After we have installed BIND as a master DNS server (NS1), we can now try to set up a secondary DNS server (NS2) with BIND on CentOS. NS2 acts as a backup if there are problems with NS1.

Make sure you’ve successfully set up NS1, as described in my previous post!

NS1 with IP 192.168.0.1
NS2 with IP 192.168.0.2
Our domain: yourdomain.com

Now we can try setting up NS2.

1.  Check your Bind package

[root@server ~]# rpm -qa bind*

bind-libs-9.2.4-2

bind-utils-9.2.4-2

bind-9.2.4-2

2. Setting file /etc/resolv.conf

[root@server ~]# nano /etc/resolv.conf

nameserver 192.168.0.1

3. Setting file /etc/named.conf

[root@server ~]# nano /etc/named.conf

//
// named.conf for Red Hat caching-nameserver
//

options {
directory “/var/named”;
dump-file “/var/named/data/cache_dump.db”;
statistics-file “/var/named/data/named_stats.txt”;

/*
* If there is a firewall between you and nameservers you want
* to talk to, you might need to uncomment the query-source
* directive below. Previous versions of BIND always asked
* questions using port 53, but BIND 8.1 uses an unprivileged
* port by default.
*/

// query-source address * port 53;
allow-transfer {208.99.198.184/32;};
};

//
// a caching only nameserver config
//

controls {
inet 127.0.0.1 allow { localhost; } keys { rndckey; };
};

zone “localhost” IN {
type master;
file “localhost.zone”;
allow-update { none; };
};

zone “yourdomain.com” IN {
type slave;
file “/var/named/yourdomain.com.zone”;
// allow-update { none; };
allow-transfer { 192.168.0.1/32; };
masters { 192.168.0.1; };
};

zone “0.168.192.in-addr.arpa” IN {
type slave;
file “/var/named/0.168.192.rev”;
// allow-update { none; };
allow-transfer { 192.168.0.1/32; };
masters { 192.168.0.1; };
};

include “/etc/rndc.key”;

4. Change permission of the directory /var/named

[root@server ~]# chmod 777 -Rvf /var/named/

mode of `/var/named/’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/named.zero’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/localhost.zone’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/data’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/named.local’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/named.ca’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/named.ip6.local’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/localdomain.zone’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/named.broadcast’ changed to 0777 (rwxrwxrwx)

mode of `/var/named/slaves’ changed to 0777 (rwxrwxrwx)

5. The files /var/named/yourdomain.com and /var/named/0.168.192.rev will automatically be copied to NS2.

6. Running service named

[root@server ~]# service named restart

Stopping named: [ OK ]

Starting named: [ OK ]

7. And check in log file what’s the matter???

[root@server ~]# tail /var/log/messages

Aug 3 04:25:42 server named[9362]: listening on IPv4 interface venet0:0, 192.168.0.2#53
Aug 3 04:25:42 server named[9362]: command channel listening on 127.0.0.1#953
Aug 3 04:25:42 server named[9362]: zone localhost/IN: loaded serial 42
Aug 3 04:25:42 server named[9362]: running
Aug 3 04:25:42 server named[9362]: zone yourdomain.com/IN: transferred serial 100
Aug 3 04:25:42 server named[9362]: transfer of ‘yourdomain.com/IN’ from 192.168.0.1#53: end of transfer
Aug 3 04:25:42 server named[9362]: zone yourdomain.com/IN: sending notifies (serial 100)
Aug 3 04:25:43 server named[9362]: zone 0.168.192.in-addr.arpa/IN: transferred serial 100
Aug 3 04:25:43 server named[9362]: transfer of ‘0.168.192.in-addr.arpa/IN’ from 192.168.0.1#53: end of transfer
Aug 3 04:25:43 server named[9362]: zone 0.168.192.in-addr.arpa/IN: sending notifies (serial 100)

Looking at this log, you can see that the yourdomain.com zone gets transferred. Actually this file is copied to NS2 so, if NS1 is dead or has a problem, NS2 has a backup configuration.

8. Result using nslookup

[root@server ~]# nslookup yourdomain.com

Server: 192.168.0.1

Address: 192.168.0.1#53

Name: yourdomain.com

Address: 192.168.0.1

answered from nslookup used server from NS1 with IP 192.168.0.1

Now we can try to deactivate NS1 to see if name resolution is still working.

9. First adding nameserver 192.168.0.2

[root@server ~]# cat /etc/resolv.conf

nameserver 192.168.0.1

nameserver 192.168.0.2

This domain is using NS2 because NS1 is not active. We don’t need to change any files on NS2 because all zone files are transferred from NS1 to NS2.

10. Trying a DNS lookup while NS1 is down

[root@server ~]# nslookup yourdomain.com

Server: 192.168.0.2

Address: 192.168.0.2#53

Name: yourdomain.com

Address: 192.168.0.1

Now if there’s any problem with NS1 you can rest calm because NS2 acts as a backup.

Google Public DNS is a free, global Domain Name System (DNS) resolution service, that you can use as an alternative to your current DNS provider.

To try it out:

Configure your network settings to use the IP addresses 8.8.8.8 and 8.8.4.4 as your DNS servers
If you decide to try Google Public DNS, your client programs will perform all DNS lookups using Google Public DNS.

Changing your DNS servers settings

Microsoft Windows

DNS settings are specified in the TCP/IP Properties window for the selected network connection.

Example: Changing DNS server settings on Microsoft Windows Vista

1. Go the Control Panel.
2. Click Network and Internet, then Network and Sharing Center, then Manage network connections.
3. Select the connection for which you want to configure Google Public DNS. For example:
   • To change the settings for an Ethernet connection, right-click Local Area Connection, and click Properties.
   • To change the settings for a wireless connection, right-click Wireless Network Connection, and click Properties.

   If you are prompted for an administrator password or confirmation, type the password or provide confirmation.

4. Select the Networking tab. Under This connection uses the following items, click Internet Protocol Version 4 (TCP/IPv4), and then click Properties.
5. Click Advanced and select the DNS tab. If there are any DNS server IP addresses listed there, write them down for future reference, and remove them from this window.
6. Click OK.
7. Select Use the following DNS server addresses. If there are any IP addresses listed in the Preferred DNS server or Alternate DNS server, write them down for future reference.
8. Replace those addresses with the IP addresses of the Google DNS servers: 8.8.8.8 and 8.8.4.4.
9. Restart the connection you selected in step 3.
10. Test that your setup is working correctly.
11. Repeat the procedure for additional network connections you want to change.

Mac OS X

DNS settings are specified in the Network window.

Example: Changing DNS server settings on Mac OS 10.5

1. From the Apple menu, click System Preferences, then click Network. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
2. Select the connection for which you want to configure Google Public DNS. For example:
   • To change the settings for an Ethernet connection, select Built-In Ethernet, and click Advanced.
   • To change the settings for a wireless connection, select Airport, and click Advanced.
3. Select the DNS tab.
4. Click + to replace any listed addresses with, or add, the Google IP addresses at the top of the list: 8.8.8.8 and 8.8.4.4.
5. Click Apply and OK.
6. Test that your setup is working correctly.
7. Repeat the procedure for additional network connections you want to change.

Linux

DNS settings are specified in /etc/resolv.conf in most distributions.

Example: Changing DNS server settings on Ubuntu

1. Edit /etc/resolv.conf:
   

   sudo vi /etc/resolv.conf

2. If any nameserver lines appear, write down the IP addresses for future reference.
3. Replace the nameserver lines with, or add, the following lines:
   

   nameserver 8.8.8.8
   nameserver 8.8.4.4

4. Save and exit.
5. Restart any Internet clients you are using.
6. Test that your setup is working correctly.

If you are using DHCP client software that overwrites the settings in /etc/resolv.conf, you will need to set up the client accordingly by editing the client’s configuration file.

Example: Configuring DHCP client sofware on Ubuntu

1. Back up /etc/resolv.conf:
   

   sudo cp /etc/resolv.conf /etc/resolv.conf.auto

2. Edit /etc/dhcp3/dhcpclient.conf:
   

   sudo vi /etc/dhcp3/dhcpclient.conf

3. If there is a line containing domain-name-servers, write down the IP addresses for future reference.
4. Replace that line with, or add, the following line:
   

   prepend domain-name-servers 8.8.8.8, 8.8.4.4;

5. Save and exit.
6. Restart any Internet clients you are using.
7. Test that your setup is working correctly.

Routers

Every router uses a different user interface for configuring DNS server settings; we provide only a generic procedure below. For more information, please consult your router documentation.

Note: Some ISPs hard-code their DNS servers into the equipment they provide; if you are using such a device, you will not be able to configure it to use Google Public DNS. Instead, you can configure each of the computers connected to the router, as described above.

To change your settings on a router:

1. In your browser, enter the IP address to access the router’s administration console.
2. When prompted, enter the password to access network settings.
3. Find the screen in which DNS server settings are specified.
4. If there are IP addresses specified in the fields for the primary and seconday DNS servers, write them down for future reference.
5. Replace those addresses with Google IP addresses: 8.8.8.8 and 8.8.4.4.
6. Save and exit.
7. Restart your browser.
8. Test that your setup is working correctly.

Mobile or other devices

DNS servers are typically specified under advanced wi-fi settings. However, as every mobile device uses a different user interface for configuring DNS server settings, we provide only a generic procedure below. For more information, please consult your mobile provider’s documentation.

To change your settings on a mobile device:

1. Go to the screen in which wi-fi settings are specified.
2. Find the screen in which DNS server settings are specified.
3. If there are IP addresses specified in the fields for the primary and seconday DNS servers, write them down for future reference.
4. Replace those addresses with Google IP addresses: 8.8.8.8 and 8.8.4.4.
5. Save and exit.
6. Test that your setup is working correctly.

Testing your new settings

To test that the Google DNS resolver is working:

1. From your browser, type in a hostname, such as http://www.google.com. If it resolves correctly, bookmark the page, and try accessing the page from the bookmark. If both of these tests work, everything is working correctly. If not, go to step 2.
2. From your browser, type in a fixed IP address. You can use http://18.62.1.6/ (which points to the website http://eecs.mit.edu/) as the URL*. If this works correctly, bookmark the page, and try accessing the page from the bookmark. If these tests work (but step 1 fails), then there is a problem with your DNS configuration; check the steps above to make sure you have configured everything correctly. If these tests do not work, go to step 3.
3. Roll back the DNS changes you made and run the tests again. If the tests still do not work, then there is a problem with your network settings; contact your ISP or network administrator for assistance.

* Google thanks MIT for granting permission to use this URL for the purposes of testing web connectivity.

Switching back to your old DNS settings

If you had not previously configured any customized DNS servers, to switch back to your old settings, in the window in which you specified the Google IP addresses, select the option to enable obtaining DNS server addresses automatically, and/or delete the Google IP addresses. This will revert your settings to using your ISP’s default servers.

If you need to manually specify any addresses, use the procedures above to specify the old IP addresses.

If necessary, restart your system.

The most basic task of DNS is to translate hostnames such as theos.in to IP address such as 74.86.49.131. In very simple terms, it can be compared to a phone book. DNS also has other important use such as email routing.

This is my list of better, fast public dns servers and free dns server (as compare to your ISP / DSL / ADSL / cable DNS service providers dns servers). These dns servers are free to all. I was able to improve my browsing speed with following DNS servers. Use any one of the following provider.

Free Public DNS Server

Service provider: ScrubIt
Public dns server address:

• 67.138.54.100
• 207.225.209.66

Service provider:dnsadvantage
Dnsadvantage free dns server list:

• 156.154.70.1
• 156.154.71.1

Service provider:OpenDNS
OpenDNS free dns server list:

• 208.67.222.222
• 208.67.220.220

Service provider: vnsc-pri.sys.gtei.net
Public Name server IP address:

• 4.2.2.1
• 4.2.2.2
• 4.2.2.3
• 4.2.2.4
• 4.2.2.5
• 4.2.2.6