Is IPv6 properly configured in the stock nvOC setup?  I first noticed an issue when trying to apt-get upgrade and the update host resolved to an IPv6 address: updates refused to install.  At first, I just worked around it with the instructions at https://unix.stackexchange.com/questions/9940/convince-apt-get-not-to-use-ipv6-method to force apt-get to use IPv4 only.

I then set about writing a mining switcher.  Getting the current dollars-per-BTC rate from Coinbase was no problem...one line of Python.  Getting current profitability from NiceHash was a bit more problematic.  Guess what?  api.coinbase.com is IPv4-only, but api.nicehash.com is offered on IPv4 and IPv6.  urllib (and most other Python libraries) prefers IPv6 over IPv4, if IPv6 is available.

ifconfig shows that my nvOC box is getting both IPv4 and IPv6 addresses assigned to it by my router, but any attempt at ping6ing known-working IPv6 hosts (api.nicehash.com, ipv6.google.com, alfter.us) fails as "address unreachable." The Windows 10 box through which I'm typing this message, OTOH, gets through to all of those hosts fine (Windows uses ping for both IPv4 and IPv6, and also appears to prefer IPv6 if available), so my network supports IPv6.  (This Windows 10 box can also boot into Gentoo Linux, and IPv6 works there as well.)

According to https://wiki.ubuntu.com/IPv6, IPv6 is supposed to work out of the box.  Has something been done in the nvOC configuration to disable it, and if so, how would one back out these changes so it works again?  I normally use Gentoo, so I'm not too familiar with how Ubuntu manages things.  The aforementioned wiki page links to another page that describes disabling IPv6, but none of that appears to have been done.  I could shut off IPv6 at the router, but I'd rather not have to do that.

Edit: For the time being, I've put api.nicehash.com's IPv4 address in /etc/hosts as a workaround.  It'll break as soon as NiceHash decides to move it to a different IP address, but it'll work for now.