DNS – How to Configure DNS to Point Main Domain at Firebase Hosting, Not Subdomain

As most of the replies have noted, you need an A record at the base of your domain-name pointing to the IP address of the web server.

However I would not recommend that www be a CNAME pointing at that base domain-name unless you understand exactly what you're doing.

Although this might seem simplest from a management point of view (only one record to change if your site changes IP address) it can have side effects.

Don't forget that a CNAME makes the left-hand-side (the "owner name" of the CNAME) equivalent to the right-hand-side for all DNS resource record types, and not just for A record queries.

So, if your zone looks like this:

$ORIGIN example.com
@       IN SOA ...
        IN NS ...
        IN NS ...
        IN A 192.0.2.1
        IN MX mail
        IN SPF ...
www     IN CNAME @

then a query for www.example.com IN MX? will return the same MX record as for example.com. Now if that's what you want, that's fine.

However it'll also do the same for the other records (SOA, NS, SPF, etc) which is not usually desired.

Hence the proper answer should be to just make www an A record too, with the same value as the base name:

$ORIGIN exmaple.com
@       IN A 192.0.2.1
wwww    IN A 192.0.2.1

Connection Reset is a server response and is not likely a firewall issue. What is occurring is during the three way handshake a reset is being sent in response instead of a SYN ACK. This is notifying you and your browser that the web server application (IIS/apache etc.) is not accepting connections. This means there is an actual issue with the web server application and not with your DNS or Web Browser.