Provide dummy interface (option?) and use only that address externally

[fingon]

Fate-share e.g. dummy interface with the lifetime of the hnetd process; use the IPv4/IPv6 addresses of that, so that addressing stays stable even in presence of network topology changes.

Question is, should this be an option / default to on?

[toreanderson]

Such a «primary» address could also be used to fix issue #54.

Not sure you need a separate dummy interface though, in my experience it's usually the router's loopback interface which is used for this purpose.

[fingon]

Linux loopback used to have some issues (hardcoded routing/firewalling logic associated with it). Not sure if that is the case still.

[fingon]

That's the main reason IIRC whole dummy network device came around looong time ago anyway ;) Dunno if it is still needed or just using 'lo' would be enough.

[toreanderson]

Local traffic is indeed treated specially and routed to the lo interface:

$ ip -6 rule list
0:  from all lookup local
32766:  from all lookup main
$ ip -6 route show table local
local ::1 dev lo  proto none  metric 0
local 2001:db8:c420:3c4::255 dev lo  proto none  metric 0
[...]

You can't override that rule because it has priority 0, and the local <addr> dev lo routes are added automatically for all addresses on the system (they don't actually have to be configured on the lo interface - in my example above, 2001:db8:c420:3c4::255 is actually configured on enp0s25). So while local traffic is treated specially I don't think it matters if the address is configured on lo or dummy0 or any other interface, as it will end up getting routed to lo anyway.

That said, I have no objection to using dummy0 or whatever else, just wanted to point out that using lo might make the implementation easier.