How to Configure Network Bonding for Redundancy

Network bonding (also called NIC teaming) combines multiple network interfaces into a single logical interface for redundancy, failover, or increased bandwidth. This is primarily useful on dedicated servers with multiple NICs.

Bonding Modes

# Mode 0 (balance-rr)    — Round-robin, load balancing
# Mode 1 (active-backup) — Active/standby failover (most common for servers)
# Mode 2 (balance-xor)   — XOR-based load balancing
# Mode 3 (broadcast)     — Sends on all interfaces
# Mode 4 (802.3ad)       — LACP, requires switch support
# Mode 5 (balance-tlb)   — Adaptive transmit load balancing
# Mode 6 (balance-alb)   — Adaptive load balancing (no switch config needed)

Setting Up Active-Backup Bond (Netplan)

# /etc/netplan/01-bonding.yaml
network:
  version: 2
  ethernets:
    eth0:
      dhcp4: false
    eth1:
      dhcp4: false
  bonds:
    bond0:
      interfaces:
        - eth0
        - eth1
      addresses:
        - 198.48.63.50/27
      routes:
        - to: default
          via: 198.48.63.33
      nameservers:
        addresses:
          - 1.1.1.1
          - 8.8.8.8
      parameters:
        mode: active-backup
        primary: eth0
        mii-monitoring-interval: 100

sudo netplan apply

Monitoring Bond Status

# Check bond status
cat /proc/net/bonding/bond0

# Shows:
# Bonding Mode: fault-tolerance (active-backup)
# Currently Active Slave: eth0
# Slave Interface: eth0 (Status: up)
# Slave Interface: eth1 (Status: up)

# Quick status
ip addr show bond0

Testing Failover

# Simulate a link failure
sudo ip link set eth0 down
cat /proc/net/bonding/bond0
# Should show eth1 as the active slave

# Restore
sudo ip link set eth0 up
# eth0 becomes active again (if primary is set)