This guide explains how to configure an active-backup (active-standby) network bond in Proxmox using two physical NICs. This setup provides network redundancy without requiring LACP or special switch configuration.

In active-backup mode, only one interface is active at a time. If the primary NIC fails, the secondary automatically takes over.

⚠️ This guide assumes Proxmox VE 7.x or 8.x using ifupdown2 (default on modern installs).

1. Edit the Network Interfaces File

Open the Proxmox network configuration file:

nano /etc/network/interfaces

2. Configure the Bond Interface (bond0)

Add or modify your configuration as follows:

auto lo
iface lo inet loopback# Bonding interface
auto bond0
iface bond0 inet manual
    bond-slaves eno1 eno2
    bond-mode active-backup
    bond-miimon 100
    bond-primary eno1

Explanation

  • bond-slaves eno1 eno2
    Replace with your actual NIC names (check using ip link)
  • bond-mode active-backup
    Enables failover mode (no LACP required)
  • bond-miimon 100
    Checks link state every 100ms
  • bond-primary eno1
    Optional — sets preferred primary interface

3. Create the Proxmox Bridge (vmbr0)

Attach the bond to a Proxmox bridge for VM and container networking:

# Virtual bridge using the bonded interface
auto vmbr0
iface vmbr0 inet static
    address 192.168.1.100/24
    gateway 192.168.1.1
    bridge-ports bond0
    bridge-stp off
    bridge-fd 0

Replace:

  • 192.168.1.100/24 → Your Proxmox host IP
  • 192.168.1.1 → Your gateway

4. Apply the Network Configuration

Instead of rebooting, safely reload networking:

ifreload -a

⚠️ If working remotely over SSH, be cautious — misconfiguration may disconnect you.

5. Verify the Bond Status

Check bond details:

cat /proc/net/bonding/bond0

You should see:

  • Bonding Mode: active-backup
  • Currently Active Slave: eno1 (or eno2 if failover occurred)
  • MII Status: up

To test failover:

Unplug the primary NIC and confirm the secondary becomes active.

How Active-Backup Bonding Works

  • Only one NIC carries traffic at a time
  • Automatic failover if link drops
  • No switch configuration required
  • Ideal for homelabs and unmanaged switches

This is different from LACP (802.3ad), which requires switch support and provides load balancing.

Optional: Identify Your Network Interfaces

If unsure of interface names:

ip link

Common names include:

  • eno1
  • eno2
  • enp3s0
  • enp4s0

Use those values in bond-slaves.

Troubleshooting Tips

If the bond does not come up:

  • Ensure both NICs are connected
  • Confirm correct interface names
  • Check for indentation errors in /etc/network/interfaces
  • Restart networking if necessary:
systemctl restart networking

Tested On

  • Proxmox VE 8.x
  • Dual NIC Intel-based systems
  • Standard home / unmanaged switches
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