Allow pings to ensure the home is up.

Just convenient, not that unsafe.

quinn/etc/nixos/configuration.nix

@@ -231,6 +231,7 @@
   # Open ports in the firewall.
   networking.firewall = {
     enable = true;
+    allowPing = true;
     allowedTCPPorts = [ 80 443 ];
     allowedUDPPortRanges = [
       #{ from = 4000; to = 4007; }