Make sure the system has loaded bonding module and confirm that the network card interface is available, use modprobe bonding and lsmod verification; 2. Create /etc/sysconfig/network-scripts/ifcfg-bond0 configuration files, set DEVICE, TYPE, BONDING_MASTER, IP parameters and BONDING_OPTS=mode=active-backup miimon=100 primary=ens33; 3. Configure ifcfg files of physical network cards ens33 and ens34, set MASTER=bond0, SLAVE=yes and remove IP configuration; 4. Restart the network service and use systemctl restart network or nmcli con reload; 5. Pass cat /proc/net/bonding/bond0, ip addr show bond0 and ping tests verify bond status and connectivity; 6. Optionally use the nmcli command to create bonds and add slave interfaces in CentOS 8 /Stream and activate them; 7. Note that the switch needs to configure LACP mode, select the appropriate bond mode and test failover. After the configuration is completed, the system will have network redundancy and high availability, and the configuration is suitable for CentOS 7, 8 and Stream versions.

Configuring network bonding (also known as link aggregation or NIC teaming) in CentOS allows you to combine multiple network interfaces into a single logical interface for redundancy, increased bandwidth, or load balancing. This guide applies to CentOS 7, 8, and Stream , using the traditional network-scripts method (still supported in CentOS 7 and 8) and briefly touches on nmcli for newer systems.

? Step 1: Check Available Interfaces and Kernel Module

Before configuring bonding, verify your network interfaces and ensure the bonding module is loaded.

 ip link show

List available network interfaces (eg, ens33 , ens34 ).

Load and check the bonding kernel module:

 modprobe bonding
lsmod | grep bonding

To load it at boot:

 echo "bonding" >> /etc/modules-load.d/bonding.conf

? Step 2: Create the Bond Interface Configuration

We'll create a bonded interface named bond0 using two physical NICs: ens33 and ens34 .

Create the bond master interface

Edit the bond interface configuration:

 vi /etc/sysconfig/network-scripts/ifcfg-bond0

Add the following (example using active-backup mode):

 DEVICE=bond0
NAME=bond0
TYPE=Bond
BONDING_MASTER=yes
BOOTPROTO=static
ONBOOT=yes
IPADDR=192.168.1.10
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
DNS1=8.8.8.8
BONDING_OPTS="mode=active-backup miimon=100 primary=ens33"

? Key Parameters:

• mode=active-backup : Only one NIC is active; another takes over if it fails.
• miimon=100 : Monitor link every 100ms.
• primary=ens33 : Use ens33 as the default active interface.

Other common modes:

• balance-rr : Round-robin (requires switch support)
• 802.3ad : LACP (dynamic aggregation, requires switch support)

? Step 3: Configure Slave (Physical) Interfaces

Now configure each physical NIC to be part of the bond.

Configure first slave: ens33

 vi /etc/sysconfig/network-scripts/ifcfg-ens33

 DEVICE=ens33
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes

Configure second slave: ens34

 vi /etc/sysconfig/network-scripts/ifcfg-ens34

 DEVICE=ens34
TYPE=Ethernet
BOOTPROTO=none
ONBOOT=yes
MASTER=bond0
SLAVE=yes

? Important: Remove any existing IP configurations from slave interfaces.

? Step 4: Restart Network Service

Apply the configuration:

 systemctl restart network

Or on some systems:

 nmcli con reload

? Step 5: Verify the Bonding Configuration

Check if the bond is up:

 cat /proc/net/bonding/bond0

This shows detailed bonding status, including active interface, link monitoring, and slave status.

Also verify with:

 ip addr show bond0

And test connectivity:

 ping -I bond0 8.8.8.8

? Optional: Using nmcli (Recommended for CentOS 8 /Stream)

For modern systems using NetworkManager, you can use nmcli :

 # Create bond
nmcli con add type bond con-name bond0 ifname bond0 mode active-backup miimon 100 primary ens33 ip4 192.168.1.10/24 gw4 192.168.1.1

# Add slaves
nmcli con add type ethernet con-name bond0-slave1 ifname ens33 master bond0
nmcli con add type ethernet con-name bond0-slave2 ifname ens34 master bond0

# Activate
nmcli con up bond0

Check status:

 nmcli con show
nmcli dev show bond0

?? Notes and Best Practices

• Switch Configuration : For 802.3ad or lacp , ensure the switch is configured for LACP.
• Mode Selection :
  • Use active-backup for failover without switch support.
  • Use 802.3ad for performance and redundancy with compatible switches.
• Always test failover by unplugging one cable and checking /proc/net/bonding/bond0 .

That's it. Your CentOS system now has a resilient network bond. The exact steps may vary slightly depending on your CentOS version and network manager, but this method works reliably across most settings.

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