Network Configuration

You edit /etc/network/interfaces on Debian to give your Ethernet card a static IP, but NetworkManager keeps overriding it. What is the underlying rule you violated?

On a headless server you have no GNOME dialogs. Which NetworkManager tools let you configure it, and what is the difference between them?

In the NetworkManager GUI, what single field decides whether an interface gets its address from DHCP versus a static address you type in?

NetworkManager has to coexist with the legacy config systems of many distros. What mechanism lets it do that, and which storage format is now the default?

A Wi-Fi password you saved is now on disk somewhere. Where NetworkManager writes it depends on the distribution — where does Fedora put it versus Ubuntu?

You want your Linux laptop's Wi-Fi card to act as a hotspot for other devices while it gets internet from Ethernet. What hardware-level condition can block this?

You have a NIC installed but ip link set <iface> up throws an error about no such device. Walk through the sequence of commands to find and load the right kernel driver.

Bringing up a NIC by hand with the ip command takes two distinct steps that beginners often collapse into one. What are they?

An old tutorial tells you to configure your interface with ifconfig and add routes with route. Why should you not follow it on a modern Linux system?

You can ping other machines on your LAN but nothing on the internet. Your addressing is fine. What one command fixes it, and how do you confirm the entry?

After experimenting with manual ip addr and ip route commands, how do you cleanly undo everything on an interface — and what's the difference between del and flush?

A machine has never been configured but the LAN has a DHCP server. What is the fastest way to get it fully online without any ip or resolv.conf work?

IPv6 config by hand differs from IPv4 in the ip command syntax. What do the address and default-route commands look like, and how do you tell a real routable IPv6 address from an autoconfigured one?

Reading ip addr output, how do you identify the MAC address, the IPv4 address, and a link-local IPv6 address?

Without any GUI, which command inspects a Wi-Fi interface's status and scans for available networks, and how do you connect to an open one?

Connecting to a WPA2 Wi-Fi from the command line needs more than iw connect. Which program handles it and what is its core job?

Why is it a bad idea to put your plaintext Wi-Fi password directly in wpa_supplicant.conf, and what generates a safer value?

What is the /etc/hosts file for, and what single entry must it always contain?

Which file decides whether Linux checks /etc/hosts or the DNS server first when resolving a name, and what does the typical setting say?

In /etc/resolv.conf, what do the nameserver and search/domain keywords do, and what's the limit on nameservers?

You cat /etc/resolv.conf and the only nameserver is 127.0.0.53. Why is your real DNS server not listed there, and how do you find it?

What command shows the current hostname, and what is the right way to change it permanently?

Modern interfaces are named things like enp0s31f6 instead of eth0. What problem does this naming scheme solve, and how do you decode the prefixes?

On RHEL 8+ and current Fedora, what changed about who controls networking — even on servers — and what happened to the old ifcfg scripts?

You wrote a NetworkManager keyfile by hand and it is silently ignored. What permission requirement did you likely miss, and what selects DHCP versus static?

After editing a NetworkManager keyfile for interface enp1s0, the change doesn't take effect. What two nmcli commands actually apply it?

On Debian, a full DHCP network setup in /etc/network/interfaces is only four lines. What do the auto and iface keywords each control?

After changing /etc/network/interfaces on Debian, which commands activate the new config, and what does the -a option do?

On SUSE, the default network backend depends on the machine type. What does YaST choose for a notebook versus a server, and why?

On Ubuntu, Netplan is described as a front-end. What does it actually render its YAML config into, and how does that differ between desktop and server?

systemd-networkd configures interfaces from .network files. Where do they live, what sections do they use, and how does Ubuntu's Netplan relate to them?

With no DHCP server and no manual config, Zeroconf can still get machines talking. What address range and name suffix does it use, and what's its key limitation?

Avahi is Linux's Zeroconf implementation. How does it relate to Apple's Bonjour, and which command lists the services it discovers?

You can ping a printer at merkur.local from Avahi-aware apps, but ordinary programs like a browser fail to resolve the .local name. What's missing?

From the console, which command lists the machines and services Avahi has discovered on the network?

What is /etc/services for, and what's special about port numbers at or below 1024?

During installation Linux asks for a computer name, and you're tempted to type localhost. Why is that a mistake?

You're joining a corporate Wi-Fi that uses WPA2-Enterprise and NetworkManager demands a CA certificate. What are your options and where do the certificates live?

You try to set up a VPN in NetworkManager but the method isn't listed. What's usually missing, and why does the package name differ across distros?

You set an HTTP proxy in the GNOME Network dialog but want to read or script that value. Where is it actually stored, and why doesn't it take effect immediately?

On a headless server with no GUI, which nmcli commands let you list interfaces and take one offline, and what dumps every parameter?

You want a script to run automatically every time a network connection comes up or goes down under NetworkManager. Where do you put it?

iw reports no such device for your wireless card wlp2s0. Before you can configure Wi-Fi, what one command creates the interface?

Besides the normal managed client mode, what interface types can iw create, and how do you remove an interface you no longer need?

Connecting to a legacy WEP-encrypted network with iw needs the key in a special format. What does that format look like?

You're starting wpa_supplicant by hand for a WPA2 network. What do the -i, -c, and -D options set, and what driver value is a safe first try?

For years wpa_supplicant has been the go-to CLI tool for WPA/WPA2 Wi-Fi. What newer daemon is positioned to eventually replace it?

On a small LAN with no nameserver, how do machines resolve each other by name, and why does the book recommend a nameserver once you pass two devices?

You try to set a hostname with an umlaut like hellö-world. What does Linux actually do with it, and which command produces the stored form?

A NetworkManager .nmconnection keyfile has to attach itself to the right NIC and come up at boot. Which keys control the NIC match and the auto-activation?

In a NetworkManager keyfile you need to pin a static IPv4 address, its gateway, and a DNS server. How are the address and gateway written on one line?

How do you assign a NetworkManager connection to a specific firewalld zone, and what happens if you don't?

On Debian you already have IPv4 working in /etc/network/interfaces. How do you add IPv6, and what do inet6 auto, dhcp, and static each mean?

Match the common service ports every admin should recognize: SSH, SMTP, DNS, HTTP, POP3, NTP, IMAP, LDAP, HTTPS, IPP, IMAPS, MySQL/MariaDB, NFS.

You are on a server with no desktop and need every tool — including apt and dnf — to route through an HTTP proxy. Where do you set this, and why isn't one file enough?

On an Ubuntu server (no NetworkManager) you must convert the default DHCP netplan to a static one. Which YAML keys set the address/gateway/DNS, and what command applies it?

You want a Debian Wi-Fi interface configured straight from /etc/network/interfaces. Which wpa- keywords set the network and password, and how do you point to an external supplicant file instead?

In /etc/network/interfaces, how can you make Debian run a command every time an interface is brought up or taken down?

Why does Zeroconf/Avahi only matter on IPv4 networks and not on IPv6?

Some Avahi-aware programs won't talk to the daemon until you flip one setting. Which file and variable, and why?

Avahi resolves .local names for its own apps, but you want ordinary programs like ping to reach external .local hosts. Which extra daemon provides that, and when is it unnecessary?