Slow wifi on MacBook Pro when connected to Thunderbolt Display

Not sure why all of a sudden you have this issue but try this: Go into preferences while your MBP is connected to the TBD, go to network. Click on the star at the bottom of the left column and select service order. Arrange to have WIFI at the top. Click apply and see if that makes a difference. Another issue may be blue tooth interference. Are you using a bluetooth mouse or keyboard with your MBP?

Any WIFI device can get slowed by other radio interference. It can come from phomes and other devices in a particular area in addition to walls, piping, etc. causing a slowdown. That is the way things are.

A repeater would probably help however I have a Windows laptop as well but my Mac Mini has a stronger signal than my PC so not sure what your issue is.

I am having an identical issue when using my 2010 iMac as an external display with my 2013 MBP. I have run very controlled tests and have concluded that there is a serious issue; my wifi basically slows to a halt when I use the iMac as an external display.

When I use the MBP in the exact same position in the room, without using the iMac as an external display, everything is perfect. As soon as I use the iMac in Target Display Mode, my wifi slows to a crawl or just stops entirely. Does anyone have a solution for this?

My new 2013 MacBook Pro 13" retina had same WiFi issue. Please go to this Website and follow the instructions to change your router's settings. http://www.s0hel.com/blog/401/fixed-slow-wifi-issue-with-new-macbook-pro/

Yesterday I changed my router's settings and now I don't see any WiFi issues. 😉

I hope this works for you.

For me what made the difference was running the laptop with the cover still open. Macbook Pro cover open and I get full speed. Run with the cover closed and display only then the wifi speed cuts in half. No idea why this happens.

Same issue here. It occurs also with non apple monitors. I think the thunderbolt-port itself is the mistake...

Windows-Laptop has 60mbits at same position with same monitor. MacBook Air, late 2013 comes only to 10 - 20 mbits...

Bluetooth mouse is additonal slowing the wifi..

Never thought, that I would have such problems with a mac.. not acceptable..

Apple's wifi hardware is senstive to everything. Experienced the same problem, many times this comes down to router hardware compatibility. I have never seen these types of issues with any other wifi device other than appls. They are sensitive to AES encryption, if you see an option on your router under WPA settings, make sure to only use TKIP. In my case, there is some out of spec compatibility problem with ubiquiti gear (unifi), the people on the forums over there are screaming about it. I was getting .5mbit upload thus blowing time machine backups, swapped to a cheapo router and I'm back up to 200mbit. It's all hit or miss with this apple stuff if you do anything deeper than open a browser.

In my case AES is working faster than TKIP. Maybe it is the router (Hitron, Kabel Deutschland), but I'n not going to replace it for now.

I am also experiencing very similar issues. For the past few weeks I have been suffering from really poor wifi performance on a Macbook Pro 13" Retina (Late 2012).

I have gone as far as purchasing a new router, changing router channels, encryption, switching back to 802.11g etc and nothing has really helped.

I downloaded a free app called NetSpot to help diagnose the problem. Today I had it open whilst plugging in my external monitor and I noticed a huge difference in signal to noise. The screenshot below shows that difference and I can re-produce it over and over again.

The external screen is plugged in via Thunderbolt. Interestingly only one of my thunderbolt ports seems to work with the screen (not sure if that is how it should be).

I can also see almost double the number of wifi networks with the screen unplugged and the internet performance is much better.

So my conclusion so far is that an external screen via thunderbolt is causing some serious performance issues. I am going to test the HDMI port later today and see if that helps the situation.

I have tested it over HDMI now too and things look a little better. It still does have a slight impact on the wireless performance but its minor compared to thunderbolt.

Quite baffled as to why an external screen would impact the wireless chips so much. Perhaps too much of a power draw?

Nearly the same for me. I just get used to it, because in the most time the 10mbit of my 100(!) are ok to surf. Windows-Laptop gets to 60mbit in Wifi WITH ExternalScreen and Bluetooth.

Nevertheless this is 100% an Apple-Issue and they have to fix it as soon as possible. Problem I see, is that the most people will not notice the slow down of the network, because anyways they have not faster connection than 10mbit. But for my 100mbit connection I can feel the impact much more... thats so embarassing for Apple.

I believe I have gotten some more information.

After having significant troubles, I called my ISP (Sonic), who informed me that the wireless signal in my house was receiving a significant amount of interference. I believe that a large amount of the wireless interference is due to the thunderbolt-connected imac used as a monitor.

They recommended a novel solution which has ameliorated this issue. I manually varied the channel on which my wireless router has been operating (1-11) until I found one which received the best download bandwidth. My speed doubled immediately and has been very good ever since. This is basically the same solution offered by poster Muhammed J. Kamal above as well. I recommend it.

Eventually I also decided to simply install a wired connection to my laptop here, to use it when I am sitting at my desk attached to my iMac. Obviously the bandwidth is perfect in this scenario.

Judging from the graphs above, it is very curious to consider the bizarre situation that using a thunderbolt display may cause the MBP's wifi to be underpowered. That would be a very unfortunate error for Apple to have let slip through QA.