[mythtv] Q about networking after recent networking improvements in master

[Stephen Worthington]

On Sun, 16 Apr 2017 12:16:29 -0500, you wrote:

>[my ISP only provides GUAs to their business customers and based on my last
>  conversation with them, they have no plans to start]

If your ISP is not assigning any GUAs to you, then you can not use
IPv6 to connect to the outside world.  Which means that enabling IPv6
ULAs may well cause problems as your devices will prefer to connect
via the IPv6 addresses and will take a long time to try using an IPv4
address when that fails.  If there is no real IPv6 connectivity with
the outside world, but a device can see an IPv6 address it thinks it
can use for that, then even if there are no IPv6 DNS settings in
place, it will use IPv4 DNS to get IPv6 addresses and try to connect
to them.

Not providing GUAs means not providing IPv6 support at all, so there
must be something wrong with your understanding of what your ISP is
saying.  Most likely, they are only providing dynamic GUA address
blocks, that will potentially change every time your router reconnects
to them.  That is not how IPv6 is supposed to work, but does seem to
be how stupid ISPs are doing it.  My ISP does that, but for those
people who pay for a static IPv4 address, they also provide static
IPv6 addresses, and as I have always had a static IPv4 I have never
had to cope with dynamic IPv6 assignments.  The way to cope with
dynamic IPv6 addresses seems to be what you are doing - use ULA
addresses for all the devices on your network, and allow automatic
assignment of dynamic GUA addresses by the router when it receives an
assignment of its GUA address block.

When the dynamic GUA assignment changes, if any of your devices are
using the GUA addresses to talk to each other, those connections will
be disrupted.  I am not sure if IPv6 will prefer to use ULA addresses
if they are present and a GUA address is also present - I hope it
works like that.  Within one subnet, IPv6 devices seem to prefer use
the link-local addresses to talk to each other, even if they have GUA
addresses assigned.  So if you only have one subnet, then IPv6 will
likely keep working right when the GUA changes.

Since you are not seeing any GUA addresses on your devices, there must
be some misconfiguration somewhere that needs fixing, most likely in
your Internet router.