Preferring internal IPv6 source address over gif tunnel IP?

[Viktor Dukhovni]

On Wed, Jul 31, 2019 at 02:46:14PM +0200, Patrick M. Hausen wrote:

> > Is it possible to configure my system to use the internal /64 address
> > as the default source address of outgoing IPv6 packets?
> 
> That is probably pretty easy depending on your preferred mail server.
> Make your mail server listen to <internal>::1 only instead of ::

Many thanks, but I was looking for the network stack to do this
automatically (and seem to have found a way, if perhaps over-specified).

I don't just use Postfix (for which I do know how to specify the
outbound IPv6 address. :-).  I also have various tools related to
the DANE/DNSSEC survey which have not to date needed knobs to specify
the outbound IPv6 address...

> It will then automatically accept connections on that address and use
> it for outbound, too, because it does not have a choice.

Actually, with Postfix, the listening address is indepdent of the
IP address for outgoing active (me as SMTP client) connections.
Both are of course configurable, the listener in master.cf, or else
via "inet_interfaces", and the SMTP client via smtp_bind_address{,6},
(defaults to inet_interfaces if non-loopback singleton).

-- 
	Viktor.