Network configuration on Linux

This is how a network needs to be configured when spinning up a linux server. For example for a fresh install of a local lab on of linux virtual machines on VMware Fusion, Virtualbox or AWS, etc. These are some of the technical details that need to be verified and configured properly.

• Host Address: The unique IP address of your system on the network.
• Network Subnet Address: Defines the local network's range.
• Default Router/Gateway: The device that routes traffic to other networks.
• System Host Name: The name by which a system is identified on a network.
• DNS Server Address: Used for resolving hostnames to IP addresses.

Network Configuration Files:

• Linux systems use systemd-networkd service for network interface detection and configuration.
• Different distributions have different files for network settings, such as:
  • Debian-based: /etc/network/interfaces
  • Red Hat-based: /etc/sysconfig/network-scripts directory
  • OpenSUSE: /etc/sysconfig/network

Configuration Methods:

1. Manual Editing: Directly modify network configuration files.
2. Graphical Tools: Use distribution-provided GUI tools.
3. Command-Line Tools: Utilize terminal commands for configuration.

Examples:

File Configuration

For CentOs file /etc/sysconfig/network-scripts/ifcfg- (such as eth0 or enp3s0)

DEVICE=<interface_name>
TYPE=Ethernet
ONBOOT=yes
NM_CONTROLLED=yes
BOOTPROTO=static
IPADDR=192.168.1.100
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
DNS1=8.8.8.8
DNS2=8.8.4.4

Command Line
There are multiple types of commands, most common are ifconfig, ip, nmcli.

• ifconfig: it's legacy but commonly known.
• nmcli: for simple network configurations.
• ip: for advanced configurations, which could involve scripting and more complex scenarios.

ip command example:

# Set IP
>> ip addr add 192.168.1.100/24 dev <interface_name>

# Activate the interface device
>> ip link set <interface_name> up

# Set Default router
>> ip route add default via 192.168.1.1

# Set DNS (not included in ip commands, gotta write directly to file)

>> echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf
>> echo "nameserver 8.8.4.4" | sudo tee -a /etc/resolv.conf

# ONBOOT=yes has to be set manually as well

nmcli command example

nmcli con mod "ConnectionName" ipv4.addresses 192.168.1.100/24
nmcli con mod "ConnectionName" ipv4.gateway 192.168.1.1
nmcli con mod "ConnectionName" ipv4.dns "8.8.8.8,8.8.4.4"
nmcli con mod "ConnectionName" ipv4.method manual
nmcli con mod "ConnectionName" connection.autoconnect yes