[mythtv-users] mythtv-setup without UPNP searching for backend?

[Stephen Worthington]

On Mon, 10 Jan 2022 07:06:48 +0800, you wrote:

>Just had another nip:
>ISP failed for days. Using PhoneHotspot. (OT I've been trying to setup another machine as a gateway but so far I'm beaten) During the switching LAN / hotspot the frontend NAME changed (need dhcp for hotspot, but manual for mythtv)
>dhcpname is setup all wrong, rebooted, realname setup is now all wrong !!
>
>In case it piques interest my ot bit is
>Was 
>ISPMODEM----------------mythbackend------------mythfrontend  with BE and FE using ISP as gateway
>
>What I'm trying to do
>
>ISPMODEN-------------GWBOX--------BE--------FE  both using GWBOX as gateway
>PhoneHotspot ) ) ) ) ) )
>
>Linux:trivially easy:so-far-impossible
>
>James

Your problem is likely the "ISPMODEM" - a really good router should be
able to support WAN failover.  You still get problems with delegated
address spaces though - you really want to keep on using the same
addresses on your network, but just change the external ones.  With
NAT on IPv4 in theory there is no problem (except configuring it
correctly), but with IPv6 you will get a different address range from
your hotspot and that makes life very difficult.  I have been
experimenting with using a form of NAT on IPv6 where the router
translates the delegated prefix part as necessary, and I think I have
made it work.  This is with a Ubiquiti ERL router.  But even there, I
can not do it with router CLI commands - I have to do it using
iptables commands to the underlying Linux kernel.  The same sort of
translations should be possible in your Linux GWBOX, but there is not
much documentation on how to do it and I have yet to succeed with IPv4
(not that I have put much effort into it recently).  The keywords to
use in Internet searches are "NPT" (Network Prefix Translation),
"NPTv4" and "NPTv6".  Google will helpfully assume you really mean NTP
so enclose them in quotes.