The ip command
a) Description
The ip command is used view and manage a Linux system’s network configuration. Its main purposes are:
- Show IP addresses: see which addresses are assigned to each network interface (ip a).
- Manage interfaces: bring network cards or Wi-Fi adapters up or down, and check their state and MAC address (ip link).
- Control routing: view or change how traffic leaves your machine, including the default gateway (ip route).
- Troubleshoot: quickly check why a machine has no connection (no IP, interface down, wrong gateway). to is the Linux command for viewing and configuring network interfaces, addresses and routes.
Changes made with ip are temporary and are lost after a reboot, so for permanent settings you configure the network through your system’s tools (NetworkManager, netplan, systemd-networkd, etc.).
b) Examples
1-It shows interface name, IP address and subnet mask in CIDR (modern) format
dacomo@inf1-dacomo:~$ ip a
2-It show the gateway (router) IP address.
dacomo@inf1-dacomo:~$ ip r
3-It shows the DNS IP addresses.
dacomo@inf1-dacomo:~$ cat /etc/resolv.conf
4-It removes IP address = 192.168.5.10 with subnet mask = 23 from device enp0s3
dacomo@inf1-dacomo:~$ sudo ip a del 192.168.5.10/23 dev enp0s3
5-It adds IP address = 172.16.1.1210 with subnet mask = 21 to device enp0s3
dacomo@inf1-dacomo:~$ sudo ip a add 172.16.1.210/21 dev enp0s3
6-It removes IP address = 192.168.1.10 with subnet mask = 22 from device enp0s3
dacomo@inf1-dacomo:~$ sudo ip a del 192.168.1.10/22 dev enp0s3
7-It sets a default router IP address to 172.16.1.1
dacomo@inf1-dacomo:~$ sudo ip route add default via 172.16.1.1
8-It removes a default router IP address equal to 192.168.1.1
dacomo@inf1-dacomo:~$ sudo ip route del default via 192.168.1.1