modules/avahi: Enable IPv6 by default

[frederictobiasc]

Avahi's default for use-ipv6 is yes as well. I see no reason why we should do this differently.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[frederictobiasc]

Does anyone know why the options nssmdns4 and nssmdns6 default to false as well?

IMO the whole point of enabling avahi is being able to resolve *.local domains and being resolveable as well. The currently required configuration to do that is big:

services.avahi = {
  enable = true;
  nssmdns6 = true;
  nssmdns4 = true;
  publish.addresses = true;
  publish.enable = true;
  ipv6 = true;
};

On other distributions like arch this just works™
Does anyone see any issue with making that the default apart from avahi.enable?

[fpletz]

@frederictobiasc I agree that these options should probably also be turned on for a better user experience. Avahi is also being used to announce and discover the presence of services on the network via dbus. For instance, pipewire/pulseaudio is able to detect other instances/sinks over the network and make them available automatically. The nss module is not needed for this to work.

[fpletz]

We also have to add release notes if we change the defaults.

[frederictobiasc]

The nss module is not needed for this to work.

@fpletz But do you support enabling nss modules by default as well? I'll update the PR accordingly.

[fpletz]

I just discovered #258424 where IPv6 was explicitly disabled. This doesn't make sense and IMHO shouldn't have been done on that PR.

@SuperSandro2000 Since it wasn't mentioned in that PR, do you recall the reasoning behind disabling IPv6?

But do you support enabling nss modules by default as well? I'll update the PR accordingly.

I would prefer another PR since IPv6 support itself should be less controversial.

[frederictobiasc]

We also have to add release notes if we change the defaults.

Done!

I would prefer another PR since IPv6 support itself should be less controversial.

I opened #361191 for that.

[SuperSandro2000]

I would prefer another PR since IPv6 support itself should be less controversial.

It is super controversial and should stay turned off.

Since it wasn't mentioned in that PR, do you recall the reasoning behind disabling IPv6?

bba808d

#258424

https://github.com/avahi/nss-mdns#:~:text=in%20such%20a%20situation%20causes%20long%20timeouts%20when%20resolving%20hosts

I don't think anything has changed about this, or has it? If not this should absolutely stay turned off otherwise most people will wait long timeouts for no reason.

[fpletz]

@SuperSandro2000 But as far as I understand the problem is NSS and not IPv6 support per se in Avahi, right? That's why I was advocating to split NSS into a different PR. IPv6 support shouldn't trigger the problem you encountered when only nssmdns4 is enabled as far as I understand it - please correct me if I'm wrong here. Note that we are not enabling NSS here.

I would personally love to have IPv6 support enabled for all applications we ship by default.

[SuperSandro2000]

oh, true, not sure how this could be related or not to avahi itself 🤔

[frederictobiasc]

Ok so it's fine to merge this now and continue the discussion regarding nss in #361191, correct?