IPv6 problem with macOS Sierra

When there were no new iMacs announced at Apple’s “Hello Again” event in October I decided to stop waiting and replace my ageing late 2009 model with an Apple refurbished late 2013 one (I had a friend who was eager to buy my old one). I had also held off installing Sierra so my old machine was running El Capitan.

I use an ISP called Andrews & Arnold which in addition to a fixed IPv4 address gives me a block of routed IPv6 addresses, and this has always worked fine. I have even tried turning off IPv4 on my iMac and was still able to connect to sites like Google over IPv6 (see Experiments with IPv6). One of the things I noticed was that the App Store didn’t work with IPv4 turned off.

My new iMac arrived and I got to work setting it up. I was expecting it to ship with the latest OS installed but found that it was running Yosemite, presumably because that was what it would have shipped with just before it was discontinued. When it was up and running I used the App Store to install a couple of updates and then downloaded Sierra. The new OS installed fine but when I tried visiting the App Store again my machine was unable to connect. At first I thought it might be a temporary problem with the App Store but I was also having trouble connecting to some websites. I tried searching for reports of the problem but nothing obvious popped up and it was then I had a brainwave – maybe it is an IPv6 issue. Since most ISPs do not provide IPv6 that could explain the lack of reports.

There was an easy test I could do, just turn off IPv6 and see if it makes a difference. So I went into System Preferences – Network – Advanced where I could see my Ethernet connection had “Configure IPv6” set to “Automatically”. There was no option to turn it off completely so I set it to “Link-local only”. I then tried the App Store and it connected fine. Since then I have tried enabling IPv6 a few times but it always results in me not being able to connect to the App Store. This is a workaround rather than a solution and it means that I can’t connect to IPv6 only sites like Loops of Zen.

I have been meaning to contact Apple Support about this but I thought it would be good to first write up what I have discovered so far, hence this blog entry. The Ars Technica review of Sierra does mention changes to IPv6 which could well be related, see Networking: Sierra brings new IPv6 addresses. I will contact Apple first since it was clearly Sierra that broke IPv6 for me but I can foresee having to talk to Andrews & Arnold too. I will report any progress in the comments.

One response to “IPv6 problem with macOS Sierra

  1. As well as my iMac being unable to connect to the App Store without disabling IPv6 it has been slow to connect from my iPad. Today I finally got round to doing something about it and called my ISP (Andrews and Arnold). The guy I spoke to asked which router I was using and I told him it was a technicolor. He said others had experienced the same problem and sent down a fix, then remotely rebooted the router. That worked for both my iPad and iMac. Apparently it was something to do with a feature called “WAN down spoofing” which had to be disabled in the router. The changes to IPv6 in Sierra must have just exacerbated the problem.

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