/etc/sysconfig/networking-scripts/ifcfg-*

The /etc/sysconfig/networking-scripts/ifcfg-* files are used for configuring network interfaces on Red Hat-based Linux distributions (such as RHEL, CentOS, Fedora, and others). These configuration files define network settings for each network interface and are processed by NetworkManager or the network service to configure and bring up network interfaces during system boot or when network settings are modified.

Overview of /etc/sysconfig/networking-scripts/ifcfg-* Files

Each ifcfg-* file corresponds to a specific network interface (e.g., ifcfg-eth0, ifcfg-enp0s3, ifcfg-eth1, etc.) and contains key-value pairs that specify configuration details such as IP addressing, DNS settings, interface status, and more.

These configuration files are generally used for static IP configuration, but can also be used for DHCP, bonding, VLANs, bridging, and other complex networking setups.

Structure of ifcfg-* Files

The basic structure of an ifcfg-* file consists of key-value pairs, where each line defines a specific network configuration option. Below are the commonly used parameters and examples of their configuration.

Common Parameters

• DEVICE: The name of the network interface (e.g., eth0, enp0s3).

• BOOTPROTO: Defines how the network interface obtains its IP address.

  • none: Static IP.

  • dhcp: Dynamically via DHCP.

• ONBOOT: Determines whether the network interface is activated at boot.

  • yes: Activate on boot.

  • no: Do not activate on boot.

• IPADDR: The static IP address to be assigned to the interface (used with BOOTPROTO=none).

• NETMASK: The subnet mask for the interface (used with BOOTPROTO=none).

• GATEWAY: The default gateway for the network (used with BOOTPROTO=none).

• DNS1/DNS2: Primary and secondary DNS servers.

• HWADDR: The MAC address of the network interface.

• MTU: The Maximum Transmission Unit size.

• TYPE: The type of network interface (e.g., Ethernet or Bridge).

• VLAN: Used to define VLAN interfaces.

Example Configurations

1. Static IP Configuration (no DHCP)

   DEVICE=eth0
   BOOTPROTO=none
   ONBOOT=yes
   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

   • This configuration sets a static IP address 192.168.1.100 for the eth0 interface with a netmask 255.255.255.0, default gateway 192.168.1.1, and DNS servers 8.8.8.8 and 8.8.4.4.

2. DHCP Configuration

   DEVICE=eth0
   BOOTPROTO=dhcp
   ONBOOT=yes

   • This configuration uses DHCP to automatically obtain an IP address for the eth0 interface when the system boots.

3. VLAN Configuration

   If you're using VLANs, you can create a virtual network interface by adding a VLAN configuration.

   DEVICE=eth0.10
   BOOTPROTO=none
   ONBOOT=yes
   VLAN=yes
   IPADDR=192.168.10.100
   NETMASK=255.255.255.0
   GATEWAY=192.168.10.1

   • This configuration creates a VLAN interface eth0.10 for VLAN ID 10 with a static IP configuration.

4. Bonding Configuration

   For network bonding, you typically have two or more physical interfaces that are bonded together for increased throughput or redundancy. The configuration for the bonding interface is done using the ifcfg-bond0 file.

   Bonding configuration (ifcfg-bond0):

   DEVICE=bond0
   TYPE=Bond
   BOOTPROTO=none
   ONBOOT=yes
   BONDING_OPTS="mode=1 miimon=100"
   IPADDR=192.168.1.200
   NETMASK=255.255.255.0
   GATEWAY=192.168.1.1

   Slave interface configurations (ifcfg-eth0, ifcfg-eth1):

   DEVICE=eth0
   MASTER=bond0
   SLAVE=yes
   ONBOOT=yes
   
   DEVICE=eth1
   MASTER=bond0
   SLAVE=yes
   ONBOOT=yes

   • This setup creates a bonded interface bond0 using two physical interfaces (eth0 and eth1). The bonding options specify mode=1 (active-backup mode) and miimon=100 (link monitoring interval of 100ms).

5. Bridge Configuration

   For configuring a bridge interface, you would typically configure ifcfg-br0 and the physical interfaces connected to the bridge.

   Bridge configuration (ifcfg-br0):

   DEVICE=br0
   TYPE=Bridge
   BOOTPROTO=none
   ONBOOT=yes
   IPADDR=192.168.1.10
   NETMASK=255.255.255.0
   GATEWAY=192.168.1.1

   Physical interface configuration (ifcfg-eth0):

   DEVICE=eth0
   BOOTPROTO=none
   ONBOOT=yes
   BRIDGE=br0

   • This configuration creates a bridge br0 and adds eth0 to it, enabling the bridge interface to obtain a static IP.

Network Configuration File Naming

Each interface configuration file in /etc/sysconfig/networking-scripts/ is named as ifcfg-<interface_name>, where <interface_name> is the name of the network interface (e.g., ifcfg-eth0, ifcfg-enp0s3, ifcfg-bond0, ifcfg-br0).

Other Configuration Files

Besides the ifcfg-* files, there are also a couple of other files that might be used in the networking scripts:

• /etc/sysconfig/network: Defines general network settings like the hostname, gateway, and network mode.

• /etc/sysconfig/network-scripts/ifup-eth and ifdown-eth**: Scripts that define actions to bring interfaces up or down.

Managing Network Interfaces

To apply changes made to the ifcfg-* files, you can use the following commands:

• Restart network service:

  sudo systemctl restart network

• Bring up an interface manually:

  sudo ifup eth0

• Bring down an interface manually:

  sudo ifdown eth0

Conclusion

The /etc/sysconfig/networking-scripts/ifcfg-* files are central to configuring network interfaces on Red Hat-based Linux distributions. These files enable static IP configuration, DHCP, VLANs, bonding, bridges, and other advanced networking setups. After editing these files, network interfaces can be brought up or down manually, or the system can be restarted to apply the changes at boot.