi-Fi channel 149 in the 5 GHz band and Wi-Fi channel 6 in the 2.4 GHz band, where the discovery process continues. Once the user selects an Apple TV and AirPlay starts, the Wi-Fi radios timeshare between channel 149 and whichever infrastructure channel each device is currently using. If possible, the AirPlay sender roams to the same infrastructure channel the Apple TV is using. If neither device is currently using an infrastructure network, the devices will utilize Wi-Fi channel 149 only for AirPlay. Peer-to-peer mirroring adheres to 802.11 standards, sharing Wi-Fi bandwidth with other Wi-Fi devices.

There are quite a few reports of Bluetooth/WiFi coexistence issues in Yosemite.

Of course because it is flopping between standard infrastructure wireless and this new peer to peer wireless.

There is already so much voodoo involved in getting wireless working at all.. this has to have a major effect on reliable wireless comms.

Thanks,LaPastenague

Have spent the last several days scouring for information. On a Yosemite Mac, I have this.

awdl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1452

ether 5e:76:3f:04:f9:b9

inet6 fe80::5c76:3fff:fe04:f9b9%awdl0 prefixlen 64 scopeid 0x9

nd6 options=1<PERFORMNUD>

media: autoselect

status: active

mDNS and discoveryd are going all over the place, with partial implementations.

http://www.google.com/patents/US20140219193

http://www.google.com/patents/US20130227647?cl=en

I have pretty much the same problem. Airport Express with guest network set up wpa2 on both main and guest.

2010 MBP (10.8.5) and 2012 mini (Yo), 3 pads and 3 iPhones, running a mix of ios7 and 8, and 2 apple tv boxes.

After moving the mini to Yosemite my internet connection flakes out--both Safari and Firefox basically just "sit and spin", and my MPB has the exclamation point on the network pie. Switching between the networks seems to help the MPB, but that is a hassle because it takes me off the network that has my printers and puts it on the network with the xbox and kids phones and the kid's friends' iPods. The phones and the pads might stall a bit sometimes but don't get locked out like the mac-mini--and switching the networks on the mini doesn't seem to help like it does on the MBP running 10.8.5.

About the only solution for the mac-mini is to restart, which is horribly annoying. It seems to have gotten a bit better the last few days, but it is definitely an intermittent issue.

I was running the main plus the guest network prior to the yosemite upgrade and there wasn't a problem. Do I need to go back to 10.8 on the mini or do you think that a patch might be in the works?

As a test, connect the Mini via Ethernet cable, turn off Wireless, and test you Mini and other devices.