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IP Configuration: Configure Network Interfaces

IP configuration sets up network interfaces. Assign IPs. Configure routing.

Here's the thing: IP configuration is essential. Learn it. You'll configure networks constantly.

Modern Tools: ip Command​

View Configuration​

ip addr show                       # All interfaces
ip addr show eth0                 # Specific interface
ip link show                      # Link status

My take: Use ip command. It's modern. ifconfig is legacy.

Configure IP Address​

# Add IP address
sudo ip addr add 192.168.1.100/24 dev eth0

# Remove IP address
sudo ip addr del 192.168.1.100/24 dev eth0

# Flush all addresses
sudo ip addr flush dev eth0

My take: ip addr manages IP addresses. Use it.

Bring Interface Up/Down​

sudo ip link set eth0 up          # Bring up
sudo ip link set eth0 down        # Bring down

My take: Interfaces need to be up to work. Check status.

Legacy Tools: ifconfig​

View Configuration​

ifconfig                           # All interfaces
ifconfig eth0                      # Specific interface

My take: ifconfig works. But ip is better. Use ip.

Configure IP​

sudo ifconfig eth0 192.168.1.100 netmask 255.255.255.0
sudo ifconfig eth0 up

My take: ifconfig is legacy. Use ip instead.

NetworkManager: GUI Tool​

nmcli Commands​

# List connections
nmcli connection show

# Show active
nmcli connection show --active

# Add connection
sudo nmcli connection add type ethernet con-name myconnection ifname eth0

# Set IP
sudo nmcli connection modify myconnection ipv4.addresses 192.168.1.100/24
sudo nmcli connection modify myconnection ipv4.method manual

# Activate
sudo nmcli connection up myconnection

My take: nmcli is NetworkManager's CLI. Useful for complex setups.

Persistent Configuration​

/etc/netplan/ (Ubuntu 18+)​

# /etc/netplan/01-netcfg.yaml
network:
  version: 2
  ethernets:
    eth0:
      dhcp4: true
      # Or static:
      # addresses:
      #   - 192.168.1.100/24
      # gateway4: 192.168.1.1
      # nameservers:
      #   addresses: [8.8.8.8, 8.8.4.4]

Apply:

sudo netplan apply

My take: Netplan is Ubuntu's new way. Use it on Ubuntu.

/etc/network/interfaces (Debian)​

# /etc/network/interfaces
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

My take: Traditional Debian way. Still works.

Common Patterns​

Static IP Configuration​

# Using ip (temporary)
sudo ip addr add 192.168.1.100/24 dev eth0
sudo ip link set eth0 up
sudo ip route add default via 192.168.1.1

DHCP Configuration​

# Using dhclient
sudo dhclient eth0

My take: DHCP is easier. Use it when possible.

Common Mistakes (I've Made These)​

  1. Not bringing interface up: Interfaces need to be up. Check with ip link.

  2. Wrong subnet mask: Subnet mask must match network. Check it.

  3. No default gateway: Without gateway, no internet. Set it.

  4. Not making persistent: Temporary changes are lost on reboot. Make them persistent.

  5. Wrong interface name: Interface names matter. Check with ip link.

Real-World Examples​

Configure Static IP​

# Temporary
sudo ip addr add 192.168.1.100/24 dev eth0
sudo ip link set eth0 up
sudo ip route add default via 192.168.1.1

# Persistent (Ubuntu)
sudo vim /etc/netplan/01-netcfg.yaml
sudo netplan apply

What's Next?​

Now that you can configure IPs, let's talk about Network Troubleshooting when networks don't work.

Personal note: When I started, I'd use ifconfig. Then I learned ip. Now I use ip for everything. It's better. Learn it.