ip / nmcli (Network Interface Management)

# -----------------------------------------------
#  ip addr — Check, add, and remove IP addresses
# -----------------------------------------------

# ip addr show [{interface}]
#   → Shows IP addresses for all interfaces (or a specific one)
#   Example: ip addr show
#   Example: ip addr show eth0

# ip addr add {IP address}/{prefix length} dev {interface}
#   → Adds an IP address to an interface (lost after reboot)
#   Example: sudo ip addr add 192.168.1.100/24 dev eth0

# ip addr del {IP address}/{prefix length} dev {interface}
#   → Removes an IP address from an interface
#   Example: sudo ip addr del 192.168.1.100/24 dev eth0

# -----------------------------------------------
#  ip link — Enable and disable interfaces
# -----------------------------------------------

# ip link show [{interface}]
#   → Shows interface state (UP/DOWN), MAC address, and other info

# ip link set {interface} up
#   → Enables the interface
#   Example: sudo ip link set eth0 up

# ip link set {interface} down
#   → Disables the interface
#   Example: sudo ip link set eth0 down

# -----------------------------------------------
#  ip route — View and manage the routing table
# -----------------------------------------------

# ip route show
#   → Displays the current routing table

# ip route add {destination network} via {gateway} [dev {interface}]
#   → Adds a static route (lost after reboot)
#   Example: sudo ip route add 10.0.0.0/8 via 192.168.1.1 dev eth0

# ip route del {destination network}
#   → Removes a static route
#   Example: sudo ip route del 10.0.0.0/8

# ip route add default via {gateway}
#   → Sets the default gateway
#   Example: sudo ip route add default via 192.168.1.1

# -----------------------------------------------
#  ip neigh — View the ARP table
# -----------------------------------------------

# ip neigh show
#   → Displays the ARP table (IP address to MAC address mappings)

# -----------------------------------------------
#  nmcli — NetworkManager command-line interface
# -----------------------------------------------

# nmcli device show [{interface}]
#   → Shows detailed device info (IP address, DNS, etc.)

# nmcli device status
#   → Lists the connection status of all devices

# nmcli connection show
#   → Lists all defined connections (connection profiles)

# nmcli connection show {connection name}
#   → Shows all settings for a specific connection

# nmcli connection modify {connection name} {property} {value}
#   → Modifies a connection setting (persists after reboot)
#   Example: sudo nmcli connection modify "ens3" ipv4.addresses "192.168.1.100/24"

# nmcli connection up {connection name}
#   → Activates (applies) the connection

# nmcli connection down {connection name}
#   → Deactivates the connection

# nmcli connection reload
#   → Reloads connection configuration files

Checking IP addresses and routing

# -----------------------------------------------
#  Check the network state on the server
# -----------------------------------------------

# Show IP addresses for all interfaces
ip addr show

# Show the routing table (check where the default gateway points)
ip route show

# Show the ARP table (check MAC addresses of hosts on the same segment)
ip neigh show

$ ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:ab:cd:ef brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.10/24 brd 192.168.1.255 scope global eth0
       valid_lft forever preferred_lft forever

$ ip route show
default via 192.168.1.1 dev eth0 proto static metric 100
192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.10 metric 100

$ ip neigh show
192.168.1.1 dev eth0 lladdr 00:1a:2b:3c:4d:5e REACHABLE
192.168.1.20 dev eth0 lladdr 00:1a:2b:3c:4d:6f STALE

Setting a static IP address with nmcli (persistent)

# -----------------------------------------------
#  Set a static IP address on the server
#  (settings persist after reboot)
# -----------------------------------------------

# First, check the current connection name and device name
nmcli connection show

# Check the current settings for the target connection
nmcli connection show "eth0"

# Change the IP assignment method to static (manual)
sudo nmcli connection modify "eth0" ipv4.method manual

# Set the static IP address and prefix length
sudo nmcli connection modify "eth0" ipv4.addresses "192.168.1.50/24"

# Set the default gateway
sudo nmcli connection modify "eth0" ipv4.gateway "192.168.1.1"

# Set the DNS servers (use commas to specify multiple)
sudo nmcli connection modify "eth0" ipv4.dns "8.8.8.8,8.8.4.4"

# Apply the settings to the system
sudo nmcli connection up "eth0"

# Verify the settings were applied
nmcli device show eth0

$ nmcli device show eth0
GENERAL.DEVICE:                         eth0
GENERAL.TYPE:                           ethernet
GENERAL.HWADDR:                         52:54:00:AB:CD:EF
GENERAL.MTU:                            1500
GENERAL.STATE:                          100 (connected)
GENERAL.CONNECTION:                     eth0
IP4.ADDRESS[1]:                         192.168.1.50/24
IP4.GATEWAY:                            192.168.1.1
IP4.ROUTE[1]:                           dst = 0.0.0.0/0, nh = 192.168.1.1, mt = 100
IP4.ROUTE[2]:                           dst = 192.168.1.0/24, nh = 0.0.0.0, mt = 100
IP4.DNS[1]:                             8.8.8.8
IP4.DNS[2]:                             8.8.4.4

The ip command is part of the iproute2 package and comes pre-installed on all major Linux distributions. Learning just three subcommands — ip addr, ip link, and ip route — covers the vast majority of everyday network tasks. However, changes made with ip are volatile and do not survive a reboot. For permanent configuration changes on a production server, the correct approach is to use nmcli connection modify and then apply with nmcli connection up. If you are connected via SSH, double-check your settings before applying — changing the IP address or gateway incorrectly will drop your connection. For checking port and socket status, see netstat / ss. For firewall configuration, see firewalld or ufw.