The best method is via the response policy zone in Bind 9.8.1 or newer. It allows you to override single records in arbitrary zones (and there's no need to create a whole subdomain for that, only the single record you want to change), it allows you to override CNAMEs, etc. Other solutions such as Unbound cannot override CNAMEs.
https://www.redpill-linpro.com/sysadvent/2015/12/08/dns-rpz.html
EDIT: Let's do this properly then. I will document what I've done based on the tutorial linked above.
My OS is Raspbian 4.4 for Raspberry Pi, but the technique should work without any changes on Debian and Ubuntu, or with minimal changes on other platforms.
Go to where your Bind config files are kept on your system - here it's in /etc/bind
. Create in there a file called db.rpz
with the following contents:
$TTL 60
@ IN SOA localhost. root.localhost. (
2015112501 ; serial
1h ; refresh
30m ; retry
1w ; expiry
30m) ; minimum
IN NS localhost.
localhost A 127.0.0.1
www.some-website.com A 127.0.0.1
www.other-website.com CNAME fake-hostname.com.
What does it do?
- it overrides the IP address for
www.some-website.com
with the fake address 127.0.0.1
, effectively sending all traffic for that site to the loopback address
- it sends traffic for
www.other-website.com
to another site called fake-hostname.com
Anything that could go in a Bind zone file you can use here.
To activate these changes there are a few more steps:
Edit named.conf.local
and add this section:
zone "rpz" {
type master;
file "/etc/bind/db.rpz";
};
The tutorial linked above tells you to add more stuff to zone "rpz" { }
but that's not necessary in simple setups - what I've shown here is the minimum to make it work on your local resolver.
Edit named.conf.options
and somewhere in the options { }
section add the response-policy
option:
options {
// bunch
// of
// stuff
// please
// ignore
response-policy { zone "rpz"; };
}
Now restart Bind:
service bind9 restart
That's it. The nameserver should begin overriding those records now.
If you need to make changes, just edit db.rpz
, then restart Bind again.
Bonus: if you want to log DNS queries to syslog, so you can keep an eye on the proceedings, edit named.conf.local
and make sure there's a logging
section that includes these statements:
logging {
// stuff
// already
// there
channel my_syslog {
syslog daemon;
severity info;
};
category queries { my_syslog; };
};
Restart Bind again and that's it.
Test it on the machine running Bind:
dig @127.0.0.1 www.other-website.com. any
If you run dig on a different machine just use @the-ip-address-of-Bind-server instead of @127.0.0.1
I've used this technique with great success to override the CNAME for a website I was working on, sending it to a new AWS load balancer that I was just testing. A Raspberry Pi was used to run Bind, and the RPi was also configured to function as a WiFi router - so by connecting devices to the SSID running on the RPi I would get the DNS overrides I needed for testing.
Addressing 1 and 2: In most cases, I would recommend doing a single "A" record for the actual IP associated with the box and CNAME everything you need to that. If you are going to have a lot of somethings.example.com, I would make use of a wildcard entry
example.com A 192.168.0.1
*.example.com CNAME example.com
The benefit being that you don't have to do a lot of DNS maintenance as whatever .example.com you use will already match. You just let apache figure out what to do with it based on the name given. This would result in 2 look-ups, and I would only do many CNAMEs to one A, and not try doing CNAME->CNAME. Additionally MX records must only point to an A record name.
If you ever need to break a vhost off to its own IP addres, you can then just add an "A" record for that one host and the most-specific answer will win.
example.com A 192.168.0.1
*.example.com CNAME example.com
new.example.com A 192.168.0.2
Best Answer
Yes,you can do it.
Test you DNS configuration from external (from a pc out of your network). If you
ping www.example.com
you should receive response from ip 1.2.3.4 and if youping mail.example.com
you should receive response from ip 1.2.3.5.Configure web server to listen only on ip 1.2.3.4 and mail server to listen only on ip 1.2.3.5.
Verify you services:
telnet www.example.com 80
andtelnet mail.example.com 25