3.1Basic Network Configuration

Before a server can do its job, its network interface needs the right IP address and the routing table needs to know where to send traffic. LinuC-2 expects you to handle both the modern ip command suite and the legacy commands (ifconfig, route, arp) still seen in the field.

3.1.1Configuring and inspecting with ip

• ip addr (ip a) lists interfaces and their IP addresses. Add with ip addr add 192.0.2.10/24 dev eth0, remove with ip addr del.
• ip link manages an interface's existence and state: ip link set eth0 up|down activates or disables the link; ip link set eth0 mtu 1400 changes MTU.
• ip route inspects and edits the routing table: ip route show lists it, ip route add default via 192.0.2.1 adds a default gateway, ip route del removes an entry.
• ip neigh (ip n) inspects the ARP table (the IP-to-MAC address cache)—the successor to the legacy arp command (equivalent to arp -a).

3.1.2Legacy commands, nmcli, and wireless tools

• ifconfig is the legacy command combining what ip addr and ip link do (e.g., ifconfig eth0 192.0.2.10 netmask 255.255.255.0 up). Deprecated on most distributions, part of the net-tools package.
• route is the legacy counterpart of ip route (route add default gw 192.0.2.1; route -n shows numeric output). arp is the legacy counterpart of ip neigh (arp -a lists, arp -d deletes).
• nmcli drives NetworkManager from the CLI: nmcli device status (interface state), nmcli connection show (list connection profiles), nmcli connection up/down <name> to activate or deactivate.
• Wireless: iw (current, netlink-based; iw dev wlan0 scan scans for APs), iwconfig/iwlist (legacy wireless-tools; iwconfig shows settings, iwlist wlan0 scan scans).

Diagnose in the order state → address → route → neighbor. First check ip link show eth0 for UP status and carrier detection (cable or radio). Then ip addr show eth0 to confirm the expected IP is assigned, fixing with ip addr add/del if not. For routing problems, ip route show reveals whether a default gateway or a specific subnet route is missing. If connectivity still fails, ip neigh shows whether the peer's MAC address resolved (an INCOMPLETE state means ARP resolution failed). On systems where NetworkManager is active (most desktops, some server distros), changes made directly via ip can be reverted on reboot or NetworkManager re-application, so permanent changes belong in a NetworkManager profile via nmcli connection modify. For wireless troubleshooting, check iw dev for the interface mode (managed/monitor), then iw dev wlan0 link for the current connection (SSID, signal strength), rescanning nearby APs with iw dev wlan0 scan as needed.

3.1.3Section summary

• ip addr = ifconfig, ip link = state (up/down), ip route = route, ip neigh = arp; use nmcli for persistent settings
• Wireless: iw (current, netlink) vs iwconfig/iwlist (legacy, ioctl). Diagnose in order: state → address → route → neighbor