Configure Multiple DNS Servers in /etc/resolv.conf

Description

Determine whether the system is using local or DNS name resolution with the following command:

$ sudo grep hosts /etc/nsswitch.conf
hosts: files dns

If the DNS entry is missing from the host's line in the "/etc/nsswitch.conf" file, the "/etc/resolv.conf" file must be empty. Verify the "/etc/resolv.conf" file is empty with the following command:

$ sudo ls -al /etc/resolv.conf
-rw-r--r-- 1 root root 0 Aug 19 08:31 resolv.conf

If the DNS entry is found on the host's line of the "/etc/nsswitch.conf" file, then verify the following:
Multiple Domain Name System (DNS) Servers should be configured in /etc/resolv.conf. This provides redundant name resolution services in the event that a domain server crashes. To configure the system to contain as least 2 DNS servers, add a corresponding nameserver ip_address entry in /etc/resolv.conf for each DNS server where ip_address is the IP address of a valid DNS server. For example:

search example.com
nameserver 192.168.0.1
nameserver 192.168.0.2

Rationale

To provide availability for name resolution services, multiple redundant name servers are mandated. A failure in name resolution could lead to the failure of security functions requiring name resolution, which may include time synchronization, centralized authentication, and remote system logging.