Network Configuration by Distribution#

Viewing Current Configuration#

Show IP addresses:

ip a
# or
ip addr show

Show specific interface:

ip a show eth0

Kali/Debian - /etc/network/interfaces#

File: /etc/network/interfaces

Basic static configuration:

auto eth0
iface eth0 inet static
    address 172.20.118.100
    netmask 255.255.255.0
    gateway 172.20.118.1

Key components:

• auto eth0 - Bring up interface automatically on boot
• iface eth0 inet static - Configure static IP (not DHCP)
• address - IP address
• netmask - Subnet mask
• gateway - Default gateway (router)

Restart networking:

sudo systemctl restart networking
# or
sudo ifdown eth0 && sudo ifup eth0

CentOS/RHEL - ifcfg Files#

Directory: /etc/sysconfig/network-scripts/

Files: One per interface (e.g., ifcfg-eth0, ifcfg-eth1)

Example ifcfg-eth0:

DEVICE=eth0
BOOTPROTO=static
ONBOOT=yes
IPADDR=172.20.118.1
NETMASK=255.255.255.0
GATEWAY=172.20.118.254

Key settings:

• DEVICE - Interface name
• BOOTPROTO - static or dhcp
• ONBOOT - yes to auto-start on boot
• IPADDR - IP address
• NETMASK - Subnet mask
• GATEWAY - Default gateway

Restart networking:

sudo systemctl restart network
# or per-interface:
sudo ifdown eth0 && sudo ifup eth0

Ubuntu - Netplan (YAML)#

Directory: /etc/netplan/

File: Usually 01-network-manager-all.yaml (or similar .yaml file)

IMPORTANT: YAML is whitespace-sensitive. Use 2-space indentation consistently.

Example configuration:

network:
  version: 2
  renderer: NetworkManager
  ethernets:
    ens18:
      addresses:
        - 192.168.195.2/24
      gateway4: 192.168.195.1

Key elements:

• ethernets: - Section for ethernet interfaces
• ens18: - Interface name (not eth0 on modern Ubuntu)
• addresses: - List of IPs (note the dash and /24 CIDR notation)
• gateway4: - Default gateway for IPv4

Apply changes:

sudo netplan apply

Test configuration (doesn't persist):

sudo netplan try

CIDR notation: /24 equals 255.255.255.0

Temporary IP Configuration#

Set IP temporarily (lost on reboot):

sudo ip addr add 192.168.1.100/24 dev eth0

Flush (remove) all IPs from interface:

sudo ip addr flush dev eth0

Common Network Issues#

1. Wrong interface name: Check with ip a first
2. Typo in config file: Double-check spelling and syntax
3. Forgotten gateway: Can't reach beyond local network
4. Netplan spacing: YAML requires exact indentation
5. Wrong subnet: Devices must be on same subnet to communicate

Interface Naming#

• Old style: eth0, eth1, lo (loopback)
• New style: ens18, enp0s3, etc. (Ubuntu/modern systems)
• Always check actual names with ip a before configuring