RHEL 9 systems using Domain Name Servers (DNS) resolution must have at least two name servers configured.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257948	RHEL-09-252035	SV-257948r925831_rule		Medium

Description
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.

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2023-12-01

Details

Check Text ( C-61689r925829_chk )
Verify the name servers used by the system with the following command: $ grep nameserver /etc/resolv.conf nameserver 192.168.1.2 nameserver 192.168.1.3 If less than two lines are returned that are not commented out, this is a finding.

Fix Text (F-61613r925830_fix)
Configure the operating system to use two or more name servers for DNS resolution based on the DNS mode of the system. If the NetworkManager DNS mode is set to "none", then add the following lines to "/etc/resolv.conf": nameserver [name server 1] nameserver [name server 2] Replace [name server 1] and [name server 2] with the IPs of two different DNS resolvers. If the NetworkManager DNS mode is set to "default" then add two DNS servers to a NetworkManager connection. Using the following commands: $ sudo nmcli connection modify [connection name] ipv4.dns [name server 1] $ sudo nmcli connection modify [connection name] ipv4.dns [name server 2] Replace [name server 1] and [name server 2] with the IPs of two different DNS resolvers. Replace [connection name] with a valid NetworkManager connection name on the system. Replace ipv4 with ipv6 if IPv6 DNS servers are used.

Fix Text (F-61613r925830_fix)

Configure the operating system to use two or more name servers for DNS resolution based on the DNS mode of the system.

If the NetworkManager DNS mode is set to "none", then add the following lines to "/etc/resolv.conf":

nameserver [name server 1]
nameserver [name server 2]

Replace [name server 1] and [name server 2] with the IPs of two different DNS resolvers.

If the NetworkManager DNS mode is set to "default" then add two DNS servers to a NetworkManager connection. Using the following commands:

$ sudo nmcli connection modify [connection name] ipv4.dns [name server 1]
$ sudo nmcli connection modify [connection name] ipv4.dns [name server 2]

Replace [name server 1] and [name server 2] with the IPs of two different DNS resolvers. Replace [connection name] with a valid NetworkManager connection name on the system. Replace ipv4 with ipv6 if IPv6 DNS servers are used.