What Is Network Bonding? Types and Setup

What is network bonding

Network bonding (also called NIC teaming) joins several network interfaces into one logical interface called bond0. Bonding gives you:

• Redundancy. If one cable or card fails, the other keeps the connection alive.
• More bandwidth in some modes, because traffic can use several links.
• Load balancing over the links.

Bonding modes

• mode=0 (balance-rr). Round-robin. Packets go out through each interface in turn. It gives load balancing and fault tolerance.
• mode=1 (active-backup). One interface is active, the others wait. If the active one fails, another takes over. It is simple and works with any switch.
• mode=2 (balance-xor). Chooses the interface by a hash of the MAC addresses. Gives load balancing and fault tolerance.
• mode=3 (broadcast). Sends every packet on all interfaces. It gives high fault tolerance.
• mode=4 (802.3ad). Link aggregation (LACP). It needs a switch that supports LACP. It gives both more bandwidth and fault tolerance.
• mode=5 (balance-tlb). Adaptive transmit load balancing. It does not need special switch support.
• mode=6 (balance-alb). Adaptive load balancing for transmit and receive. It does not need special switch support.

Configure bonding on CentOS and Red Hat (network-scripts)

Create the bond interface:

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

DEVICE=bond0
TYPE=Bond
BONDING_MASTER=yes
IPADDR=192.168.1.10
NETMASK=255.255.255.0
GATEWAY=192.168.1.1
ONBOOT=yes
BOOTPROTO=none
BONDING_OPTS="mode=1 miimon=100"

Edit each physical interface (here eth0; do the same for eth1):

vi /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE=eth0
TYPE=Ethernet
ONBOOT=yes
BOOTPROTO=none
MASTER=bond0
SLAVE=yes

Load the bonding module with the mode (older style):

vi /etc/modprobe.d/bonding.conf

alias bond0 bonding
options bond0 mode=1 miimon=100

miimon=100 checks the link every 100 milliseconds.

Restart the network:

service network restart

Check it:

ip addr show bond0
cat /proc/net/bonding/bond0

Configure bonding with NetworkManager (CentOS 8+, AlmaLinux, Rocky)

nmcli con add type bond con-name bond0 ifname bond0 bond.options "mode=active-backup,miimon=100"
nmcli con add type ethernet slave-type bond con-name bond0-port1 ifname eth0 master bond0
nmcli con add type ethernet slave-type bond con-name bond0-port2 ifname eth1 master bond0
nmcli con mod bond0 ipv4.addresses 192.168.1.10/24 ipv4.gateway 192.168.1.1 ipv4.method manual
nmcli con up bond0

Configure bonding on Ubuntu (Netplan)

network:
  version: 2
  ethernets:
    eth0: {}
    eth1: {}
  bonds:
    bond0:
      interfaces: [eth0, eth1]
      addresses: [192.168.1.10/24]
      routes:
        - to: default
          via: 192.168.1.1
      parameters:
        mode: active-backup
        mil-monitor-interval: 100

Apply it with sudo netplan try and then sudo netplan apply.

Quick recap

• Mode 1 (active-backup) is the safest choice, mode 4 (LACP) gives the most speed with a supporting switch.
• Check the state with cat /proc/net/bonding/bond0.