LPIC-1 109.2 — Persistent Network Configuration

Exam weight: 4 — LPIC-1 v5, Exam 102

What You Need to Know

From the official LPIC-1 objectives:

• Understand basic TCP/IP host configuration.
• Configure Ethernet and Wi-Fi network using NetworkManager.
• Awareness of systemd-networkd.

Key files and commands: /etc/hostname, /etc/hosts, /etc/nsswitch.conf, /etc/resolv.conf, /etc/network/interfaces, ifup, ifdown, ip, ifconfig, route, nmcli, hostnamectl.

Network Interface Naming

Naming Prefixes

Naming Policies (predictable names)

The kernel assigns names in order of priority:

1. BIOS onboard index — eno1, eno2
2. PCI slot number — ens1, ens3
3. Bus topology (PCI bus/slot/function) — enp2s0
4. MAC address — enx001122334455
5. Legacy — eth0, eth1 (fallback)

Listing Interfaces

ip link show          # modern
ifconfig -a           # all interfaces, including inactive
nmcli device          # NetworkManager device list

/etc/network/interfaces (Debian/Ubuntu)

The traditional network configuration file used with ifupdown.

# Loopback
auto lo
iface lo inet loopback

# DHCP
auto eth0
iface eth0 inet dhcp

# Static
auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 8.8.8.8 8.8.4.4

Key directives:

ifup / ifdown

ifup eth0      # bring up interface
ifdown eth0    # bring down interface

Hostname Configuration

/etc/hostname

Contains the system’s static hostname as a single line:

myserver

hostnamectl

hostnamectl                          # show current hostname info
hostnamectl set-hostname myserver    # set static hostname
hostnamectl set-hostname "My Server" --pretty   # set pretty hostname
hostnamectl set-hostname "" --transient          # set transient hostname
hostnamectl status                   # show all hostname types

Three hostname types:

Name Resolution Files

/etc/nsswitch.conf

Controls the order and sources for name resolution. The hosts line determines how hostnames are resolved:

hosts:    files dns

This checks /etc/hosts first, then DNS.

/etc/hosts

Maps IP addresses to hostnames locally, bypassing DNS:

127.0.0.1       localhost
127.0.1.1       myserver
::1             localhost ip6-localhost ip6-loopback
192.168.1.10    fileserver fs

Format: IP ADDRESS hostname [alias ...]

/etc/resolv.conf

Configures DNS servers and search domains:

nameserver 8.8.8.8
nameserver 8.8.4.4
search example.com

Note: NetworkManager and other tools may overwrite this file automatically.

NetworkManager and nmcli

NetworkManager is the standard network management daemon on most distributions. nmcli is its command-line client.

nmcli Object Overview

Common nmcli Commands

# Status
nmcli general status
nmcli device status
nmcli device show eth0

# Connections
nmcli connection show
nmcli connection up myconn
nmcli connection down myconn
nmcli connection delete myconn

# Add a static Ethernet connection
nmcli connection add type ethernet ifname eth0 con-name myconn \
  ipv4.addresses 192.168.1.100/24 \
  ipv4.gateway 192.168.1.1 \
  ipv4.dns 8.8.8.8 \
  ipv4.method manual

# Modify an existing connection
nmcli connection modify myconn ipv4.dns 1.1.1.1

# Networking on/off
nmcli networking on
nmcli networking off

# Wi-Fi
nmcli radio wifi on
nmcli device wifi list
nmcli device wifi connect "MySSID" password "MyPass"

systemd-networkd

systemd-networkd is a systemd-based network configuration daemon.

Configuration Directories

.network File Format

Files must end in .network. The [Match] section selects the interface; [Network] sets the configuration.

# DHCP example: /etc/systemd/network/10-eth0.network
[Match]
Name=eth0

[Network]
DHCP=yes

# Static example
[Match]
Name=eth0

[Network]
Address=192.168.1.100/24
Gateway=192.168.1.1
DNS=8.8.8.8

Quick Reference

Interface prefixes: en (Ethernet)  wl (Wi-Fi)  ww (WWAN)
  eno1 (onboard)  ens1 (PCI slot)  enp2s0 (bus)  enx... (MAC)

ip link show         list interfaces
ifconfig -a          all interfaces (legacy)
nmcli device         NetworkManager device list

/etc/network/interfaces:
  auto IFACE           bring up at boot
  iface IFACE inet dhcp/static/loopback
  address / netmask / gateway / dns-nameservers
  ifup IFACE / ifdown IFACE

Hostname:
  /etc/hostname          static hostname file
  hostnamectl set-hostname NAME   set static
  hostnamectl status              show all types

Name resolution:
  /etc/nsswitch.conf    hosts: files dns
  /etc/hosts            IP hostname [alias]
  /etc/resolv.conf      nameserver / search / domain

nmcli:
  nmcli general status
  nmcli connection show/add/modify/up/down/delete
  nmcli device status/show/wifi list
  nmcli device wifi connect SSID password PASS

systemd-networkd .network file:
  [Match] Name=eth0
  [Network] DHCP=yes  or  Address=.../24  Gateway=...  DNS=...
  Config dir: /etc/systemd/network/

Exam Questions

1. What prefix identifies a wireless LAN interface? → wl
2. What naming convention produces interface names like enp2s0? → PCI bus topology (bus/slot/function)
3. What directive in /etc/network/interfaces brings an interface up automatically at boot? → auto IFACE
4. What command brings down interface eth0 in the ifupdown system? → ifdown eth0
5. Where is the static hostname stored? → /etc/hostname
6. What hostnamectl command sets the static hostname to webserver? → hostnamectl set-hostname webserver
7. What are the three hostname types managed by hostnamectl? → Static, transient, and pretty.
8. What file controls the order in which name resolution sources are consulted? → /etc/nsswitch.conf
9. What is the format of an /etc/hosts entry? → IP_ADDRESS hostname [alias ...]
10. How many nameserver entries can /etc/resolv.conf hold? → Up to 3.
11. What is the difference between search and domain in /etc/resolv.conf? → They are mutually exclusive; if both are present, the last one wins.
12. What nmcli command shows all saved connections? → nmcli connection show
13. What nmcli command connects to a Wi-Fi network named Office? → nmcli device wifi connect "Office" password "pass"
14. What nmcli object is used to manage network interfaces? → device
15. In which directory does a system administrator place systemd-networkd configuration files? → /etc/systemd/network/
16. What section in a .network file selects the interface to configure? → [Match]
17. What nmcli command disables all networking? → nmcli networking off
18. What tool may overwrite /etc/resolv.conf automatically? → NetworkManager (indicated by a comment # Generated by NetworkManager in the file).

Exercises

Exercise 1 — Static Interface Configuration

Write an /etc/network/interfaces stanza that configures eth1 statically with IP 10.0.0.50/24, gateway 10.0.0.1, and DNS 10.0.0.53.

auto eth1
iface eth1 inet static
    address 10.0.0.50
    netmask 255.255.255.0
    gateway 10.0.0.1
    dns-nameservers 10.0.0.53

Exercise 2 — Hostname Change

Change the system’s static hostname to dbserver using hostnamectl, then verify the change.

hostnamectl set-hostname dbserver
hostnamectl status

Exercise 3 — nmcli Static Connection

Use nmcli to create a static Ethernet connection named corp on eth0 with IP 192.168.10.20/24, gateway 192.168.10.1, and DNS 192.168.10.5.

nmcli connection add type ethernet ifname eth0 con-name corp \
  ipv4.addresses 192.168.10.20/24 \
  ipv4.gateway 192.168.10.1 \
  ipv4.dns 192.168.10.5 \
  ipv4.method manual
nmcli connection up corp

Exercise 4 — systemd-networkd

Write a systemd-networkd configuration file that enables DHCP on interface ens3.

[Match]
Name=ens3

[Network]
DHCP=yes

Exercise 5 — nsswitch.conf

Modify the hosts line in /etc/nsswitch.conf so that /etc/hosts is checked first, and DNS is only consulted if the host is not found there.

hosts:    files dns

LPIC-1 Study Notes | Topic 109: Networking Fundamentals