Whether to open the UDP port used for multicast peer discovery. The NixOS firewall blocks link-local communication, so in order to make incoming local peering work you will also need to configure MulticastInterfaces in your Yggdrasil configuration (settings or configFile). You will then have to add the ports that you configure there to your firewall configuration (networking.firewall.allowedTCPPorts or networking.firewall.interfaces.<name>.allowedTCPPorts).
option