Hack and / - Your Own Personal Server: DNS

Many registrars on the Internet require that any domain you register have at least two DNS servers configured with it. It's a good practice to have, because if you have a single DNS server and it goes down, it effectively will make all your servers under that domain inaccessible. This means you need to set up a second DNS server on a different IP, ideally on a different network, or have a friend with a DNS server act as a slave to your master DNS server. In either case, it's a relatively simple process. Let's say that my second DNS server is going to be at the IP address 98.76.54.32. First, I would log in to my Master DNS server and add the new NS and A records to my zone file:

;
; BIND data file for example.org
;
$TTL 4h
@  IN  SOA ns1.example.org. root.example.org. (
	    2		; Serial
	    604800 	; Refresh
	    86400 	; Retry
	    2419200 	; Expire
	    604800 ) 	; Negative Cache TTL
;
@	IN NS	ns1.example.org.
@	IN NS	ns2.example.org.
@ 	IN A	123.12.34.57
www	IN A	123.12.34.57
ns1 	IN A 	123.12.34.56
ns2 	IN A 	98.76.54.32

Next, I edit named.conf and add a line to the configuration of example.org so that it will allow zone transfers from my DNS slave:

zone "example.org" {
	type master;
	file "/etc/bind/db.example.org";
	allow-transfer { 98.76.54.32; };
};

Finally, I would install BIND on the second server, or if it already exists, all I would have to do is add a new entry at the end of the named.conf file to define the example.org zone and tell this server the IP address of the master:

zone "example.org" {
	type slave;
	file "/var/cache/bind/db.example.org";
	masters { 123.12.34.56; };
};

Note that in this case the slave zone is being stored under /var/cache/bind. That's the default location for slave zone files under Debian-based systems. Under Red Hat, you would store them under /var/named/. Once I reload BIND on the slave server, it will pull the new zone information from the master, and I should be able to perform DNS queries against it.

Once you have set up a slave, keep in mind that anytime you make a change to the master, you will need to increment the Serial field in the Master's zone file (in my example, it is set to 2, but a lot of administrators like to set it to the current date plus two extra number fields, such as 2010120500). When the slave needs to know whether its zone information is up to date, it compares its serial number with the serial number on the master. If the master's serial number for a zone is higher, it copies down the new zone information; otherwise, it sticks with what it has cached.

Once you have a functioning DNS server, all that's left is to tell the world to use it. If you haven't already registered your domain with a registrar, find a domain registration service on the Internet (there are too many for me to list here, but a search for domain name registration should turn up plenty). When you register the domain, most registrars will let you use their own DNS servers for your domain, but you don't need them! When you get to the point in the registration process where it asks you about your DNS servers, just give them the public IP address for your own DNS server (in my case, it would be ns1.example.org or 123.12.34.56). Note that many registrars require you to have two DNS servers defined for a domain, so in that case, set up a slave DNS server and add its IP address as well. Once you complete the registration process and allow the new domain information time to propagate around the Internet, you will have the ability make IP changes for your Web, mail and other servers all from your own machines.