LPIC-2 201-450: Networking Configuration

Networking Configuration tests interface addressing, routing, name resolution and troubleshooting with modern Linux tools, including how to make runtime changes persistent.

Core commands and persistence

• ip link shows interfaces; ip addr add 192.0.2.10/24 dev eth0 adds an address; ip route add default via 192.0.2.1 sets a gateway.
• ip -s link exposes errors and drops; ss -tulpn lists listeners; ping, traceroute, and dig isolate layers.
• Persistence depends on the stack: Debian ifupdown uses /etc/network/interfaces; NetworkManager uses nmcli con mod; systemd-networkd uses .network files.
• Name resolution order comes from /etc/nsswitch.conf; /etc/hosts is consulted before DNS if configured; /etc/resolv.conf is often overwritten by DHCP or a manager.
• ip route show displays connected, static, and default routes; persistent routes belong in the distro's configuration, not only the running kernel.

Worked example

A host reaches its own subnet but not 198.51.100.0/24. ip addr shows 192.0.2.10/24; ip route contains only 192.0.2.0/24. Add ip route add 198.51.100.0/24 via 192.0.2.1, test with ping, then persist the route in the network configuration. Reasoning: the connected route covers only the local prefix; without a specific or default route, packets have no next hop. If a default route exists, check firewall and reverse-path filtering.

Traps

• Assuming ip changes survive reboot.
• Expecting hand-edited /etc/resolv.conf to survive DHCP.
• Mixing NetworkManager and ifupdown on one interface.
• Confusing a down interface with a missing address.