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names: Use systemd-resolved for DNS resolution

Sunil Mohan Adapa requested to merge sunilmohan/freedombox:switch-to-systemd-resolved into main

  • Disable mDNS resolution. While we can migrate our DNS-SD service definition files to systemd-resolved and switch from using avahi to systemd-resolved, many programs still solely depend on avahi-daemon. Examples include cups and GNOME. It is not clear if they will work any mDNS daemon or if they interact with avahi-daemon in other ways that the mDNS protocol. So, for now, disable mDNS in systemd-resolved and continue to use avahi-daemon for it. This is also Fedora's default.

  • Re-introduce Fallback DNS servers with the value same as the upstream systemd project. Debian removes the default fallback DNS servers likely because they could be considered a privacy violation. However, when systemd-resolved package is first installed, the post install script recommends a reboot instead of feeding the currently configured nameservers from /etc/resolve.conf into systemd-resolved. Immediately, this causes the system not be able to connect to any external servers. While this may be acceptable solution for interactive systems and pre-built images, FreedomBox has to a) be available for remote access b) perform upgrades without user intervention (and without reboot until a day). To mitigate privacy concerns, an option to disable these fallback servers will be provided in the UI.

  • systemd-resolved's stub resolver runs on 127.0.0.53%lo:53 and 127.0.0.54. This does not conflict either with shared connections which listen on 10.42.x.1 or with bind which listens on 127.0.0.1 (and other IP addresses). This MR does not address the existing conflict between bind and shared network connections. However, it does not cause any further conflicts.

Tests:

mDNS

  • Avahi diagnostics works. daemon is running. mdns port is exposed in the firewall.

  • systemd-resolved does not listen on mDNS ports.

  • Running avahi-browse shows freedombox on local network.

  • Running avahi-browse shows the services ssh, sftp-ssh, http and ejabberd.

  • Machine can be discovered in Gnome Files.

NetworkManager shared connections

  • After install/upgrade to systemd-resolved, 'shared' connections can be created.

  • With a 'shared' connection configured and active, it is possible to upgrade to using systemd-resolved.

  • Resolving domains from a machine on shared network goes via systemd-resolved on FreedomBox.

Bind

  • Installing, running tests on bind works.

  • Programs connecting from outside network can connect to bind as expected.

  • Programs connecting from local machine can connect to bind as expected.

Upgrading works

  • Upgrading to new FreedomBox package works

  • systemd-resolved is installed and running. 'resolvectl' shows a proper name server (or fallback nameserver like 1.1.1.1).

  • libnss-resolve is installed and configured in /etc/nsswitch.conf

  • /etc/resolv.conf has proper link to /run/systemd/resolve/stub-resolv.conf.

  • Programs using /etc/resolv.conf directly work. Install python3-pycares. python3 -m pycares freedombox.org.

  • NetworkManager has passed on proper DNS entries. In logs dns=systemd-resolved, rc-manager=unmanaged, plugin=systemd-resolved

  • DNS resolution works after first setup. Installing packages works.

  • 'resolvectl query' resolution works.

  • Programs using glibc API resolution such as 'ping' work.

Fresh image

  • Building an image with new freedombox package works without error.

  • Booting from fresh images works.

  • systemd-resolved is installed and running. 'resolvectl' show proper name server.

  • libnss-resolve is installed and configured in /etc/nsswitch.conf

  • /etc/resolv.conf has proper link to /run/systemd/resolve/stub-resolv.conf

  • Programs using /etc/resolv.conf directly work. Install python3-pycares. python3 -m pycares wikipedia.org

  • NetworkManager has passed on proper DNS entries. In logs dns=systemd-resolved, rc-manager=unmanaged, plugin=systemd-resolved

  • DNS resolution works after first setup. Installing packages works.

Installing package on Debian

  • Installing new freedombox package in Debian machine works.

  • systemd-resolved is installed and running.

  • libnss-resolve is installed and configured.

  • /etc/resolv.conf has proper link to /run

  • NetworkManager has passed on proper DNS entries to systemd-resolved using 'nmcli reload dns-rc'.

  • Resolution works with fallback DNS servers when network interfaces are configured with /etc/network/interfaces

OpenVPNs works

  • As a server, we don't push DNS servers to the client. So, a client continues to use its old DNS servers. With systemd-resolved running on server, the client is able to connect to OpenVPN server, route traffic to the internet, and resolve DNS queries.

WireGuard works

  • As a server, we can't push DNS servers to the client. So, a client continues to use its old DNS servers. With systemd-resolved running on server, the client is able to connect to WireGuard server, route traffic to the internet, and resolve DNS queries.

  • As a client, server does not push DNS servers to the client. So, a client continues to use its old DNS servers. With systemd-resolved running on the client, the client is able to connect to WireGuard server, route traffic to the internet, and resolve DNS queries.

Signed-off-by: Sunil Mohan Adapa sunil@medhas.org

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