Network Configurations in Linux Distros

1/9/2024
6-minute read

Changing IP Address

Changing the IP address on a Linux system can be done in several ways, depending on whether you want to change it temporarily (for the current session) or permanently (so it persists across reboots). The method you choose will depend on your specific needs and the environment you’re working in.

Methods to Change the IP Address:

Using the ip Command:

Temporary Change: The ip command can change the IP address for the current session.

Command:

sudo ip addr add <new-ip-address>/<subnet-mask> dev <interface>
sudo ip addr del <old-ip-address>/<subnet-mask> dev <interface>

Example:

sudo ip addr add 192.168.1.100/24 dev eth0
sudo ip addr del 192.168.1.50/24 dev eth0

Persistent?: No, this change will be lost after a reboot.

Using the ifconfig Command:
- Temporary Change: Similar to the ip command but older and less powerful.
- Command:
```
sudo ifconfig <interface> <new-ip-address> netmask <subnet-mask>
```
- Example:
```
sudo ifconfig eth0 192.168.1.100 netmask 255.255.255.0
```
- Persistent?: No, this change will also be lost after a reboot.
Editing Network Configuration Files:
- Permanent Change: This method ensures the IP address change persists across reboots.
- For Ubuntu/Debian:
  - Edit the /etc/network/interfaces file:
```
sudo nano /etc/network/interfaces
```
  - Example configuration:
```
auto eth0
iface eth0 inet static
    address 192.168.1.100
    netmask 255.255.255.0
    gateway 192.168.1.1
```
  - Apply changes:
```
sudo systemctl restart networking
```
- For Red Hat/CentOS/Fedora:
  - Edit the configuration file for your interface in /etc/sysconfig/network-scripts/ (e.g., ifcfg-eth0):
```
sudo nano /etc/sysconfig/network-scripts/ifcfg-eth0
```
  - Example configuration:
```
BOOTPROTO=static
IPADDR=192.168.1.100
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
```
  - Apply changes:
```
sudo systemctl restart network
```
Using Network Manager (for GUI-based environments):
- Temporary or Permanent Change: This method is more common in desktop environments or systems using NetworkManager.
- Command Line with nmcli:
```
sudo nmcli con mod <connection-name> ipv4.addresses <new-ip-address>/<subnet-mask>
sudo nmcli con up <connection-name>
```
- GUI Method:
  - Go to Network settings.
  - Select the network interface.
  - Modify the IPv4 settings to static, then enter the new IP address, subnet mask, and gateway.
- Persistent?: Yes, changes made through nmcli or the GUI will persist after reboots.

Choosing the Right Method:

Temporary vs. Permanent:
- If you need a temporary change (e.g., for testing or troubleshooting), use the ip or ifconfig command.
- For a permanent change (to ensure the IP address stays the same after reboot), edit the appropriate network configuration files or use Network Manager.
Distribution:
- On Ubuntu/Debian systems, the /etc/network/interfaces method is commonly used, although newer systems may rely on netplan (which uses YAML configuration files).
- On Red Hat/CentOS/Fedora systems, you typically edit /etc/sysconfig/network-scripts/.
GUI vs. Command Line:
- If you prefer a GUI and are using a desktop environment, the Network Manager tool (accessible through system settings) might be the easiest option.
- For servers or command-line only environments, editing the network configuration files or using nmcli is recommended.

Additional Considerations:

DHCP vs. Static: Ensure you’re aware of whether your system should be using a DHCP or a static IP. Switching from DHCP to static may require additional configuration, such as setting up DNS servers.
Network Services: After changing the IP address, you may need to restart network services or the system to apply changes fully.
Compatibility: Ensure that the method you choose is compatible with your Linux distribution and version, as there might be slight variations in the file paths or commands.

By choosing the right method based on these factors, you can effectively change the IP address on your Linux system to suit your needs.

Configure DNS Servers

Setting DNS servers in Linux can be done in several ways, depending on your distribution, system configuration, and whether the change should be temporary or permanent. Here’s a breakdown of the different methods and how to choose the best one for your needs.

Methods to Set DNS Servers in Linux

Modifying /etc/resolv.conf Directly:
- Description: The /etc/resolv.conf file contains the DNS server addresses that the system will use for resolving domain names.
- Command:
```
sudo nano /etc/resolv.conf
```
- Example:
```
nameserver 8.8.8.8
nameserver 8.8.4.4
```
- Persistent?: No, this method is not persistent across reboots if your system uses a service like NetworkManager, systemd-resolved, or DHCP, which may overwrite this file.
Using Network Manager:
- GUI Method:
  - Go to Network settings in your desktop environment.
  - Select your connection, then go to the “IPv4” or “IPv6” settings.
  - Set the DNS servers under the DNS field.
- Command Line with nmcli:
```
sudo nmcli con mod <connection-name> ipv4.dns "8.8.8.8 8.8.4.4"
sudo nmcli con up <connection-name>
```
- Persistent?: Yes, changes made through NetworkManager will persist across reboots.
- Note: This is common in desktop environments or systems where NetworkManager manages the network settings.
Using systemd-resolved:
- Description: systemd-resolved is a service that provides network name resolution to local applications.
- Edit Configuration:
```
sudo nano /etc/systemd/resolved.conf
```
- Example:
```
[Resolve]
DNS=8.8.8.8 8.8.4.4
FallbackDNS=1.1.1.1 1.0.0.1
```
- Apply Changes:
```
sudo systemctl restart systemd-resolved
```
- Link to /etc/resolv.conf:
```
sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
```
- Persistent?: Yes, changes are persistent and managed by systemd-resolved.

Editing Interface-Specific Configuration Files:

For Ubuntu/Debian (with netplan):

Edit Netplan Configuration:
```
sudo nano /etc/netplan/01-netcfg.yaml
```

Example:

network:
  version: 2
  ethernets:
    eth0:
      dhcp4: yes
      nameservers:
        addresses: [8.8.8.8, 8.8.4.4]

Apply Changes:
```
sudo netplan apply
```

For Red Hat/CentOS/Fedora:

Edit Interface Configuration:

sudo nano /etc/sysconfig/network-scripts/ifcfg-eth0

Example:
```
DNS1=8.8.8.8
DNS2=8.8.4.4
```
Restart Network Service:
```
sudo systemctl restart network
```

Persistent?: Yes, these changes are persistent across reboots.

Configuring DHCP Client:
- Description: If you’re using DHCP and want to configure specific DNS servers, you can set this in the DHCP client configuration.
- For dhclient:
  - Edit the configuration:
```
sudo nano /etc/dhcp/dhclient.conf
```
  - Example:
```
supersede domain-name-servers 8.8.8.8, 8.8.4.4;
```
- Restart Network Interface:
```
sudo dhclient -r && sudo dhclient
```
- Persistent?: Yes, this method is persistent and instructs the DHCP client to use specified DNS servers instead of those provided by the DHCP server.

Choosing the Right Method:

Temporary vs. Permanent:
- If you need a temporary change for testing or troubleshooting, directly editing /etc/resolv.conf might be sufficient, but it won’t persist across reboots.
- For a permanent solution, use Network Manager, systemd-resolved, or modify the interface-specific configuration files.
Distribution and Configuration Management:
- Ubuntu/Debian: If you’re using Netplan or systemd-resolved, follow those specific methods. Older systems or minimal installations may still use the traditional /etc/network/interfaces method.
- Red Hat/CentOS/Fedora: Configuration typically happens within /etc/sysconfig/network-scripts/. If you’re using NetworkManager, that should be your go-to method.
Network Manager vs. Manual Configuration:
- If NetworkManager is managing your network, use nmcli or the GUI. It’s the preferred tool as it manages all aspects of networking on systems where it’s enabled.
- For servers or non-GUI environments, where NetworkManager may not be installed, manual configuration of the network scripts or using systemd-resolved is more appropriate.
Consistency and Control:
- If you want full control over DNS settings and consistency across different networking tools and environments, consider using systemd-resolved. It centralizes DNS resolution and can be more robust in complex setups.
DHCP Considerations:
- If your system receives IP configuration via DHCP but you need to override the DNS settings, modify the DHCP client configuration (dhclient.conf) to enforce the use of specific DNS servers.

By selecting the method that best matches your system setup, administrative practices, and persistence needs, you can effectively manage DNS server settings on your Linux system.