Ubuntu – bind9: example.com works, www.example.com doesnt, and how to block urls

There's really no difference in these two names other than the fact that one has a subdomain prepended to it and the other doesn't. You can set up resource records to take advantage of an almost unlimited amount of subdomains once you own a domain name.

There are at least 30 different types of resource records. For now you can probably get by with focusing on two:

• aname ("a" record - primary address record)
• cname (Alias of one name to another)

www is by far the most common subdomain but there are many others. Take a look at the following examples:

• gmail.google.com
• my.yahoo.com

What you need to understand is that google.com and yahoo.com are domain names. Anything before that is referred to as a host name or a subdomain. As long as you take the necessary steps to set up your DNS resolution to resolve these subdomains to either their own IP address (use A Name) or as an alias (use a Cname) and you set up your webserver to understand such requests you'll be set.

In your case you should use a cname to point www.domainname.com to domainname.com. A cname is more appropriate as an answer only if you intend to point both to the same IP. That way if you need to change your IP in the future, you'll only need to adjust one record.

As for getting your webserver to understand both requests there are lots of examples for both Apache and IIS on serverfault. Do a search and you'll find everything you need. Look for virtual hosts.

Edit: Here's a cross reference about cnames. They have their place too. Use the tool that best suites your circumstances.

Your original config:

$TTL    3600
@   IN  SOA example.com. admin.example.com. (
            2011101601  ; Serial
            3600        ; Refresh 1h
            60      ; Retry 1m
            86400       ; Expire 1d
            600 )       ; Negative Cache TTL 1h
;
@   IN  NS  localhost.

;
example.com.    IN CNAME localhost.
example.com.    IN A 127.0.0.1

should be changed to this:

$TTL    3600
@   IN  SOA example.com. admin.example.com. (
            2011101801  ; Serial
            3600        ; Refresh 1h
            60      ; Retry 1m
            86400       ; Expire 1d
            600 )       ; Negative Cache TTL 1h
;
@   IN  NS  ns1.example.com.

;
example.com.        IN A 127.0.0.1
ns1.example.com.    IN A 127.0.0.1
www.example.com.    IN CNAME example.com.

(did you notice that I also changed the serial? for every change you make on the config you need to alter the Serial. It's format is YEARMMDD and a two digit ID starting at 01 which you need to +1 every time you make a change. So for example if you made a second change on the config today, you should change it to 2011101802, on a third change it should be 2011101803, or if you would make a change tomorrow it should be 2011101901 etc. this is very important!)

Also make sure that on your webserver you have a virtual host configured as example.com

Check that your /etc/resolv.conf points to your local BIND and has nameserver 127.0.0.1 entry first. If you are using debian with Gnome then Network Manager might overwrite resolv.conf. One solution for this is just to add the nameserver to Network Manager through the GUI, but make sure that it is first in the list.