Change DNS settings on Linux

  • Last updated on: 2016-06-29
  • Authored by: Jered Heeschen

You might need to change your server’s DNS settings, either because you find that they are misconfigured or because you want to use your own. This article describes how to change your server’s DNS settings.

Add name servers to the configuration file

On Linux, the DNS servers that the system uses for name resolution are defined in the /etc/resolv.conf file. That file should contain at least one nameserver line. Each nameserver line defines a DNS server. The name servers are prioritized in the order the system finds them in the file. Use the IP addresses of the name servers when entering them, because the system won’t know what to do with domain names until after it knows how to get to the DNS servers.

  1. Open the resolv.conf file with an editor, such as nano, to make the necessary changes (if it doesn’t exist already, this command creates the file):

    sudo nano /etc/resolv.conf

  2. Add lines for the name servers that you want to use. The following table displays which name server IP addresses to use depending on which datacenter houses your cloud servers. The “Name server IP address” column shows the lines to add to the configuration file:

    Data center Name server IP address
    Hong Kong (HKG) nameserver 120.136.32.63
    nameserver 120.136.32.62
    Northern Virginia (IAD) nameserver 69.20.0.164
    nameserver 69.20.0.196
    London (LON) nameserver 83.138.151.80
    nameserver 83.138.151.81
    Chicago (ORD) nameserver 173.203.4.8
    nameserver 173.203.4.9
    Dallas/Fort Worth (DFW) nameserver 73.3.128.240
    nameserver 72.3.128.241
    Sydney (SYD) nameserver 119.9.60.63
    nameserver 119.9.60.62
  3. Save the file.

  4. To ensure that your new settings are working, ping the domain name:

    ping -c 3 rackspace.com

You should see a result similar to the following one:

PING rackspace.com (173.203.44.122) 56(84) bytes of data.
64 bytes from 173.203.44.122: icmp_req=1 ttl=249 time=25.3 ms
64 bytes from 173.203.44.122: icmp_req=2 ttl=249 time=25.2 ms
64 bytes from 173.203.44.122: icmp_req=3 ttl=249 time=25.2 ms

--- rackspace.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 25.236/25.292/25.392/0.147 ms

If you receive an unknown host message, double-check the IP addresses that you set as your DNS servers.

Add same servers with IPv6 addresses

If you’re using IPv6 on your server, you might need to add the IPv6 addresses of your name servers to the resolv.conf file. You can see if a DNS server has an IPv6 address by performing the following steps:

  1. Use host to get the name of the server:

    $ host 72.3.128.240
    240.128.3.72.in-addr.arpa domain name pointer cachens1.dfw1.rackspace.com.
    
  2. Use the domain name you got back in another host lookup:

    $ host cachens1.dfw1.rackspace.com
    cachens1.dfw1.rackspace.com has address 72.3.128.240
    cachens1.dfw1.rackspace.com has IPv6 address 2001:4800:d::1
    

If an IPv6 address is returned, you can add that as another nameserver line in the resolv.conf file, as follows:

nameserver 2001:4800:d::1

Then test as previously shown, by using the ping6 command instead of the regular ping command to force the system to use IPv6.

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