Interface Bonding

Network interface bonding is a critical technique for enhancing redundancy and load balancing in Linux systems. By aggregating multiple physical interfaces into a single logical bond, administrators can achieve fault tolerance, increased bandwidth, and optimized traffic distribution. This section covers configuring bonding modes like active-backup (for redundancy) and balance-alb (for load balancing), along with practical examples and best practices.

Prerequisites and Kernel Support¶

Before configuring bonding, ensure:
- Physical interfaces are connected and functional.
- The bonding kernel module is loaded (modprobe bonding).
- The bonding driver is supported by your kernel (check /boot/config-$(uname -r) for CONFIG_BONDING).

Configuring Bonding Modes¶

1. Active-Backup Mode¶

Use Case: Redundancy with a single active interface and a backup.
Steps:
1. Create the bond interface:

sudo ip link add bond0 type bond mode active-backup

2. Add slaves (e.g., eth0 and eth1):

sudo ip link set eth0 master bond0
sudo ip link set eth1 master bond0

3. Set the primary interface (optional):

sudo ip link set bond0 primary eth0

4. Bring the bond online:

sudo ip link set bond0 up

5. Assign an IP address:

sudo ip addr add 192.168.1.100/24 dev bond0
sudo ip route add default via 192.168.1.1 dev bond0

Note: Failover occurs automatically if the primary interface fails.

2. Balance-ALB Mode¶

Use Case: Load balancing with ARP-based traffic distribution.
Steps:
1. Create the bond interface:

sudo ip link add bond0 type bond mode balance-alb

2. Add slaves:

sudo ip link set eth0 master bond0
sudo ip link set eth1 master bond0

3. Bring the bond online:

sudo ip link set bond0 up

4. Assign an IP address (same as above).

Key Behavior:
- Traffic is distributed based on ARP tables.
- Requires the balance-alb mode to be supported by the bonding driver.

Persistent Configuration with `systemd-networkd`¶

To ensure bonding survives reboots, configure it in /etc/systemd/network/ (e.g., bond0.network):

[Match]
Name=bond0

[Network]
BondMode=balance-alb
BondSlaves=eth0 eth1
Address=192.168.1.100/24
Gateway=192.168.1.1
Routes=8.8.8.8

Enable and start the service:

sudo systemctl enable systemd-networkd
sudo systemctl start systemd-networkd

Troubleshooting and Monitoring¶

Check bond status:
```
ip -s link show bond0
```
Verify ARP tables:
```
arp -a
```
Check kernel logs:
```
dmesg | grep bonding
```
Common issues:
Missing bonding module.
Incorrect mode configuration (e.g., balance-alb requires specific kernel support).
Misconfigured ARP settings for load balancing.

Key takeaways¶

Bonding modes like active-backup (redundancy) and balance-alb (load balancing) address different use cases.
Persistent configuration via systemd-networkd or nmcli ensures reliability across reboots.
Monitoring tools like ip and dmesg help diagnose bonding issues.
Always verify kernel support and ARP settings for advanced modes.
Use modprobe to load the bonding module if it’s not already active.