Crap... I didn't notice the .com 

Thanks a lot for the help.

Sophos XGS firewall works fine. Set up a tunnel, route to it, firewall rules to allow traffic, RA. (Don't do anything with the Gateway, that would be for native IPv6.) Should therefore also work with the Sophos XG Home firewall software on your own hardware -- given that your hardware is supported by XG Home.

Personally, I dislike the modern barbarism of considering the domain to be a website.

I don’t like it either.  That’s why I program my web server to send an HTTP redirection response to the preferred URL, except for “/robots.txt” and robot-read XML site maps which don’t need it.  Omitting the “www” hostname is just laziness, just like writing hexadecimal numbers and addresses with lower case alphabetics.  Whoever put %x into the C language printf function should be drawn, quartered, and shot.  Always use %X instead.

One thing to add: it works for me (v19) without the Routing > Gateways step. Just having the tunnel and static routing ::/0 to that works for me.

You'll also need to add IPv6 Firewall rules for outbound traffic. And it's useful to have an ICMPv6 incoming firewall rule since ICMPv6 is so integral to IPv6 properly functioning.

Also, I created a Local ACL Exception in Administration > Device Access to allow Ping/Pingv6 from the HE IPv4 server. They mention they need to be able to ping your firewall to keep the tunnel up or something.

(When I did try setting up the Gateway, things did not work. But I don't have an IPv6 Gateway now and things work fine.

Well, the CNAME is working... it is just pointing at a non-existant domain.

www.landsurveyilia.gr.  3600    IN      CNAME   landsurveyilia.com.

That should be landsurveyilia.gr.

Personally, I dislike the modern barbarism of considering the domain to be a website.  I would rather see people directed to the www.... form.  This allows for reasonably using other forms as well.  So you could add (instead of the CNAME):

www.landsurveyilia.gr.  3600    IN      A       72.52.138.232

Correct.  The "also-notify" line for BIND will look something like this in context:

        zone "example.com" {
                type master;
                file "db.example.com";
                also-notify { 216.218.130.2; };
                allow-update { none; };
        };

Thanks for the reply.

The site is landsurveyilia.gr

After some research, I read that I must also add an A and a CNAME record.

I added the A record and the system automatically inserted the CNAME record! (name:www.landsurveyilia.gr, hostname:landsurveyilia.com)

The site works, but not if I add the www.landsurveyilia.gr

Will the www. work after sometime, or should I edit some settings?

1) Classically, it may take a day or two for the update of your DNS delegation to take.

2) There may be issues getting delegation to take properly, as both sides can require the other side be working first.  (I think HE.org does, and has a magic cookie to override the check.  if .gr does too, then see point 6.)

3) You can check the delegation from .gr using host/dig/nslookup, and whois.

4) If the delegation is in place, any DNS records you've added to the zone should be visible on the net.

5) If you tell us the domain name (and the name of added records), we can look at it, and may be able to tell you what went wrong.

6) You can also try contacting he.net's help desk, but you should probably do that after you've exhausted other help.

I believe you must notify slave.dns.he.net

See https://forums.he.net/index.php?topic=1994.0

You probably want the autodetect form.

Then you just write something like (python):

    import urllib
    f = urllib.request.urlopen(your_url)
    f.read()

and then error-check