Linux Network Configuration — ip, nmcli, and Name Resolution

Overview

Network configuration on Red Hat Enterprise Linux 9 is managed by NetworkManager (NM) — the daemon responsible for detecting, connecting, and maintaining network interfaces. All persistent configuration changes should go through NetworkManager rather than editing network configuration files directly. NetworkManager stores connection profiles in /etc/NetworkManager/system-connections/ as INI-format files, and these profiles survive reboots and interface re-plugs.

Three tools interact with NetworkManager from the command line and desktop: nmcli is the primary CLI used in scripts and automation; nmtui is a text-based user interface suitable for interactive terminal sessions where a full terminal emulator is unavailable; and GNOME network settings provide a graphical interface for desktop installations. All three write to the same backend — changes made in one are visible in the others.

Understanding the distinction between temporary and persistent configuration is critical on RHEL. The ip command can modify addresses, routes, and link state immediately, but those changes exist only in the kernel’s network state and disappear on the next reboot or network restart. NetworkManager, accessed through nmcli, writes changes to profile files that persist.

Inspecting Network State with the ip Command

The ip command from the iproute2 package replaces the older ifconfig and route commands. It communicates directly with the kernel via netlink sockets and provides a complete view of the network stack.

The ip addr show output displays each interface with its index, flags (including UP, LOWER_UP, BROADCAST, MULTICAST), MTU, MAC address, and all assigned IPv4 and IPv6 addresses. The state UP line confirms the interface is administratively up and has carrier. A state DOWN or missing LOWER_UP flag indicates a physical or link-layer problem.

All changes made with ip are temporary. After NetworkManager restarts or the system reboots, the kernel network state is rebuilt from the NM connection profiles. Use nmcli for any change that must survive a restart.

Managing Connections with nmcli

nmcli (NetworkManager command-line interface) is the standard tool for managing NetworkManager from scripts and the terminal. It can show device and connection status, create new connections, modify existing connection parameters, and activate or deactivate connections.

After modifying a connection with nmcli connection modify, the changes are written to the profile file but are not applied to the live interface until the connection is deactivated and reactivated, or until nmcli device reapply is used. The connection reload command is needed when profile files are edited manually outside of nmcli.

To configure a static IP fully — address, gateway, DNS, and method — run the three modify commands for ipv4.addresses, ipv4.gateway, ipv4.dns, set ipv4.method manual, and then bring the connection back up with nmcli connection up "name".

Hostname Management

The system hostname appears in the shell prompt, in log entries, and is returned when other systems query the machine by name. RHEL 9 uses hostnamectl to manage all hostname types.

hostnamectl set-hostname server1.example.com

RHEL tracks three hostname types simultaneously:

• Static hostname: the persistent name stored in /etc/hostname, applied at boot. This is what hostnamectl set-hostname writes.
• Transient hostname: set dynamically by DHCP or mDNS at runtime. Overrides the static hostname while active, returns to static when DHCP lease expires.
• Pretty hostname: a free-form human-readable label, can include spaces and Unicode. Used only for display purposes (for example, GNOME desktop).

Running hostnamectl without arguments shows all three values plus machine information. The FQDN (fully qualified domain name) combines the hostname with the domain name from DNS or /etc/hosts. Setting the static hostname to an FQDN (server1.example.com) is the recommended practice for servers.

Name Resolution

When a RHEL system resolves a hostname to an IP address, it follows the order defined in /etc/nsswitch.conf. The relevant line is:

hosts: files dns

This means the system checks /etc/hosts first, then queries DNS. The order can be changed by editing this line — for example, adding myhostname to resolve the local hostname without a DNS entry.

/etc/hosts provides static name-to-IP mappings that override DNS. The format is one entry per line: IP address, followed by the FQDN, followed by any short aliases. This file is evaluated before DNS for every lookup and is commonly used for local lab entries or to override external DNS for testing.

/etc/resolv.conf contains the addresses of upstream DNS nameservers, one per nameserver line. On systems running NetworkManager, this file is managed automatically — NM writes it based on the DNS servers configured in active connection profiles. Editing /etc/resolv.conf directly is not recommended because NM will overwrite it.

Troubleshooting Network Connectivity

A systematic approach to network troubleshooting on RHEL works from the physical layer upward: confirm the interface is up, confirm addressing is correct, confirm routing is in place, then confirm DNS works.

The getent hosts command is particularly useful because it mirrors exactly what applications experience — it follows the same nsswitch.conf order that the system library uses, so a hostname that resolves with getent will resolve for any normal application. A hostname that resolves with nslookup but not getent often indicates an /etc/hosts entry that takes precedence.

When an interface shows no address or an unexpected address, nmcli device status quickly confirms whether NetworkManager has successfully activated a connection on that device. A device shown as unmanaged means NM is not controlling it — this sometimes occurs when a network interface was manually configured outside of NM’s knowledge.

Summary

RHEL 9 centralises network configuration in NetworkManager, accessed primarily through nmcli for persistent changes and the ip command for temporary state inspection. Connection profiles in /etc/NetworkManager/system-connections/ survive reboots. Hostname management goes through hostnamectl, and name resolution order is controlled by /etc/nsswitch.conf, with /etc/hosts evaluated before DNS by default. Troubleshooting follows a layered approach: interface state, addressing, routing, and finally name resolution.