Global IPv6 addresses in local network

[seijikun]

Version: 0.98.1

One of IPv6's design goals was to eradicate NATs.
For that reason, many setups assign public IPv6 addresses to hosts even in local networks.

In my network, my ISP uses IPv6 prefix delegation to assign a public IPv6 subnet to the router.
The router then assigns randomized (IPv6 Privacy Extensions) IPv6 addresses inside this public IPv6 subnet to all local hosts.

As far as I know, iroh prefers IPv6 over IPv4. However, I noticed that:

• The list of candidate addresses does not contain the fe80::* addresses
• Local connections (behind the router, inside the house), always use IPv4

From this, these questions arose:

• Are IPv6 link-local addresses ignored? I would've expected iroh to prefer these over local IPv4 addresses
• Is there a logic in place that regards IPv6 addresses between two peers as local (= no hole punching required), if they are in the same subnet?
• Does the candidate address list sent over the wire only contain IP addresses, or also their corresponding subnet mask?

[dignifiedquire]

We currently do not use linklocal addresses in discovery services, as they are expected to not work across the wider internet, and we try to avoid leaking information we don't expect to work.

n0-computer/net-tools#50 starts to change this, but it is right now unclear how we can land this in a sensible way.

[flub]

I would like to add thought that we want to improve on this. IPv6 link-local is one of the things I'd like to properly support after 1.0, because as you rightly point out the current situation is not great.

I don't think there's anything stopping us from doing this. Privacy wise we only share IP addresses to authenticated peers. But this does need a bit of careful design and working through the entire feature.