NETW-2705 - Properly functioning name servers

(Networking)

This information is provided as part of the Lynis community project. It is related to Lynis control NETW-2705 and should be considered as-is and without guarantees. Any advice and commands should be tested before implementing them in production environments.

Description

Connectivity is the central link for systems to communicate. Most communication occurs on layer 3 (network) for interconnected systems. There DNS resolving is very important for proper functioning.DNS resolving, while it is part of the basics, is often overlooked. To limit the chance of failure or bad performance, at least two working name servers are advised.Lynis tests the availability of name servers and if they actually respond to queries. To determine what DNS servers are used, consult the /etc/resolv.conf file.

How to solve

Nowadays, most systems are connected. At least via the internal network, but often also via the internet. An important requisite in this interconnected web of systems is the ability to use a naming convention, like names for hosts, or names for websites. By using DNS (Domain Name System), we can translate between names and IP addresses.

Many systems have a weak configuration when it comes to this name translation. It is common to find a missing fallback system, when the primary DNS server is not available. Another issue is that one or more of the name servers listed in /etc/resolv.conf are not even accessible or functioning. With this Lynis control the connectivity is tested.

Depending on your system, you might need to make changes in your /etc/resolv.conf file, or otherwise. Debian based systems might use /etc/network/interfaces to define name servers (dns-nameservers 1.2.3.4 5.6.7.8 9.10.11.12), or /etc/resolvconf/resolv.conf.d/tail.

Additional resources

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Lynis is a technical security auditing tool for Unix flavors like Linux, macOS, AIX, Solaris, and *BSD. It is open source software and free to use. Typical usage include system hardening, compliance testing, and vulnerability scanning. The project has an active community, including development via GitHub.

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