High Sierra Wifi Poor Performance Fix for 2010 MacBook Pro

I’ve been working remotely at an AirBNB this week and was having a really frustrating time of it. The 2010-vintage MacBook Pro I have would connect to the Wifi, go for awhile — sometimes a half-hour, sometimes not more than a minute, — and then drop the connection. Shutting off wireless and reinstating it would restart the connection, but it would be unstable and drop again. The length of time it would stay connected was completely unpredictable, and whether or not it would reconnect, and how long it would take was also completely random.

I was getting speed test results of 0.15 MB/s up and 0.18 down. This was unusable, and I fell back on my hotspot for any sustained connection. Weirdly, I could connect fine with the Amazon Dot I’d brought along – flawlessly, in fact. What was going on?

Late Friday evening, after a particularly frustrating session attempting to get Netflix to work (I really wanted to see Disenchantment — great show, by the way!), I started doing some research and came across an article that recommended reducing the MTU for the wireless device to 1453 (from the default somewhere in the 1500’s). Really? Okay…

Magic. It has now been solid for several hours, including streaming video. If you’re having any trouble at all, I’d recommend at least trying it. The article shows you how to set up a separate “location” with the different MTU, so it’s simple to switch it on or off as you choose.

Update: 12 hours later, I’m getting terrible performance again. A little more searching turned up a tutorial on readjusting the MTU to optimum with ping. Reset your MTU size to default, then starting at your 1500, try the following commad (replacing mtusize with the actual number!):

ping -D -s mtusize -c 2 google.com

If you get “message too long” in the ping output, drop the MTU size a bit a try again. If you have no idea what MTU size is good, start at 1500, which will be too big, and go down by 100s until you start seeing “xxxx bytes from google.com:…” messages, which let you know your ping is getting through. You can then go up by tens until you get “message too long” again, then back down by 1’s until you find the maximum MTU size that doesn’t get “message too long”.

I had to reduce my MTU size further to 1425, and I’m near 10 megabits/second again.