NIC Bonding on Linux: High Performance and Redundancy

This guide explains what NIC bonding is, why it is used, and how it can be configured step by step on Ubuntu 22.04.

✨ What Is NIC Bonding?

NIC bonding combines multiple physical network interfaces into a single logical interface. This can improve both performance through combined bandwidth and redundancy through high availability.

Also known as:

Link Aggregation (LAG)
LACP (802.3ad / 802.1AX)
Interface Bonding

🧠 Why Use NIC Bonding?

Redundancy

If one NIC or switch port fails, another NIC can take over and keep the connection alive.

A critical database server may have ens33 and ens37 joined under bond0 with mode=active-backup. If the switch port connected to ens33 fails, traffic moves to ens37 automatically and services continue without interruption.

Performance / Load Balancing

Multiple NICs can carry traffic at the same time. This can increase total available bandwidth depending on mode, workload, and switch support.

Common Use Cases

Web servers
Proxy, DLP, SIEM, and security appliances
Switch uplinks
High-volume server-to-server transfers

📊 NIC Bonding Modes

Mode	Name	Purpose	Switch Required?
0	balance-rr	Round-robin load balancing	No
1	active-backup	Redundancy	No
2	balance-xor	Hash-based balancing	Sometimes
3	broadcast	Send through all interfaces	No
4	802.3ad (LACP)	Standard link aggregation	Yes
5	balance-tlb	Adaptive transmit load balancing	No
6	balance-alb	Adaptive load balancing	No

⚙ Ubuntu 22.04 Netplan Configuration

sudo apt update
sudo apt install ifenslave -y
sudo modprobe bonding

active-backup

network:
  version: 2
  renderer: networkd
  ethernets:
    ens33: {}
    ens37: {}
  bonds:
    bond0:
      interfaces:
        - ens33
        - ens37
      addresses:
        - 192.168.1.200/24
      routes:
        - to: default
          via: 192.168.1.1
      nameservers:
        addresses: [8.8.8.8, 1.1.1.1]
      parameters:
        mode: active-backup
        primary: ens33
        mii-monitor-interval: 100

sudo netplan apply

balance-rr

network:
  version: 2
  renderer: networkd
  ethernets:
    ens33: {}
    ens37: {}
    ens38: {}
  bonds:
    bond0:
      interfaces:
        - ens33
        - ens37
        - ens38
      addresses:
        - 192.168.1.200/24
      routes:
        - to: default
          via: 192.168.1.1
      nameservers:
        addresses: [8.8.8.8, 1.1.1.1]
      parameters:
        mode: balance-rr
        mii-monitor-interval: 100

balance-rr distributes traffic across interfaces but may cause packet ordering issues for some TCP workloads.

📈 Testing with iperf3

Server side:

iperf3 -s

Bonding side:

iperf3 -c 192.168.1.165 -t 10 -P 4

📊 Verifying Traffic Distribution

watch -n 1 cat /sys/class/net/ens33/statistics/tx_bytes
watch -n 1 cat /sys/class/net/ens37/statistics/tx_bytes
watch -n 1 cat /sys/class/net/ens38/statistics/tx_bytes
ip -s link show ens33

Simple monitoring script:

#!/bin/bash
interfaces=("ens33" "ens37" "ens38")
declare -A last
for iface in "${interfaces[@]}"; do
  last[$iface]=$(cat /sys/class/net/$iface/statistics/tx_bytes)
done

while true; do
  clear
  echo "NIC Bonding Traffic Monitor (tx_bytes/sec)"
  echo "-------------------------------------------"
  for iface in "${interfaces[@]}"; do
    current=$(cat /sys/class/net/$iface/statistics/tx_bytes)
    diff=$((current - last[$iface]))
    kbps=$((diff / 1024))
    printf "%-8s: %8d KB/s\n" "$iface" "$kbps"
    last[$iface]=$current
  done
  sleep 1
done

Virtual Environment Notes

mode=802.3ad usually does not work in VMware Workstation because switch support is missing
balance-rr is often the most compatible lab mode
Each virtual NIC must be connected

Conclusion

NIC bonding is useful for network availability and, depending on the selected mode, throughput improvement. Use active-backup for redundancy, and balance-rr or 802.3ad for performance-focused scenarios after proper testing.

Prepared by: Aziz Ortanç

GitHub: github.com/Aziz4706